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  • Articles  (5,616)
  • Institute of Physics  (4,205)
  • Hindawi  (1,411)
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  • Electrical Engineering, Measurement and Control Technology  (5,616)
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  • Articles  (5,616)
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  • 2010-2014  (2,706)
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  • 1
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    Photocatalytic Water Splitting for Hydrogen Production with Novel M2YbSbO7 (M = In, Gd, Y) by Using Visible Light Photoenergy (2012)
    Hindawi
    Details
    Publication Date: 2012-02-24
    Description: Novel photocatalysts M2YbSbO7 (M=In, Gd, Y) were synthesized by solid state reaction method for the first time. A comparative study on the structural and photocatalytic properties of M2YbSbO7 M2YbSbO7 (M=In, Gd, Y) was reported. The results showed that In2YbSbO7, Gd2YbSbO7, and Y2YbSbO7 crystallized with the pyrochlore-type structure, cubic crystal system and space group Fd3m. For the photocatalytic water splitting reaction, H2 or O2 evolution was observed from pure water with In2YbSbO7, Gd2YbSbO7, or Y2YbSbO7 as the photocatalyst under visible light irradiation. (wavelength>420 nm). Moreover, under visible light irradiation (λ>420 nm), H2 and O2 were also evolved by using In2YbSbO7, Gd2YbSbO7, or Y2YbSbO7 as catalyst from CH3OH/H2O and AgNO3/H2O solutions respectively. The In2YbSbO7 photocatalyst showed the highest activity compared with Gd2YbSbO7 or Y2YbSbO7. At the same time, The Y2YbSbO7 photocatalyst showed higher activity compared with Gd2YbSbO7. The photocatalytic activities were further improved under visible light irradiation with In2YbSbO7, Gd2YbSbO7, or Y2YbSbO7 being loaded by Pt, NiO, or RuO2. The effect of Pt was better than that of NiO or RuO2 for improving the photocatalytic activity of In2YbSbO7, Gd2YbSbO7, or Y2YbSbO7.
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  • 2
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    Eosin Yellowish Dye-Sensitized ZnO Nanostructure-Based Solar Cells Employing Solid PEO Redox Couple Electrolyte (2012)
    Hindawi
    Details
    Publication Date: 2012-03-13
    Description: ZnO nanostructures are synthesized by low-temperature methods, and they possess polycrystalline hexagonal wurtzite structure with preferential c-axial growth. Morphological study by SEM shows the presence of ~30 nm sized spherical-shaped ZnO nanoparticle, the branched flower-like ZnO composed of many nanorods (length: 1.2 to 4.2 μm and diameter: 0.3 to 0.4 μm), and ~50 nm diameter of individual ZnO nanorods. Reduction in photoemission intensity of nanorods infers the decrease in electron-hole recombination rate, which offers better photovoltaic performance. The dye-sensitized solar cell (DSSC) based on ZnO nanorods sensitized with Eosin yellowish dye exhibits a maximum optimal energy conversion efficiency of 0.163% compared to that of nanoparticles and nanoflowers, due to better dye loading and direct conduction pathway for electron transport.
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  • 3
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    An -Firm Real-Time Aware Fault-Tolerant Mechanism in Wireless Sensor Networks (2012)
    Hindawi
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    Publication Date: 2012-12-25
    Description: Many real-time routing mechanisms have been proposed to support the newly developed wireless sensor networks (WSNs) applications such as the transmission and retrieval of multimedia traffic. However, the inherent source constraints of sensor network and instability of wireless communication set quite a problem for the existing routing mechanisms to meet the quality of service (QoS) requirements of some specific QoS-aware applications. Hence, real-time fault-tolerant schemes are highly desired for WSNs to address these challenges. In this paper, we propose an -firm-based real-time fault-tolerant mechanism, which helps routing mechanisms to achieve specific QoS requirement by employing a local status indicator (LSI) at each sensor node to monitor and evaluate the local conditions of node and network. Therefore, specific fault recovery mechanisms could be implemented for ensuring an acceptable QoS performance, according to the evaluated LSI values. By using this fault-tolerant scheme, each node dynamically adjusts its transmission capability to mitigate the performance degradation of real-time service caused by network faults and to maintain the desired reliability and timeliness. Simulation result shows that LSI cannot only help to reduce the effects of congestion, link failure, and void, but also reach higher successful transmission ratio and smaller transmission delay.
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  • 4
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    Benzothiazine Dyes/2,4,6-Tris(trichloromethyl)-1,3,5-triazine as a New Visible Two-Component Photoinitiator System (2012)
    Hindawi
    Details
    Publication Date: 2012-12-25
    Description: Novel photoinitiator systems working under visible radiation were studied. The photoredox pair constructed with dye derivatives of 12H-quinoxalino-[2,3-b][1,4]-benzothiazine (1–3) and 2,4,6-tris(trichloromethyl)-1,3,5-triazine (Tz) were found to be effective initiators for free radical polymerization of trimethylolpropane triacrylate (TMPTA) using VIS light. Photosensitization occurred through electron transfer, which was confirmed by the observation of a radical cation of the studied dyes. The 1•+ was also characterized in cryogenic matrices (mixture of CH2Cl2 and ionic liquid: 1-butyl-3-methylimidazolium hexafluorophosphate ( −)) and its reactivity was investigated by means of pulse radiolysis in solution at room temperature. In a halogenated solvent and in a mixture of CH2Cl2 and  −, the radical cation 1•+ underwent deprotonation to form a neutral radical 1•, which was stable in the second time scale. During photolysis of the 1/Tz photoredox pair in 1-methyl-2-pyrrolidone and monomer, the formation of a neutral radical 1• was not observed.
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  • 5
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    Distributed Compressed Video Sensing in Camera Sensor Networks (2012)
    Hindawi
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    Publication Date: 2012-12-31
    Description: With the booming of video devices ranging from low-power visual sensors to mobile phones, the video sequences captured by these simple devices must be compressed easily and reconstructed by relatively more powerful servers. In such scenarios, distributed compressed video sensing (DCVS), combining distributed video coding (DVC) and compressed sensing (CS), is developed as a novel and powerful signal-sensing and compression algorithm for video signals. In DCVS, video frames can be compressed to a few measurements in a separate manner, while the interframe correlation is explored by the joint recovery algorithm. In this paper, a new DCVS joint recovery scheme using side-information-based belief propagation (SI-BP) is proposed to exploit both the intraframe and interframe correlations, which is particularly efficient over error-prone channels. The DCVS scheme using SI-BP is designed over two frame signal models, the mixture Gaussian (MG) model and the wavelet hidden Markov tree (WHMT) model. Simulation results evaluated on two video sequences illustrate that the SI-BP-based DCVS scheme is error resilient when the measurements are transmitted through the noisy wireless channels.
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  • 6
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    A Compact Multiband Notch UWB Antenna (2012)
    Hindawi
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    Publication Date: 2012-12-21
    Description: A simple and a compact coplanar waveguide (CPW) ultrawide band (UWB) antenna is presented. Multiband stop function is achieved by two different types of band stop resonators. One is a tilted square spiral slot resonator of different size and length etched on the patch and the other is a coupled resonator etched on the ground plane. These resonators provide considerable increase in notch bandwidth at the stop bands. The proposed antenna has a total size of  mm2. The designed antenna achieves pass band performance at 1.8–2.1 GHz (15.38%), 3.0–3.2 GHz (6.45%), 4.4–4.7 GHz (6.59%), 6.3-6.4 GHz (1.57%), and 8–11.2 GHz (33.33%) where VSWR
    Print ISSN: 1687-5869
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  • 7
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    Development of a Novel Double-Ring Deployable Mesh Antenna (2012)
    Hindawi
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    Publication Date: 2012-12-11
    Description: This paper addresses a type of deployable mesh antenna consisting of the double-ring deployable truss edge frame and the cable net reflector. The structural design concept of the deployable antennas is presented. The deployable truss is designed and the geometric relationship of each strut length is formulated. Two types of radial truss elements are described and compared. The joint pattern and the active cables of the final design concept are determined. The pattern of the cable net is the three-orientation grid. Two connection schemes between the reflector and the deployable edge frame are investigated. The design parameters and the shape adjustment mechanism of this cable net are determined. The measurement test technologies of the antennas on the ground including test facilities, deployment test, and measurement and adjustment test are proposed. The antenna patterns are analyzed based on the real surfaces of the reflector obtained by the reflective surface accuracy measurement. The tests and analytic results indicated that the accuracy of the reflective surface is high and is suitable for low-frequency communication.
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  • 8
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    A Systemic Approach to the Compensation of Rain Attenuation in Ka-Band Communication Satellites (2012)
    Hindawi
    Details
    Publication Date: 2012-12-05
    Description: Rain attenuation at Ka-band is a severe phenomenon that drastically impairs satellite communications at these frequencies. Several adaptive compensation techniques have been elaborated to counteract its effects and most often applied one at a time. The present paper proposes the contemporary exploitation of different techniques in a combined approach. Such an integrated approach is thoroughly analyzed in a simplified scenario and will be shown to achieve a very effective solution, making the Ka-band spectrum fully available for broadband satellite applications and network-centric systems.
    Print ISSN: 1687-5826
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  • 9
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    GPR-Based Landmine Detection and Identification Using Multiple Features (2012)
    Hindawi
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    Publication Date: 2012-10-11
    Description: This paper presents a method to identify landmines in various burial conditions. A ground penetration radar is used to generate data set, which is then processed to reduce the ground effect and noise to obtain landmine signals. Principal components and Fourier coefficients of the landmine signals are computed, which are used as features of each landmine for detection and identification. A database is constructed based on the features of various types of landmines and the ground conditions, including the different levels of moisture and types of ground and the burial depths of the landmines. Detection and identification is performed by searching for features in the database. For a robust decision, the counting method and the Mahalanobis distance-based likelihood ratio test method are employed. Four landmines, different in size and material, are considered as examples that demonstrate the efficiency of the proposed method for detecting and identifying landmines.
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  • 10
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    Performance Comparison of UWB Pulse Modulation Schemes under White Gaussian Noise Channels (2012)
    Hindawi
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    Publication Date: 2012-10-03
    Description: In this paper, and for the first time, the performance of various ultra wideband pulse modulation schemes are discussed and compared in terms of narrowband interference robustness, symbol error rate, system complexity, data rate, and maximum transmit power with respect to transceiver distance and channel capacity. The channel model is the UWB IEEE 802.15.3a multipath indoor channel model under additive white Gaussian noise. The transmit power was evaluated by integrating the fifth derivative of the power spectrum density of the Gaussian pulse over the whole bandwidth.
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  • 11
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    Transforming Area Coverage to Target Coverage to Maintain Coverage and Connectivity for Wireless Sensor Networks (2012)
    Hindawi
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    Publication Date: 2012-10-04
    Description: Area coverage is one of the key issues for wireless sensor networks. It aims at selecting a minimum number of sensor nodes to cover the whole sensing region and maximizing the lifetime of the network. In this paper, we discuss the energy-efficient area coverage problem considering boundary effects in a new perspective, that is, transforming the area coverage problem to the target coverage problem and then achieving full area coverage by covering all the targets in the converted target coverage problem. Thus, the coverage of every point in the sensing region is transformed to the coverage of a fraction of targets. Two schemes for the converted target coverage are proposed, which can generate cover sets covering all the targets. The network constructed by sensor nodes in the cover set is proved to be connected. Compared with the previous algorithms, simulation results show that the proposed algorithm can prolong the lifetime of the network.
