ALBERT

Description: Aerosol-assisted CVD synthesis, characterisation and gas-sensing application of gold-functionalised tungsten oxide Journal of Sensors and Sensor Systems, 3, 325-330, 2014 Author(s): F. Di Maggio, M. Ling, A. Tsang, J. Covington, J. Saffell, and C. Blackman Tungsten oxide nanoneedles (NNs) functionalised with gold nanoparticles (NPs) have been integrated with alumina gas-sensor platforms using a simple and effective co-deposition method via aerosol-assisted chemical vapour deposition (AACVD) utilising a novel gold precursor, (NH 4 )AuCl 4 . The gas-sensing results show that gold NP functionalisation of tungsten oxide NNs improves the sensitivity of response to ethanol, with sensitivity increasing and response time decreasing with increasing amount of gold.

Description: Objectifying user attention and emotion evoked by relevant perceived product components Journal of Sensors and Sensor Systems, 3, 315-324, 2014 Author(s): R. Schmitt, M. Köhler, J. V. Durá, and J. Diaz-Pineda A company's aim is to develop products that engage user attention and evoke positive emotions. Customers base their emotional evaluation on product components that are relevant for their perception. This paper presents findings of both identifying relevant product components and measuring emotions evoked by relevant perceived product components. To validate results, the comparison with self-reporting methods identifies similarities and differences between explicit expressed and implicit recorded customer requirements. On the one hand, eye tracking is applied to deduce the attention provoked by perceived product components. In order to link the product strategy with product components, the paper presents results considering the fact that the gaze track is affected by current thoughts. (Köhler et al., 2013, 2014a, b; Köhler and Schmitt, 2012) On the other hand, since self-reporting tools are only useful for obtaining information about the conscious part of customers' emotions, there is a need for measurement methods that measure the changes in physiological signals (bio-signals). Arousal is similar to emotional intensity and is related to the galvanic skin response. Positive or negative emotions are defined by the valence that is measured by facial electromyography. Findings are presented that relate changes in bio-signals on the aesthetical design to the global product impression as well as to emotions and, subsequently, linking changes in physiological signals to the evaluation of semantic concepts and design parameters. The presented approach provides conclusions and valid information about products as well as product components that provoke certain emotions and about product components linked to a certain product concept, which could be part of a product strategy. Consequently, hard facts and special design rules for emotional product design can be deduced.

Description: Equivalent circuit models of two-layer flexure beams with excitation by temperature, humidity, pressure, piezoelectric or piezomagnetic interactions Journal of Sensors and Sensor Systems, 3, 187-211, 2014 Author(s): U. Marschner, G. Gerlach, E. Starke, and A. Lenk Two-layer flexure beams often serve as basic transducers in actuators and sensors. In this paper a generalized description of their stimuli-influenced mechanical behavior is derived. For small deflection angles this description includes a multi-port circuit or network representation with lumped elements for a beam part of finite length. A number of coupled finite beam parts model the dynamic behavior including the first natural frequencies of the beam. For piezoelectric and piezomagnetic interactions, reversible transducer models are developed. The piezomagnetic two-layer beam model is extended to include solenoid and planar coils. Linear network theory is applied in order to determine network parameters and to simplify the circuit representation. The resulting circuit model is the basis for a fast simulation of the dynamic system behavior with advanced circuit simulators and, thus, the optimization of the system. It is also a useful tool for understanding and explaining this multi-domain system through basic principles of general system theory.

Description: A simple method to recover the graphene-based chemi-resistor signal Journal of Sensors and Sensor Systems, 3, 241-244, 2014 Author(s): F. Fedi, F. Ricciardella, M. L. Miglietta, T. Polichetti, E. Massera, and G. Di Francia We present the development of a simple and fast method for restoring exhaust graphene-based chemi-resistors used for NO 2 detection. Repeatedly exposing the devices to gases or to air for more than 2 days, an overall worsening of the sensing signal is observed; we hypothesized that the poisoning effect in both cases is caused by the exposure to NO 2 . Starting from this hypothesis and from the observation that NO 2 is soluble in water, we performed a recovery method consisting in the dipping of exhaust devices into ultrapure water at 100 °C for 60 s. The device performances are compared with those obtained after the restoration is achieved using the typical annealing under vacuum method.

Description: Devices based on series-connected Schottky junctions and β-Ga 2 O 3 /SiC heterojunctions characterized as hydrogen sensors Journal of Sensors and Sensor Systems, 3, 231-239, 2014 Author(s): S. Nakagomi, K. Yokoyama, and Y. Kokubun Field-effect hydrogen gas sensor devices were fabricated with the structure of a series connection between Schottky junctions and β-Ga 2 O 3 /6H-SiC heterojunctions. β-Ga 2 O 3 thin films were deposited on n-type and p-type 6H-SiC substrates by gallium evaporation in oxygen plasma. These devices have rectifying properties and were characterized as hydrogen sensors by a Pt electrode. The hydrogen-sensing properties of both devices were measured in the range of 300–500 °C. The Pt/Ga 2 O 3 /n-SiC device revealed hydrogen-sensing properties as conventional Schottky diode-type devices. The forward current of the Pt/Ga 2 O 3 /p-SiC device was significantly increased under exposure to hydrogen. The behaviors of hydrogen sensing of the devices were explained using band diagrams of the Pt/Ga 2 O 3 /SiC structure biased in the forward and reverse directions.

Description: Catalytic and thermal characterisations of nanosized PdPt / Al 2 O 3 for hydrogen detection Journal of Sensors and Sensor Systems, 3, 273-280, 2014 Author(s): T. Mazingue, M. Lomello-Tafin, M. Passard, C. Hernandez-Rodriguez, L. Goujon, J.-L. Rousset, F. Morfin, and J.-F. Laithier Palladium platinum (PdPt) has been intensively studied these last decades due to high conversion rate in hydrogen oxidation at room temperature with significant exothermic effects. These remarkable properties have been studied by measuring the temperature variations of alumina (Al 2 O 3 ) supported nanosized PdPt nanoparticles exposed to different hydrogen concentrations in dry air. This catalyst is expected to be used as a sensing material for stable and reversible ultrasensitive hydrogen sensors working at room temperature (low power consumption). Structural and gas sensing characterisations and catalytic activity of PdPt / Al 2 O 3 systems synthesised by co-impregnation will be presented. Catalytic characterisations show that the system is already active at room temperature and that this activity sharply increases with rise in temperature. Moreover, the increase of the PdPt proportion in the co-impregnation process improves the activity, and very high conversion can be reached even at room temperature. The thermal response (about 3 °C) of only 1 mg of PdPt / Al 2 O 3 is reversible, and the time response is about 5 s. The integration of PdPt / Al 2 O 3 powder on a flat substrate has been realised by the deposition onto the powder of a thin porous hydrophobic layer of parylene. The possibility of using PdPt in gas sensors will be discussed.

Description: Thermal imaging as a modern form of pyrometry Journal of Sensors and Sensor Systems, 3, 265-271, 2014 Author(s): U. Kienitz Pyrometers and thermography cameras used to be characterized by different specifications and technical definitions. After an analysis of the market situation and the physical basics, the following article describes common methods to determine optical and thermal key parameters. Based on this, aspects of future sensor developments and certain applications of infrared (IR) cameras are discussed. (This article was first published in the journal tm – Technisches Messen, Vol. 81, No. 3, 2014 , a volume which is dedicated to the memory of Prof. Dr.-Ing. habil. Ludwig Walther.)

Description: Selective detection of hazardous VOCs for indoor air quality applications using a virtual gas sensor array Journal of Sensors and Sensor Systems, 3, 253-263, 2014 Author(s): M. Leidinger, T. Sauerwald, W. Reimringer, G. Ventura, and A. Schütze An approach for detecting hazardous volatile organic compounds (VOCs) in ppb and sub-ppb concentrations is presented. Using three types of metal oxide semiconductor (MOS) gas sensors in temperature cycled operation, formaldehyde, benzene and naphthalene in trace concentrations, reflecting threshold limit values as proposed by the WHO and European national health institutions, are successfully identified against a varying ethanol background of up to 2 ppm. For signal processing, linear discriminant analysis is applied to single sensor data and sensor fusion data. Integrated field test sensor systems for monitoring of indoor air quality (IAQ) using the same types of gas sensors were characterized using the same gas measurement setup and data processing. Performance of the systems is reduced due to gas emissions from the hardware components. These contaminations have been investigated using analytical methods. Despite the reduced sensitivity, concentrations of the target VOCs in the ppb range (100 ppb of formaldehyde; 5 ppb of benzene; 20 ppb of naphthalene) are still clearly detectable with the systems, especially when using the sensor fusion method for combining data of the different MOS sensor types.

