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  • Articles  (3,775)
  • Institute of Electrical and Electronics Engineers (IEEE)  (3,775)
  • Public Library of Science (PLoS)
  • 2015-2019  (3,775)
  • 1945-1949
  • IEEE Transactions on Magnetics  (2,308)
  • IEEE Geoscience and Remote Sensing Letters  (1,467)
  • 1416
  • 40722
  • 1
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    An Adaptive-MSSA-Based Algorithm for Detection of Trapped Victims Using UWB Radar (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-08-11
    Description: Postdisaster search and rescue is an important application of ultrawideband (UWB) radar systems, which mainly detect trapped victims by their respiratory-motion response. The development of a respiratory-motion detection (RMD) algorithm that can eliminate nonstationary clutter and noise is a challenging task for the application. A new algorithm is proposed to deal with the task in this letter. It uses the multichannel singular spectrum analysis (MSSA) technique to reconstruct the respiratory-motion response detected by a UWB radar. During the reconstruction, the periodicity and range interrelation characteristics of the response are exploited to adaptively identify signal subspaces. The performance of the algorithm is verified both by simulated and real data. The results show its improved performance over the reference algorithms, e.g., a singular-value-decomposition-based algorithm. The adaptive-MSSA-based RMD algorithm has great promise not only in practical use but also for future research of UWB-radar-based human being remote sensing.
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  • 2
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    Impact of Correlator Efficiency Errors on SMOS Land–Sea Contamination (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-08-11
    Description: Land–sea contamination observed in Soil Moisture and Ocean Salinity (SMOS) brightness temperature images is found to have two main contributions: the floor error inherent of image reconstruction and a multiplicative error either in the antenna temperature or in the visibility samples measured by the correlator. The origin of this last one is traced down to SMOS calibration parameters to yield a simple correction scheme, which is validated against several geophysical scenarios. Autoconsistency rules in interferometric synthesis together with redundant and complementary calibration procedures provide a robust SMOS calibration scheme.
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  • 3
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    An Estimation Algorithm for Phase Errors in Synthetic Aperture Radar Imagery (2015)
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    Publication Date: 2015-08-11
    Description: This letter proposes a novel algorithm, which is based on the generalized method of moments (GMM), for the estimation and correction of phase errors induced in synthetic aperture radar (SAR) imagery. The GMM algorithm is used to replace the original phase-estimation kernel in the basic structure of the phase-gradient-autofocus algorithm. Since this novel algorithm does not require the observed signal to be a certain distribution model, it is able to estimate arbitrary phase errors. The GMM algorithm has the ability of estimating range-dependent phase errors, which makes it an efficient estimator. As a result, higher accuracy of the estimated phase errors and a better focused image can be achieved. Excellent results have been obtained in autofocusing and imaging experiments on real SAR data.
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  • 4
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    Efficient Clutter Suppression in SAR Images With Shedding Irrelevant Patterns (2015)
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    Publication Date: 2015-08-11
    Description: Strong clutter reflections of terrain and marine surfaces obscure the contrast between the target-of-interest and clutter (terrain and marine surface reflections) in synthetic aperture radar (SAR) images and consequently hinder the efficiency of image interpretation and analysis. To overcome this problem, this letter proposes an efficient clutter suppression method in SAR images, which is named shedding irrelevant patterns (SIP). The essence is to construct a regression function that can suppress clutter and preserve the target patterns concurrently. We assume that the clutter is irrelevant to the target-of-interest and distinguishable in patterns in terms of image-pixel distribution and intensity (spatial information). Experimental results show the efficiency of the proposed method in both clutter suppression and target pattern preservation.
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  • 5
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    Classification of Hyperspectral Images Using Subspace Projection Feature Space (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-08-11
    Description: A concern in hyperspectral image classification is the high number of required training samples. When traditional classifiers are applied, feature reduction (FR) techniques are the most common approaches to deal with this problem. Subspace-based classifiers, which are developed based on high-dimensional space characteristics, are another way to handle the high dimension of hyperspectral images. In this letter, a novel subspace-based classification approach is proposed and compared with basic and improved subspace-based classifiers. The proposed classifier is also compared with traditional classifiers that are accompanied by an FR technique and the well-known support vector machine classifier. Experimental results prove the efficiency of the proposed method, especially when a limited number of training samples are available. Furthermore, the proposed method has a very high level of automation and simplicity, as it has no parameters to be set.
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  • 6
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    Mathematical Framework for Phase-Triangulation Algorithms in Distributed-Scatterer Interferometry (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-08-11
    Description: To improve the spatial density of measurement points of persistent-scatterer interferometry, distributed scatterer (DS) should be considered and processed. An important procedure in DS interferometry is the phase triangulation (PT). This letter introduces two modified PT algorithms (i.e., equal-weighted PT and coherence-weighted PT) and analyzes the mathematical relations between different published PT methods (i.e., the maximum-likelihood phase estimator, least squares estimator, and eigendecomposition-based phase estimators). The analysis shows that the above five PT methods share very similar mathematical forms with different weight values in the estimation procedure.
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  • 7
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    Hyperspectral Image Classification via Sparse Code Histogram (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-08-11
    Description: Sparse representation-based classifier and its variants have been widely adopted for hyperspectral image (HSI) classification recently. However, sparse representation is unstable so that similar features might obtain significantly different sparse codes. Despite the instability, we find that the sparse codes follow a class-dependent distribution under the structured dictionary consisting of training samples from all classes. Based on this observation, a novel discriminative feature, sparse code histogram (SCH), is developed for HSI classification. By counting the SCH of each sample from the sparse codes of its spatial neighbors, we can statistically obtain the distribution pattern of sparse codes of the class to which the sample belongs, and then treat the SCH as a new feature for classification. To reduce the possible outliers among the neighbors, a shape-adaptive neighborhood extractor is also employed to enhance the stability of the histogram feature. Experimental results demonstrate that SCH enjoys a strong discriminative power, which can achieve notably better performance than several state-of-the-art methods for HSI classification with limited training samples.
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  • 8
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    A Generalized Likelihood Ratio Test for Coherent Change Detection in Polarimetric SAR (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-08-11
    Description: Several detection statistics have been proposed for detecting fine ground disturbances between two synthetic aperture radar (SAR) images, such as vehicle tracks. The standard method involves estimating a local correlation coefficient between images. Other methods have been proposed using various statistical hypothesis tests. One of these alternative methods is a generalized likelihood ratio test (GLRT), which compares a full-correlation image model to a no-correlation image model. In this letter, we expand the GLRT to polarimetric SAR data and derive the appropriate GLRT detection statistics. Additionally, we explore relaxing the equal variance/equal polarimetric covariance assumptions used in previous results and find improved performance on macroscopic scene changes.
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  • 9
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    Truncated SVD-Based Compressive Sensing for Downward-Looking Three-Dimensional SAR Imaging With Uniform/Nonuniform Linear Array (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-08-11
    Description: For downward-looking linear array 3-D synthetic aperture radar, the resolution in cross-track direction is much lower than the ones in range and azimuth. Hence, superresolution reconstruction algorithms are desired. Since the cross-track signal to be reconstructed is sparse in the object domain, compressive sensing algorithm has been used. However, the imaging processing on the 3-D scene brings large computational loads, which renders challenges in both data acquisition and processing. To cover this shortage, truncated singular value decomposition is utilized to reconstruct a reduced-redundancy spatial measurement matrix. The proposed algorithm provides advantages in terms of computational time while maintaining the quality of the scene reconstructions. Moreover, our results on uniform linear array are generally applicable to sparse nonuniform linear array. Superresolution properties and reconstruction accuracies are demonstrated using simulations under the noise and clutter scenarios.
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  • 10
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    An Experimental Study of Passive Bistatic Radar Using Uncooperative Radar as a Transmitter (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-08-11
    Description: This letter proposes a signal processing method of passive bistatic radar (PBR) exploiting an uncooperative radar as an illuminator. Compared with other opportunity illuminators, the transmitting signal of a radar usually has a better ambiguity function, which leads to a higher range resolution. Two channels are needed in PBR system. The reference channel is used to estimate radar signal parameters and reconstruct directly propagated signal. The surveillance channel is used to receive scattered wave. An array antenna and a simultaneous multibeam algorithm are necessary in the surveillance channel due to the flexible beam scanning of the uncooperative radar. The procedure of the proposed method is explained in detail, which is then followed by a field experiment. Preliminary results from the field experiment show that the proposed method can be applied to target angle and bistatic range measurement successfully.
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  • 11
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    Statistical Analysis of the Effects of Virtual Element Position Errors on Airborne Down-Looking LASAR 3-D Imaging (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-08-11
    Description: In order to achieve 3-D imaging with an airborne down-looking linear-array synthetic aperture radar (LASAR), a uniform virtual antenna array may be obtained by aperture synthesis of the cross-track sparse multiple-input–multiple-output array. However, the actual 3-D imaging quality is unavoidably degraded by errors in the virtual element position. In this letter, we investigate the effects of these errors on the forms and the degrees of image quality degradation by decomposing the error-related stochastic processes via an orthogonal transform based on discrete Legendre polynomials. It should be noted that these analyses are helpful for designing a LASAR system and providing a reference for specifying the requisite precision of measurement devices and calibration methods. Finally, we briefly consider the use of calibration methods to eliminate the effects of errors.
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  • 12
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    Semisupervised Hyperspectral Image Classification via Neighborhood Graph Learning (2015)
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    Publication Date: 2015-08-11
    Description: In problems where labeled data are scarce, semisupervised learning (SSL) techniques are an attractive framework that can exploit both labeled and unlabeled data. These approaches typically rely on a smoothness assumption such that examples that are similar in input space should also be similar in label space. In many domains, such as remotely sensed hyperspectral image (HSI) classification, the data violate this assumption. In response, we propose a general method by which a neighborhood graph used in SSL is learned using binary classifiers that are trained to predict whether a pair of pixels shares the same label. Working within the framework of semisupervised neural networks (SSNNs), we show that our approach improves on the performance of the SSNN on two HSI data sets.
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  • 13
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    New Spatial Correlation Models for Sea Clutter (2015)
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    Publication Date: 2015-08-11
    Description: In this letter, new models for the spatial correlation of sea clutter texture and intensity are proposed as improved versions of current power law models or exponential decay model. The models for texture have three unknown parameters, and thus can be called triparametric models. The structure of the models is a weighted sum of two components, which can describe the decaying process of the correlation coefficient with spatial lags, as well as the periodic behavior due to the existence of transient coherent structures in sea clutter. Unknown parameters are optimized by the nonlinear least square fit method. Models for sea clutter intensity can be obtained through a linear transform for uncorrelated speckle based on the compound-Gaussian representation of sea clutter. The proposed models are validated and compared with current models using S- and C-band measured sea clutter data. Analysis results indicate the effectiveness of the proposed models in that they can describe the behavior of spatial correlation coefficients with higher accuracy.