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  • 12
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    Design and Analysis of Printed Yagi-Uda Antenna and Two-Element Array for WLAN Applications (2012)
    Hindawi
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    Publication Date: 2012-10-05
    Description: A printed director antenna with compact structure is proposed. The antenna is fed by a balanced microstrip-slotline and makes good use of space to reduce feeding network area and the size of antenna. According to the simulation results of CST MICROWAVE STUDIO software, broadband characteristics and directional radiation properties of the antenna are explained. The operating bandwidth is 1.8 GHz–3.5 GHz with reflection coefficient less than −10 dB. Antenna gain in band can achieve 4.5–6.8 dBi, and the overall size of antenna is smaller than . Then the antenna is developed to a two-element antenna array, working frequency and relative bandwidth of which are 2.15–2.87 GHz and 28.7%, respectively. Compared with antenna unit, the gain of the antenna array has increased by 2 dB. Thus the proposed antenna has characteristics of compact structure, relatively small size, and wideband, and it can be widely used in PCS/UMTS/WLAN/ WiMAX fields.
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  • 13
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    Improved DV-Hop Node Localization Algorithm in Wireless Sensor Networks (2012)
    Hindawi
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    Publication Date: 2012-08-17
    Description: An improved algorithm is put forward to improve the poor locating performance of the DV-Hop algorithm, which is one of the range-free algorithms in wireless sensor networks. Firstly, we set some anchor nodes at the border land of monitoring regions. Secondly, the average one-hop distance between anchor nodes is modified, and the average one-hop distance used by each unknown node for estimating its location is modified through weighting the received average one-hop distances from anchor nodes. Finally, we use the particle swarm optimization to correct the position estimated by the 2D hyperbolic localization algorithm, which makes the result closer to the actual position. The simulation results show that the proposed algorithm has better localization performance in the localization precision and stability than the basic DV-Hop algorithm and some existing improved algorithms.
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  • 14
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    Metallisation and Interconnection of e-Beam Evaporated Polycrystalline Silicon Thin-Film Solar Cells on Glass (2012)
    Hindawi
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    Publication Date: 2012-10-12
    Description: One inherent advantage of thin-film technology is the possibility of using monolithic integration for series interconnection of individual cells within large-area modules. Polycrystalline silicon thin-film solar cells do not rely on transparent conducting oxide layers as the high sheet conductivity of the emitter and BSF layers enables the lateral flow of current from the film to the metal contacts. This paper presents a new method for the fabrication of e-beam evaporated polycrystalline thin-film photovoltaic minimodules on glass. The method involves electrically isolating minicells, by laser scribing, and then forming an isolation layer on each laser scribe. The main advantage of this metallisation is to have a single aluminium evaporation step for the formation of finger and busbar features, as well as for series interconnection.
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  • 15
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    An Energy-Efficient MAC Protocol Employing Dynamic Threshold for Wireless Sensor Networks (2012)
    Hindawi
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    Publication Date: 2012-10-18
    Description: Energy efficiency is a critical issue for sensor network since the network lifetime depends on efficient management of the energy resource of sensor nodes. Particularly, designing energy efficient MAC protocol has a significant influence on the performance of wireless sensor network with regards to the energy. The existing MAC protocols developed for sensor network try to avoid energy waste during idle listening time by controlling the duty cycle of the transmission period. Since the traffic conditions are diverse, they may not always display improvements in energy consumption. In this paper we propose a new energy efficient MAC protocol called dynamic threshold MAC (DT-MAC), which employs a dynamic threshold for the buffer of each sensor node to maximize the energy efficiency regardless of specific network traffic condition. Here the packets are stored in the buffer, and then transmitted when the number of packets in the buffer exceeds the threshold dynamically decided according to the number of hops of the node from the source in the path of packet forwarding. The simulation results using OMNnet++ show that DT-MAC enables significant improvement in energy consumption compared to the existing MAC protocols. The proposed DT-MAC protocol also reduces the number of transmissions of control packets.
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  • 16
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    A Consensus-Based Protocol for Spectrum Sharing Fairness in Cognitive Radio Ad Hoc and Sensor Networks (2012)
    Hindawi
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    Publication Date: 2012-10-25
    Description: Spectrum sharing fairness is an important topic in cognitive radio ad hoc networks (CRAHNs) and cognitive radio sensor networks (CRSNs). Consensus-based protocols can provide light-weight and efficient solutions for CRAHNs and CRSNs but the theoretical ground needs to be investigated for spectrum sharing fairness. In this paper, we investigate the convergence condition when applying a consensus-based protocol to spectrum sharing while ensuring spectrum sharing fairness. Based on the local observation and local control scheme using spectrum-related information, an individual cognitive node can effectively perform the spectrum sharing. Then we propose a consensus-based protocol for spectrum sharing. Supported with computer simulation results, we show the effectiveness of using the proposed consensus-based protocol to solve the spectrum sharing problems in CRAHNs and CRSNs.
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  • 17
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    Multislot Antenna with a Screening Backplane for UWB WBAN Applications (2012)
    Hindawi
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    Publication Date: 2012-10-25
    Description: A novel multislot antenna with a conducting backplane reflector (MSA-BP) designed for ultrawideband wireless body area networks (WBANs) applications is presented. The objective is to achieve a desensitization of the antenna behavior regarding the proximity effects of the human body, thanks to the field screening operated by the backplane. Partly because of the latter, the antenna is fed with a tapered CPW. The influence of antenna parameters and human body proximity on the radiation characteristics of the MSA-BP is analyzed. Simulated results of the antenna close to a three-layer arm phantom are presented. Impedance and radiation measurements of the isolated antenna as well as propagation characteristics along the human body demonstrating the desensitization effect are also presented. The characteristics of the MSA-BP, in terms of the on-body total radiation efficiency, are significantly improved compared to any (quasi-) omnidirectional counterpart.
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  • 18
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    A Study on the Working Performance of Dimming Methods for Single- and Multichip Power LEDs (2012)
    Hindawi
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    Publication Date: 2012-10-25
    Description: Light emitting diodes (LEDs) have many positive features, such as long life, low power consumption, and high luminous efficacy. Consequently, they are very attractive for use in many applications. Also, the use of LEDs ensures energy savings. Power LEDs have increasingly been used for general lighting via multichip module technology. The output of power LEDs should be controlled to obtain life and illuminance values in catalog. In this study, the effects of different dimming methods are investigated for single-and multichip LEDs. To achieve this aim, pulse width modulation (PWM) and current variation (CV) dimming methods are applied to single and multichip power LEDs during ten stages of dimming. A current-regulated DC source is used for current variation (CV) dimming, and a driver designed by the researcher is used for pulse width modulation (PWM) dimming. Moreover, all of the applications are made for active and passive cooling. Finally, the results are compared.
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  • 19
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    Microcrystalline-Silicon-Oxide-Based N-Type Reflector Structure in Micromorph Tandem Solar Cells (2012)
    Hindawi
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    Publication Date: 2012-04-09
    Description: N-type microcrystalline silicon oxide thin films (n-μc-SiOx:H) have been deposited by VHF-PECVD (40 MHz) with reactant gas mixtures of CO2/SiH4 and H2. N-μc-SiOx thin films exhibiting low refractive index value (n600 nm~2), and medium/high conductivity (≧10-9 S/cm) are suitable to be used as an “n-type reflector” in micromorph tandem solar cells. Transmission electron microscopy (TEM) results show that microstructures of n-μc-SiOx:H thin films contain nanocrystalline Si particles, which are randomly embedded in the a-SiOx matrix. This specific microstructure provides n-μc-SiOx:H thin films excellent optoelectronic properties; therefore, n-μc-SiOx:H thin films are appropriate candidates for “n-type reflector” structures in Si tandem solar cells.
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  • 20
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    UV Filtering of Dye-Sensitized Solar Cells: The Effects of Varying the UV Cut-Off upon Cell Performance and Incident Photon-to-Electron Conversion Efficiency (2012)
    Hindawi
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    Publication Date: 2012-04-09
    Description: With current technology, UV filters are essential to ensure long-term dye-sensitized solar cell (DSC) stability. Blocking photons, however, will have an obvious effect on device performance and upon its incident photon-to-current conversion efficiency (IPCE). Filters have been applied to DSC devices with a range of cut-off wavelengths in order to assess how different levels of filtering affect the performance and IPCE of devices made with three different dyes, namely N719, Z907, and N749. It is shown that dyes that extend their IPCE further into the NIR region suffer lesser relative efficiency losses due to UV filtering than dyes with narrower action spectra. Furthermore, the results are encouraging to those working towards the industrialisation of DSC technology. From the results presented it can be estimated that filtering at a level intended to prevent direct band gap excitation of the TiO2 semiconductor should cause a relative drop in cell efficiency of no more than 10% in forward illuminated devices and no more than 2% in reverse illuminated devices.
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  • 21
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    Improved ESPRIT Method for Joint Direction-of-Arrival and Frequency Estimation Using Multiple-Delay Output (2012)
    Hindawi
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    Publication Date: 2012-08-28
    Description: An automatic pairing joint direction-of-arrival (DOA) and frequency estimation is presented to overcome the unsatisfactory performances of estimation of signal parameter via rotational invariance techniques- (ESPRIT-) like algorithm of Wang (2010), which requires an additional pairing. By using multiple-delay output of a uniform linear antenna arrays (ULA), the proposed algorithm can estimate joint angles and frequencies with an improved ESPRIT. Compared with Wang’s ESPRIT algorithm, the angle estimation performance of the proposed algorithm is greatly improved. The frequency estimation performance of the proposed algorithm is same with that of Wang’s ESPRIT algorithm. Furthermore, the proposed algorithm can obtain automatic pairing DOA and frequency parameters, and it has a comparative computational complexity in contrast to Wang’s ESPRIT algorithm. By the way, this proposed algorithm can also work well for nonuniform linear arrays. The useful behavior of this proposed algorithm is verified by simulations.
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  • 22
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    Two- and Three-Component Visible Light Photoinitiating Systems for Radical Polymerization Based on Onium Salts: An Overview of Mechanistic and Laser Flash Photolysis Studies (2012)
    Hindawi
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    Publication Date: 2012-08-28
    Description: A review of our work on two- and-three component photoinitiator systems is presented. The emphasis is in on visible light polymerization in aqueous media. The systems discussed comprise a synthetic dye as sensitizer and an onium salt as coinitiator, or a dye-amine-onium salt with the amine as coinitiator and the onium salt as an enhancer of the polymerization efficiency. The effect of the composition of the system on the photopolymerization kinetics was analyzed. To this end, the photophysics and photochemistry of the dye under polymerization conditions was explored by means of stationary and time-resolved spectroscopic methods. Different dyes and onium salts were investigated. The action mechanism of the different photoinitiators systems is discussed.
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  • 23
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    Photocatalytic Activity of Nanostructured Titanium Dioxide Thin Films (2012)
    Hindawi
    Details
    Publication Date: 2012-08-29
    Description: The aim of this paper is to investigate the properties and photocatalytic activity of nanostructured TiO2 layers. The glancing angle deposition method with DC sputtering at low temperature was applied for deposition of the layers with various columnar structures. The thin-film structure and surface morphology were analyzed by XRD, SEM, and AFM analyses. The photocatalytic activity of the films was determined by the rate constant of the decomposition of the Acid Orange 7. In dependence on the glancing angle deposition parameters, three types of columnar structures were obtained. The films feature anatase/rutile and/or amorphous structures depending on the film architecture and deposition method. All the films give the evidence of the photocatalytic activity, even those without proved anatase or rutile structure presence. The impact of columnar boundary in perspective of the photocatalytic activity of nanostructured TiO2 layers was discussed as the possible factor supporting the photocatalytic activity.