Description: Aerosol-deposited BaFe 0.7 Ta 0.3 O 3-δ for nitrogen monoxide and temperature-independent oxygen sensing Journal of Sensors and Sensor Systems, 3, 223-229, 2014 Author(s): M. Bektas, D. Hanft, D. Schönauer-Kamin, T. Stöcker, G. Hagen, and R. Moos The gas sensing properties of resistive gas sensors of BaFe 0.7 Ta 0.3 O 3-δ (BFT30) prepared by the so-called aerosol deposition method, a method to manufacture dense ceramic films at room temperature, were investigated. The electrical response of the films was investigated first under various oxygen concentrations and in a wide temperature range between 350 and 900 °C. Between 700 and 900 °C, the conductivity of BaFe 0.7 Ta 0.3 O 3-δ (BFT30) depends on the oxygen concentration with a slope of almost 1/4 in the double-logarithmic plot vs. oxygen partial pressure. In addition, the sensor response is temperature independent. BFT30 responds fast and reproducibly to changing oxygen partial pressures even at 350 °C. The cross-sensitivity has been investigated in environments with various gases (C 3 H 8 , NO, NO 2 , H 2 , CO, CO 2 , and H 2 O) in synthetic air between 350 and 800 °C. BFT30 exhibits good sensing properties to NO between 350 and 400 °C in the range from 1.5 to 2000 ppm with a high selectivity to the other investigated gas species. Thus this semiconducting ceramic material is a good candidate for a temperature-independent oxygen sensor at high temperatures with the application in exhausts and for a selective nitrogen monoxide (NO) sensor at low temperatures for air quality monitoring.

Description: Metal oxide semiconductor gas sensor self-test using Fourier-based impedance spectroscopy Journal of Sensors and Sensor Systems, 3, 213-221, 2014 Author(s): M. Schüler, T. Sauerwald, and A. Schütze For the self-test of semiconductor gas sensors, we combine two multi-signal processes: temperature-cycled operation (TCO) and electrical impedance spectroscopy (EIS). This combination allows one to discriminate between irreversible changes of the sensor, i.e., changes caused by poisoning, as well as changes in the gas atmosphere. To integrate EIS and TCO, impedance spectra should be acquired in a very short time period, in which the sensor can be considered time invariant, i.e., milliseconds or less. For this purpose we developed a Fourier-based high-speed, low-cost impedance spectroscope. It provides a binary excitation signal through an FPGA (field programable gate array), which also acquires the data. To determine impedance spectra, it uses the ETFE (empirical transfer function estimate) method, which calculates the impedance by evaluating the Fourier transformations of current and voltage. With this approach an impedance spectrum over the range from 61 kHz to 100 MHz is acquired in ca. 16 μs. We carried out TCO–EIS measurements with this spectroscope and a commercial impedance analyzer (Agilent 4294A), with a temperature cycle consisting of six equidistant temperature steps between 200 and 450 °C, with lengths of 30 s (200 °C) and 18 s (all others). Discrimination of carbon monoxide (CO) and methane (CH 4 ) is possible by LDA (linear discriminant analysis) using either TCO or EIS data, thus enabling a validation of results by comparison of both methods.

Description: Characterization of ash particles with a microheater and gas-sensitive SiC field-effect transistors Journal of Sensors and Sensor Systems, 3, 305-313, 2014 Author(s): C. Bur, M. Bastuck, A. Schütze, J. Juuti, A. Lloyd Spetz, and M. Andersson Particle emission from traffic, power plants or, increasingly, stoves and fireplaces poses a serious risk for human health. The harmfulness of the particles depends not only on their size and shape but also on adsorbates. Particle detectors for size and concentration are available on the market; however, determining content and adsorbents is still a challenge. In this work, a measurement setup for the characterization of dust and ash particle content with regard to their adsorbates is presented. For the proof of concept, ammonia-contaminated fly ash samples from a coal-fired power plant equipped with a selective non-catalytic reduction (SNCR) system were used. The fly ash sample was placed on top of a heater substrate situated in a test chamber and heated up to several hundred degrees. A silicon carbide field-effect transistor (SiC-FET) gas sensor was used to detect desorbing species by transporting the headspace above the heater to the gas sensor with a small gas flow. Accumulation of desorbing species in the heater chamber followed by transfer to the gas sensor is also possible. A mass spectrometer was placed downstream of the sensor as a reference. A clear correlation between the SiC-FET response and the ammonia spectra of the mass spectrometer was observed. In addition, different levels of contamination can be distinguished. Thus, with the presented setup, chemical characterization of particles, especially of adsorbates which contribute significantly to the harmfulness of the particles, is possible.

Description: Carbon monoxide gas sensing properties of Ga-doped ZnO film grown by ion plating with DC arc discharge Journal of Sensors and Sensor Systems, 3, 331-334, 2014 Author(s): S. Kishimoto, S. Akamatsu, H. Song, J. Nomoto, H. Makino, and T. Yamamoto The carbon monoxide (CO) gas sensing properties of low-resistance heavily Ga-doped ZnO thin films were evaluated. The ZnO films with a thickness of 50 nm were deposited at 200 °C by ion plating. The electrical properties of the ZnO films were controlled by varying the oxygen assist gas flow rate during deposition. The CO gas sensitivity of ZnO films with Au electrodes was investigated in nitrogen gas at a temperature of 230 to 330 °C. CO gas concentration was varied in the range of 0.6–2.4% in nitrogen gas. Upon exposure to CO gas, the current flowing through the film was found to decrease. This response occurred even at the lowest temperature of 230 °C, and is thought to be the result of a mechanism different than the previously reported chemical reaction.

Description: Electrophoretic deposition of Au NPs on CNT networks for sensitive NO 2 detection Journal of Sensors and Sensor Systems, 3, 245-252, 2014 Author(s): E. Dilonardo, M. Penza, M. Alvisi, C. Di Franco, D. Suriano, R. Rossi, F. Palmisano, L. Torsi, and N. Cioffi In the present study, Au-surfactant core-shell colloidal nanoparticles (NPs) with controlled dimension and composition were synthesized by sacrificial anode electrolysis. Transmission electron microscopy (TEM) revealed that Au NPs core diameter is between 8 and 12 nm, as a function of the electrosynthesis conditions. Moreover, surface spectroscopic characterization by X-ray photoelectron spectroscopy (XPS) analysis confirmed the presence of nanosized gold phase. Controlled amounts of Au NPs were then deposited electrophoretically on carbon nanotube (CNT) networked films. The resulting hybrid materials were morphologically and chemically characterized using TEM, SEM (scanning electron microscopy) and XPS analyses, which revealed the presence of nanoscale gold, and its successful deposition on CNTs. Au NP/CNT networked films were tested as active layers in a two-pole resistive NO 2 sensor for sub-ppm detection in the temperature range of 100–200 °C. Au NP/CNT exhibited a p-type response with a decrease in the electrical resistance upon exposure to oxidizing NO 2 gas and an increase in resistance upon exposure to reducing gases (e.g. NH 3 ). It was also demonstrated that the sensitivity of the Au NP/CNT-based sensors depends on Au loading; therefore, the impact of the Au loading on gas sensing performance was investigated as a function of the working temperature, gas concentration and interfering gases.