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  • 14
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    Accuracy of Digital Elevation Models Derived From Terrestrial Laser Scanning Data (2015)
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    Publication Date: 2015-08-11
    Description: Terrestrial laser scanning (TLS) has become a popular tool for acquiring source data points which can be used to construct digital elevation models (DEMs) for a wide number of applications. A TLS point cloud often has a very fine spatial resolution, which can represent well the spatial variation of a terrain surface. However, the uncertainty in DEMs created from this relatively new type of source data is not well understood, which forms the focus of this letter. TLS survey data representing four terrain surfaces of different characteristics were used to explore the effects of surface complexity and typical TLS data density (in terms of data point spacing) on DEM accuracy. The spatial variation in TLS data can be decomposed into parts corresponding to the signal of spatial variation (of terrain surfaces) and noise due to measurement error. We found a linear relation between the DEM error and the typical TLS data spacings considered (30–100 mm) which arises as a function of the interpolation error, and a constant contribution from the propagated data noise. This letter quantifies these components for each of the four surfaces considered and shows that, for the interpolation method considered here, higher density sampling would not be beneficial.
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  • 15
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    Estimation of Grassland Live Fuel Moisture Content From Ratio of Canopy Water Content and Foliage Dry Biomass (2015)
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    Publication Date: 2015-08-11
    Description: A novel way to estimate the live fuel moisture content (LFMC) was explored from the ratio of canopy water content (CWC) and foliage dry biomass (FDB). The CWC was estimated using the PROSAIL (PROSPECT + SAIL) radiative transfer model from the Landsat 8 product. A weak constraint 4-D variational data assimilation method was employed to assimilate the temporally estimated leaf area index into a soil-water-atmosphere-plant (SWAP) model for optimizing the model control variables. Then, the SWAP model was reinitialized with this optimum set of control variables, and better prediction of FDB was obtained. Results showed that a high accuracy level was achieved for the estimated CWC ( $R^{2}=0.91$ , $mbox{RMSE}=84.74 mbox{g/m}^2$ ) and FDB ( $R^2=0.88$ , $mbox{RMSE}=48.54 mbox{g/m} ^2$ ) when compared with in situ measured values. However, the accuracy level of estimated LFMC was poor ( $R^2=0.59$ , $mbox{RMSE} =30.85%$ ) . Further analyses find that the estimated LFMC is reliable for low LFMC but challenged for high LFMC, which indicates that the presented method still makes sense to the assessment of wildfire risk since the wildfire generally occurs when the vegetation is in low LFMC condition.
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  • 16
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    Classification of Unarmed/Armed Personnel Using the NetRAD Multistatic Radar for Micro-Doppler and Singular Value Decomposition Features (2015)
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    Publication Date: 2015-08-11
    Description: In this letter, we present the use of experimental human micro-Doppler signature data gathered by a multistatic radar system to discriminate between unarmed and potentially armed personnel walking along different trajectories. Different ways of extracting suitable features from the spectrograms of the micro-Doppler signatures are discussed, particularly empirical features such as Doppler bandwidth, periodicity, and others, and features extracted from singular value decomposition (SVD) vectors. High classification accuracy of armed versus unarmed personnel (between 90% and 97% depending on the walking trajectory of the people) can be achieved with a single SVD-based feature, in comparison with using four empirical features. The impact on classification performance of different aspect angles and the benefit of combining multistatic information is also evaluated in this letter.
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    Accurate Urban Area Detection in Remote Sensing Images (2015)
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    Publication Date: 2015-08-11
    Description: Automatic urban area detection in remote sensing images is an important application in the field of earth observation. Most of the existing methods employ feature classifiers and thereby contain a data training process. Moreover, some methods cannot detect urban areas in complex scenes accurately. This letter proposes an automatic urban area detection method that uses multiple features that have different resolutions. First, a downsampled low-resolution image is used to segment the candidate area. After the corner points of the urban area are extracted, a weighted Gaussian voting matrix technique is employed to integrate the corner points into the candidate area. Then, the edge features and homogeneous region are extracted by using the original high-resolution image. Using these results as the input, the processes of guided filtering and contrast enhancement can finally detect accurately the urban areas. This method combines multiple features, such as corner, edge, and regional characteristics, to detect the urban areas. The experimental results show that the proposed method has better detection accuracy for urban areas than the existing algorithms.
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    Advanced Spectral Analysis and Cross Correlation Based on the Empirical Mode Decomposition: Application to the Environmental Time Series (2015)
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    Publication Date: 2015-08-11
    Description: In marine sciences, time series are often nonlinear and nonstationary. Adequate and specific methods are needed to analyze such series. In this letter, an application of the empirical mode decomposition method (EMD) associated to the Hilbert spectral analysis (HSA) is presented. Furthermore, EMD-based time-dependent intrinsic correlation (TDIC) analysis is applied to consider the correlation between two nonstationary time series. Four temperature time series obtained from automatic measurements in nearshore waters of the Réunion island are considered, recorded every 10 min from July 2011 to January 2012. The application of the EMD on these series and the estimation of their power spectra using the HSA are illustrated. The authors identify low-frequency tidal waves and display the pattern of correlations at different scales and different locations. By TDIC analysis, it was concluded that the high-frequency modes have small correlation, whereas the trends are perfectly correlated.
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  • 19
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    Fast Multiclass Vehicle Detection on Aerial Images (2015)
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    Publication Date: 2015-08-11
    Description: Detecting vehicles in aerial images provides important information for traffic management and urban planning. Detecting the cars in the images is challenging due to the relatively small size of the target objects and the complex background in man-made areas. It is particularly challenging if the goal is near-real-time detection, i.e., within few seconds, on large images without any additional information, e.g., road database and accurate target size. We present a method that can detect the vehicles on a 21-MPixel original frame image without accurate scale information within seconds on a laptop single threaded. In addition to the bounding box of the vehicles, we extract also orientation and type (car/truck) information. First, we apply a fast binary detector using integral channel features in a soft-cascade structure. In the next step, we apply a multiclass classifier on the output of the binary detector, which gives the orientation and type of the vehicles. We evaluate our method on a challenging data set of original aerial images over Munich and a data set captured from an unmanned aerial vehicle (UAV).
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  • 20
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    Comparison of Five Slope Correction Methods for Leaf Area Index Estimation From Hemispherical Photography (2015)
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    Publication Date: 2015-08-11
    Description: We compare five slope correction methods developed by Walter et al. , Montes et al. , Schleppi et al. , España et al. , and Gonsamo et al. (referred to as WAL, MON, SCH, ESP, and GON, respectively) using artificial fisheye pictures simulated by graphics software and a lookup table (LUT) retrieval method. The LUT is built by simulating the directional gap fraction as a function of leaf area index (LAI) and average leaf inclination angle (ALIA) using the Poisson law. LAI and ALIA estimates correspond to the case of the LUT that provides the lowest root-mean-square error between the observed gap fractions after slope correction and the simulated ones. Three LAI values (1.5, 3.5, and 5.5), four ALIA values (26.8°, 45°, 57.5°, and 63.2°), and three slope angles (0°, 20°, and 50°) constituted 36 samples of random scenes. ESP is recommended because its results are accurate and independent on the leaf angle distribution (LAD), while GON only performs well for spherical LAD. The three other methods present less good performances with underestimation or overestimation of LAI and/or ALIA depending on the LAD, and the recommended order for them is MON, SCH, and WAL.
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  • 21
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    An Improved Phase Correlation Method Based on 2-D Plane Fitting and the Maximum Kernel Density Estimator (2015)
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    Publication Date: 2015-08-11
    Description: In this letter, an improved phase correlation (PC) method based on 2-D plane fitting and the maximum kernel density estimator (MKDE) is proposed, which combines the idea of Stone's method and robust estimator MKDE. The proposed PC method first utilizes a vector filter to minimize the noise errors of the phase angle matrix and then unwraps the filtered phase angle matrix by the use of the minimum cost network flow unwrapping algorithm. Afterward, the unwrapped phase angle matrix is robustly fitted via MKDE, and the slope coefficients of the 2-D plane indicate the subpixel shifts between images. The experiments revealed that the improved method can effectively avoid the impact of outliers on the phase angle matrix during the plane fitting and is robust to aliasing and noise. The matching accuracy can reach 1/50th of a pixel using simulated data. The real image sequence tracking experiment was also undertaken to demonstrate the effectiveness of the proposed PC method with a registration accuracy of root-mean-square error better than 0.1 pixels.
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    Improvement of Forest Carbon Estimation by Integration of Regression Modeling and Spectral Unmixing of Landsat Data (2015)
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    Publication Date: 2015-08-11
    Description: Accurately mapping forest carbon density by combining sample plots and remotely sensed images has become popular because this method provides spatially explicit estimates. However, mixed pixels often impede the improvement of the estimation. In this letter, regression modeling and spectral unmixing analysis were integrated to improve the estimation of forest carbon density for the You County of Hunan, China, using Landsat Thematic Mapper images. Linear spectral unmixing with and without a constraint (LSUWC and LSUWOC) and nonlinear spectral unmixing (NSU) were compared to derive the fractions of five endmembers, particularly forests. Stepwise regression, logistic regression, and polynomial regression (PR) with and without the forest fraction used as an independent variable and the product of the forest fraction image and the map from the best model without the forest fraction were compared. The models were developed using 56 sample plots, and their results were validated using 26 test plots. The decomposition of mixed pixels was assessed using higher spatial resolution SPOT images and a corresponding land cover map. The results showed that 1) LSUWC more accurately estimated the endmember fractions than LSUWOC and NSU, 2) PR had the greatest estimation accuracy of forest carbon, and 3) combining regression modeling and spectral unmixing increased the estimation accuracy by 31%–39%, and introducing the forest fraction into the regressions performed better than the product of forest fraction image and the results from PR without the fraction. This implied that the integrations provided great potential in reducing the impacts of mixed pixels in mapping forest carbon.
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  • 23
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    Reliable and Fast Mapping of Keypoints on Large-Size Remote Sensing Images by Use of Multiresolution and Global Information (2015)
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    Publication Date: 2015-08-11
    Description: This letter proposes a multiresolution technique to address the high computational cost in remote sensing image registration. The scale-invariant feature transform is applied to detect keypoints and descriptors, and then, global information combined with descriptors is utilized to establish keypoint mappings. Keypoints are first classified according to their octaves. Then, in the lowest resolution, the keypoints of the largest octave are mapped with descriptors and the global information, giving an initial affine transformation $T_0$ . In the next octave, the keypoints of the second largest octave are mapped by employing $T_0$ to narrow the space of matching keypoints. By this means, the process of establishing keypoint correspondences is conducted from one resolution (octave) to the next as the obtained transformation gets finer until we get to the highest resolution. Due to the high computational expense of computing global information, the proposed technique is important for aligning large-size remote sensing imagery. Experimental results show that the proposed method can achieve a comparable registration accuracy but with a less computational cost than directly building keypoint mappings on images of large size.
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    GPU Implementation of Composite Kernels for Hyperspectral Image Classification (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-08-11
    Description: In this letter, we present an efficient parallel implementation of composite kernels in support vector machines (SVMs) for hyperspectral image (HSI) classification. Our implementation makes effective use of commodity graphics processing units (GPUs). Specifically, we port the calculation of composite kernels to GPUs, perform intensive computations based on NVidia's compute unified device architecture, and execute the rest of the operations related with control and small data calculations in the CPU. Our experimental results, conducted using real hyperspectral data sets and NVidia GPU platforms, indicate significant improvements in terms of computational effectiveness, achieving near-real-time performance of spatial–spectral HSI classification for the first time in the literature.