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    Location Privacy and Energy Preservation in Sensor Allocation Systems (2012)
    Hindawi
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    Publication Date: 2012-08-31
    Description: We propose sensor-to-task assignments algorithms that take into account location privacy issues. Our solutions enable the network to choose the “best” assignment of the available sensors to the tasks to maximize the utility of the network while preserving sensors’ location privacy. We focus on preserving the sensors’ locations during the assignment process in contrast to previous works, which considered location privacy while sensors are in operation. We also propose an energy-based algorithm that uses the remaining energy of a sensor as a factor to scale the distance between a sensor and a task such that sensors that have more energy appear to be closer than ones with less energy left. This does not only provide location privacy but will also consume the sensing resources more evenly, which leads to extending the lifetime of the network. From our simulations, we found that our algorithms can successfully hide sensors’ locations while providing performance close to the algorithms, which use the exact locations. In addition, our energy-based algorithm, while achieving results close to the exact location algorithm, was found to increase the network lifetime by as much as 40%.
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    A Novel Internal Dual-Polarized EBG Antenna for Indoor Reception of UHF Terrestrial Digital TV Broadcasting (2012)
    Hindawi
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    Publication Date: 2012-08-31
    Description: A novel internal antenna has been developed for indoor reception of UHF terrestrial digital TV broadcasting. The overall size of some configurations of the new antenna is less than 2 cm3, and its weight is less than 1 gm. It is made of a flexible material that can be bent or folded and shaped in any form. It is an unbalanced resonant antenna that does not need a matching circuit. The new antenna can be fully embedded inside TV sets or portable computers. It has a bandwidth of about 68%. Thus, it can also cover the bands of GSM and CDMA, which is advantageous in case of portable computers. The new antenna is linearly polarized. It can be easily modified to be dual polarized by combining two orthogonal antennas with one or two feed points. The overall efficiency of some configurations of the new indoor digital TV receiving antenna is more than 80%, and its peak gain is about 2 dBi over the whole UHF band. The peak gain can be increased to more than 5 dBi by adding EBG (electromagnetic bandgap) structures. The EBG structure also increases the efficiency to around 90%.
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    Sliding-Mode and Spring-Relaxation-Like Technique for Location Estimation in Wireless Sensor Networks (2012)
    Hindawi
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    Publication Date: 2012-08-25
    Description: In order to reduce the location estimation error in wireless sensor network (WSN), a localization algorithm is proposed combining sliding-mode and spring-relaxation-like techniques for wireless sensor networks in this paper. Our proposed method takes advantage of the spring-relaxation technique. The overall accuracy of the location estimations is improved by sliding-mode technique. The convergence of the proposed algorithm is proved using the convergence conditions of discrete sliding-mode. Moreover, it requires only a few beacons with known locations to compute the location estimations of all sensors. Simulation examples demonstrate the overall accuracy of the proposed method.
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    Distributed Collaborative Camera Actuation Scheme Based on Sensing-Region Management for Wireless Multimedia Sensor Networks (2012)
    Hindawi
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    Publication Date: 2012-08-27
    Description: Considering the high energy consumption of image acquisition, computation, and transmission in wireless multimedia sensor networks (WMSNs), two-tier network structure is usually used to lighten the energy consumption burden on camera sensors. Thus, a camera sensor can only be actuated when an event is detected by scalar sensors within its field of view (FoV). In this paper, we study the event-driven camera actuation problem and propose a distributed collaborative camera actuation scheme based on sensing-region management (DCCA-SM). The basic idea of this scheme is to divide the whole sensing field into many sensing regions which are covered by different sets of camera sensors. During the running of the network, by forming a cluster of the scalar sensors in each sensing region, the events occurring in each sensing region can be managed by the scalar cluster head. Therefore, by hearing from the scalar cluster heads, each camera sensor can know the exact coverage overlaps without changing information with the neighboring camera sensors. Meanwhile, sensing-region management avoids repeatedly event reporting from scalar sensors. In order to show the performance of the DCCA-SM, a simulation has been conducted. The comparative performance evaluations demonstrate effectiveness and energy efficiency of the proposed scheme.
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    A Volume-Surface Integral Equation Solver for Radiation from Microstrip Antenna on Anisotropic Substrate (2012)
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    Publication Date: 2012-08-27
    Description: A volume-surface integral equation (VSIE) solver is presented for the calculation of electromagnetic radiation from arbitrary shaped microstrip antenna on anisotropic substrate. The method of moments (MoM) is used to convert the integral equation into a matrix equation, where the equivalent volume current and surface current are expanded into a finite series of SWG and RWG basis function, respectively. A simple strip model is incorporated in the VSIE to simplify the analysis of the probe-fed microstrip antenna. The present approach is sufficiently versatile in handling microstrip antenna with arbitrary shaped anisotropic dielectric substrate. Numerical results indicate the reliability and accuracy of the proposed method.
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    Silicon Nitride Film by Inline PECVD for Black Silicon Solar Cells (2012)
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    Publication Date: 2012-08-23
    Description: The passivation process is of significant importance to produce high-efficiency black silicon solar cell due to its unique microstructure. The black silicon has been produced by plasma immersion ion implantation (PIII) process. And the Silicon nitride films were deposited by inline plasma-enhanced chemical vapor deposition (PECVD) to be used as the passivation layer for black silicon solar cell. The microstructure and physical properties of silicon nitride films were characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), spectroscopic ellipsometry, and the microwave photoconductance decay (μ-PCD) method. With optimizing the PECVD parameters, the conversion efficiency of black silicon solar cell can reach as high as 16.25%.
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    A High-Order Compact 2D FDFD Method for Waveguides (2012)
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    Publication Date: 2012-08-28
    Description: A high-order compact two-dimensional finite-difference frequency-domain (2D FDFD) method is proposed for the analysis of the dispersion characteristics of waveguides. A surface impedance boundary condition (SIBC) for the high-order compact 2D FDFD method is also given to model lossy metal waveguides. Four transverse field components are involved in the final eigenequation. Numerical examples are given, which show that this high-order compact 2D FDFD method is more efficient than the low-order compact 2D FDFD method and has a less storage cost.
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    A Domain Decomposition Method for Hybrid Shell Vector Element with Boundary Integral Method (2012)
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    Publication Date: 2012-09-04
    Description: For the conducting body coated with thin-layer material, plenty of fine meshes are required in general. In this paper, shell vector element (SVE) is used for modeling of thin coating dielectric. Further, a domain decomposition (DD) method for hybrid shell vector element method boundary integral (SVE-BI) is proposed for analysis of electromagnetic problem of multiple three-dimensional thin-coating objects. By this method, the whole computational domains are divided into sub-SVE domains and boundary element domains. With shell element, not only the unknowns are far less than the one by traditional vector element method, but only surface integral is required. The DDM framework used for hybrid SVE-BI also enhances the computational efficiency of solving scattering from multiple coating objects greatly. Finally, several numerical examples are presented to prove the accuracy and efficiency of this DDM-SVE-BI method.
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    A Two-Level Routing Scheme for Wireless Sensor Network (2012)
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    Publication Date: 2012-07-17
    Description: A new two-level routing scheme is proposed using the energy features of wireless sensor network. The proposed scheme consists of two levels: (i) sink node level and (ii) sensor node level. The proposed scheme exploits independent gradients for each sink node so that the exploratory messages forwarded by the intermediate sensor nodes can be significantly reduced. Experiments are conducted using two evaluation criterions, which are average dissipated energy and hop counts, to demonstrate the superior performance of the proposed scheme.
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    PV Power-Generation System with a Phase-Shift PWM Technique for High Step-Up Voltage Applications (2012)
    Hindawi
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    Publication Date: 2012-07-20
    Description: A PV power-generation system with a phase-shift pulse-width modulation (PWM) technique for high step-up voltage applications is proposed. The proposed power-generation system consists of two stages. In the input stage, all power switches of the full-bridge converter with phase-shift technique can be operated with zero-current switching (ZCS) at turn-on or turn-off transition. Hence, the switching losses of the power switches can be reduced. Then, in the DC output stage, a voltage-doubler circuit is used to boost a high dc-link bus voltage. To supply a utility power, a dc/ac inverter is connected to induce a sinusoidal source. In order to draw a maximum power from PV arrays source, a microcontroller is incorporated with the perturbation and observation method to implement maximum power point tracking (MPPT) algorithm and power regulating scheme. In this study, a full load power of 300 W prototype has been built. Experimental results are presented to verify the performance and feasibility of the proposed PV power-generation system.
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    Preparation and Properties of SnO2 Film Deposited by Magnetron Sputtering (2012)
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    Publication Date: 2012-07-26
    Description: Tin oxide SnO2 films were prepared by RF magnetron sputtering. The effects of oxygen partial pressure percentage on the SnO2 property have been investigated to obtain relatively high-resistivity SnO2 films which could be used as buffer layers to optimize the performance of CdTe/CdS solar cells. The oxygen partial pressure percentage varied in the range of 1%~10%. The results show that the introduction of oxygen would suppress the deposition and growth of SnO2 films. Electrical measurement suggests that the film resistivity decreases with the increase of oxygen pressure. The SnO2 films with resistivity of 232 Ω cm were obtained in pure Ar atmosphere. All SnO2 films fabricated with different oxygen partial pressure percentage have almost the same optical band gap.
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    Adaptive Source Location Estimation Based on Compressed Sensing in Wireless Sensor Networks (2012)
    Hindawi
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    Publication Date: 2012-06-21
    Description: Source localization is an important problem in wireless sensor networks (WSNs). An exciting state-of-the-art algorithm for this problem is maximum likelihood (ML), which has sufficient spatial samples and consumes much energy. In this paper, an effective method based on compressed sensing (CS) is proposed for multiple source locations in received signal strength-wireless sensor networks (RSS-WSNs). This algorithm models unknown multiple source positions as a sparse vector by constructing redundant dictionaries. Thus, source parameters, such as source positions and energy, can be estimated by ℓ1-norm minimization. To speed up the algorithm, an effective construction of multiresolution dictionary is introduced. Furthermore, to improve the capacity of resolving two sources that are close to each other, the adaptive dictionary refinement and the optimization of the redundant dictionary arrangement (RDA) are utilized. Compared to ML methods, such as alternating projection, the CS algorithm can improve the resolution of multiple sources and reduce spatial samples of WSNs. The simulations results demonstrate the performance of this algorithm.
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    A Lightweight Lap Time Measurement System for Alpine Ski Sport Using a TDMA-Based Linear Wireless Sensor Network (2012)
    Hindawi
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    Publication Date: 2012-06-21
    Description: In Alpine ski sport, traditional lap time measurement systems record a skier's departure and arrival using time-of-day timers through wires, which is not cost effective in unofficial or training games. This paper develops a lightweight lap time measurement system using a wireless sensor network, which employs a practical TDMA-based linear wireless sensor network protocol for multihop communications in long strap-shaped environments where sensor nodes are linearly deployed. We evaluate the performance of this protocol through the implementation and deployment of the lap time measurement system. The experimental results show that the proposed protocol transmits data at a success rate of 99.66% and maintains the time synchronization errors between two adjacent nodes within 183 μs without using any other time synchronization protocols. In an experimental deployment for a 1.5 km ski slope covered by 31 nodes, the system provides lap time measurements with a measurement error of 1.255 ms, which satisfies the official measurement error of 5.0 ms.