Description: Principal component analysis for fast and automated thermographic inspection of internal structures in sandwich parts Journal of Sensors and Sensor Systems, 3, 105-111, 2014 Author(s): D. Griefahn, J. Wollnack, and W. Hintze Rising demand and increasing cost pressure for lightweight materials – such as sandwich structures – drives the manufacturing industry to improve automation in production and quality inspection. Quality inspection of honeycomb sandwich components with infrared (IR) thermography can be automated using image classification algorithms. This paper shows how principal component analysis (PCA) via singular value decomposition (SVD) is applied to compress data in an IR-video sequence in order to save processing time in the subsequent step of image classification. According to PCA theory, an orthogonal transformation can project data into a lower dimensional subspace with linearly uncorrelated principal components preserving all original information. The effect of data reduction is confirmed with experimental data from IR-video sequences of simple square-pulsed thermal loadings on aramid honeycomb-sandwich components with CFRP/GFRP (carbon-/glass-fiber-reinforced plastic) facings and GFRP inserts. Hence, processing time for image classification can be saved by reducing the dimension of information used by the classification algorithm without losing accuracy.

Description: Compensation for the influence of temperature and humidity on oxygen diffusion in a reactive polymer matrix Journal of Sensors and Sensor Systems, 3, 291-303, 2014 Author(s): P. Marek, J. J. Velasco-Veléz, T. Doll, and G. Sadowski In a previous work (Marek et al., 2013) a time-monitoring oxygen sensor was proposed. This sensor is based on a diffusion-controlled oxygen reaction of the indicator system methylene blue (MB)/leuco methylene blue (LMB) and riboflavin embedded in a water-loaded poly(vinyl alcohol) (PVA) matrix. It can be used in packaging, sensors, and biotechnology applications. Since the oxygen diffusion coefficient in the PVA matrix strongly depends on temperature and humidity, two different approaches were developed within this work to compensate for these two effects. To compensate for faster oxygen diffusion at higher temperatures, iron particles were added to the PVA matrix, resulting in a novel PVA/iron composite matrix. Adding silicone particles allows compensating the influence of humidity. Both temperature and humidity compensation were modeled using the finite-element method in good accordance with the experimental data. This allows tuning the sensor for application at different conditions of temperature and humidity and therewith in different environments.

Description: Data fusion of surface normals and point coordinates for deflectometric measurements Journal of Sensors and Sensor Systems, 3, 281-290, 2014 Author(s): B. Komander, D. Lorenz, M. Fischer, M. Petz, and R. Tutsch Measuring specular surfaces can be realized by means of deflectometric measurement systems with at least two reference planes as proposed proposed by Petz and Tutsch (2004). The results are the point coordinates and the normal direction of each valid measurement point. The typical evaluation strategy for continuous surfaces involves an integration or regularization of the measured normals. This method yields smooth results of the surface with deviations in the nanometer range but it is sensitive to systematic deviations. The measured point coordinates are robust against systematic deviations but the noise level is in the order of micrometers. As an alternative evaluation strategy a data-fusion process that combines both the normal direction and the point coordinates has been developed. A linear fitting technique is proposed to increase the accuracy of the point coordinate measurements by forming an objective functional as the mean squared misfit of the gradients with respect to the point coordinates on the one hand and to the normals on the other hand. Moreover, a constraint on the maximal change of the coordinate measurements is added to the optimization problem. To minimize to objective under the constraint a projected gradient method is used. The results show that the proposed method is able to adjust the point coordinate measurement to the measured normals and hence decrease the spatial noise level by more than an order of magnitude.

Description: Encapsulation of implantable integrated MEMS pressure sensors using polyimide epoxy composite and atomic layer deposition Journal of Sensors and Sensor Systems, 3, 335-347, 2014 Author(s): P. Gembaczka, M. Görtz, Y. Celik, A. Jupe, M. Stühlmeyer, A. Goehlich, H. Vogt, W. Mokwa, and M. Kraft Implantable MEMS sensors are an enabling technology for diagnostic analysis and therapy in medicine. The encapsulation of such miniaturized implants remains a largely unsolved problem. Medically approved encapsulation materials include titanium or ceramics; however, these result in bulky and thick-walled encapsulations which are not suitable for MEMS sensors. In particular, for MEMS pressure sensors the chip surface comprising the pressure membranes must be free of rigid encapsulation material and in direct contact with tissue or body fluids. This work describes a new kind of encapsulation approach for a capacitive pressure sensor module consisting of two integrated circuits. The micromechanical membrane of the pressure sensor may be covered only by very thin layers, to ensure high pressure sensitivity. A suitable passivation method for the high topography of the pressure sensor is atomic layer deposition (ALD) of aluminium oxide (Al 2 O 3 ) and tantalum pentoxide (Ta 2 O 5 ). It provides a hermetic passivation with a high conformity. Prior to ALD coating, a high-temperature resistant polyimide–epoxy composite was evaluated as a die attach material and sealing compound for bond wires and the chip surface. This can sustain the ALD deposition temperature of 275 °C for several hours without any measurable decomposition. Tests indicated that the ALD can be deposited on top of the polyimide–epoxy composite covering the entire sensor module. The encapsulated pressure sensor module was calibrated and tested in an environmental chamber at accelerated aging conditions. An accelerated life test at 60 °C indicated a maximum drift of 5% full scale after 1482 h. From accelerated life time testing at 120 °C a maximum stable life time of 3.3 years could be extrapolated.

Description: Humidity measurement with capacitive humidity sensors between −70°C and 25°C in low vacuum Journal of Sensors and Sensor Systems, 3, 177-185, 2014 Author(s): A. Lorek At the German Aerospace Center (DLR), capacitive humidity sensors are used to measure relative humidity in experiments under extreme atmospheric conditions such as on Mars or in the coldest regions on Earth. This raises the question whether such experiments can be performed using low-cost humidity sensors with a tolerable measurement uncertainty. As part of the standardizing project SMADLUSEA (project no. SF11021A), nine capacitive humidity sensors (Sensirion SHT75) were investigated for pressure ranging from 10 to 1000 hPa (low vacuum) and temperatures from −70 to 25 °C. It has been shown that these sensors worked reliably and with reproducibly measured values over the entire investigated pressure and temperature range. There was no aging of the sensors observable. In addition to the known strong temperature dependency, the SHT75 also shows a pressure dependency below −10 °C. A characteristic curve for the SHT75 was calculated with an expanded uncertainty of 7% of the measured values. In conclusion, low-cost capacitive humidity sensors offer the option to obtain reliably measured values even under extreme conditions with comparatively little effort.

Description: Fabrication and characterization of a piezoresistive humidity sensor with a stress-free package Journal of Sensors and Sensor Systems, 3, 167-175, 2014 Author(s): T. Waber, M. Sax, W. Pahl, S. Stufler, A. Leidl, M. Günther, and G. Feiertag A highly miniaturized piezoresistive humidity sensor has been developed. The starting point of the development was a 1 × 1 mm 2 piezoresistive pressure sensor chip. As sensing material, a polyimide was used that swells with increasing adsorption of water molecules. To convert the swelling into an electrical signal, a thin layer of the polyimide was deposited onto the bending plate of the pressure sensor. The humidity sensor was characterized in a climate chamber. The measurements show a sensitivity of 0.25 mV per percent relative humidity (%RH) and a non-linearity of 3.1% full scale (FS) in the range of 30–80% RH. A high cross-sensitivity to temperature of around 0.5 mV °C −1 was measured, so temperature compensation is necessary. For stress-free packaging of the sensor chip, a novel packaging technology was developed.

Description: A novel horizontal to vertical spectral ratio approach in a wired structural health monitoring system Journal of Sensors and Sensor Systems, 3, 145-165, 2014 Author(s): F. P. Pentaris This work studies the effect ambient seismic noise can have on building constructions, in comparison with the traditional study of strong seismic motion in buildings, for the purpose of structural health monitoring. Traditionally, engineers have observed the effect of earthquakes on buildings by usage of seismometers at various levels. A new approach is proposed in which acceleration recordings of ambient seismic noise are used and horizontal to vertical spectra ratio (HVSR) process is applied, in order to determine the resonance frequency of movement due to excitation of the building from a strong seismic event. The HVSR technique is widely used by geophysicists to study the resonance frequency of sediments over bedrock, while its usage inside buildings is limited. This study applies the recordings inside two university buildings attached to each other, but with different construction materials and different years of construction. Also there is HVSR application in another much older building, with visible cracks in its structure. Sensors have been installed on every floor of the two university buildings, and recordings have been acquired both of ambient seismic noise and earthquakes. Resonance frequencies for every floor of every building are calculated, from both noise and earthquake records, using the HVSR technique for the ambient noise data and the receiver function (RF) for the earthquake data. Differential acceleration drift for every building is also calculated, and there is correlation with the vulnerability of the buildings. Results indicate that HVSR process on acceleration data proves to be an easy, fast, economical method for estimation of fundamental frequency of structures as well as an assessment method for building vulnerability estimation. Comparison between HVSR and RF technique shows an agreement at the change of resonance frequency as we move to higher floors.