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    Retrieval and Accuracy Assessment of Tree and Stand Parameters for Chinese Fir Plantation Using Terrestrial Laser Scanning (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-08-11
    Description: Compared with airborne laser scanning, terrestrial laser scanning (TLS) offers ground-based point cloud data of trees and provides greater potential to accurately estimate tree and stand parameters. However, there is a lack of effective methods to accurately identify locations of individual trees from TLS point cloud data. It is also unknown whether the estimation accuracy of the parameters, including tree height (H), diameter at breast height (DBH), and so on, using TLS can meet the requirement of forest management and planning. In this letter, a novel method to effectively process point cloud data and further determine the locations of individual trees in a stand based on the central coordinates of point cloud data on a defined grid according to the largest DBH was developed. Moreover, a point-cloud-data-based convex hull algorithm and the cylinder method were, respectively, used to estimate DBH and H of individual trees. This study was conducted in a pure Chinese fir plantation of 45 trees located in Huang-Feng-Qiao forest farm, You County of Hunan, China. The comparison of the estimated and observed values showed that the obtained tree locations had errors of less than 20 cm, and the relative root mean square errors for the estimates of both DBH and H were less than 5%. This implies that TLS is very promising for the retrieval of tree and stand parameters in forest stands. For the applications of these methods to mixed forests with a structure of multilayer canopies, further examination is needed.
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    A 3-D Electromagnetic-Model-Based Algorithm for Absolute Attitude Measurement Using Wideband Radar (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-08-11
    Description: In this letter, a novel algorithm for attitude measurement based on a 3-D electromagnetic model (3-D em-model) is proposed. The 3-D em-model is established offline based on the geometric structure of the target, and it can be used to predict the scattering features at different target attitudes. In order to measure the attitude of the air target, we design a bistatic step frequency radar system. The directions of the two radars' lines of sight (LOSs) relative to the target are acquired by matching the high-resolution range profiles (HRRPs) from the target echoes to the HRRPs generated from the 3-D em-model. Since the directions of two radars' LOSs relative to the Earth are already known, the absolute attitude of the target can be acquired. The innovative contributions of this letter are as follows: 1) A comprehensive theoretical analysis of air target attitude measurement based on its own 3-D em-model is proposed; 2) the method can be applied to different kinds of air targets such as aircraft, satellite, missile, etc.; 3) the proposed attitude measurement method does not require target motion model in advance; and 4) the proposed algorithm can be applied to any kind of step frequency waveforms. Experiments using both data predicted by a high-frequency electromagnetic code and data measured in the chamber verify the validity of the method.
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    Converting Between SMOS and SMAP Level-1 Brightness Temperature Observations Over Nonfrozen Land (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-08-11
    Description: The Soil Moisture and Ocean Salinity (SMOS) and Soil Moisture Active Passive (SMAP) missions provide Level-1 brightness temperature (Tb) observations that are used for global soil moisture estimation. However, the nature of these Tb data differs: the SMOS Tb observations contain atmospheric and select reflected extraterrestrial (“Sky”) radiation, whereas the SMAP Tb data are corrected for these contributions, using auxiliary near-surface information. Furthermore, the SMOS Tb observations are multiangular, whereas the SMAP Tb is measured at 40° incidence angle only. This letter discusses how SMOS Tb, SMAP Tb, and radiative transfer modeling components can be aligned in order to enable a seamless exchange of SMOS and SMAP Tb data in soil moisture retrieval and assimilation systems. The aggregated contribution of the atmospheric and reflected Sky radiation is, on average, about 1 K for horizontally polarized Tb and 0.5 K for vertically polarized Tb at 40° incidence angle, but local and short-term values regularly exceed 5 K.
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    Magnetic Properties and Magnetization Reversal of Thin Films and Nanodots Consisting of Exchange-Coupled Composite Co/Pd Multi-Layer and Co Layer With Orthogonal Anisotropies (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-08-18
    Description: We report on the fabrication and measurement of the switching characteristics of Co/Pd multi-layer thin films and nanodots. We used the method of anomalous Hall effect to obtain the hysteresis curves of both in-plane and out-of-plane magnetization. While Co/Pd thin film is found to switch by nucleation followed by domain propagation, Co/Pd nanodots switch by quasi-coherent rotation. We found that the coercivity of Co/Pd increases by a power law with respect to decreasing dots size. The coercivity can be reduced by exchange coupling the Co/Pd multi-layer to a 2 nm thick Co layer. Adding a Cu spacer layer between the Co/Pd multi-layer and Co layer provides a reliable way to modulate the strength of exchange coupling and tailoring the coercivity. As the Cu spacer becomes thicker, the coercivity increases. The exchange energy density is estimated to be 14.6 Merg/cm 3 and the exchange constant, 2.92 erg/cm 2 . The dependence of saturation field and coercivity on the thickness of the Cu spacer layer is fitted to the same empirical model and the exchange interaction is found to decay exponentially with distance. The exchange-coupled samples switch by quasi-domain propagation for both thin films and nanodots.
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    Microstructural Characterization of Quenched AISI D2 Tool Steel Using Magnetic/Electromagnetic Nondestructive Techniques (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-08-18
    Description: In the past decade, nondestructive electromagnetic techniques have been extensively used for the characterization of materials. In this paper, the relation between the microstructural/mechanical characteristics of D2 tool steel with magnetic and electrical properties and eddy current (EC) test outputs has been established. Quenched samples obtained from different austenitizing temperatures (from 1000 °C to 1130 °C) were used to investigate the effect of retained austenite, martensite, and carbides phase fraction as well as prior austenite grain size, on the electromagnetic properties such as electrical resistivity and magnetic saturation. Variations of induced voltage in the pickup coil and location of impedance point in the impedance plane as a function of austenitizing temperature were interpreted by considering the changes in magnetic saturation and electrical resistivity and their effects on the EC outputs. This paper indicated that there is a good correlation between the EC parameters and retained austenite.
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    A Method for Improving SNR of Drill Pipe Leakage Flux Testing Signals by Means of Magnetic Concentrating Effect (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-08-18
    Description: Magnetic flux leakage (MFL) technique is generally considered as an efficient and effective nondestructive testing method, which has been widely used in the drill pipe detection in oil field. This paper aims at studying the magnetic concentrating effect, and proposing a method of gathering the MFL by means of magnetic concentrating device. Electromagnetic finite-element analysis shows that pipe MFL signals centralize near defects obviously and the leakage signals detected by Hall elements enhance greatly as magnetic concentrating structure can collect useful magnetic component. A drill pipe MFL experiment confirms the analysis results that the probe with magnetic concentrating device could obviously improve SNR of MFL signals, increase measuring the width of defects and reduce the requirements of liftoff value. Therefore, it is of great help to improve pipe leakage flux testing sensitivity.
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    A Compact and High-Performance Eddy-Current Sensor Based on Meander-Spiral Coil (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-08-18
    Description: In this paper, a novel meander–spiral coil (MSC) was designed as an eddy-current sensor (ECS) probe, which has small sensing area and spot size, nearly no limitation of mounting space, and can perform better than the regular-spiral coil (RSC). The results of the finite-element analysis show that the MSC has a magnetic active area that was only a quarter of that of the RSC. The MSC has much smaller inductance and resistance than the RSC, though the former has high sensitivity similar to the latter. These types of spiral coils were manufactured by printed circuit board technology and tested, which proves that the MSC has a small sensing range. Owing to MSC’s small magnetic active area and high performance, this type of spiral coil is suitable for applications in sensor arrays and micro-electromechanical systems. Furthermore, using the MSC, ECSs have the potential to be used for micro-gap measurement, accelerometers, and pressure measurement applications, as in the case of capacitive sensors. Moreover, ECSs are inherently immune to environmental contaminations.
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    Influence of Phase Magnetic Couplings on Phase Current Characteristics of Multiphase BLDC Machines With Overlapping Phase Windings (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-08-18
    Description: Multiphase brushless dc (BLDC) machines are implemented in electric and hybrid electric vehicle applications due to their high torque/power density, good fault tolerance capability, and low torque ripple. Moreover, the per-phase converter rating can be reduced by increasing the phase number. However, the number of magnetic couplings between phases increases with the phase number, and these magnetic couplings can have an important influence on the machine performance. Therefore, they need to be considered in simulation models and their effect should be considered in control algorithms. Accordingly, the objective of this paper is to analyze the effect of magnetic phase couplings on the performance of multiphase BLDC machines with an overlapping phase winding configuration. First, a detailed electric machine model, in which the machine parameters that are determined by 2-D finite-element method analysis are implemented, is developed. Using this model, the influence of mutual inductances on phase current characteristics with pulse amplitude modulation (PAM) and pulsewidth modulation (PWM) controls is investigated. In addition, a novel PAM-based control strategy, in which the effect of phase mutual inductances is considered, is proposed and analyzed. After demonstrating the influence of mutual inductances on phase current characteristics, the dependence of mutual inductances on the winding configuration is studied. Finally, experimental results with the PAM control and the new PAM-based control are used to validate the simulation results.
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    Communication Turbo Equalization of 2-D Intersymbol Interference Using Multiple 1-D Constituent Equalizers (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-08-18
    Description: A 2-D soft-in, soft-out equalizer consisting of multiple low-complexity constituent equalizers is proposed for the turbo equalization of 2-D intersymbol interference. The constituent equalizers are simple 1-D linear equalizers running in different directions over a 2-D array of storage cells. Simulation results as well as an extrinsic information transfer chart analysis indicate that the proposed concatenation provides performance comparable with finite-window trellis-based equalizers while requiring a much lower complexity level.
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    Multicontextual Mutual Information Data for SAR Image Change Detection (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-08-11
    Description: How to produce the difference data of the two temporal images is a crucial factor in image change detection. In this letter, we propose multicontextual mutual information data (MMID) based on the bivariate Gaussian distribution (BGD) for synthetic aperture radar (SAR) image change detection and illustrate their superiorities over the classical difference data. MMID, which are an improved form of image spatial mutual information, are constructed based on the quadrilateral Markov random field (QMRF) and can be factored into the linear combination of the entropies. Then to adapt MMID to the change detection, we construct the 2-D entropies based on the BGD. In this way, MMID are able to capture the intertemporal statistical dependence of the two temporal images and thus can be taken as the feature-level difference data rather than the pixel-level data. The maximum-likelihood method, the automatic threshold method, and the Markov random field method are performed on the MMID of the real two temporal SAR images for the change detection. Experimental results demonstrate the superiorities of MMID over the traditional difference data.
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    HyperMix: An Open-Source Tool for Fast Spectral Unmixing on Graphics Processing Units (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-08-11
    Description: Spectral unmixing has been a popular technique for analyzing remotely sensed hyperspectral images. The goal of unmixing is to find a collection of pure spectral constituents (called endmembers ) that can explain each (possibly mixed) pixel of the scene as a combination of endmembers, weighted by their coverage fractions in the pixel or abundances . Over the last years, many algorithms have been presented to address the three main parts of the spectral unmixing chain: 1) estimation of the number of endmembers; 2) identification of the endmember signatures; and 3) estimation of the per-pixel fractional abundances. However, to date, there is no standardized tool that integrates these algorithms in a unified framework. In this letter, we present HyperMix, an open-source tool for spectral unmixing that integrates different approaches for spectral unmixing and allows building unmixing chains in graphical fashion, so that the end-user can define one or several spectral unmixing chains in fully configurable mode. HyperMix provides efficient implementations of most of the algorithms used for spectral unmixing, so that the tool automatically recognizes if the computer has a graphics processing unit (GPU) available and optimizes the execution of these algorithms in the GPU. This allows for the execution of spectral unmixing chains on large hyperspectral scenes in computationally efficient fashion. The tool is available online from http://hypercomphypermix.blogspot.com.es and has been validated with real hyperspectral scenes, providing state-of-the-art unmixing results.