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    Design and Realization of GaAs Digital Circuit for Mixed Signal MMIC Implementation in AESA Applications (2012)
    Hindawi
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    Publication Date: 2012-06-21
    Description: A complete design flow starting from the technological process development up to the fabrication of digital circuits is presented. The aim of this work is to demonstrate the GaAs Enhancement/Depletion (E/D) double stop-etch technology implementation feasibility for digital applications, aimed at mixed signal circuit integration. On the basis of the characterization of small E/D devices with different Gate peripheries, developed by the SELEX-SI foundry, and the analysis of several GaAs-based logical families, the most suitable logic for the available technology has been selected. Then, simple test vehicles (level shifters, NOR logic gates and D Flip-Flops) have been designed, realized, and measured to validate the design strategy applied to the GaAs E/D process. These logical circuits are preliminary to the design of a more complex serial-to-parallel converter, to be implemented onto the same chip together with RF analog blocks, such as stepped attenuators and phase shifters.
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    High Q-Factor Wideband Resonators for Millimeter and Submillimeter Applications (2012)
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    Publication Date: 2012-06-21
    Description: Physical principles for designing a multipurpose set of high Q-factor quasioptical and corrugated resonators with automatic frequency tuning (Q>6×104, VSWR<1.6) that can operate in the frequency band from 37.5 to 400 GHz are presented. The electrodynamical calculation methods of resonators, the constructive particularities of resonators, the methods and results of the experimental researches are considered. This set of resonators can be used as a universal measuring resonator for measuring radio-signal fluctuations and parameters of different media, in particular, nanotube composites and high-temperature superconductors.
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    Fully Distributed Tunable Bandpass Filter Based on Ba0.5Sr0.5TiO3 Thin-Film Slow-Wave Structure (2012)
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    Publication Date: 2012-06-21
    Description: This paper presents simulation and measurement results of fully distributed tunable coplanar bandpass filters (BPFs) with center frequencies around 6 GHz that make use of ferroelectric Barium Strontium Titanate (BaxSr1−xTiO3 or BST-x) thin film as tunable material. The two experimental bandpass filters tested are based on a novel frequency-agile structure composed of cascaded half wavelength slow-wave resonators (2 poles) and three coupled interdigital capacitors (IDCs) optimized for bias voltage application. Devices with gap dimensions of 10 and 3 μm are designed and fabricated with a two-step process on polycrystalline Ba0.5Sr0.5TiO3 thin films deposited on alumina substrate. A frequency tunability of 9% is obtained for the 10 μm gap structure at ±30 V with 7 dB insertion loss (the BST dielectric tunability being 26% with 0.04 loss tangent for this gap size). When the structure gap is reduced to 3 μm the center frequency shifts with a constant 9 dB insertion loss from 6.95 GHz at 0 V to 9.05 GHz at ±30 V, thus yielding a filter tunability of 30% (the BST dielectric tunability being 60% with 0.04 loss tangent for this gap size), a performance comparable to some extent to localized or lumped element BPFs operating at microwave frequency (>2 GHz).
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    Time Reversal in Subwavelength-Scaled Resonant Media: Beating the Diffraction Limit (2012)
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    Publication Date: 2012-06-21
    Description: Time reversal is a physical concept that can focus waves both spatially and temporally regardless of the complexity of the propagation medium. Time reversal mirrors have been demonstrated first in acoustics, then with electromagnetic waves, and are being intensively studied in many fields ranging from underwater communications to sensing. In this paper, we will review the principles of time reversal and in particular its ability to focus waves in complex media. We will show that this focusing effect depends on the complexity of the propagation medium rather than on the time reversal mirror itself. A modal approach will be utilized to explain the physical mechanism underlying the concept. A particular focus will be given on the possibility to break the diffraction barrier from the far field using time reversal. We will show that finite size media made out of coupled subwavelength resonators support modes which can radiate efficiently in the far field spatial information of the near field of a source. We will show through various examples that such a process, due to reversibility, permits to beat the diffraction limit using far field time reversal, and especially that this result occurs owing to the broadband inherent nature of time reversal.
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    An Online Relay Selection Scheme in Power Controllable Wireless Sensor Networks (2012)
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    Publication Date: 2012-07-19
    Description: We propose a data forwarding scheme termed dynamic energy-based relaying (DER) for wireless sensor networks (WSNs). In the DER scheme, all nodes try to forward their data packets toward the nodes that are optimal distance closer to the data sink. They also take the relaying node estimated lifetime into consideration in the selection process. When necessary, they will choose nodes that are closer to the data sink as relays or even the data sink itself. This distributed approach equalizes energy consumption of different relaying nodes based on their residual energy, balancing their expected lifetimes. We analyze our proposed scheme in both one-dimensional and two-dimensional networks with different setups including different residual energy, traffic rate, and network regions. Our study shows that the proposed scheme achieves a network lifetime close to the scheme based on linear programming techniques and global information or centralized processing.
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    Effect of Fe Concentration on Fe-Doped Anatase TiO2 from GGA + U Calculations (2012)
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    Publication Date: 2012-07-16
    Description: To comprehend the photocatalytic mechanisms of anatase Ti1-xFexO2 with various concentrations of Fe, this study performed first principles calculations based on density functional theory with Hubbard U on-site correction to evaluate the crystal structure, impurity formation energy, and electronic structure. We adopted the effective Hubbard U values of 8.47 eV for Ti 3d and 6.4 eV for Fe 3d. The calculations show that higher concentrations of Fe are easily formed in anatase TiO2 due to a reduction in the formation energy. The band gap of Fe-doped TiO2 decreases Fe doping level increases as a result of the overlap among the Fe 3d, Ti 3d, and O 2p states, which enhances photocatalytic activity in the visible light region. Additionally, a broadening of the valence band and Fe impurity states within the band gap might also contribute to the photocatalytic activity.
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    Design of Novel S-Shaped Quad-Band Antenna for MedRadio/WMTS/ISM Implantable Biotelemetry Applications (2012)
    Hindawi
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    Publication Date: 2012-07-25
    Description: A novel S-shaped quad-band planar inverted-F antenna (PIFA) is proposed for implantable biotelemetry in the Medical Device Radiocommunications Service (MedRadio) band (401–406 MHz), Wireless Medical Telemetry Service (WMTS) band (1427–1432 MHz), and industrial, scientific, and medical (ISM) bands (433-434 MHz and 2.4–2.4835 GHz). The proposed antenna reveals compact dimension of 254 mm3 (10×10×2.45 mm3) and is composed of three substrates and a superstrate, which are constructed from an S-shaped radiator (layer 1) and two twin radiators of spiral structures (layer 2 and layer 3). The optimal antenna characteristics were measured in the ground pork skin, and the measured bandwidths are 150 MHz for the MedRadio and ISM bands (433 MHz), 52 MHz for the WMTS band, and 102 MHz for the ISM band (2.4 GHz), respectively. The characteristics of proposed antenna are enough to support the applications of implantable body area networks (BAN) for biotelemetry and can completely cover main available frequency bands of BAN for biotelemetry below 3 GHz.
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    A Robust Baseband Demodulator for ISO 18000-6C RFID Reader Systems (2012)
    Hindawi
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    Publication Date: 2012-09-11
    Description: One key challenge for ultra-high frequency (UHF) radio-frequency identification (RFID) reader design is to demodulate the weak tag response signal which tends to be easily distorted and has considerable frequency deviations. In this paper, a baseband demodulator based on a matched filter (MF) is proposed to enhance the reliability of signal processing for the EPCglobal Class-1 Generation-2 (Gen2) RFID reader systems. The proposed demodulator is very robust against strong signal distortions and large frequency deviations happening on the received backscattered signal from a passive RFID tag. The validity and usefulness is demonstrated by both computer simulations and implementation experiments.
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    Fracture Toughness of Vinyl Ester Composites Reinforced with Sawdust and Postcured in Microwaves (2012)
    Hindawi
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    Publication Date: 2012-09-14
    Description: A commercial vinyl ester resin supplied by Hetron Chemical Pty. was reinforced with varying percentages by weight of sawdust. The sawdust particles were sieved into 3 different sizes, which were
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    Digital Architectures for UWB Beamforming Using 2D IIR Spatio-Temporal Frequency-Planar Filters (2012)
    Hindawi
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    Publication Date: 2012-09-18
    Description: A design method and an FPGA-based prototype implementation of massively parallel systolic-array VLSI architectures for 2nd-order and 3rd-order frequency-planar beam plane-wave filters are proposed. Frequency-planar beamforming enables highly-directional UWB RF beams at low computational complexity compared to digital phased-array feed techniques. The array factors of the proposed realizations are simulated and both high-directional selectivity and UWB performance are demonstrated. The proposed architectures operate using 2's complement finite precision digital arithmetic. The real-time throughput is maximized using look-ahead optimization applied locally to each processor in the proposed massively-parallel realization of the filter. From sensitivity theory, it is shown that 15 and 19-bit precision for filter coefficients results in better than 3% error for 2nd- and 3rd-order beam filters. Folding together with Ktimes multiplexing is applied to the proposed beam architectures such that throughput can be traded for K-fold lower complexity for realizing the 2-D fan filter banks. Prototype FPGA circuit implementations of these filters are proposed using a Virtex 6 xc6vsx475t-2ff1759 device. The FPGA-prototyped architectures are evaluated using area (A), critical path delay (T), and metrics AT and AT2. The L2 error energy is used as a metric for evaluating fixed-point noise levels and the accuracy of the finite precision digital arithmetic circuits.
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    Fractal-Based Thinned Planar-Array Design Utilizing Iterative FFT Technique (2012)
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    Publication Date: 2012-09-14
    Description: This paper investigated the synthesis problem of fractal-based thinned planar arrays by using the iterative Fourier technique (IFT). Since an inverse discrete Fourier transform relationship exists between the array factor and the element excitations for a periodic array antenna, an iterative Fourier technique is introduced to derive the array element excitation from the prescribed array factor based on this peculiar property. However, considering the IFT technique is sensitive to the initial values, the fractal-thinned array technique is employed and combined in the synthesis process to exploit the advantages of these two techniques. Moreover, the DRR of the excitation amplitude is controlled to achieve a reduction of the cost of the feeding network. Numerical examples have been carried out to validate the proposed approach.
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    Photomechanical Energy Conversion of Photoresponsive Fibers Exhibiting Bending Behavior (2012)
    Hindawi
    Details
    Publication Date: 2012-09-14
    Description: Photoresponsive fibers based on poly(acrylamide) (PAA) with methylene blue (MB) dye were prepared. All semicircular fibers show bending towards the direction of the flat surface of the fiber when illuminated. The fibers recover their initial shape when the illumination stops. The fiber is heated upon illumination and cooled to room temperature once the illumination is stopped. The fiber also is sensitive to humidity, showing bending behavior towards the direction of the flat surface of the fiber upon changing the humidity. The mechanical energy of the PAA/MB fiber is approximately 0.6 mN for the bending direction when it is illuminated. A possible mechanism for the bending behavior is as follow: (1) the fiber is heated upon illumination because of the photothermal effect, (2) the fiber loses water molecules, (3) the fiber shrinks; bending towards the direction of the flat surface of the fiber occurs because of a difference in the shrinkage for the flat surface and the other side of the fiber. Finally, we demonstrated that a PP ball (1.5 mg) can be moved by the mechanical energy produced by the changing shape of the fiber upon illumination.