Description: Work area monitoring in dynamic environments using multiple auto-aligning 3-D sensors Journal of Sensors and Sensor Systems, 3, 113-120, 2014 Author(s): Y. Wang, D. Ewert, T. Meisen, D. Schilberg, and S. Jeschke Compared to current industry standards future production systems will be more flexible and robust and will adapt to unforeseen states and events. Industrial robots will interact with each other as well as with human coworkers. To be able to act in such a dynamic environment, each acting entity ideally needs complete knowledge of its surroundings, concerning working materials as well as other working entities. Therefore new monitoring methods providing complete coverage for complex and changing working areas are needed. While single 3-D sensors already provide detailed information within their field of view, complete coverage of a complete work area can only be achieved by relying on a multitude of these sensors. However, to provide useful information all data of each sensor must be aligned to each other and fused into an overall world picture. To be able to align the data correctly, the position and orientation of each sensor must be known with sufficient exactness. In a quickly changing dynamic environment, the positions of sensors are not fixed, but must be adjusted to maintain optimal coverage. Therefore, the sensors need to autonomously align themselves in real time. This can be achieved by adding defined markers with given geometrical patterns to the environment which can be used for calibration and localization of each sensor. As soon as two sensors detect the same markers, their relative position to each other can be calculated. Additional anchor markers at fixed positions serve as global reference points for the base coordinate system. In this paper we present a prototype for a self-aligning monitoring system based on a robot operating system (ROS) and Microsoft Kinect. This system is capable of autonomous real-time calibration relative to and with respect to a global coordinate system as well as to detect and track defined objects within the working area.

Description: Chain of refined perception in self-optimizing assembly of micro-optical systems Journal of Sensors and Sensor Systems, 3, 87-95, 2014 Author(s): S. Haag, D. Zontar, J. Schleupen, T. Müller, and C. Brecher Today, the assembly of laser systems requires a large share of manual operations due to its complexity regarding the optimal alignment of optics. Although the feasibility of automated alignment of laser optics has been shown in research labs, the development effort for the automation of assembly does not meet economic requirements – especially for low-volume laser production. This paper presents a model-based and sensor-integrated assembly execution approach for flexible assembly cells consisting of a macro-positioner covering a large workspace and a compact micromanipulator with camera attached to the positioner. In order to make full use of available models from computer-aided design (CAD) and optical simulation, sensor systems at different levels of accuracy are used for matching perceived information with model data. This approach is named "chain of refined perception", and it allows for automated planning of complex assembly tasks along all major phases of assembly such as collision-free path planning, part feeding, and active and passive alignment. The focus of the paper is put on the in-process image-based metrology and information extraction used for identifying and calibrating local coordinate systems as well as the exploitation of that information for a part feeding process for micro-optics. Results will be presented regarding the processes of automated calibration of the robot camera as well as the local coordinate systems of part feeding area and robot base.

Description: Capacitive strain gauges on flexible polymer substrates for wireless, intelligent systems Journal of Sensors and Sensor Systems, 3, 77-86, 2014 Author(s): R. Zeiser, T. Fellner, and J. Wilde This paper presents a novel capacitive strain gauge with interdigital electrodes, which was processed on polyimide and LCP (liquid crystal polymer) foil substrates. The metallization is deposited and patterned using thin-film technology with structure sizes down to 15 μm. We determined linear strain sensitivities for our sensor configuration and identified the most influencing parameters on the output signal by means of an analytical approach. Finite-element method (FEM) simulations of the strain gauge indicated the complex interaction of mechanical strains within the sensitive structure and their effect on the capacitance. The influence of geometry and material parameters on the strain sensitivity was investigated and optimized. We implemented thin films on 50 μm thick standard polymer foils by means of a temporary bonding process of the foils on carrier wafers. The characterization of the strain sensors after fabrication revealed the gauge factor as well as the cross sensitivities on temperatures up to 100 °C and relative humidity up to 100%. The gauge factor of a sensor with an electrode width of 45 μm and a clearance of 15 μm was −1.38 at a capacitance of 48 pF. Furthermore, we achieved a substantial reduction of the cross sensitivity against humidity from 1435 to 55 ppm % −1 RH when LCP was used for the sensor substrate and the encapsulation instead of polyimide. The gauge factor of a sensor half-bridge consisting of two orthogonal capacitors was 2.3 and the cross sensitivity on temperature was reduced to 240 ppm K −1 . Finally, a sensor system was presented that utilizes a special instrumentation Integrated Circuit (IC). For this system, performance data comprising cross sensitivities and power consumption are given.

Description: Towards assessing online uncertainty for three-phase flow metering in the oil and gas industry Journal of Sensors and Sensor Systems, 3, 97-103, 2014 Author(s): M. P. Henry, M. S. Tombs, and F. B. Zhou A new three-phase (oil/water/gas) flow metering system has been developed for use in the oil and gas industries, based on Coriolis mass flow metering. To obtain certification for use in the Russian oil and gas industries, trials have taken place at the UK and Russian national flow laboratories, NEL in Glasgow and VNIIR in Kazan, respectively. The metrology of three-phase flow is complex, and the uncertainty of each measurement varies dynamically with the operating point, as well as the metering technology, and other aspects. To a limited extent this is reflected in the error limits allowed in national standards, which may vary with operating point. For example, the GOST standard allows errors in the oil flow rate of ±6% for water cuts of less than 70%, which is increased to ±15% for water cuts between 70 and 95%. The provision of online uncertainty for each measurement, for example in accordance with the British Standard BS-7986, would be highly desirable, allowing the user to observe in real time variations in measurement quality. This paper will discuss how an online uncertainty assessment could be implemented in the Coriolis meter-based system.

Description: A micro optical probe for edge contour evaluation of diamond cutting tools Journal of Sensors and Sensor Systems, 3, 69-76, 2014 Author(s): S. H. Jang, Y. Shimizu, S. Ito, and W. Gao This paper presents a micro optical probe, which is employed to evaluate edge contours of single point diamond tools with a size in a range of several millimetres. The micro optical probe consists of a laser source with a wavelength of 405 nm, an objective lens with a numerical aperture of 0.25, a photodiode for measurement, and a compensating optical system including another photodiode for compensation of laser intensity. A collimated laser beam, which is divided by a beam splitter in the compensating optical system, is focused by the objective lens so that the focused spot can be used as the micro optical probe. The micro optical probe traces over an edge contour of an objective tool while the signals of both the two photodiodes are monitored. The output of the photodiode for measurement is compensated by using that of the photodiode for laser intensity compensation to eliminate the influence of the laser instability. The signal of the photodiode for measurement is used to define the deviation of edge contour within the diameter of the micro optical probe. To verify the feasibility of the developed optical probe, the optical system was mounted on a diamond turning machine, and some experiments were carried out. Two types of edge contours of the diamond tools having a straight cutting edge and a round cutting edge were measured on the machine.

Description: Multi-channel IR sensor system for determination of oil degradation Journal of Sensors and Sensor Systems, 3, 121-132, 2014 Author(s): T. Bley, E. Pignanelli, and A. Schütze A miniaturized infrared (IR) multi-channel sensor system was realized to determine chemical oil degradation, e.g., oxidation, increasing water content. Different artificially aged oil samples (synthetic motor oil, mineral hydraulic oil and ester-based hydraulic fluid) were prepared by oxidative degradation at elevated temperatures or addition of water, and characteristic degradation features in the IR spectrum were detected using FTIR spectroscopy. In addition, the absorption behavior of water contaminated synthetic motor oil was analyzed with increasing temperature. To determine the influence of different degradation effects on the measurement results the sensor system was characterized with the various oil samples. The system uses a reference channel to suppress the effect of decreasing transmission over the entire spectrum caused, e.g., by increasing soot content in the oil or contamination of the optical path.