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    Adaptive Fission Particle Filter for Seismic Random Noise Attenuation (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-08-11
    Description: Seismic signals are nonlinear, and the seismic state-space model can be described as a nonlinear system. The particle filter (PF) method, as an effective method for estimating the state of a nonlinear system, can be applied to deal with seismic random noise attenuation. However, PF suffers from sample impoverishment caused by resampling, which results in serious loss of valid seismic information and leads to inaccurate representation of the reflected signal. To address the impoverishment issue and to further improve the particle quality, we propose a novel method to suppress seismic random noise—the adaptive fission particle filter (AFPF). In AFPF, all the particles undergo a fission process and produce “offspring” particles to maintain particle diversity. To implement the adaptation and to monitor the degree of fission, we apply a fission factor, which takes into account weights that indicate the quality of the particles. This leads to significant improvements in the particle quality, i.e., the proportion of highly weighted particles is increased. The effective seismic information provided by the resulting particles reproduces the true signal more reliably, reducing the bias of PF. In addition, we establish a dynamic state-space model suitable for seismic signals. Experimental results on synthetic records and field data illustrate the superior performance of AFPF in noise attenuation and reflected signal preservation compared with the PF.
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    Global Mosaics of the Relative Height Error From TanDEM-X Quicklooks (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-08-11
    Description: The primary objective of the TanDEM-X mission is the generation of a global high-precision digital elevation model (DEM) by using synthetic aperture radar interferometry. This letter presents the developed strategy for estimating the relative height error of the TanDEM-X DEM on a global scale. The mosaicking process of the final DEM combines all acquisitions at full resolution and is expected to be finished by late 2016. On the other hand, global mosaics can be generated starting from quicklook images already available for each single input data take. These downsized mosaics are operationally used to analyze the performance improvement that can be achieved by combining multiple acquisitions over the same ground areas and are a powerful mean for optimizing further acquisition planning. This letter reports the expected global performance of the final TanDEM-X product in advance of the full-resolution DEM. Knowledge of the global status of the TanDEM-X DEM relative height error is fundamental for optimizing the acquisition strategy and, therefore, the final performance and represents a valuable input for the scientific community as well as for selecting suitable areas for further interferometric experiments on a global scale.
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    A Support Vector Machine-Based Particle Filter Method for Improved Flooding Classification (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-08-11
    Description: Support vector machines (SVMs) have been applied to land cover classification, and a number of studies have demonstrated their ability to increase classification accuracy. The high correlation between the data set and SVM training model parameters indicates the high performance of the classification model. To improve the correlation, research has focused on the integration of SVMs and other algorithms for data set selection and SVM training model parameter estimation. This letter proposes a novel method, based on a particle filter (PF), of estimating SVM training model parameters according to an observation system. By treating the SVM training function as the observation system of the PF, the new method automatically updates the SVM training model parameters to values that are more appropriate for the data set and can provide a better classification model than can the original model, wherein the parameters are set by trial and error. Various experiments were conducted using Radarsat-2 synthetic aperture radar data from the 2011 Thailand flood. The proposed method provides superior performance and a more accurate analysis compared with the standard SVM.
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    Height Extraction of Maize Using Airborne Full-Waveform LIDAR Data and a Deconvolution Algorithm (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-08-11
    Description: Maize is a widely planted crop in China and in other areas of the world and plays an important role in grain production. Monitoring the growth status of maize using remote sensing technology is an important component of precision agriculture and height, as a crucial growth indicator for maize, can be retrieved from light detection and ranging (LIDAR) data. However, height extraction for crops, such as maize using airborne laser scanning point clouds results in a great number of uncertainties and challenges. Here, airborne full-waveform LIDAR data were used to extract maize height. In the first step, a workflow was designed based on the Gold deconvolution algorithm combined with a basic data process technique. The method was then tested and was determined to be effective for capturing the portion of the waveform interacting with the tops of vegetation, characterized by lower amplitude stemming from the ground. Therefore, the number of second returns from point clouds was dramatically increased. During the experiment, the number of point clouds increased nearly 50% for three of the four maize plots, as compared with the original point clouds. Compared with the commonly used Gaussian fitting algorithm, the deconvolution algorithm had the advantage of extracting an accurate position for overlapping weak signals. The height percentiles indicated that the original and Gaussian decomposition derived point clouds data underestimated and deconvolution algorithm can accurately reflect the true height of maize, particularly for the 75% and 95% height percentiles.
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    Burned-Area Mapping at the Subpixel Scale With MODIS Images (2015)
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    Publication Date: 2015-08-11
    Description: The Moderate Resolution Imaging Spectroradiometer (MODIS) is an important data set in global burned-area mapping. The MODIS global burned-area product has a coarse spatial resolution at approximately 500 m, which often introduces errors to the mapped burned areas. In this letter, a novel subpixel mapping (SPM) approach was proposed to produce burned-area maps at the fine spatial resolution similar to Landsat imagery, by exploring the spectral and spatial information provided by the second and fifth bands of MODIS. The proposed SPM approach aims to refine the estimate of burned areas, which have been detected by the MODIS global burned-area product. The performance of the proposed SPM approach was assessed with an experiment area containing six burned areas, by comparing with the MODIS burned-area product MCD45. The result shows that the average omission error decreased from 52.26% for MCD45 to 16.74% for SPM, and the average commission error decreased from 21.76% for MCD45 to 12.54% for SPM. The kappa value increased from 0.5583 for MCD45 to 0.8756 for SPM, indicating that the proposed SPM approach is effective in reducing the influence of the coarse spatial resolution of MODIS imagery in mapping a burned area and refining existing global burned-area products.
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    Local Parameter Estimation of Topographic Normalization for Forest Type Classification (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-08-11
    Description: Radiometric distortions caused by rugged terrain make the classification of forest types from satellite imagery a challenge. Various band-specific topographic normalization models are expected to eliminate or reduce these effects. The quality of these models also depends on the approach to estimate empirical parameters. Generally, a global estimation of these parameters from a whole satellite image is simple, but it may tend to overcorrection, particularly for larger areas. A land-cover-specific method usually performs better, but it requires obtaining a priori land classification, which presents another challenge in many cases. Empirical parameters can be directly estimated from local pixels in a given window. In this letter, we propose and evaluate a central-pixel-based parameter estimation method for topographic normalization using local window pixels. We tested the method with Landsat 8 imagery and the Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model (ASTER GDEM) in very rough terrain with diverse forest types. Visual comparison and statistical analyses showed that the proposed method performed better at a range of window sizes compared with an uncorrected image or with a global parameter estimation approach. The intraclass spectral variability of each forest type has been reduced significantly, and it can yield higher accuracy of forest type classification. The proposed method does not require the a priori knowledge of land covers. Its simplicity and robustness suggest that this method has the potential to be a standard preprocessing approach for optical satellite imagery, particularly for rough terrain.
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    Unsupervised Detection of Earthquake-Triggered Roof-Holes From UAV Images Using Joint Color and Shape Features (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-08-11
    Description: Many methods have been developed to detect damaged buildings due to earthquake. However, little attention has been paid to analyze slightly affected buildings. In this letter, an unsupervised method is presented to detect earthquake-triggered “ roof-holes ” on rural houses from unmanned aerial vehicle (UAV) images. First, both orthomosaic and gradient images are generated from a set of UAV images. Then, a modified Chinese restaurant franchise model is used to learn an unsupervised model of the geo-object classes in the area by fusing both oversegmented orthomosaic and gradient images. Finally, “roof-holes” on rural houses are detected using the learned model. The performance of the proposed method is evaluated in terms of both qualitative and quantitative indexes.
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    Recursive Automatic Target Generation Process in Subpixel Detection (2015)
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    Publication Date: 2015-08-11
    Description: Automatic target generation process (ATGP) has been used in a wide range of applications in hyperspectral image analysis. It performs a sequence of orthogonal subspace projections to extract potential targets of interest. This letter presents a recursive version of the ATGP, which is referred to as the recursive ATGP (RATGP) and has three advantages over the ATGP as follows: 1) there is no need of inverting a matrix as the ATGP does for finding each new target; 2) there is a significant reduction in the computational complexity in the hardware design due to its recursive structure; and 3) there is an automatic stopping rule that can be derived by the Neyman–Pearson detection theory to terminate the algorithm.
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    Automatic Road Extraction From Remote Sensing Images Based on a Normalized Second Derivative Map (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-08-11
    Description: In this letter, we propose a novel automatic algorithm for road extraction from remote sensing images. The algorithm includes low- and high-level processing. In the low-level processing, we determine a normalized second derivative map of road profiles of a generalized bar shape, which is width invariant and contrast proportional, and accordingly obtain initial road center pixels. In the high-level processing, using the map and initial center pixels, we initially determine road segments. The segments are then locally refined using their orientation randomness and length-to-width ratio and further refined via global graph-cut optimization. A final road network is thereby extracted in a robust manner. Experimental results demonstrate that the proposed algorithm provides noticeably more robust and higher road extraction performance in various images compared with the existing algorithms.
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    Cell-Based Two-Step Scalar Deadzone Quantization for High Bit-Depth Hyperspectral Image Coding (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-08-11
    Description: Remote sensing images often need to be coded and/or transmitted with constrained computational resources. Among other features, such images commonly have high spatial, spectral, and bit-depth resolution, which may render difficult their handling. This letter introduces an embedded quantization scheme based on two-step scalar deadzone quantization (2SDQ) that enhances the quality of transmitted images when coded with a constrained number of bits. The proposed scheme is devised for use in JPEG2000. It is named cell-based 2SDQ since it uses cells, i.e., small sets of wavelet coefficients within the codeblocks defined by JPEG2000. Cells permit a finer discrimination of coefficients in which to apply the proposed quantizer. Experimental results indicate that the proposed scheme is especially beneficial for high bit-depth hyperspectral images.
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    Combining Landsat TM/ETM+ and HJ-1 A/B CCD Sensors for Monitoring Coastal Water Quality in Hong Kong (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-08-11
    Description: High suspended solid (SS) concentrations in coastal waters are aesthetically undesirable, and adversely affect fisheries and coastal ecosystems. Environmental agencies usually require frequent measurements of SS over coastal regions at a spatially detailed level for water quality assessment and control. To develop a method for SS estimation in the complex coastal waters of Hong Kong, an archive of 57 Landsat Thematic Mapper (TM), Enhanced Thematic Mapper Plus (ETM+), and HJ-1 A/B Charged Couple Device (CCD) images over a 13-year period from January 2000 to December 2012 was used. Atmospherically corrected Landsat TM/ETM+ and HJ-1 A/B CCD bands 1–4 along with 240 in situ field samples of SS concentration collected within 2 h of image acquisition, were used to develop and validate regression models over a wide range of SS concentrations from 0.5–56.0 mg/L. The best representation of actual SS concentrations was given by the log-transformed combination of Band 2 (Green, 0.52–0.60 $mumbox{m}$ ) and Band 3 (Red, 0.63–0.69 $mumbox{m} $ ), with correlation coefficient (R) of 0.85, root-mean-square error of 2.60 mg/L and mean absolute error of 2.04 mg/L. This is attributed to the sensitivity of SS to green and red wavelengths specific to the characteristic refractive index and grain size of SS found in Hong Kong waters. This letter is considered more robust than previous studies, due to the much larger number of images and in situ samples used for model development and validation, as well as the different times of year and wide range of SS concentrations investigated.