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    A Scalable Multi-Target Tracking Algorithm for Wireless Sensor Networks (2012)
    Hindawi
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    Publication Date: 2012-09-11
    Description: Multi-target tracking is a representative real-time application of sensor networks as it exhibits different aspects of sensor networks such as event detection, sensor information fusion, multihop communication, sensor management, and real-time decision making. The task of tracking multiple objects in a wireless sensor network is challenging due to constraints on a sensor node such as short communication and sensing ranges, a limited amount of memory, and limited computational power. In addition, since a sensor network surveillance system needs to operate autonomously without human operators, it requires an autonomous real-time tracking algorithm which can track an unknown number of targets. In this paper, we develop a scalable real-time multi-target tracking algorithm that is autonomous and robust against transmission failures, communication delays, and sensor localization error. The algorithm is based on a rigorous probabilistic model and an approximation scheme for the optimal Bayesian filter. In particular, an extensive simulation study shows that there is no performance loss up to an average localization error of 0.7 times the separation between sensors and the algorithm tolerates up to 50% lost-to-total packet ratio and 90% delayed-to-total packet ratio. The proposed algorithm has been successfully applied to real-time multi-target tracking problems using wireless sensor networks.
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    A Comparative Performance Analysis of Two Printed Circular Arrays for Power-Based Vehicle Localization Applications (2012)
    Hindawi
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    Publication Date: 2012-09-18
    Description: A comparative study of the performance characteristics of a printed 8-element V-shaped circular antenna array and an 8-element Yagi circular array operating at 2.45 GHz for vehicular direction finding applications is presented. Two operating modes are investigated; switched and phased modes. The arrays were fabricated on FR-4 substrates with 0.8 mm thickness. Measured and simulated results were compared. Radiation gain patterns were measured on a 1 m diameter ground plane that resembles the rooftop of a vehicle. The HPBW of the Yagi was found to be about 3° narrower than its V-shaped counterpart when measured above a reflecting ground plane and operated in switched mode. The printed V-shaped antenna array offers 2.5 dB extra gain compared to the printed Yagi array.
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    Range-Angle-Dependent Beamforming by Frequency Diverse Array Antenna (2012)
    Hindawi
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    Publication Date: 2012-08-18
    Description: This paper proposes a range-angle-dependent beamforming for frequency diverse array (FDA) antenna systems. Unlike conventional phased-array antenna, the FDA antenna employs a small amount of frequency increment compared to the carrier frequency across the array elements. The use of frequency increment generates an antenna pattern that is a function of range, time and angle. The range-angle-dependent beamforming allows the FDA antenna to transmit energy over a desired range or angle. This provides a potential to suppress range-dependent clutter and interference which is not accessible for conventional phased-array systems. In this paper, a FDA radar signal model is formed and the range-angle-dependent beamforming performance is examined by analyzing the transmit/receive beampatterns and the output signal-to-interference-plus-noise ratio (SINR) performance. Extensive simulation examples and results are provided.
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    Characterization of a Coplanar Waveguide Open Stub-Based Discontinuity for MMICs and Filter Applications (2012)
    Hindawi
    Details
    Publication Date: 2012-08-17
    Description: This paper presents the analysis and design of an open stub-based two-port discontinuity in a coplanar waveguide. The discontinuity has a good bandpass response and the required design characteristics were achieved by using the method of moments (MOM) and the finite integration technique (FIT). The analysis is found to be computationally efficient which makes the discontinuity suitable for use in complex structure applications. The analysis of the discontinuity is also formulated using the quasi-static finite-difference technique. The proposed discontinuity structure finds applications in RFICs and MMICs. Finally, the application of the discontinuity is supported by the simulated design of a broadband bandpass filter on an MMIC with a relative bandwidth of 96%. The filter is found to have a miniature size and a fairly good stop band rejection.
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    Current Mechanism in HfO2-Gated Metal-Oxide-Semiconductor Devices (2012)
    Hindawi
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    Publication Date: 2012-06-20
    Description: The present study aimed to examine the current density-voltage (J-V) characteristics of Al/HfO2/p-Si (MOS) structure at temperatures ranging between 100 and 320 K and to determine the structure’s current transport mechanism. The HfO2 film was coated on a single side of the p-Si (111) crystal using the spin coating method. The J-V measurements of the obtained structure at the temperatures between 100 and 320 K revealed that the current transport mechanism in the structure was compatible with the Schottky emission theory. The Schottky emission theory was also used to calculate the structure’s Schottky barrier heights (ϕB), dielectric constants (εr) and refractive index values of the thin films at each temperature value. The dielectric constant and refractive index values were observed to decrease at decreasing temperatures. The capacitance-voltage (C-V) and conductance-voltage (G/ω-V) characteristics of Al/HfO2/p-Si (MOS) structure was measured in the temperature range of 100–320 K. The values of measured C and G/ω decrease in accumulation and depletion regions with decreasing temperature due to localized Nss at Si/HfO2 interface.
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    Single Feed Aperture-Coupled Wideband Dielectric Resonator Antenna with Circular Polarization for Ku-Band Applications (2012)
    Hindawi
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    Publication Date: 2012-06-21
    Description: A novel single feed aperture-coupled wideband dielectric resonator antenna (DRA) exhibiting righ-handed circular polarization (RHCP) operating in the Ku-band frequency range is presented. The aperture-coupled single feed design utilizes back-side microstrip excitation through a novel bow-tie-shaped cross-slots in the ground plane. Extensive simulation parametric studies resulted in a 3 dB axial ratio (AR) bandwidth of 17.24% at a center frequency of 13 GHz, where the dielectric resonator is excited in its HEM11δ resonant mode. A prototype DRA was fabricated with some limitations and experimentally verified for the impedance matching and radiation patterns showing circular polarization.
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    Isolation Improvement Technique for Two Closely Spaced Loop Antennas Using MTM Absorber Cells (2012)
    Hindawi
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    Publication Date: 2012-06-21
    Description: This paper presents a new method to improve isolation between two loop antennas with absorber cells exhibiting negative permittivity and permeability at the aimed frequency of 2.54 GHz. The metamaterial (MTM) unit cell was constructed by two open complementary split ring resonator (OCSRR) and a split ring resonator (SRR) arrangement. The proposed antenna structure consists of two loop antennas occupying a space with the dimensions of 51 mm×24 mm×2 mm and three absorber cells. The size of each absorber unit cell is 7.4 mm×7 mm×2 mm. The isolation of more than 20 dB was achieved with three absorber cells loaded between two loop antennas; interantenna spacing (center to center) is 0.23 λ0 at 2.54 GHz. The results show that port-to-port isolation between two antennas can be improved with absorber.
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    Isolation Enhancement between Indoor Repeater Antennas with Chip Resistor Embedded FSS (2012)
    Hindawi
    Details
    Publication Date: 2012-06-21
    Description: The isolation enhancement between the donor antenna and the service antenna for indoor repeater systems is presented by using a frequency-selective surface (FSS). A unit cell of the proposed FSS consists of a quarter-wavelength resonator, a chip resistor, an FR4 substrate, and a ground plane. Applying the unit cells of the proposed FSS embedded a chip resistor on the side walls of each reflector for indoor WCDMA repeater antennas and aligning them along with the cross-polarization of each antenna, the isolation is improved by about 13 dB at the WCDMA band.
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    The Case for Higher Computational Density in the Memory-Bound FDTD Method within Multicore Environments (2012)
    Hindawi
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    Publication Date: 2012-06-21
    Description: It is argued here that more accurate though more compute-intensive alternate algorithms to certain computational methods which are deemed too inefficient and wasteful when implemented within serial codes can be more efficient and cost-effective when implemented in parallel codes designed to run on today's multicore and many-core environments. This argument is most germane to methods that involve large data sets with relatively limited computational density—in other words, algorithms with small ratios of floating point operations to memory accesses. The examples chosen here to support this argument represent a variety of high-order finite-difference time-domain algorithms. It will be demonstrated that a three- to eightfold increase in floating-point operations due to higher-order finite-differences will translate to only two- to threefold increases in actual run times using either graphical or central processing units of today. It is hoped that this argument will convince researchers to revisit certain numerical techniques that have long been shelved and reevaluate them for multicore usability.
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    Joint Angles and Mutual Coupling Estimation Algorithm for Bistatic MIMO Radar (2012)
    Hindawi
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    Publication Date: 2012-06-21
    Description: We study the problem of angle estimation for a bistatic multiple-input multiple-output (MIMO) radar with unknown mutual coupling and proposed a joint algorithm for angles and mutual coupling estimation with the characteristics of uniform linear arrays and subspaces exploitation. We primarily obtain an initial estimate of DOA and DOD, then employ the local one-dimensional searching to estimate exactly DOA and DOD, and finally evaluate the parameters of mutual coupling coefficients via the estimated angles. Exploiting twice of the one-dimensional local searching, our method has much lower computational cost than the algorithm in (Liu and Liao (2012)), and automatically obtains the paired two-dimensional angle estimation. Slightly better performance for angle estimation has been achieved via our scheme in contrast to (Liu and Liao (2012)), while the two methods indicate very close performance of mutual coupling estimation. The simulation results verify the algorithmic effectiveness of our scheme.
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    Design and Optimization of a Millimetre Wave Compact Folded Magic-T (2012)
    Hindawi
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    Publication Date: 2012-06-21
    Description: A millimetre wave-folded magic-T junction compensated with metal cone is designed using a particle swarm optimization (PSO) algorithm. An off-centred metallic frustum was used to enhance the bandwidth and a metallic post is used to compensate the mismatched E-arm. The geometrical parameters of the frustum and the post are optimized by PSO. The optimized magic-T for W-band application is designed and tested. The design features are simple in structure and easy to fabricate. The 2% bandwidth with centre frequency of 94 GHz and return loss less than −20 dB is achieved.
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    Closely Mounted Compact Wideband Diversity Antenna for Mobile Phone Applications (2012)
    Hindawi
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    Publication Date: 2012-06-21
    Description: Here a compact wideband diversity antenna covering the PCS/UMTS/WiMAX bands with high isolation and low enveloped correlation coefficient (ECC) is proposed. To widen the bandwidth, the proposed antenna uses a structure with a gap-coupled feed and an inductively shorted line that has capacitive compensation between the radiator and the ground plane. Also, a suspended line with a parasitic element is used to enhance the isolation between the two antennas.
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    CPW-Fed Fractal Slot Antenna for UWB Application (2012)
    Hindawi
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    Publication Date: 2012-06-21
    Description: A novel printed ultrawideband (UWB) CPW-fed Koch fractal slot antenna is proposed. The UWB bandwidth is largely enhanced by the three-iteration Koch fractal slot whose extrusive angle is 900 instead of 600 to obtain better convoluted shape and self-similarity. The −10 dB impedance bandwidth is 3400 MHz (1270–4670 MHz) or about 114% in comparison with 1290 MHz (1620–2910 MHz) or about 57% of the referenced square slot antenna. Details of the proposed antenna design and performance are presented and discussed.