Description: Electrochemical analysis of water and suds by impedance spectroscopy and cyclic voltammetry Journal of Sensors and Sensor Systems, 3, 133-140, 2014 Author(s): R. Gruden, A. Buchholz, and O. Kanoun Optimum detergent dosage during a washing process depends on water quality, degree of pollution and quantity of laundry. Particularly, water quality is an important factor. Other parameters like carbonate- or non-carbonate hardness and calcium / magnesium (Ca / Mg) ratio in addition to total hardness of water have an impact on the amount of detergent. This work discusses the possibilities realizing a detergent sensor that measures important parameters for the washing process and assess the ideal necessary amount of detergent during the washing process. The approach is to combine impedance spectroscopy with cyclic voltammetry in order to determine both water quality and concentration of detergent in the suds which build up the basis for an optimum detergent dosage. The results of cyclic voltammetry show that it is possible to identify the Ca / Mg ratio and the carbonate hardness separately, which is necessary for the optimization of the washing process. Impedance measurements identify total hardness and detergent concentrations.

Description: A catalytic combustion-type CO gas sensor incorporating aluminum nitride as an intermediate heat transfer layer for accelerated response time Journal of Sensors and Sensor Systems, 3, 141-144, 2014 Author(s): A. Hosoya, S. Tamura, and N. Imanaka A catalytic combustion-type carbon monoxide gas sensor exhibiting good sensing performance even at moderate temperatures was previously developed by employing a Pt loaded CeO 2 –ZrO 2 –SnO 2 solid solution as the CO oxidizing catalyst. The addition of aluminum nitride as an intermediate heat transfer layer between the Pt coil and the CO oxidizing catalyst drastically accelerated the response of this device to CO at temperatures as low as 70 °C.

Description: Room temperature carbon nanotube based sensor for carbon monoxide detection Journal of Sensors and Sensor Systems, 3, 349-354, 2014 Author(s): A. Hannon, Y. Lu, J. Li, and M. Meyyappan Sulfonated single-walled carbon nanotubes have been used in an integrated electrode structure for the detection of carbon monoxide. The sensor responds to 0.5 ppm of CO in air at room temperature. All eight sensors with this material in a 32-sensor array showed good repeatability and reproducibility, with response and recovery times of about 10 s. Pristine nanotubes generally do not respond to carbon monoxide and the results here confirm sulfonated nanotubes to be a potential candidate for the construction of an electronic nose that requires at least a few materials for the selective detection of CO.

Description: Development of a portable active long-path differential optical absorption spectroscopy system for volcanic gas measurements Journal of Sensors and Sensor Systems, 3, 355-367, 2014 Author(s): F. Vita, C. Kern, and S. Inguaggiato Active long-path differential optical absorption spectroscopy (LP-DOAS) has been an effective tool for measuring atmospheric trace gases for several decades. However, instruments were large, heavy and power-inefficient, making their application to remote environments extremely challenging. Recent developments in fibre-coupling telescope technology and the availability of ultraviolet light emitting diodes (UV-LEDS) have now allowed us to design and construct a lightweight, portable, low-power LP-DOAS instrument for use at remote locations and specifically for measuring degassing from active volcanic systems. The LP-DOAS was used to measure sulfur dioxide (SO 2 ) emissions from La Fossa crater, Vulcano, Italy, where column densities of up to 1.2 × 10 18 molec cm −2 (~ 500 ppmm) were detected along open paths of up to 400 m in total length. The instrument's SO 2 detection limit was determined to be 2 × 10 16 molec cm −2 (~ 8 ppmm), thereby making quantitative detection of even trace amounts of SO 2 possible. The instrument is capable of measuring other volcanic volatile species as well. Though the spectral evaluation of the recorded data showed that chlorine monoxide (ClO) and carbon disulfide (CS 2 ) were both below the instrument's detection limits during the experiment, the upper limits for the X / SO 2 ratio (X = ClO, CS 2 ) could be derived, and yielded 2 × 10 −3 and 0.1, respectively. The robust design and versatility of the instrument make it a promising tool for monitoring of volcanic degassing and understanding processes in a range of volcanic systems.

Description: A company's aim is to develop products that engage user attention and evoke positive emotions. Customers base their emotional evaluation on product components that are relevant for their perception. This paper presents findings of both identifying relevant product components and measuring emotions evoked by relevant perceived product components. To validate results, the comparison with self-reporting methods identifies similarities and differences between explicit expressed and implicit recorded customer requirements. On the one hand, eye tracking is applied to deduce the attention provoked by perceived product components. In order to link the product strategy with product components, the paper presents results considering the fact that the gaze track is affected by current thoughts. (Köhler et al., 2013, 2014a, b; Köhler and Schmitt, 2012) On the other hand, since self-reporting tools are only useful for obtaining information about the conscious part of customers' emotions, there is a need for measurement methods that measure the changes in physiological signals (bio-signals). Arousal is similar to emotional intensity and is related to the galvanic skin response. Positive or negative emotions are defined by the valence that is measured by facial electromyography. Findings are presented that relate changes in bio-signals on the aesthetical design to the global product impression as well as to emotions and, subsequently, linking changes in physiological signals to the evaluation of semantic concepts and design parameters. The presented approach provides conclusions and valid information about products as well as product components that provoke certain emotions and about product components linked to a certain product concept, which could be part of a product strategy. Consequently, hard facts and special design rules for emotional product design can be deduced.

Description: An approach for detecting hazardous volatile organic compounds (VOCs) in ppb and sub-ppb concentrations is presented. Using three types of metal oxide semiconductor (MOS) gas sensors in temperature cycled operation, formaldehyde, benzene and naphthalene in trace concentrations, reflecting threshold limit values as proposed by the WHO and European national health institutions, are successfully identified against a varying ethanol background of up to 2 ppm. For signal processing, linear discriminant analysis is applied to single sensor data and sensor fusion data. Integrated field test sensor systems for monitoring of indoor air quality (IAQ) using the same types of gas sensors were characterized using the same gas measurement setup and data processing. Performance of the systems is reduced due to gas emissions from the hardware components. These contaminations have been investigated using analytical methods. Despite the reduced sensitivity, concentrations of the target VOCs in the ppb range (100 ppb of formaldehyde; 5 ppb of benzene; 20 ppb of naphthalene) are still clearly detectable with the systems, especially when using the sensor fusion method for combining data of the different MOS sensor types.

Description: We present the development of a simple and fast method for restoring exhaust graphene-based chemi-resistors used for NO2 detection. Repeatedly exposing the devices to gases or to air for more than 2 days, an overall worsening of the sensing signal is observed; we hypothesized that the poisoning effect in both cases is caused by the exposure to NO2. Starting from this hypothesis and from the observation that NO2 is soluble in water, we performed a recovery method consisting in the dipping of exhaust devices into ultrapure water at 100 °C for 60 s. The device performances are compared with those obtained after the restoration is achieved using the typical annealing under vacuum method.

Description: For the self-test of semiconductor gas sensors, we combine two multi-signal processes: temperature-cycled operation (TCO) and electrical impedance spectroscopy (EIS). This combination allows one to discriminate between irreversible changes of the sensor, i.e., changes caused by poisoning, as well as changes in the gas atmosphere. To integrate EIS and TCO, impedance spectra should be acquired in a very short time period, in which the sensor can be considered time invariant, i.e., milliseconds or less. For this purpose we developed a Fourier-based high-speed, low-cost impedance spectroscope. It provides a binary excitation signal through an FPGA (field programable gate array), which also acquires the data. To determine impedance spectra, it uses the ETFE (empirical transfer function estimate) method, which calculates the impedance by evaluating the Fourier transformations of current and voltage. With this approach an impedance spectrum over the range from 61 kHz to 100 MHz is acquired in ca. 16 μs. We carried out TCO–EIS measurements with this spectroscope and a commercial impedance analyzer (Agilent 4294A), with a temperature cycle consisting of six equidistant temperature steps between 200 and 450 °C, with lengths of 30 s (200 °C) and 18 s (all others). Discrimination of carbon monoxide (CO) and methane (CH4) is possible by LDA (linear discriminant analysis) using either TCO or EIS data, thus enabling a validation of results by comparison of both methods.