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    Spectral Indices for Estimating Exposed Carbonate Rock Fraction in Karst Areas of Southwest China (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-08-11
    Description: The quantitative estimation of the fractional cover of carbonate rock (CR) is critical for natural resource management and ecological conservation in karst areas. Based on the analysis of spectral properties of CR together with other land cover types, we proposed two CR indices (CRIs) and established the model that represents the relationships between the CRIs and the fractional cover of CR. Then, the fractional cover of CR was estimated by using the developed model. Experimental results on Landsat-8 Operational Land Imager images acquired at Southwestern China demonstrated the effectiveness of the developed model. Compared with other indices, the proposed CRIs show the highest correlations with the fractional cover of CR.
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    Alternative Formulations of the Fields’ Constitutive Relations for the Efficiency of the Time Domain Analysis of Magnetized Ferrites (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-09-18
    Description: In this paper, the constitutive relation of longitudinally magnetized ferrites (LMF) is simplified and transformed to an equivalent relation involving tensors with first-order dispersive components more suitable for use in the time domain analysis. Further treatment leads to a diagonal permeability tensor that yields approximating formulas to relate the magnetic field to the magnetic flux density, which allows eliminating this later and reducing the number of field variables involved. Later, a similar result is achieved using a variable transformation. This reveals that magnetized ferrites actually have a permeability tensor simpler than the Polder tensor, in addition to a permittivity tensor with first-order dispersive components, which contradicts the known theory about ferrites. Finally, it is shown that the results obtained for the LMF case could be extended to the transversely magnetized ferrite case and to the general case of arbitrary state of magnetization. Some examples are presented with numerical results to validate the proposed formulations.
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    IEEE Transactions on Magnetics publication information (2015)
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    Publication Date: 2015-09-18
    Description: Provides a listing of the editors, board members, and current staff for this issue of the publication.
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    Magnetization-Switching Study of fcc Fe–Pd Nanowire and Nanowire Arrays Studied by In-Field Magnetic Force Microscopy (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-09-18
    Description: Using electrodeposition into anodic aluminum oxide (AAO) membranes, we have successfully fabricated near-equiatomic Fe 48±3 Pd 52±3 nanowires (NWs) with the diameter of $approx 200$ nm and the length of $approx 3.5~mu{rm m}$ . X-ray diffraction and transmission electron microscopy/selected-area electron diffraction analyses revealed that the as-deposited NWs are isotropic and polycrystalline with an average crystal size of 5 nm and have an fcc crystal structure. Magnetic force microscopy (MFM) on a single Fe–Pd NW revealed its single-domain behavior with the easy axis of magnetization along the long axis of the NW. The magnetizationswitching behavior of a single Fe–Pd NW studied with the MFM suggested a square-shaped magnetization curve $(M/Ms = 1)$ with $H_{CVert} approx 3.2$ kA/m. In addition, using in-field MFM techniques, the effects of dipolar interactions in an Fe–Pd array of NWs still embedded in the AAO were determined. It was found that the dipolar interactions greatly reduce the parameters of the magnetization hysteresis loop, such as the coercivity, the remanence, and the switching-field distribution of the Fe–Pd NW array.
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    Roadmap for Emerging Materials for Spintronic Device Applications (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-09-18
    Description: The Technical Committee of the IEEE Magnetics Society has selected seven research topics to develop their roadmaps, where major developments should be listed alongside expected timelines: 1) hard disk drives; 2) magnetic random access memories; 3) domain-wall devices; 4) permanent magnets; 5) sensors and actuators; 6) magnetic materials; and 7) organic devices. Among them, magnetic materials for spintronic devices have been surveyed as the first exercise. In this roadmap exercise, we have targeted magnetic tunnel and spin-valve junctions as spintronic devices. These can be used, for example, as a cell for a magnetic random access memory and a spin-torque oscillator in their vertical form as well as a spin transistor and a spin Hall device in their lateral form. In these devices, the critical role of magnetic materials is to inject spin-polarized electrons efficiently into a nonmagnet. We have accordingly identified two key properties to be achieved by developing new magnetic materials for future spintronic devices: 1) half-metallicity at room temperature (RT) and 2) perpendicular anisotropy in nanoscale devices at RT. For the first property, five major magnetic materials are selected for their evaluation for future magnetic/spintronic device applications: 1) Heusler alloys; 2) ferrites; 3) rutiles; 4) perovskites; and 5) dilute magnetic semiconductors. These alloys have been reported or predicted to be half-metallic ferromagnets at RT. They possess a bandgap at the Fermi level $E_{F}$ only for its minority spins, achieving 100% spin polarization at $E_{F}$ . We have also evaluated $text{L1}_{0}$ alloys and $D0_{22}$ –Mn alloys for the development of a perpendicula- ly anisotropic ferromagnet with large spin polarization. We have listed several key milestones for each material on their functionality improvements, property achievements, device implementations, and interdisciplinary applications within 35 years time scale. The individual analyses and the projections are discussed in the following sections.
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    Signal Processing for Dedicated Servo Recording System (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-09-18
    Description: Perpendicular magnetic recording (PMR) in the hard disk drive is approaching its physical limits. In an earlier work, the dedicated servo (DS) recording system has been proposed to provide continuous position error signal for servo, enable higher servo sampling rate, and improve the overall servo performance. A further benefit is that the DS layer results in surface area savings at the data layer. However, it was also reported that the embedded servo layer introduces baseline variation and non-linear transition shift (NLTS) to the readback signal of the data layer. In this paper, we propose novel signal processing techniques to improve the bit error rate (BER) in DS recording. The synchronous averaging technique is proposed to improve the BER in the presence of baseline variation distortions. Further, the servo and data-dependent noise prediction method is proposed to mitigate the effect of the NLTS. Through the use of these techniques the linear density loss from the conventional PMR media is reduced.
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    Quantity Determination of Magnetic Particles Intravenously Administered to Mice Tissues Using Magnetization Measurements (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-09-18
    Description: This paper presents a method that has been developed to determine the quantity of accumulated magnetic particles in mice tissues using magnetization measurements. Dispersions of platelet Fe 3 O 4 particles with the size of 30–50 nm and a saturation magnetization of $sim 80$ Am 2 /kg were intravenously administered to mice. Primary tissues were dried to measure the magnetization. The amounts of Fe 3 O 4 particles accumulated in the tissues were obtained by dividing the magnetization of tissues by the magnetization of Fe 3 O 4 particles under a magnetic field of 39.8 kA/m. A remarkable accumulation of particles was observed in the liver and the spleen, being supported by the observation of tissues using Prussian blue staining. Total Fe 3 O 4 particles accumulated in primary tissues were $sim 38$ –40 and 40–44 wt% against the particles in administered dispersions with 3 and 0.4 wt% contents, respectively. The method developed in this paper is considered to be effective for verifying magnetic hyperthermia and thermoablation therapies, in which the quantity of accumulated particles directly reflects the heating power required for those therapies.
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    Magnetic Anisotropy in Bicomponent Self-Assembled Ni and Ni-Pd Nanowires Studied by Magnetic Resonance Spectroscopy (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-09-18
    Description: Self-ordered arrays of Ni, Ni(50)Pd(50), and Ni(78)Pd(22) nanowires were synthesized by simultaneous electrochemical deposition of Ni and Pd components into porous templates of anodic aluminum oxide using alternating current. This paper is focused on the interplay of structure and chemical composition of Ni and Ni–Pd bicomponent nanowires arrays and the peculiarities of its magnetic anisotropy.
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    All Spin Logic: A Micromagnetic Perspective (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-09-18
    Description: Most investigations of all spin logic (ASL) have been based on the monodomain approximation of magnetization switching. The sensitive and stochastic nature of spin transfer torque (STT) switching creates pressing requirements for analyzing ASL from a micromagnetic perspective also. Hence, in this paper, ASL is studied from a micromagnetic perspective by developing a simulation framework that can capture diffusive spin transport. The spin transport model is calibrated from the existing experimental results on nonlocal spin valve measurements. Then, using this framework, STT switching is studied for input–output nanomagnets with in-plane and perpendicular magnetic anisotropy for ASL devices (ASLDs). Precisely defined architecture and design constraints for such input–output nanomagnets are presented. Further, a previously proposed switching mechanism by driving the nanomagnet into a metastable state is also incorporated into micromagnetic framework. Using the aforementioned mechanism, the critical current required for STT switching can be reduced to as low as 20 $mu $ A. Moreover, the graphene channel ASLD using tunnel contact at the injector is demonstrated for copy and invert logic operations.
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    Coupled Spin Torque Nano Oscillators for Low Power Neural Computation (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-09-18
    Description: We present coupled spin torque nano oscillators (STNOs) as electronic neurons for efficient brain-inspired computation. The coupled STNOs show two distinct outputs, depending on whether the frequencies are locked or not. The locking mechanisms are based on magnetic coupling or injection locking. The neuron firing threshold can be set by tuning the locking range of the coupled STNOs. We employ a crossbar array of programmable memory devices like memristors to implement electronic synapses that work seamlessly with the coupled STNOs for hardware implementation of neural networks. Results show that injection locking-based neuron model can be attractive from scaling point of view and computation like character recognition can be performed with energy consumption per neuron of $sim $ 1.8X and $sim $ 3X lower than the digital and the analog CMOS counterpart, respectively.
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    Electromagnetic Tomography Rail Defect Inspection (2015)
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    Publication Date: 2015-09-18
    Description: With the train’s speed improving, and running interval time decreasing, traditional rail defect inspection methods cannot meet the efficiency requirement of railway industrial standards. In this paper, we propose a new online rail defect inspection method which is using electromagnetic tomography (EMT) technique. The method uses the tomographic approach to measure the alternating magnetic signal modulated by cracks in the rail and then reconstruct the distribution of cracks. The difference to common eddy-current rail defect inspection is, that the EMT can acquire the defect shape and position information. The sensor and signal processing hardware of the EMT rail defect inspection system can be installed on the common passenger or freight train. This solution allows continuous inspection, and therefore reduces the critical accident events caused by rail defect. A model is designed and the forward problem of the model is calculated using electromagnetic finite-element method. Rail defect reconstruction simulations are done using linear backprojection and Tikhonov regularization algorithm to verify the principle of this method. Furthermore, an experimental system is built to simulate the rail defect. The laboratory experiment results show that the electromagnetic rail defect inspection is a feasible approach for reconstruction of the shape and position information of rail defect.