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    A Genetic and Simulated Annealing Combined Algorithm for Optimization of Wideband Antenna Matching Networks (2012)
    Hindawi
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    Publication Date: 2012-06-21
    Description: A genetic and simulated annealing combined algorithm is presented and applied to optimize broadband matching networks for antennas. As a result, advantages of both the genetic algorithm (GA) and simulated annealing (SA) are taken. Effectiveness and efficiency of the presented combined algorithm are demonstrated by optimization of a wideband matching network for a VHF/UHF discone-based antenna. The optimized parameters provide significant improvements of VSWR and transducer power gain for the antenna.
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    Solving Scattering from Conducting Body Coated by Thin-Layer Material by Hybrid Shell Vector Element with Boundary Integral Method (2012)
    Hindawi
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    Publication Date: 2012-06-21
    Description: The finite element boundary integral (FEM-BI) method is widely used in the scattering and radiating problems. But for the conducting body coated by thin-layer material, plenty of fine meshes are required to discretize the geometry in the traditional FEM. It requires very expensive storage and CPU time. In this paper, the hybrid shell vector element with the boundary integral method is used to expedite the solution of thin coating problems. The shell vector elements are used to discretize thin-layer material instead of traditional tetrahedral elements. Consequently, the volume integral can be simplified into surface integral. This method reduces the number of unknowns greatly and is also extended into the complicated case of multi-thin-layer coating materials. Several numerical results are presented to prove the accuracy and efficiency of this present method.
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    Omnidirectional Dual-Reflector Antenna with GO Shaped Main Reflector for Pattern Control in the Elevation Plane: OADC Case (2012)
    Hindawi
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    Publication Date: 2012-06-21
    Description: This paper presents a formulation for shaping the main reflector of an axis-symmetric dual-reflector antenna designed to offer an omnidirectional coverage with an arbitrary radiation pattern in the vertical plane. The subreflector is generated by an axis-displaced conic, and the main reflector is shaped to achieve a prescribed far-field radiation pattern. The procedure is based on geometrical optics (GO) principles. Two distinct far-field ray structures are explored and their limitations are identified. The GO shaping results are validated by analysis provided by the accurate method of moments technique.
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    Design of High Gain and Broadband Antennas at 60 GHz for Underground Communications Systems (2012)
    Hindawi
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    Publication Date: 2012-06-21
    Description: A new broadband and high gain dielectric resonator antenna for millimeter wave is presented. The investigated antenna configuration consists of a periodic square ring frequency selective surfaces on a superstrate, an aperture-coupled scheme feed, an intermediate substrate, and a cylindrical dielectric resonator. This antenna is designed to cover the ISM frequency band at 60 GHz (57 GHz–64 GHz). It was numerically designed using CST microwave Studio simulation software package. Another prototype with a plain dielectric superstrate is also studied for comparison purposes. A bandwidth of 13.56% at the centered frequency of 61.34 GHz and a gain of 11 dB over the entire ISM band have been achieved. A maximum gain of 14.26 dB is obtained at 60 GHz. This is an enhancement of 9 dB compared to a single DRA. HFSS is used to validate our antenna designs. Good agreement between the results of the two softwares is obtained. With these performances, these antennas promise to be useful in the design of future wireless underground communication systems operating in the unlicensed 60 GHz frequency band.
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    Study of the Interference Affecting the Performance of the Theremin (2012)
    Hindawi
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    Publication Date: 2012-06-21
    Description: The theremin is one of the earliest electronic musical instruments. It is named after the Russian physics Professor Lev S. Termen who invented it in 1919. This musical instrument belongs to a very short list of devices which are played without physical contact between the musician and the instrument. theremin players complain about the interference that any object in a radius of approximately 3 meters produces when playing the theremin, modifying the intonation of the instrument. This is a problem when playing in small scenarios, with other musicians which move around it. With the aim of reducing the degree of interference from nearby obstacles, some metallic isolating bars conforming an antenna array can be placed around the theremin pitch antenna. The paper shows different simulations calculated with the commercial software Ansoft HFSS, a tool which allows three-dimensional full wave electromagnetic field simulation, with radio frequencies, millimeter and micro waves, and experimental measures, both showing a reduction in the effect of the interference.
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    Analysis of Horn Antennas in Receiving Mode as an EM Field Sensor (2012)
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    Publication Date: 2012-06-21
    Description: Electromagnetic (EM) field measurement uses antenna in receiving mode as EM field sensor (EMFS). FDTD technique is applied to analyze the horn antenna in this mode. The performances of horn antenna as EMFS are predicted in terms of antenna factor (AF), and the results are compared with measurements. New empirical formula for quick calculation of antenna factor of pyramidal horn is also presented. Also, the gain of horn antennas are computed in receiving mode using FDTD technique, and the results are compared with published measured result and far-field gain formula.
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    Investigation of Range Profiles from a Simplified Ship on Rough Sea Surface and Its Multipath Imaging Mechanisms (2012)
    Hindawi
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    Publication Date: 2012-06-21
    Description: The range profiles of a two-dimension (2 D) perfect electric conductor (PEC) ship on a wind-driven rough sea surface are derived by performing an inverse discrete Fourier transform (IDFT) on the wide band backscattered field. The rough sea surface is assuming to be a PEC surface. The back scattered field is computed based on EM numerical simulation when the frequencies are sampled between 100 MHz and 700 MHz. Considering the strong coupling interactions between the ship and sea, the complicated multipath effect to the range profile characteristics is fully analyzed based on the multipath imaging mechanisms. The coupling mechanisms could be explained by means of ray theory prediction and numerical extraction of the coupling currents. The comparison of the range profile locations between ray theory prediction and surface current simulation is implemented and analyzed in this paper. Finally, the influence of different sea states on the radar target signatures has been examined and discussed.
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    Trends in Adaptive Array Processing (2012)
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    Publication Date: 2012-06-21
    Description: Enormous progress has been made during the past five decades in the area of adaptive array processing. Increased computational power has resulted in many practical applications of optimum algorithms. The present paper deals with many facets of array signal processing and adaptive beam forming. It provides a comprehensive description of various beam-forming schemes, adaptive algorithms to adjust the required weighting on antenna elements, direction-of-arrival estimation methods, including their performance comparison. The effects of various types of errors on the performance of an array system are illustrated along with their remedial measures. Since array signal processing has widespread applications, the study is carried out across various disciplines.
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    Very Compact and Broadband Active Antenna for VHF Band Applications (2012)
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    Publication Date: 2012-06-21
    Description: An active receiving antenna with small size consisting of a monopole loaded with a transistor bipolar is presented in this paper. A transistor is used in order to miniaturize the receiving active antenna size in VHF band. The vertical size of the structure is equal to λ/175, where λ is the wavelength at the lower frequency of the bandwidth. Despite the very small size of the antenna, the frequency bandwidth is very wide and the gain is suitable for FM application with sensitive receivers.
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    Multiobjective Coverage Control Strategy for Energy-Efficient Wireless Sensor Networks (2012)
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    Publication Date: 2012-06-21
    Description: A multiobjective optimization coverage control strategy is proposed for solving the contradictory problem among energy consumption, equilibrium of energy, and network coverage in wireless sensor networks. A new evolutionary algorithm named Multiobjective free search algorithm (MOFS) is designed for WSN optimization problem based on fitness functions and binary coding schemes. The proposed strategy is used to estimate the number of active nodes because individual nodes cannot have their working state information readily. Simulation shows that MOFS is effective to solve the typical combinatorial optimization problem, and the coverage control strategy can obtain high network coverage and reduce energy consumption effectively by the reasonable selecting parameters, while equilibrium of energy consumption is also considered.
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    Achieving a Realistic Notion of Time in Discrete Event Simulation (2012)
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    Publication Date: 2012-06-21
    Description: Distributed sensor systems require clock synchronization between all sensor nodes to provide consistent view of the overall system. Owing the growing size of networks, the evaluation of the synchronization performance becomes difficult, if done by means of experiments. Simulation is another method to tackle this issue. Realistic simulation of synchronization schemes requires accurate modelling of oscillators which are the driving timers generating various events. One way to characterise oscillators is to utilize the Allan variance, which can be used to generate a phenomenological model based on power spectral density. Since discrete event simulation (DES) tools are widely used to model network protocols, models which combine accuracy and performance are needed. This paper presents a model that was optimised for use in DES. To verify that the simulation results sufficiently match measurements, an implementation in OMNeT++ was done. The results show that the behaviour of distributed sensor systems, resulting from imperfect timebases, can be accurately simulated.
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    A Truthful Bilateral Multiunit Auction for Heterogeneous Cognitive Radio Networks (2012)
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    Publication Date: 2012-06-21
    Description: Dynamic spectrum access technology has attracted much attention for its capability of improving spectrum efficiency. For attracting primary users to participate in secondary spectrum market, an auction was proposed as an alternative for spectrum trade. Existing auction schemes are either to be unilateral trade which only supports heterogeneous cognitive radio networks without guarantee of bid truthfulness, or to be truthful single-unit auction which only supports homogeneous channels. Few of them could comprehensively take all aspects of actual spectrum trade into consideration, such as spectrum allocation and reusability, channel diversity, and economic property. A truthful bilateral multiunit auction scheme which has characteristics of supporting heterogeneous networks (TBMAH) and polynomial complexity is proposed in this paper. We do experiments with both simulation and real networks, and the results show that TBMAH trades more spectrum resources than TRUST by 13.01% on average.
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    Analysis and Design of Ultra-Wideband 3-Way Bagley Power Divider Using Tapered Lines Transformers (2012)
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    Publication Date: 2012-06-21
    Description: An ultra-wideband (UWB) modified 3-way Bagley polygon power divider (BPD) that operates over a frequency range of 2–16 GHz is presented. To achieve the UWB operation, the conventional quarter-wave transformers in the BPD are substituted by two tapered line transformers. For verification purposes, the proposed divider is simulated, fabricated, and measured. The agreement between the full-wave simulation results and the measurement ones validates the design procedure.
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    The Effect of Bulk Density on Emission Behavior of Soil at Microwave Frequencies (2012)
    Hindawi
    Details
    Publication Date: 2012-06-21
    Description: Dielectric constant and dielectric loss (ε′ and ε″) of different soil samples with bulk densities varying from 1.3 to 2.0 gm/cm3 are determined at a single microwave frequency 9.78 GHz and at temperature 37.0°C. Different bulk densities of same soil are achieved by filling the wave guide cell with an equal volume but a different mass of soil. Further, ε′ and ε″ of these soil samples are also estimated by semiempirical model and compared with the experimental results. The values of ε′ and ε″ increase as bulk density of the soil increases. In view of microwave remote sensing, the Fresnel reflectivity of soil is computed from the knowledge of the complex dielectric constant and the surface boundary condition. Using Kirchhoff’s reciprocity theorem the microwave emissivity is estimated from Fresnel reflectivity of the surface. It is observed that the microwave emission from the soil surface inhibits as bulk density of soil increases. Further, the roughness of soil surface has been taken into consideration in the emissivity computation and observed that the emissivity increases with increasing roughness of the soil surface.
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    Influence of System Variables on the Heating Characteristics of Water during Continuous Flow Microwave Heating (2012)
    Hindawi
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    Publication Date: 2012-06-21
    Description: A domestic microwave oven (1000 W) was modified to permit the continuous flow of liquids run through a helical coil centrally located inside the oven cavity. Heating characteristics were evaluated by measuring inlet and outlet temperatures of coil as a function of system variables. The influence of number of turns, coil diameter, tube diameter, pitch and initial temperature were evaluated at different flow rates. The average residence time of water was computed by dividing the coil volume by the volumetric flow rate. The influence of Dean number was evaluated. Results from this study showed that (1) higher number of turns resulted in lower heating rate, lower temperature fluctuations, higher exit temperature and longer time to achieve temperature equilibrium; (2) larger tube or coil diameter gave larger coil volume causing the heating rate to decrease; (3) faster flow rates resulted in lower exit temperatures, lower temperature fluctuation, higher Dean number and slightly higher heating rate; (4) higher initial temperatures resulted in higher exit temperatures; (5) higher Dean number resulted in more uniform heating and slightly higher heating rate. Overall, the coil volume was the more dominant factor affecting heating rate as compared with flow rate and Dean number.