Description: A solid electrolyte type sulfur dioxide (SO2) gas sensor that can operate at moderate temperatures was fabricated using Zr4+ ion conducting Zr39/40TaP2.9W0.1O12 solid electrolyte with 0.7La2O2SO4 − 0.3(0.8Li2SO4 + 0.2K2SO4) having a large surface area and Zr metal as the auxiliary sensing electrode and reference electrode, respectively. Since the present sensor showed a quantitative, reproducible and rapid response which obeys the theoretical Nernst relationship even at 400 °C, it is a potential on site SO2 gas sensing tool operable at moderate temperatures around 400 °C.

Description: Implantable MEMS sensors are an enabling technology for diagnostic analysis and therapy in medicine. The encapsulation of such miniaturized implants remains a largely unsolved problem. Medically approved encapsulation materials include titanium or ceramics; however, these result in bulky and thick-walled encapsulations which are not suitable for MEMS sensors. In particular, for MEMS pressure sensors the chip surface comprising the pressure membranes must be free of rigid encapsulation material and in direct contact with tissue or body fluids. This work describes a new kind of encapsulation approach for a capacitive pressure sensor module consisting of two integrated circuits. The micromechanical membrane of the pressure sensor may be covered only by very thin layers, to ensure high pressure sensitivity. A suitable passivation method for the high topography of the pressure sensor is atomic layer deposition (ALD) of aluminium oxide (Al2O3) and tantalum pentoxide (Ta2O5). It provides a hermetic passivation with a high conformity. Prior to ALD coating, a high-temperature resistant polyimide–epoxy composite was evaluated as a die attach material and sealing compound for bond wires and the chip surface. This can sustain the ALD deposition temperature of 275 °C for several hours without any measurable decomposition. Tests indicated that the ALD can be deposited on top of the polyimide–epoxy composite covering the entire sensor module. The encapsulated pressure sensor module was calibrated and tested in an environmental chamber at accelerated aging conditions. An accelerated life test at 60 °C indicated a maximum drift of 5% full scale after 1482 h. From accelerated life time testing at 120 °C a maximum stable life time of 3.3 years could be extrapolated.

Description: Measuring specular surfaces can be realized by means of deflectometric measurement systems with at least two reference planes as proposed proposed by Petz and Tutsch (2004). The results are the point coordinates and the normal direction of each valid measurement point. The typical evaluation strategy for continuous surfaces involves an integration or regularization of the measured normals. This method yields smooth results of the surface with deviations in the nanometer range but it is sensitive to systematic deviations. The measured point coordinates are robust against systematic deviations but the noise level is in the order of micrometers. As an alternative evaluation strategy a data-fusion process that combines both the normal direction and the point coordinates has been developed. A linear fitting technique is proposed to increase the accuracy of the point coordinate measurements by forming an objective functional as the mean squared misfit of the gradients with respect to the point coordinates on the one hand and to the normals on the other hand. Moreover, a constraint on the maximal change of the coordinate measurements is added to the optimization problem. To minimize to objective under the constraint a projected gradient method is used. The results show that the proposed method is able to adjust the point coordinate measurement to the measured normals and hence decrease the spatial noise level by more than an order of magnitude.

Description: Field-effect hydrogen gas sensor devices were fabricated with the structure of a series connection between Schottky junctions and β-Ga2O3/6H-SiC heterojunctions. β-Ga2O3 thin films were deposited on n-type and p-type 6H-SiC substrates by gallium evaporation in oxygen plasma. These devices have rectifying properties and were characterized as hydrogen sensors by a Pt electrode. The hydrogen-sensing properties of both devices were measured in the range of 300–500 °C. The Pt/Ga2O3/n-SiC device revealed hydrogen-sensing properties as conventional Schottky diode-type devices. The forward current of the Pt/Ga2O3/p-SiC device was significantly increased under exposure to hydrogen. The behaviors of hydrogen sensing of the devices were explained using band diagrams of the Pt/Ga2O3/SiC structure biased in the forward and reverse directions.

Description: A catalytic combustion-type carbon monoxide gas sensor exhibiting good sensing performance even at moderate temperatures was previously developed by employing a Pt loaded CeO2–ZrO2–SnO2 solid solution as the CO oxidizing catalyst. The addition of aluminum nitride as an intermediate heat transfer layer between the Pt coil and the CO oxidizing catalyst drastically accelerated the response of this device to CO at temperatures as low as 70 °C.

Description: Two-layer flexure beams often serve as basic transducers in actuators and sensors. In this paper a generalized description of their stimuli-influenced mechanical behavior is derived. For small deflection angles this description includes a multi-port circuit or network representation with lumped elements for a beam part of finite length. A number of coupled finite beam parts model the dynamic behavior including the first natural frequencies of the beam. For piezoelectric and piezomagnetic interactions, reversible transducer models are developed. The piezomagnetic two-layer beam model is extended to include solenoid and planar coils. Linear network theory is applied in order to determine network parameters and to simplify the circuit representation. The resulting circuit model is the basis for a fast simulation of the dynamic system behavior with advanced circuit simulators and, thus, the optimization of the system. It is also a useful tool for understanding and explaining this multi-domain system through basic principles of general system theory.

Description: Compared to current industry standards future production systems will be more flexible and robust and will adapt to unforeseen states and events. Industrial robots will interact with each other as well as with human coworkers. To be able to act in such a dynamic environment, each acting entity ideally needs complete knowledge of its surroundings, concerning working materials as well as other working entities. Therefore new monitoring methods providing complete coverage for complex and changing working areas are needed. While single 3-D sensors already provide detailed information within their field of view, complete coverage of a complete work area can only be achieved by relying on a multitude of these sensors. However, to provide useful information all data of each sensor must be aligned to each other and fused into an overall world picture. To be able to align the data correctly, the position and orientation of each sensor must be known with sufficient exactness. In a quickly changing dynamic environment, the positions of sensors are not fixed, but must be adjusted to maintain optimal coverage. Therefore, the sensors need to autonomously align themselves in real time. This can be achieved by adding defined markers with given geometrical patterns to the environment which can be used for calibration and localization of each sensor. As soon as two sensors detect the same markers, their relative position to each other can be calculated. Additional anchor markers at fixed positions serve as global reference points for the base coordinate system. In this paper we present a prototype for a self-aligning monitoring system based on a robot operating system (ROS) and Microsoft Kinect. This system is capable of autonomous real-time calibration relative to and with respect to a global coordinate system as well as to detect and track defined objects within the working area.

Description: Knowledge of temperature fluctuations in fast reactor subassembly is very important from a safety point of view. The time constant of thermocouples which are used for measuring coolant temperature in a fast reactor varies owing to various factors. Hence, it becomes necessary to investigate the effect of change in the time constant on sensed fluctuations. This paper investigates the dependence of temperature fluctuations on thermocouple time constants. A Scilab model consisting of source temperature profile, second-order thermocouple and histogram calculation is designed. Simulation is performed for various levels of fluctuations, fixed and variable thermocouple time constants. Kurtosis for each condition is calculated with the help of a histogram. It is found that the effect of true source fluctuations on sensor output is very large compared to that of a similar percentage of time-constant variations. Hence in systems like fast reactors, where the degree of source fluctuations (fluid enthalpy) is large in comparison to that of time-constant variations, the overall effect can be considered with great confidence to be the outcome of coolant temperature rather than thermocouple time-constant variations.

Description: This paper presents a micro optical probe, which is employed to evaluate edge contours of single point diamond tools with a size in a range of several millimetres. The micro optical probe consists of a laser source with a wavelength of 405 nm, an objective lens with a numerical aperture of 0.25, a photodiode for measurement, and a compensating optical system including another photodiode for compensation of laser intensity. A collimated laser beam, which is divided by a beam splitter in the compensating optical system, is focused by the objective lens so that the focused spot can be used as the micro optical probe. The micro optical probe traces over an edge contour of an objective tool while the signals of both the two photodiodes are monitored. The output of the photodiode for measurement is compensated by using that of the photodiode for laser intensity compensation to eliminate the influence of the laser instability. The signal of the photodiode for measurement is used to define the deviation of edge contour within the diameter of the micro optical probe. To verify the feasibility of the developed optical probe, the optical system was mounted on a diamond turning machine, and some experiments were carried out. Two types of edge contours of the diamond tools having a straight cutting edge and a round cutting edge were measured on the machine.