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    Oscillatory Motion of Permanent Magnets Above a Conducting Slab (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-09-18
    Description: This paper provides the 3-D time-dependent analytical solution of the electromagnetic fields and forces emerging if a coil or a permanent magnet moves with a sinusoidal velocity profile relative to a conducting slab of finite thickness. The results can be readily used in application scenarios related to electromagnetic damping, eddy current braking, energy harvesting, or nondestructive testing in order to efficiently analyze diffusion and advection processes in case of harmonic motion. This paper is performed for rectangular and circular coils as well as for cuboidal and cylindrical permanent magnets. The back reaction of the conductor and therewith associated inductive effects are considered. The solutions of the governing equations and the integral expressions for the time-dependent drag and lift force are provided. The analytical results are verified by a comparison with numerical simulations obtained by the finite-element method. The relative difference between the analytically and numerically evaluated force profiles was <0.1%. Exemplary calculations show that the waveforms of both force components strongly depend on the level of constant nominal velocity $v_{0}$ , the magnitude of the velocity oscillation amplitude $v_{1}$ , and the underlying oscillation frequency $f_{v}$ .
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    IEEE Magnetics Society Information (2015)
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    Publication Date: 2015-09-18
    Description: Provides a listing of board members, committee members and society officers.
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    On-Load Voltage Distortion in Fractional-Slot Interior Permanent Magnet Machines (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-09-18
    Description: The mechanism and the influence of the on-load terminal phase voltage distortion by the armature reaction in interior permanent magnet (IPM) machines with fractional-slot concentrated windings (FSCWs) are investigated in this paper, by taking a 12-slot/8-pole machine as an example. The phenomenon is presented first, which shows that the peak voltage will be much higher than the fundamental value, especially under the flux-weakening operation. Then, the mechanism is investigated with the aid of the frozen permeability method. Due to the geometric feature of the FSCW IPM rotor, the armature reaction flux will asymmetrically enhance the local magnetic saturation in the tooth-tips and the rotor lamination region near the rotor ribs, which disrupt the smooth variation of phase flux linkage and lead to a voltage distortion. With the increasing of current advancing angle ( $beta $ ), this effect will become more obvious and result in the higher distortion level. Furthermore, the influences of voltage distortion on the machine torque performance are investigated, which show that it will only contribute to the torque ripple in the constant torque region, but will largely reduce the flux-weakening operation region compared with the ideal one calculated by the fundamental voltages only. Finally, a prototype is manufactured and tested to validate the analyses.
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    Motor-Driven Giant Magnetostrictive Actuator (2015)
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    Publication Date: 2015-09-18
    Description: A typical giant magnetostrictive actuator (GMA) expands a magnetostrictive rod to generate strain by varying the current in the coil that surrounds the magnetostrictive rod. The heat generated by the current deteriorates the GMA performance. In particular, a constant current in the coil is required to produce the desired magnetic field when an output strain should be maintained. The GMA does not produce any mechanical power in this condition, but constant power is being consumed by the excitation coil. This paper presents a new type of motor-driven GMA (MDGMA), which works in a coil-free driven manner. The magnetic field in the iron–gallium alloy (Galfenol), which is a type of magnetostrictive material, is periodically altered by rotating the permanent magnets instead of varying the coil current in the traditional GMA. The proposed MDGMA not only achieves continuous adjustment of the output strain, but can also maintain a constant output strain without consuming any power. In addition, the coil-free design releases the new MDGMA from the heat generated by the excitation coil, which allows the MDGMA to work more stably.
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    3-D Analytical Model for Axial-Flux Eddy-Current Couplings and Brakes Under Steady-State Conditions (2015)
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    Publication Date: 2015-09-18
    Description: This paper presents a 3-D analytical model for axial-flux eddy-current couplings and brakes, leading to closed-form expressions for the torque and the axial force. The proposed model is valid under a steady-state condition (constant speed operation). It takes into account the reaction field due to induced currents in the moving conducting part. In order to simplify the analysis, we adopt the assumption of linearization at the mean radius, and the problem is then solved in 3-D Cartesian coordinates (curvature effects are neglected). The solution is obtained by solving the Maxwell equations with a magnetic scalar potential formulation in the nonconductive regions (magnets and air gap) and a magnetic field strength formulation in the conductive region (copper). Magnetic field distribution, axial force, and torque computed with the 3-D analytical model are compared with those obtained from the 3-D finite-element simulations and experimental results.
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    IEEE Geoscience and Remote Sensing Letters institutional listings (2015)
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    Publication Date: 2015-11-24
    Description: Provides a listing of the editors, board members, and current staff for this issue of the publication.
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    Publication Date: 2015-11-24
    Description: Provides a listing of the editors, board members, and current staff for this issue of the publication.
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    Publication Date: 2015-08-28
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    IEEE International Magnetics Conference 2015 Publication Chair’s Preface (2015)
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    Publication Date: 2015-10-27
    Description: On behalf of the Publication Committee of the IEEE International Magnetic Conference (Intermag 2015), I am pleased to present a selection of papers from Intermag 2015 held at the China National Convention Center, Beijing, China, on May 11-15, 2015. Among the 1759 oral and poster presentations in Intermag 2015, 1076 papers were submitted for a peer review and possible publication in the present volume of the IEEE TRANSACTIONS ON MAGNETICS, covering various aspects of magnetic materials and devices. After a rigorous review process, 590 manuscripts were selected for publication in this issue of the Transactions, strictly following the IEEE rules for conference-related papers.
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    Combustion Synthesis and Characterization of Sm 1– x Tb x FeO 3 Powder (2015)
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    Publication Date: 2015-10-27
    Description: A series of orthorhombic perovskite Sm 1– x Tb x FeO 3 ( $x$ = 0, 0.3, 0.35, 0.4, 0.45, and 0.5) powder was readily prepared by sol–gel combustion process. The Tb-doping effects on the structure, morphology, and magnetic properties of SmFeO 3 have been studied in detail. Pure phase SmFeO 3 was obtained when calcinated at 900 °C for 3 h. By Tb doping, the synthesis temperature of orthorhombic perovskite-type Sm 1– x Tb x FeO 3 powder increased to 1100 °C. Moreover, the ferromagnetic (FM) interactions within the system are effectively enhanced, while the anti-FM coupling is greatly weakened, which is ascribed to the exchange coupling between Tb and Fe ions.
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    Intermag 2015 Chairman’s Foreword (2015)
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    Publication Date: 2015-10-27
    Description: On behalf of the Organizing Committee of the International Magnetics Conference 2015 (Intermag 2015), it is our pleasure to present this issue of the IEEE T ransactions on M agnetics comprising selected papers from Intermag 2015. These categories this year included: Magnetic Recording, Spintronics and Applications, Sensor/MEMS or RF Materials and Devices, Electric Machines and Power Devices, Life Sciences and Applications, Magnetic Thin Film and Nanostructures, Functional Magnetic Materials, Soft Magnetic Materials, Permanent Magnet Materials, and Microscopy Imaging and Characterization.
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    IEEE Transactions on Magnetics publication information (2015)
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    Publication Date: 2015-10-27
    Description: Provides a listing of the editors, board members, and current staff for this issue of the publication.
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    Multihead Multitrack Detection With Reduced-State Sequence Estimation (2015)
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    Publication Date: 2015-10-27
    Description: In shingled magnetic recording, the multihead multitrack (MHMT) detector can better combat the effect of intertrack interference than the single-head single-track detector. Such a detector, however, has prohibitive implementation complexity. In this paper, we propose to use the reduced-state sequence estimation algorithm to significantly reduce the complexity, and render MHMT practical. A commonly used symmetric two-head two-track channel model is considered in this paper. Well-structured reduced-state trellises are constructed by evaluating the effective symbol pair distances and designing proper set partitioning principles. Different trellis configurations are obtained based on the desired performance/complexity tradeoff. Simulation results show that the MHMT detector can achieve near maximum-likelihood performance with a small fraction of the original number of trellis states.
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    Performance Evaluation of TDMR R/W Channel With Head Skew by LDPC Coding and Iterative Decoding System (2015)
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    Publication Date: 2015-10-27
    Description: 2-D magnetic recording (TDMR) exploits 2-D signal processing using the waveforms reproduced by array head from the intended and adjacent tracks to mitigate the effects of intertrack interference. However, an array head has the issue on the degradation of bit error rate (BER) performance due to head skew. In this paper, we evaluate the BER performance of TDMR R/W channel with head skew under a specification of 4 Tbit/in $^{2}$ employing low-density parity check coding and iterative decoding system using a 2-D finite-impulse response filter by computer simulation. The results show that our system can achieve the reliable BER performances by appropriately setting the reader scanning positions at the head skew angle between 0° and 3°.
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    Microwave-Assisted Shingled Magnetic Recording (2015)
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    Publication Date: 2015-10-27
    Description: Simulations of shingled, microwave-assisted magnetic recording were carried out. First, a simplified model of the head field near the corner of the main pole of a write head was used to understand the effect of the spin torque oscillator (STO) position relative to the head. Next, shingled tracks were written and evaluated for two different write head and STO geometries. For shingled recording, locating a rotated STO on the side of the main pole may provide some advantages in that medium grains experience the high-frequency (HF) field for a longer time and the chirality of the HF field does not change as the grains pass by the STO. Recording simulations show that the rotated STO writes smoother track edges at lower densities, but there is little difference in signal-to-noise ratio at high linear densities.
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    Simulation Study of Pulse Laser Quality Effects on Recording Performances of Heat-Assisted Magnetic Recording by Short-Pulse Laser Heating (2015)
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    Publication Date: 2015-10-27
    Description: In heat-assisted magnetic recording (HAMR), a higher recording density is pursued. Short-pulse laser heating is a good way to improve the thermal distribution in the media and to reach the full potential of recording density for the HAMR technology. In this paper, the effects of short-pulse laser qualities, such as pulse frequency deviation, pulse power deviation, and pulsewidth deviation, on recording performances for the HAMR with 100 ps pulse laser heating have been analyzed by simulation. The results indicated that the frequency jitter has the most significant effect on the recording performance among these three parameters. The decreases of signal-to-noise ratio (SNR) for 6% deviations of pulse frequency, pulse power, and pulsewidth are 5, 2, and 1.5 dB, respectively. A certain degree phase delay of pulse laser related to magnetic field switching time is beneficial to reducing the effect of pulse frequency deviation on SNR. When the phase delay changes from 0° to 180°, an SNR improvement of $sim 2$ dB is obtained. The measurement result of a real laser diode output (pulsewidth of 97 ps and pulse frequency of 2 GHz) by gain-switching technology presents a very low frequency deviation (<0.5%). It indicates that the gain-switching technology is a suitable approach for a short-pulse laser generation for the HAMR application.
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    A Study of Timing Recovery for High-Recording-Density Tape Systems (2015)
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    Publication Date: 2015-10-27
    Description: A timing recovery method for a high-density tape storage system is studied in this paper. Since tape systems suffer from large speed variations compared with disk systems, the design of a stable timing recovery scheme that can operate under low signal-to-noise ratio (SNR) conditions is important. In such low SNR scenarios, decision errors made by the detector occasionally cause the phase-locked loop circuit to lose track of the correct signal, which is often called the loss-of-lock (LOL) phenomenon. In order to mitigate the LOL issue, soft information from the Viterbi detector is utilized. It is clarified that the negative effect of unreliable decisions from the detector can be compensated for by dynamically controlling the feedback gain of the timing recovery loop as a function of decision reliability. It is shown that the LOL rate performance can be improved by this approach, with only a minor increase in the implementation complexity.