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    Trapped-Mode Resonance Regime of Thin Microwave Electromagnetic Arrays with Two Concentric Rings in Unit Cell (2012)
    Hindawi
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    Publication Date: 2012-06-21
    Description: We present a theoretical study of reflection and transmission characteristics of a microwave planar array on a thin dielectric substrate with unit cell made of two concentric rings. This array possesses high quality factor transmission resonance with polarization insensitivity for normally incident plane wave. This resonance is defined by the trapped-mode regime. We show that for oblique incidence, there are some differences in characteristics of the array and a small change in quality factor of the trapped-mode resonance.
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    Microwave Attenuation and Prediction of Rain Outage for Wireless Networks in Pakistan's Tropical Region (2012)
    Hindawi
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    Publication Date: 2012-06-21
    Description: The microwave attenuation due to rainfall in tropical regions has not been very widely studied yet. In Pakistan's tropical environment, line-of-sight microwave communication links were set up and have been operated for several years to study the microwave attenuation characteristics due to tropical rainfall. In this paper the experimental results are presented, including the cumulative distributions of microwave attenuation and the relationship between specific attenuation and rainfall rate. In addition, a rain outage prediction model is proposed which not only predicts microwave radio link performance but will also be useful in calculating the link degradations due to interference issues. The main focus of this research work has been done keeping in mind the wireless networks of Pakistan. The results show that the rainfall rate, the microwave propagation characteristics, and outage predictions in Pakistan differ from the International Radio Consultative Committee predictions and ITU recommendation P530.7/8, respectively.
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    Design and Comparison of 24 GHz Patch Antennas on Glass Substrates for Compact Wireless Sensor Nodes (2012)
    Hindawi
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    Publication Date: 2012-06-21
    Description: Three patch antennas suitable for integration and operation in a compact 24 GHz wireless sensor node with radar and communication functions are designed, characterized, and compared. The antennas are manufactured on a low loss glass wafer using thin film (BCB/Cu) wafer level processing (WLP) technologies. This process is well suited for 3D stacking. The antennas are fed through a microstrip line underneath a ground plane coupling into the patch resonator through a slot aperture. Linear polarization (LP), dual mode (DM) operation, and circular polarization (CP) are achieved through the layout of the slot aperture and rectangular patch dimensions. Antenna gain values of ∼5.5 dBi are obtained in addition to the 10 dB impedance bandwidths of 900 MHz and 1.3 GHz as well as 500 MHz CP bandwidth with a 3 dB axial ratio for the LP, DM, and CP patch antennas, respectively.
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    A New Process for On-Chip Inductors with High Q-Factor Performance (2012)
    Hindawi
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    Publication Date: 2012-06-21
    Description: A novel technological method to improve the quality factor (Q) of RF-integrated inductors for wireless applications is presented in this paper. A serious reduction of substrate losses caused by capacitive coupling is provided. This is realised by removing the oxide layers below the coils with optimized underetching techniques. This special etching procedure is used to establish an environment in the inductor substructure with very low permittivity. A set of solid oxide-metal-columns placed below the metal windings stabilize the coil and prevent the hollowed out structure from mechanical collapse. The oxide capacitance is lowered significantly by the reduction of the permittivity εr from values around 4 to nearly 1. Capacitive coupling losses into substrate are decreasing in the same ratio. The resulting maximum Q-factors of the new designs are up to 100% higher compared to the same devices including the oxide layers but shifted significantly to higher frequencies. Improvements of Q from 10 up to 15 have been obtained at a frequency of 3 GHz for a 2.2 nH inductor with an outer diameter of 213 μm. The resonance frequency (fres) and frequency at maximum Q (f(Qmax)) are shifted to higher frequencies, caused by the shrunk total capacitance of the structure. This enables the circuit designer to use the inductors for applications working at higher frequencies. Coils with different layouts and values for inductance (L) were verified and showed similar results.
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    A UWB Bidirectional Rectangular Ring Antenna Fed by CDM with a Rod and Ridges for Constant Beam Direction (2012)
    Hindawi
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    Publication Date: 2012-06-21
    Description: This paper presents an ultra-wideband (UWB) rectangular ring antenna excited by a circular disc monopole (CDM) with a conducting rod and two double ridges to radiate bidirectional pattern with constant beam direction along the entire UWB frequency range of 3.1–10.6 GHz. The conducting rod and double ridges at the upper wall of the ring are added to solve the tilted beam problem at the higher edge frequency whereas the double ridges at the lower wall are used to enhance the impedance bandwidth. The dimensions of the rectangular ring and the CDM are initially considered to achieve the bidirectional pattern with the suitable resonant frequencies and bandwidth. Then, the parameters of copper rod and two double ridges are determined by parametric study using CST Microwave Studio simulation software. The prototype antenna was fabricated, and the measured results show good agreement with the simulated ones. The obtained bandwidth of |S11|<-10 dB can cover the UWB frequency range as well as the bidirectional beam radiation with constant beam direction (θ=0°,180° and ϕ=90°). The minimum and maximum measured gains are 3.1 dBi to 5.3 dBi, respectively. The proposed antenna possesses compact size with good radiation performance that can be a promising candidate for UWB applications.
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    Scalable RFCMOS Model for 90 nm Technology (2012)
    Hindawi
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    Publication Date: 2012-06-21
    Description: This paper presents the formation of the parasitic components that exist in the RF MOSFET structure during its high-frequency operation. The parasitic components are extracted from the transistor's S-parameter measurement, and its geometry dependence is studied with respect to its layout structure. Physical geometry equations are proposed to represent these parasitic components, and by implementing them into the RF model, a scalable RFCMOS model, that is, valid up to 49.85 GHz is demonstrated. A new verification technique is proposed to verify the quality of the developed scalable RFCMOS model. The proposed technique can shorten the verification time of the scalable RFCMOS model and ensure that the coded scalable model file is error-free and thus more reliable to use.
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    Design of a Two-Element Antenna Array Using Substrate Integrated Waveguide Technique (2012)
    Hindawi
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    Publication Date: 2012-06-21
    Description: The design of a two-element antenna array using the substrate integrated waveguide (SIW) technique and operating at 10 GHz is presented. The proposed antenna array consists of two SIW phase shifter sections with two SIW slot antennas. The phase shifting is achieved by changing the position of two inductive posts inserted inside each element of the array. Numerical simulations and experimental measurements have been carried out for three differential phases between the two antenna array elements, namely, 0°, 22.5°, and 67.5°. A prototype for each differential phase has been fabricated and measured. Results have shown a fairly good agreement between theory and experiments. In fact, a reflection coefficient of better than 20 dB has been achieved around 10 GHZ. The E-plane radiation pattern has shown a beam scan between 5° and 18° and demonstrated the feasibility of designing an SIW antenna phased array.
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    Nonuniformly Spaced Linear Antenna Array Design Using Firefly Algorithm (2012)
    Hindawi
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    Publication Date: 2012-06-21
    Description: A nonuniformly spaced linear antenna array with broadside radiation characteristics is synthesized using firefly algorithm and particle swarm optimization. The objective of the work is to find the optimum spacing between the radiating antenna elements which will create a predefined arbitrary radiation pattern. The excitation amplitudes of all the antenna elements are assumed to be constant. The optimum spacing between the array elements are obtained using firefly algorithm. The minimum allowed distance between the antenna elements is defined in such a way that mutual coupling between the elements can be ignored. Numerical analysis is performed to calculate the far-field radiation characteristics of the array. Two numerical examples are shown to form two different desired predefined radiation patterns. The performance of the firefly algorithm and particle swarm optimization is compared in terms of convergence rate and global best solution achieved. The performances of the optimized nonuniformly spaced arrays are analyzed. Finally, contour plots of the radiated power from the optimized array in the horizontal plane and vertical plane in the far-field region are provided.
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    Temperature Dependence of GaN HEMT Small Signal Parameters (2012)
    Hindawi
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    Publication Date: 2012-06-21
    Description: This study presents the temperature dependence of small signal parameters of GaN/SiC HEMTs across the 0–150°C range. The changes with temperature for transconductance (gm), output impedance (Cds and Rds), feedback capacitance (Cdg), input capacitance (Cgs), and gate resistance (Rg) are measured. The variations with temperature are established for gm, Cds, Rds, Cdg, Cgs, and Rg in the GaN technology. This information is useful for MMIC designs.
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    Optimization of Microwave-Osmotic Pretreatment of Apples with Subsequent Air-Drying for Preparing High-Quality Dried Product (2012)
    Hindawi
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    Publication Date: 2012-06-21
    Description: Prepared apple (Red Gala) cylinders were subjected to microwave-osmotic dehydration treatment under continuous flow medium spray (MWODS) conditions and then air-dried to a final 20% moisture content. The dried samples were evaluated for color and textural properties, and rehydration capacity. The MWODS pretreatments were based on a central composite rotatable design and a response surface methodology using five levels of sucrose concentration, temperature, and contact time at a constant flow rate of 2800 mL/min. The air-drying was carried out at 60°C, 15±1% relative humidity, and 0.64±0.02 m/s air velocity. The results were compared to untreated air-dried (AD) (worst-case scenario) and freeze-dried (FD) (best-case scenario) apples without the MWODS treatment. Color properties were affected regardless of the type of treatment. Conventional AD apples were darker in color, whereas MWODS-treated samples were lighter with higher L∗ and b∗ values, higher Hue and Chroma values but lower a∗ value and ΔE. Further the color parameters of MWODS-treated samples were closer or equal to the FD apples. The texture properties were also affected by the osmotic variables with MWODS treatment resulting in softer and chewier products. The AD samples were hard, and FD apples were brittle.
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    Theoretical and Experimental Results of Substrate Effects on Microstrip Power Divider Designs (2012)
    Hindawi
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    Publication Date: 2012-06-21
    Description: The effects of substrate materials on the design of microstrip power divider are investigated theoretically and experimentally. Three dielectric substrate materials, Duroid 3003, G10/FR4 epoxy Glass, and Duroid 3010, are chosen to be studied. A three-way two-stage power divider is designed at S-band frequency of 2.25 GHz and etched on each studied substrate separately. The substrate effects on the characteristics and performance of the microsrip circuits are studied taking into consideration the large difference in dielectric constant and the dissipation factor. The circuit designs presented here are analyzed using the Genesys CAD program and implemented and tested experimentally. The simulated and measured results are compared and discussed, and they indicate that significant changes in the characteristics of the microstrip power divider are observed.
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    A Two-Step Identification Approach for Twin-Box Models of RF Power Amplifier (2012)
    Hindawi
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    Publication Date: 2012-06-21
    Description: We propose a two-step identification approach for twin-box model (Wiener or Hammerstein) of RF power amplifier. The linear filter block and the static nonlinearity block are extracted, respectively, based on least-squares method, by iterative calculation. Simulations show that the method can get quite accurate parameters to model different nonlinear models with memory such as Wiener, Hammerstein, Wiener-Hammerstein (W-H), and memory polynomial models, hence, demonstrating its robustness. Furthermore, experimental results show excellent agreement between measured output and modeled output, where one carrier WCDMA signal is used as the excitation for a wideband RF amplifier.