Description: Stable isotopic analysis of water in plant, soil, and hydrological studies often requires the extraction of water from plant or soil samples. Cryogenic vacuum extraction is one of the most widely used and accurate extraction methods to obtain such water samples. Here, we present a new design of a cryogenic vacuum extraction system with 18 extraction slots and an innovative mechanism to aerate the vacuum system after extraction. This mobile and extendable multi-port extraction system overcomes the bottleneck of time required for capturing unfractionated extracted water samples by providing the possibility to extract a larger number of samples per day simultaneously. The aeration system prevents the loss or mixture of water vapor during defrosting by purging every sample with high-purity nitrogen gas. A set of system functionality tests revealed that the extraction device guarantees stable extraction conditions with no changes in the isotopic composition of the extracted water samples. Surprisingly, extractions of dried and rehydrated soils showed significant differences of the isotopic composition of the added water and the extracts. This observation challenges the assumption that cryogenic extraction systems to fully extract soil water. Furthermore, in a plant water uptake study different results for hydrogen and oxygen isotope data were obtained, raising problems in the definition from which depths plants really take up water. Results query whether the well-established and widely used cryogenic vacuum distillation method can be used in a standard unified method of fixed extraction times as it is often done.

Description: Induction sensors are used in a wide range of scientific and industrial applications. One way to improve these is rigorous modelling of the sensor combined with a low voltage and current input noise preamplifier aiming to optimize the whole induction magnetometer. In this paper, we explore another way, which consists in the use of original ferromagnetic core shapes of induction sensors, which bring substantial improvements. These new configurations are the cubic, orthogonal and coiled-core induction sensors. For each of them we give modelling elements and discuss their benefits and drawbacks with respect to a given noise-equivalent magnetic induction goal. Our discussion is supported by experimental results for the cubic and orthogonal configurations, while the coiled-core configuration remains open to experimental validation. The transposition of these induction sensor configurations to other magnetic sensors (fluxgate and giant magneto-impedance) is an exciting prospect of this work.

Description: We present a hybrid tri-axes magnetometer designed to measure weak magnetic fields in space from DC (direct current) up to a few kHz with a better sensitivity than fluxgate magnetometers at frequencies above a few Hz. This magnetometer combines a wire-wound ferromagnetic ribbon and a classical induction sensor. The nature of the wire-wound ferromagnetic ribbon sensor, giant magneto-impedance or magneto-inductance, is discussed. New configurations of wire-wound ferromagnetic ribbon sensors based on closed magnetic circuits are suggested and the hybrid sensor is described. The electronic conditioning of the wire-wound ribbon makes use of an alternating bias field to cancel the offset and linearize the output. Finally we summarize the main performances of the hybrid magnetometer and we discuss its advantages and drawbacks. A prototype has been built and was part of the scientific payload of the NASA rocket experiment CHARM-II (Correlation of High Frequency and Auroral Roar Measurements) launched in the auroral ionosphere. Unfortunately the launch campaign ended without any noticeable magnetic event and the rocket was eventually launched on 16 February 2010, through a very quiescent arc in the magnetic cusp and no wave activity was detected at frequencies observable by the hybrid magnetometer.

Description: Figures of merit condensing the performance parameters of radiation sensors such as responsivity, noise equivalent power, and time constant in a single number can be useful for rating the performance of a particular sensor in comparison to other ones or to fundamental performance limits. The classification system and the figures of merit of radiation sensors introduced by R. C. Jones are revisited for thermal radiation sensors with the focus on thermopiles and bolometers. As a result it is stated that radiation thermopiles and bolometers should be classified differently: type III detectors for thermopiles vs. type II detectors for bolometers. Modified figures of merit are suggested and relations between them given. The figures of merit are applied in an overview on state-of-the-art thermopiles and bolometers operated at room temperature.

Description: This paper presents a semi-active broadband vibrational-energy harvesting system. Based on a non-resonant rotational generator, electronic circuitry was used to overcome the physical start-up restrictions. Due to the functional design it remains an energy harvester suitable for battery-less devices. For the first time a vibrational energy harvester is presented that allows standardization and thus higher volume production. A system layout, simulation, and measurement data will be shown.

Description: Wireless sensor nodes inside buildings are used to read out sensor data and to control actuators. The nodes need to operate for a long time with a single battery. Often the sensor data should be accessible via Internet from every point of the world. When using a standard Wi-Fi connection, the battery of the node would be depleted after a few hours due to idle currents in receive state. Using sensor nodes with included wake-up receivers can prolong the lifetime of the sensor network to several years. However, no gateway exists that can, on the one hand, connect itself to the Internet and on the other hand can send out the special coded wake-up signal needed by the wake-up receivers on the nodes. In this work we want to bridge this gap by introducing the SmartGate. It is a gateway that has two transceivers incorporated on a single printed circuit board (PCB). A Wi-Fi module connects itself to an existing Wi-Fi network and listens for incoming messages. A CC430 microcontroller analyzes the incoming Wi-Fi messages and builds up the corresponding wake-up signal with included 16-bit address coding. The wake-up signal is sent out using the integrated CC1101 transceiver core from Texas Instruments. A woken-up node will read out its sensor data and will transmit it back to the gateway, where it will be packed into a TCP/IP packet and sent back to the user. The use of the gateway allows the implementation of a wireless sensor network with wake-up receivers that can be accessed via Internet from every point of the world.

Description: The review presents the fundamental ideas, assumptions and methods of non-invasive density measurements via ultrasound at solid–liquid interface. Since the first investigations in the 1970s there has been steady progress with regard to both the technological and methodical aspects. In particular, the technology in electronics has reached such a high level that industrial applications come within reach. In contrast, the accuracies have increased slowly from 1–2% to 0.15% for constant temperatures and to 0.4% for dynamic temperature changes. The actual work reviews all methodical aspects, and highlights the lack of clarity in major parts of the measurement principle: simplifications in the physical basics, signal generation and signal processing. With respect to process application the accuracy of the temperature measurement and the presence of temperature gradients have been identified as a major source of uncertainty. In terms of analytics the main source of uncertainty is the reflection coefficient, and as a consequence of this, the amplitude accuracy in time or frequency domain.

Description: Diesel particulate filters are emission-relevant devices of the exhaust gas aftertreatment system. They need to be monitored as a requirement of the on-board diagnosis. In order to detect a malfunction, planar sensors with interdigital electrodes on an insulating substrate can be installed downstream of the filter. During the loading phase, soot deposits onto the electrodes, but the sensor remains blind until the percolation threshold has been reached (initiation time) and the sensor current starts to flow. In order to detect small soot concentrations downstream of the filter from small defects, this initiation time needs to be as low as possible. One may reduce the initiation time by covering the interdigital electrodes with an electrically conductive layer. Using finite element method (FEM) simulations, the influence of conductivity and thickness of such a coating on the initiation time are determined. It is found that a thin, screen printable coating with a thickness of 20 μm and a conductivity in the range of 10−3 to 10−1 S m−1 may reduce the initiation time by about 40%. The FEM results were verified by a commercially available thick film resistor paste with a conductivity of 0.45 mS m−1, showing an improvement of about 40% compared to an uncoated sensor.

Description: Pyrometers and thermography cameras used to be characterized by different specifications and technical definitions. After an analysis of the market situation and the physical basics, the following article describes common methods to determine optical and thermal key parameters. Based on this, aspects of future sensor developments and certain applications of infrared (IR) cameras are discussed. (This article was first published in the journal tm – Technisches Messen, Vol. 81, No. 3, 2014, a volume which is dedicated to the memory of Prof. Dr.-Ing. habil. Ludwig Walther.)