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    Adjacent and Far Track Erasure Dependence on Media Soft Underlayer Permeability in Shielded Head Recording (2015)
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    Publication Date: 2015-10-27
    Description: The permeability of the magnetic soft underlayer (SUL) was systematically varied by changing the antiferromagnetic exchange coupling, and the effect on recording performance and adjacent track erasure (ATE) and far track erasure (FTE) was investigated. Perpendicular magnetic recording performance highly depends on SUL permeability. Highly permeable SUL can reduce the head erasure field located at far tracks from a stressing track but generates more erasure at adjacent tracks near the side shield. Optimum SUL permeability can improve on-track performance with tolerable ATE or FTE. Finite element method models of a shielded write head and media with different SUL permeabilities were performed. A high-permeability SUL has a larger impact on short-time high FTE fields and potentially affects the erasure at 3–6 tracks from main pole. This shows agreement with experimental results.
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    A Portable Dynamic Switching Model for Perpendicular Magnetic Tunnel Junctions Considering Both Thermal and Process Variations (2015)
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    Publication Date: 2015-10-27
    Description: In this paper, we develop a portable dynamic switching model for perpendicular magnetic tunnel junctions (MTJs) considering both thermal fluctuation and process variations. The model uses macro-spin approximations where the free layer (FL) of MTJ is assumed to be in a single-domain structure. The model can generate dynamic switching transience curves at different current densities and simulate the switching successful rates for the given pulse lengths at different current densities. We also use the model to study the impact of temperature and device process variations on the switching performance, such as switching time variations. It is shown that the temperature effect is not significant when the switching current is relatively larger, and hence the spin current effect is strong enough to overtake the temperature effect. As for the process variations, it is shown that the FL thickness has a more significant effect on the switching time than the size of the FL does.
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    Time-Dependent Transport in Gated Topological Insulators (2015)
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    Publication Date: 2015-10-27
    Description: We investigate the transport property of the surface states of a topological insulator (TI) in the presence of a time-dependent potential. We find that the normally incident electrons can be perfectly transmitted through the time-dependent region under symmetrical potential configuration. But the perfect transmission is broken upon application of an asymmetrical potential. The contour plot of the transmission shows a fishlike transmission profile, which varies according to the potential configuration, and the strength and frequency of the time-dependent potential. This distinct transmission characteristic may be utilized to modulate the transport property of the TI.
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    Magnetic Stochastic Oscillators: Noise-Induced Synchronization to Underthreshold Excitation and Comprehensive Compact Model (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-10-27
    Description: Superparamagnetic tunnel junctions (SMTJs) are noise powered stochastic oscillators, which can harness thermal energy through phenomena such as stochastic resonance and noise-induced synchronization. This enables them to operate with the minimal externally supplied energy, and therefore, makes them promising candidates for implementing bioinspired computing schemes. These applications require understanding how SMTJs can be integrated into CMOS circuits. In this paper, we present a compact model of SMTJ, written in the VerilogA language, that can be used within standard integrated circuit design tools. This compact model is based on the Néel–Brown model and allows for fast simulations. We show that this model can reproduce the experimental characterization of a sample subjected to different values of dc currents. Then, we definitively demonstrate the validity of the model by confronting it to the experimental results in the case of a complex phenomenon: noise-induced synchronization.
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    Spin-Orbitronics Memory Device With Matching and Self-Reference Functionality (2015)
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    Publication Date: 2015-10-27
    Description: Spin–orbit torque generated by spin-torque interaction provides a new writing mechanism for spintronic devices. This paper investigates spintronic memory devices for match-in-space, content addressable, and self-reference applications, utilizing spin–orbit torque generated by spin-torque interaction combined with the conventional spin torque generated by magnetization polarization. New system and device solutions are proposed for targeting different spintronic technology development stages. These proposals include spin content addressable memory (CAM) structure of DRAM cell with embedded MRAM, dual spin Hall magnetic tunneling junction CAM device, and spin-orbitronics memory device, capable of multi-bit match-in-space and single-bit nondestructive self-reference functionality.
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    Modulation Rate Study in a Spin-Torque Oscillator-Based Wireless Communication System (2015)
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    Publication Date: 2015-10-27
    Description: We study a wireless communication system based on a magnetic tunnel junction spin-torque nano-oscillator (STNO) by employing amplitude-shift-keying modulation. By varying the pulse modulation frequency ( $f_{m}$ ) from 1 kHz to 2 MHz and distance ( $D$ ) between the antenna from 25 to 150 cm, we show a maximum data rate of 6 Mb/s (at $D=25$ cm and $f_{m}=1$ MHz), a limit imposed by our setup and noise generated by the STNO itself. We also report the average amplitude noise ( $S_{delta a}$ ) and average white frequency noise ( $S_{rm wh}$ ) of the wireless communication system and discuss their dependence on the distance between the antennas.
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    Spin-Torque Diode-Based Radio-Frequency Detector by Utilizing Tilted Fixed-Layer Magnetization and In-Plane Free-Layer Magnetization (2015)
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    Publication Date: 2015-10-27
    Description: We report a novel spin-torque diode (STD) radio-frequency detector by utilizing tilted fixed-layer magnetization and in-plane free-layer magnetization. Through macrospin modeling and numerical simulation, we study both the direct current (dc) dependence and the perpendicular external field dependence of the output voltage of the detector. We systematically investigate both the fixed-layer magnetization tilt angle dependence and the dc dependence of the resonance detection regime of the detector. It is found that an ultrawide resonance detection regime 6.5 GHz can be achieved, which is 1200% higher than the traditional STD magnetic tunnel junction detector with in-plane fixed-layer magnetization.
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    High-Frequency Low-Power Magnetic Full-Adder Based on Magnetic Tunnel Junction With Spin-Hall Assistance (2015)
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    Publication Date: 2015-10-27
    Description: Perpendicular-anisotropy magnetic tunnel junction (MTJ) is one of the most promising candidates to build hybrid logic-in-memory architecture, because of its nonvolatility, infinite endurance, and 3-D integration with a CMOS technology. A novel magnetic full-adder (MFA) based on this architecture is proposed, with MTJs switched by spin-Hall-assisted spin-transfer torque (STT). Owing to the assistance of spin-Hall effect (SHE), MTJ switching time can significantly be reduced, and high operation frequency can be achieved. Moreover, the endurance of oxide barrier is largely enhanced as the requirement of lower write voltage. Using an industrial CMOS 28 nm design kit and a physics-based three-terminal spin-Hall-assisted STT-MTJ model, functionality and performance of the proposed MFA have been simulated and validated. A 1 ns STT current pulse assisted by 0.35 ns SHE current pulse is sufficient to switch the MTJ configuration. When compared with the previous MFAs based on STT-MTJ, the proposed MFA achieves 38% less operation time and 31% less power consumption to perform read and write operations.
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    Preparation of Anomalous Magnetoresistance and Transport Properties of Itinerant Ferromagnet Fe 1– x Co x Si (2015)
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    Publication Date: 2015-10-27
    Description: DC magnetization, electrical transport, and magnetoresistance (MR) measurements of Fe 1– x Co x Si single crystals with $x approx $ 0.7–0.3 are reported. Fe 1– x Co x Si series presents a typical Stoner band excitation characteristic in the field-dependent magnetization profile. Co-doping ( x > 0.3) in the Fe 1– x Co x Si compound shows a semiconductor–to–metal transition. Enhanced positive MR has been observed when $sim$ 1/3 of the Fe was substituted with Co, which suggests that the spin density of states in the minor band (semiconductor characteristic) dominates the electronic properties.
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    The Oxygen Vacancies Correlated Ferromagnetism in Transition Metal-Doped ZnO Nanowires (2015)
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    Publication Date: 2015-10-27
    Description: The magnetic properties of $3d$ transition metal ( ${mathrm{ TM}}={mathrm{ V}}$ , Cr, and Mn)-doped ZnO nanowires (NWs) with and without oxygen vacancy are investigated by ab initio calculations. The magnetic moments can be induced by TM impurities in ZnO NWs, localized on the $3d$ TM atoms and their neighboring O atoms. Furthermore, the ferromagnetism in V-, Cr-, and Mn-doped ZnO NWs is strongly correlated with oxygen vacancies.
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    Investigation of Magnetic Properties of Sr-Doped Ba 3– x Sr x Co 2 Fe 24 O 41 Z-type Hexaferrite by Mössbauer Spectroscopy (2015)
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    Publication Date: 2015-10-27
    Description: The polycrystalline Ba 3– x Sr x Co 2 Fe 24 O 41 ( $x = 0.0, 0.5, 1.0$ , and 1.5) samples were synthesized by the solid-state reaction method. The crystalline structure of the samples was found to be a hexagonal structure with a space group of $P6_{3}/mmc$ . The lattice constants $a_{0}$ , $c_{0}$ , and $V_{u}$ of the samples decrease with increasing Sr concentration. From the field-dependent hysteresis curves under 10 kOe at 295 K, the values of $M_{s}$ increase while the values of $H_{c}$ decrease. The zero-field-cooled magnetization curves under 100 Oe between 4.2 and 300 K show the spin transition, and the value of $T_{s}$ decreases from 230 K for $x=0.0$ to 135 K for $x = 1.5$ with increasing Sr concentration due to the reduction of planar anisotropy with the difference in ionic radius between Ba 2+ and Sr 2+ ions. From the isomer shift value ( $delta $ ) obtained from Mössbauer spectra, the charge states of all samples are determined to be Fe 3+ high spin state. With increasing Sr concentration, the reduction of hyperfine field $langle H_{mathrm {hf}}rangle $ suggests the change in hyperfine interaction between Fe ions because of the larger ionic radius of Ba 2+ ion than that of Sr 2+ ion, leading to decreasing $M_{s}$ .
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    Effects of Annealing Temperature on Magnetic Properties of Co Thin Films on Si (100) (2015)
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    Publication Date: 2015-10-27
    Description: The effects of silicide formation on the surface structure and magnetic properties of Co thin films on Si (100) were investigated. Annealing temperature significantly changed the formation of silicide. CoSi phase was formed during annealing at 600 °C and 700 °C. CoSi 2 phase was formed during annealing at 800 °C. The anisotropy of Co/Si (100) films changed due to the formation of silicide. In addition, both the particle size and the surface roughness increased with the increase of annealing temperature, which led to the increase of coercivity up to 700 °C. However, the better crystallinity $ {H_{C}}$ decreased at 800 °C.
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    Co-Based Amorphous Material for Giant Magnetoimpedance and Fluxgate Sensing Cores (2015)
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    Publication Date: 2015-10-27
    Description: Alloy composition (Co 94 Fe 6 ) 72.75 Si 12.25 B 13.25 Cr 1.75 was designed to develop nearly zero-magnetostrictive materials in the form of ribbons and wires to obtain suitable magnetic properties for use as giant magnetoimpedance (GMI) and low-noise fluxgate sensor cores. During the development of magnetic sensing core using amorphous wires of diameter 80 $mu text{m}$ for GMI sensing, we observed a maximum impedance change (GMI ratio) of 430% with as-cast wires, which further enhanced to 650% when annealed at 300 °C for 5 min. The effect of annealing temperature and stress on the magnetic properties of fluxgate sensing core materials has been studied. Magnetic hysteresis loops were measured with 3-mm-wide and 45- $mu text{m}$ -thick amorphous ribbons on a toroidal ring of 50 mm diameter for fluxgate sensor core. A coercivity of 10.57 A/m and saturation field of $sim$ 150 A/m were observed with as-quenched ribbon, which improved to a coercivity of 2.16 A/m and saturation field $sim$ 100 A/m when annealed without stress just above its Curie temperature. An induced anisotropy transverse to excitation direction was achieved by applying temperature with stress and time (300 °C/ 100 MPa/ 20 min) to use it for fluxgate sensor core.