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    Reduction of Mutual Coupling and Return Loss in Microstrip Array Antennas Using Concave Rectangular Patches (2012)
    Hindawi
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    Publication Date: 2012-06-21
    Description: An effective solution to reduce both the mutual coupling and return loss of a microstrip array antenna consisting of rectangular patches is proposed. The patch is made concave in both horizontal and vertical sides. Applying the proposed structure to a microstrip array antenna having two elements, the effects of patch concavity on the mutual coupling and return loss are simulated and studied. To obtain a concave rectangular patch array antenna having low amounts of mutual coupling and return loss, the patch length and width as well as the amounts of concavities are optimized using an enhanced genetic algorithm. To verify the simulation results, then, the optimal array antenna is fabricated. The simulation and experimental results confirm that the optimal concave rectangular array antenna has low amounts of mutual coupling and return loss.
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    Very Wideband, Compact Microstrip Bandstop Filter Covering S-Band to Ku-Band (2012)
    Hindawi
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    Publication Date: 2012-06-21
    Description: This paper reports a wide bandwidth planar bandstop filter with improved RF characteristics. The proposed filter on alumina is realized incorporating tapped open stub along with spurline topology. Further, stepped impedance resonator (SIR) approach has been introduced in the tapped stubs to achieve wider band performance with improved selectivity. The proposed topology effectively controls the transmission poles. Fabrication of this BSF has been carried out on glass substrate showing minimal effect of permittivity variation on bandwidth performance. This validates the applied approach with achievable bandwidth of more than 100% ranging from S- to Ku-band. Close agreement with simulation and practical results have been demonstrated with measured insertion loss of less than 1 dB and attenuation loss better than 30 dB at C-band.
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    Construction and Study of Hetreojunction Solar Cell Based on Dodecylbenzene Sulfonic Acid-Doped Polyaniline/n-Si (2012)
    Hindawi
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    Publication Date: 2012-07-10
    Description: Polyaniline/n-type Si heterojunctions solar cell are fabricated by spin coating of soluble dodecylbenzene sulfonic acid (DBSA)-doped polyaniline onto n-type Si substrate. The electrical characterization of the Al/n-type Si/polyaniline/Au (Ag) structure was investigated by using current-voltage (I-V), capacitance-voltage (C-V), and impedance spectroscopy under darkness and illumination. The photovoltaic cell parameters, that is, open-circuit voltage (Voc), short-circuit current density (Jsc), fill factor (FF), and energy conversion efficiency (η) were calculated. The highest Jsc, Voc, and efficiency of these heterojunctions obtained using PANI-DBSA as a window layer (wideband gap) and Au as front contact are 1.8 mA/cm2, 0.436 V, and 0.13%, respectively. From Mott-Schottky plots, it was found that order of charge carrier concentrations is 3.5×1014 and 1.0×1015/cm3 for the heterojunctions using Au as front contact under darknessness and illumination, respectively. Impedance study of this type of solar cell showed that the shunt resistance and series resistance decreased under illumination.
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    Topics: Electrical Engineering, Measurement and Control Technology , Energy, Environment Protection, Nuclear Power Engineering
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    Wide Angular Aperture Circularly Polarized Low-Profile EBG Antenna (2012)
    Hindawi
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    Publication Date: 2012-07-04
    Description: This paper describes the design of a compact and wide angular circularly polarized low-profile EBG antenna. Except at 3.7 GHz and for θ lower than −25° in the plane Φ equals to 0°, the modelized structure provides an axial ratio lower than 3 dB, over a wide angular aperture of 60° and over a bandwidth of 5.3% ([3.7 GHz–3.9 GHz]). It has a very low height of 11.9 mm (λ/7 at 3.8 GHz). A prototype has been manufactured, and the measured performances, considering the tolerance of the measurement base (±0.5 dB), are quite similar to the simulated ones.
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    Efficient Evaluation of the External Mutual Coupling in Dielectric-Covered Waveguide Slot Arrays (2012)
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    Publication Date: 2012-07-06
    Description: An accurate and efficient procedure is devised to evaluate the mutual coupling in dielectric-covered planar arrays of longitudinal slots. This approach takes full advantage of the discrete complex image method to cast the spatial-domain Green's functions into closed forms, and hence a direct calculation of mutual coupling in the spatial-domain is available. The computation time reduces significantly compared to the previous spectral-domain procedure, without any loss in the accuracy, rendering this approach very attractive for the design of large dielectric-covered planar arrays.
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    Design of a MIMO Antenna with Improved Isolation Using MNG Metamaterial (2012)
    Hindawi
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    Publication Date: 2012-07-06
    Description: A multi-input multi-output (MIMO) antenna with improved isolation using an interdigital split ring resonator (SRR) is proposed. The necessary impedance bandwidth is obtained by utilizing the coupling between the meander strip and an inverted L strip. Using interdigital SRR, a negative permeability was generated, while achieving improved isolation between the two radiating elements. The fabricated antenna satisfies the 10 dB return loss in the long-term evolution (LTE) band 40 from 2.3 GHz to 2.4 GHz. The measured peak gains of the two elements were 2.0 dBi and 1.3 dBi. The measured envelope correlation coefficient was less than 0.16 over the frequency band of interest.
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    Modeling and Simulation of MIMO Mobile-to-Mobile Wireless Fading Channels (2012)
    Hindawi
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    Publication Date: 2012-07-06
    Description: Analysis and design of multielement antenna systems in mobile fading channels require a model for the space-time cross-correlation among the links of the underlying multipleinput multiple-output (MIMO) Mobile-to-Mobile (M-to-M) communication channels. In this paper, we propose the modified geometrical two-ring model, a MIMO channel reference model for M-to-M communication systems. This model is based on the extension of single-bounce two-ring scattering model for flat fading channel under the assumption that the transmitter and the receiver are moving. Assuming single-bounce scattering model in both isotropic and nonisotropic environment, a closed-form expression for the space-time cross-correlation function (CCF) between any two subchannels is derived. The proposed model provides an important framework in M-to-M system design, where includes many existing correlation models as special cases. Also, two realizable statistical simulation models are proposed for simulating both isotropic and nonisotropic reference model. The realizable simulation models are based on Sum-of-Sinusoids (SoS) simulation model. Finally, the correctness of the proposed simulation models is shown via different simulation scenarios.
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    Can λ/4 Radiators Be Really Isotropic? (2012)
    Hindawi
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    Publication Date: 2012-06-21
    Description: In search for isotropic radiators with reasonable quality Factor (Q), bandwidth, and efficiency, one looks for practical radiators with a typical resonant length of λ/4. We present here a Green's function analysis in Fourier of a λ/4 microstrip element and a far-field integral method in configuration (real) space of single and dual U-shaped λ/4 elements. Both solutions analytically prove that the power radiation patterns are isotropic in nature (while the thickness and the width tend to zero), although the polarizations are not symmetrical in all cuts. It is also shown that the power isotropic U-shaped radiator, for which the surface current density is infinite, can be replaced by another finite-size radiator, having finite-surface current density, such that its far-field is exactly the same as the far-field of the U-shaped isotropic radiator.
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    Electromagnetic Radiation from Arbitrarily Shaped Microstrip Antenna Using the Equivalent Dipole-Moment Method (2012)
    Hindawi
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    Publication Date: 2012-06-21
    Description: The equivalent dipole-moment method (EDM) is extended and applied in the analysis of electromagnetic (EM) radiation by arbitrarily shaped microstrip antenna in this paper. The method of moments (MoM) is used to solve the volume-surface integral equation (VSIE). A strip model is applied in the treatment of the feeding probe of the microstrip antenna, in which the discretized triangular elements of the excitation source are equivalent as dipole models. The proposed approach is sufficiently versatile in handling arbitrarily shaped microstrip antenna and is easily constructed through a simple procedure. Numerical results are given to demonstrate the accuracy and efficiency of this method.
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    A Large-Scale Space-Time Stochastic Simulation Tool of Rain Attenuation for the Design and Optimization of Adaptive Satellite Communication Systems Operating between 10 and 50 GHz (2012)
    Hindawi
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    Publication Date: 2012-06-21
    Description: The design and optimization of propagation impairment techniques for space telecommunication systems operating at frequencies above 20 GHz require a precise knowledge of the propagation channel both in space and time. For that purpose, space-time channel models have to be developed. In this paper the description of a model for the simulation of long-term rain attenuation time series correlated both in space and time is described. It relies on the definition of a stochastic rain field simulator constrained by the rain amount outputs of the ERA-40 reanalysis meteorological database. With this methodology, realistic propagation conditions can be generated at the scale of satellite coverage (i.e., over Europe or USA) for many years. To increase the temporal resolution, a stochastic interpolation algorithm is used to generate spatially correlated time series sampled at 1 Hz, providing that way valuable inputs for the study of the performances of propagation impairment techniques required for adaptive SatCom systems operating at Ka band and above.
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    Dual-Band Dielectric Resonator Antenna for C and X Band Application (2012)
    Hindawi
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    Publication Date: 2012-06-21
    Description: The proposed technique combines a slot antenna and a dielectric resonator antenna (DRA) to effectively design a dual band dielectric resonant antenna without compromising miniaturization or its efficiency. It is observed that the resonance of the slot and that of the dielectric structure merged to achieve extremely wide bandwidth over which the antenna polarization and radiation pattern are preserved. Here the effect of slot size on the radiation performance of the DRA is studied. The antenna structure is simulated using two simulators (Ansoft HFSS and CST-Studio software). The simulated results are presented and compared with the measured results. This DRA has a gain of 6 dBi and 5.5 dBi at 6.1 and 8.3 GHz, respectively, 10 dB return impedance bandwidth of nearly 4% and 6% at two resonating frequencies and 98% efficiency has been achieved from the configuration. It is shown that the size of the slot can significantly affect the radiation properties of the DRA, and there are good agreements between simulation and measured results.
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    Topics: Electrical Engineering, Measurement and Control Technology
    Published by Hindawi
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    Design of UWB Filter with WLAN Notch (2012)
    Hindawi
    Details
    Publication Date: 2012-06-21
    Description: UWB technology- (operating in broad frequency range of 3.1–10.6 GHz) based filter with WLAN notch has shown great achievement for high-speed wireless communications. To satisfy the UWB system requirements, a band pass filter with a broad pass band width, low insertion loss, and high stop-band suppression are needed. UWB filter with wireless local area network (WLAN) notch at 5.6 GHz and 3 dB fractional bandwidth of 109.5% using a microstrip structure is presented. Initially a two-transmission-pole UWB band pass filter in the frequency range 3.1–10.6 GHz is achieved by designing a parallel-coupled microstrip line with defective ground plane structure using GML 1000 substrate with specifications: dielectric constant 3.2 and thickness 0.762 mm at centre frequency 6.85 GHz. In this structure a λ/4 open-circuited stub is introduced to achieve the notch at 5.6 GHz to avoid the interference with WLAN frequency which lies in the desired UWB band. The design structure was simulated on electromagnetic circuit simulation software and fabricated by microwave integrated circuit technique. The measured VNA results show the close agreement with simulated results.
    Print ISSN: 1687-5869
    Electronic ISSN: 1687-5877
    Topics: Electrical Engineering, Measurement and Control Technology
    Published by Hindawi
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