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    Temperature Dependence of Lancet Domains in Grain-Oriented Fe-3%Si Steels (2015)
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    Publication Date: 2015-10-27
    Description: The change in the lancet domains of grain-oriented steels in the range from the room temperature (RT) to far above the Curie temperature ( $T_{c}$ ) was investigated using the domain observations by the photoemission electron microscopy combined with X-ray magnetic circular dichroism and the domain theory. Lancet domains were observed to be annihilated at the temperature below $T_{c}$ , with 180° basic domains occurring. The minimization of the magnetic free energy considering the intrinsic physical constants as the functions of the temperature enabled us to quantitatively explain the observed temperature dependence of lancet domains. The present model revealed that the temperature dependence of the cubic anisotropic constant greatly contributes to the annihilation of lancet domains at the temperature below $T_{c}$ . The improvement of the crystal misorientation, the thinner thickness, and the enhancement of the tensile stress applied to the steels are predicted to reduce the annihilation temperature of lancet domains. The tensile stress required to annihilate lancet domains at 200 °C is predicted to allow approximately half the stress to annihilate them at RT.
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    Multidomain Structures in Magnetic Microwire (2015)
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    Publication Date: 2015-10-27
    Description: We report investigations on temperature-induced transformation of magnetic domain structures in the Fe-rich amorphous glass-covered microwires. The images of domain structures and magnetization reversal process were registered by means of magnetooptical Kerr microscopy. The coexistence of two different types of surface domain structures with helical magnetization components has been found. The obtained results discussed in the frame of the model supposed the stress influence on the domain structure.
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    Study on the Contribution of Magnetization Mechanisms in NiZn Ferrites (2015)
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    Publication Date: 2015-10-27
    Description: NiZn ferrites with different amounts of CuO have been synthesized by the conventional ceramic method and their spectra of complex permeability were investigated. The CuO contents affect the grain size and microstructure of NiZn ferrite obviously, which also result in the variation of saturation magnetization, magnetocrystalline anisotropy, and porosity. Along with these relevant magnetic properties, the superposition of magnetizing mechanisms was testified to be predominant in determining the value of permeability. To manifest the increase of initial permeability, the permeability spectra of NiZn ferrite were resolved into two components, including domain wall movement and spin rotation magnetization. The fitting results show that, with the increasing amounts of CuO, the dominant contribution to dynamic magnetization changes from spin rotation magnetization mechanism to domain wall movement.
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    Fe-Based Soft Magnetic Composites With High ${B}_{s}$ and Low Core Loss by Acidic Bluing Coating (2015)
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    Publication Date: 2015-10-27
    Description: Fe-based soft magnetic composites (SMCs) with high $B_{s}$ and low core loss were fabricated by acidic bluing coating. Effects of reaction time and annealing temperature on the magnetic properties of the SMCs have been investigated. The Fe 3 O 4 grows as the coating layer of the Fe powders and converts to Fe 2 O 3 with increased reaction time. The iron oxide coating layer gives rise to highly normalized saturation magnetization (0.954–0.928) and low core loss due to its high electrical resistivity. The lowest core loss (785.1 mW/cm 3 measured at 50 mT and 100 kHz) of the Fe SMCs can be achieved with the reaction time of 30 min and annealing temperature of 550 °C.
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    The Structure and Magnetic Moment Study of Fe–Si–Al by First-Principles Calculation (2015)
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    Publication Date: 2015-10-27
    Description: In general, the contribution to the reinforcement of the magnetism in the order–disorder transition of FeAl alloys depends on their Fe content and the order–disorder transition. However, the Fe 75 Si 15 Al 10 alloys were investigated by means of first-principles calculation and experimental verification. We found that the mechanism of the magnetic moment ( $mu _{m}$ ) reinforcement is the exchange interaction of Fe atom with its nearest neighbor Fe atoms. In addition, the exchange interaction of Fe–Fe atoms is affected by internal stress, lattice distortion, the Fe content, and the position of nearest neighbor nonferrous atoms (Si and Al atoms). At the annealing temperature of 600 °C , the $mu _{m}$ is the maximum value, as the ordered DO3 structure is transformed extremely.
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    Microstructure and Texture Evolution of Strip Casting Grain-Oriented Silicon Steel (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-10-27
    Description: A 0.23 mm thick grain-oriented silicon steel sheet was successfully produced based on strip casting and two-stage cold rolling route. The evolutions of microstructure and texture along the complete processing route were briefly investigated. It was shown that the as-cast strip was composed of coarse ferrite grains and martensite, and the texture was mainly characterized by strong {001} $langle 0vwrangle $ texture. Goss texture was absent in the hot-rolled strip, which was distinct from the well accepted results that Goss texture had its origin during hot rolling. After the cycle of the first-stage cold rolling, an intermediate annealing, the second-stage cold rolling, and a primary annealing, the strip exhibited a fully recrystallized microstructure with a weak $alpha $ -fiber texture and a relatively strong $gamma $ -fiber texture. Goss texture was not observed through the thickness of the primary annealed strip. This was significantly different from the previous results that Goss texture was the most populous component in the primary recrystallization texture of two-stage route in conventional process. After secondary recrystalization annealing, the magnetic induction $B_{8}$ of the sheet was as high as 1.84 T.
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    Electronic ISSN: 1941-0069
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  • 95
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    Mössbauer Studies Magnetic Properties of BaCo 2− x Zn x Fe 16 O 27 (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-10-27
    Description: The BaCo 2− x Zn x Fe 16 O 27 ( x = 0, 0.5, 1) samples were prepared by solid-state reaction method. The prepared samples are single-phased, and their crystal structures are determined to be hexagonal with a space group of P6 3 /mmc from Rietveld refinement analysis. The magnetic saturation values were increasing, and the values of coercivity were decreasing with increasing Zn contents. The experimentally measured temperature dependence of magnetization curves shows magnetic transitions. We have measured Mössbauer spectroscopy at various temperatures to investigate microscopic magnetic properties. We analyze the obtained spectra with the five magnetic sites of $4f_{mathrm {VI}}$ , $6g$ + $4f_{mathrm {VI}}$ , $4e_{mathrm {IV}}$ , + $4f_{mathrm {IV}}$ , $12k_{mathrm {VI}}$ , and $2d_{mathrm {V}}$ . In addition, from the Mössbauer spectra, we notice the changes in the magnetic hyperfine field and electric quadrupole shift. The substituted Zn 2+ ions are located at tetrahedral site, and increase the $M_{s}$ . Curie temperatures were determined from zero-field-cooled magnetizations measurement.
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  • 96
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    Modeling of Temperature Effects on Magnetic Property of Nonoriented Silicon Steel Lamination (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-10-27
    Description: This paper proposed a temperature-dependent iron loss model and corresponding dynamic hysteresis model, where temperature coefficient ${k}$ is introduced to consider the thermal effect on eddy-current loss. The iron loss model is validated by massive experimental measurement of test samples, 1174 combinations of various temperatures, magnetic inductions, and frequencies for nonoriented silicon steel specimen. The relative error of the model is $sim 11$ % in a wide range of 50–400 Hz, 26 °C–200 °C, and 0–2 T. The proposed method can be applicable to other types of magnetic materials as long as whose resistivity rate exhibits approximately linear thermal dependence within a temperature range of 26 °C–200 °C.
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  • 97
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    Magnetic Behavior of Soft Magnetic FeMoCuB Metallic Glass at Low Temperature (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-10-27
    Description: We have studied a NANOPERM-type Fe 76 Mo 8 Cu 1 B 15 metallic glass with emphasis upon its magnetic properties at low temperatures. Temperature evolution of magnetization measured under zero-field cooling and field cooling conditions upon samples with different amounts of nanocrystalline grains have unveiled a two-phase behavior in temperature range from 50 up to about 200 K. In order to understand the correlation between the structural arrangement and resulting magnetic properties, we have employed a local probe method of 57 Fe Mössbauer spectrometry performed at 300 and 4.2 K. The latter experiments were also accomplished in an external magnetic field of 6 T. Magnetically distinct regions were unveiled in the amorphous structure of the as-quenched and annealed samples. They are demonstrated by the distributions of hyperfine magnetic fields.
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  • 98
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    Studies of High-Frequency Giant Magnetoimpedance Effect in Co-Rich Amorphous Microwires (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-10-27
    Description: We studied giant magnetoimpedance (GMI) effect and magnetic properties of various Co-rich amorphous microwires. We measured the values of magnetic field dependence of the GMI ratio up to gigahertz frequency range, and observed quite high GMI ratio in as-prepared Co-rich microwires even at gigahertz frequencies. We observed the different values of the magnetic anisotropy field obtained from the hysteresis loops and the impedance curves. Observed dependence can be explained considering different magnetic anisotropy in the surface layers and in the inner part of metallic nucleus and skin depth effect. Features of high-frequency GMI effect have been analyzed using ferromagnetic resonance-like approximation.
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  • 99
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    Preparation and Application on Antenna of Soft Ferrite Core for Wireless Sensor Networks (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-10-27
    Description: In this paper, soft magnetic Mn–Zn ferrite samples have been prepared through oxide processes. The magnetic properties and the phase structures were investigated. It was found that the optimal sintering temperature is about 1360 °C. The initial permeability of the samples is 1700–2300, Curie temperature $T_{c}$ is about 140 °C−180 °C, and cutoff frequency fr is about 1 MHz. Moreover, the initial permeability of the samples is relatively stable, and its temperature coefficient is $sim 10^{-6}$ /°C at the temperature range of 20 °C−60 °C. High-frequency simulation results show that the Mn–Zn ferrites samples are suitable for the application of the wireless sensor networks in theory.
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    Enhancement of Coercivity of Nd-Fe-B Ultrafine Powders Comparable With Single-Domain Size by the Grain Boundary Diffusion Process (2015)
    Institute of Electrical and Electronics Engineers (IEEE)
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    Publication Date: 2015-10-27
    Description: We describe the enhancement of coercivity of Nd-Fe-B ultrafine powders by the grain boundary diffusion (GBD) process. An effective method for increasing coercivity in Nd-Fe-B sintered magnets is the refinement of the Nd 2 Fe 14 B grains. We decreased the powder size of the grains to <1 $mu$ m by combining hydrogenation-disproportionation-desorption-recombination, hydrogen decrepitation, and helium jet milling (He-JM). The powder size was comparable with the single-domain size of Nd 2 Fe 14 B. However, the coercivity of the ultrafine powders was lower than the value expected from their powder size, which was due to the decrease in the Nd content of the powders and lack of the Nd-rich phase on the powder surface. We performed the GBD process at 700 °C for 30 min before He-JM to increase the amount of Nd-rich phase on the powder surface. The powder showed a high coercivity of $mu_{0}{rm H}_{cJ} = 2$ T after annealing at 600 °C for 30 min. Therefore, the GBD process is an effective method for increasing the coercivity of ultrafine He-JM powders. The process increases the amount of the Nd-rich phase on the powder surface, which is converted to the liquid phase by annealing, and reduces the number of sites for reverse domain nucleation.
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