Description: This work studies the effect ambient seismic noise can have on building constructions, in comparison with the traditional study of strong seismic motion in buildings, for the purpose of structural health monitoring. Traditionally, engineers have observed the effect of earthquakes on buildings by usage of seismometers at various levels. A new approach is proposed in which acceleration recordings of ambient seismic noise are used and horizontal to vertical spectra ratio (HVSR) process is applied, in order to determine the resonance frequency of movement due to excitation of the building from a strong seismic event. The HVSR technique is widely used by geophysicists to study the resonance frequency of sediments over bedrock, while its usage inside buildings is limited. This study applies the recordings inside two university buildings attached to each other, but with different construction materials and different years of construction. Also there is HVSR application in another much older building, with visible cracks in its structure. Sensors have been installed on every floor of the two university buildings, and recordings have been acquired both of ambient seismic noise and earthquakes. Resonance frequencies for every floor of every building are calculated, from both noise and earthquake records, using the HVSR technique for the ambient noise data and the receiver function (RF) for the earthquake data. Differential acceleration drift for every building is also calculated, and there is correlation with the vulnerability of the buildings. Results indicate that HVSR process on acceleration data proves to be an easy, fast, economical method for estimation of fundamental frequency of structures as well as an assessment method for building vulnerability estimation. Comparison between HVSR and RF technique shows an agreement at the change of resonance frequency as we move to higher floors.

Description: A miniaturized infrared (IR) multi-channel sensor system was realized to determine chemical oil degradation, e.g., oxidation, increasing water content. Different artificially aged oil samples (synthetic motor oil, mineral hydraulic oil and ester-based hydraulic fluid) were prepared by oxidative degradation at elevated temperatures or addition of water, and characteristic degradation features in the IR spectrum were detected using FTIR spectroscopy. In addition, the absorption behavior of water contaminated synthetic motor oil was analyzed with increasing temperature. To determine the influence of different degradation effects on the measurement results the sensor system was characterized with the various oil samples. The system uses a reference channel to suppress the effect of decreasing transmission over the entire spectrum caused, e.g., by increasing soot content in the oil or contamination of the optical path.

Description: We approached the problem of sensing gaseous pollutants and malodors originating as a result of decomposition of organic compounds via chemoresistive sensors. A set of four screen-printed films based on two types of mixed tin and titanium oxides, mixed tungsten and tin oxides, and zinc oxide has been tested vs. the main gaseous components of malodors. N-butanol was also considered because of its importance as a reference gas in the odorimetric intensity scale. We found that, under proper working conditions, the films can sensitively detect such gases either in dry or in wet environments, within the range of concentrations of interest for their monitoring. We also demonstrated that the array is robust under solicitation by harmful interference gases such as CO, C6H6, NO2 and NO.

Description: The aim of this article is to introduce the operation principles of conductometric solid-state dosimeter-type gas sensors, which have found increased attention in the past few years, and to give a literature overview on promising materials for this purpose. Contrary to common gas sensors, gas dosimeters are suitable for directly detecting the dose (also called amount or cumulated or integrated exposure of analyte gases) rather than the actual analyte concentration. Therefore, gas dosimeters are especially suited for low level applications with the main interest on mean values. The applied materials are able to change their electrical properties by selective accumulation of analyte molecules in the sensitive layer. The accumulating or dosimeter-type sensing principle is a promising method for reliable, fast, and long-term detection of low analyte levels. In contrast to common gas sensors, few devices relying on the accumulation principle are described in the literature. Most of the dosimeter-type devices are optical, mass sensitive (quartz microbalance/QMB, surface acoustic wave/SAW), or field-effect transistors. The prevalent focus of this article is, however, on solid-state gas dosimeters that allow a direct readout by measuring the conductance or the impedance, which are both based on materials that change (selectively in ideal materials) their conductivity or dielectric properties with gas loading. This overview also includes different operation modes for the accumulative sensing principle and its unique features.

Description: This paper presents a novel capacitive strain gauge with interdigital electrodes, which was processed on polyimide and LCP (liquid crystal polymer) foil substrates. The metallization is deposited and patterned using thin-film technology with structure sizes down to 15 μm. We determined linear strain sensitivities for our sensor configuration and identified the most influencing parameters on the output signal by means of an analytical approach. Finite-element method (FEM) simulations of the strain gauge indicated the complex interaction of mechanical strains within the sensitive structure and their effect on the capacitance. The influence of geometry and material parameters on the strain sensitivity was investigated and optimized. We implemented thin films on 50 μm thick standard polymer foils by means of a temporary bonding process of the foils on carrier wafers. The characterization of the strain sensors after fabrication revealed the gauge factor as well as the cross sensitivities on temperatures up to 100 °C and relative humidity up to 100%. The gauge factor of a sensor with an electrode width of 45 μm and a clearance of 15 μm was −1.38 at a capacitance of 48 pF. Furthermore, we achieved a substantial reduction of the cross sensitivity against humidity from 1435 to 55 ppm %−1 RH when LCP was used for the sensor substrate and the encapsulation instead of polyimide. The gauge factor of a sensor half-bridge consisting of two orthogonal capacitors was 2.3 and the cross sensitivity on temperature was reduced to 240 ppm K−1. Finally, a sensor system was presented that utilizes a special instrumentation Integrated Circuit (IC). For this system, performance data comprising cross sensitivities and power consumption are given.

Description: The aim of the work is to find an analytical model of a pneumatic micropump which was integrated into a cell-culture system. This allows the estimation of peak velocities and wall-shear stress influencing the cultured cells in our multi-organ-chip (MOC) with respect to the applied pressure and the geometric properties of the pump. By adjusting those parameters, one can imitate physiological or pathological heart activity. The calculated flow within the MOC was compared to experimental results obtained via the non-invasive micro-PIV method.

Description: A new three-phase (oil/water/gas) flow metering system has been developed for use in the oil and gas industries, based on Coriolis mass flow metering. To obtain certification for use in the Russian oil and gas industries, trials have taken place at the UK and Russian national flow laboratories, NEL in Glasgow and VNIIR in Kazan, respectively. The metrology of three-phase flow is complex, and the uncertainty of each measurement varies dynamically with the operating point, as well as the metering technology, and other aspects. To a limited extent this is reflected in the error limits allowed in national standards, which may vary with operating point. For example, the GOST standard allows errors in the oil flow rate of ±6% for water cuts of less than 70%, which is increased to ±15% for water cuts between 70 and 95%. The provision of online uncertainty for each measurement, for example in accordance with the British Standard BS-7986, would be highly desirable, allowing the user to observe in real time variations in measurement quality. This paper will discuss how an online uncertainty assessment could be implemented in the Coriolis meter-based system.

Description: Most huge forest fires start in partial combustion. In the beginning of a smouldering fire, emission of hydrogen in low concentration occurs. Therefore, hydrogen can be used to detect forest fires before open flames are visible and high temperatures are generated. We have developed a hydrogen sensor comprising of a metal/solid electrolyte/insulator/semiconductor (MEIS) structure which allows an economical production. Due to the low energy consumption, an autarkic working unit in the forest was established. In this contribution, first experiments are shown demonstrating the possibility to detect forest fires at a very early stage using the hydrogen sensor.

Description: This work focuses on the basic suitability assessment of polymeric materials and the corresponding technological methods for the production of infrared (micro-) bolometer arrays. The sensitive layer of the microbolometer arrays in question is composed of an electrically conductive polymer composite. Semi-conducting tellurium and vanadium dioxide, as well as metallic silver, are evaluated concerning their suitability as conductive filling agents. The composites with the semi-conducting filling agents display the higher temperature dependence of electrical resistance, while the silver composites exhibit better noise performance. The particle alignment – homogeneous and chain-shaped alike – within the polymer matrix is characterized regarding the composites' electrical properties. For the production of microbolometer arrays, a technology chain is introduced based on established coat-forming and structuring standard technologies from the field of polymer processing, which are suitable for the manufacture of a number of parallel structures. To realize the necessary thermal isolation of the sensitive area, all pixels are realized as self-supporting structures by means of the sacrificial layer method. Exemplarily, 2 × 2 arrays with the three filling agents were manufactured. The resulting sensor responsivities lie in the range of conventional microbolometers. Currently, the comparatively poor thermal isolation of the pixels and the high noise levels are limiting sensor quality. For the microbolometers produced, the thermal resolution limit referring to the temperature of the object to be detected (NETD) has been measured at 6.7 K in the superior sensitive composite layer filled with silver particles.

Description: This contribution presents the analysis of an earlier proposed double membrane sensor for measuring mass density and rheological properties of liquids with respect to different driving modes. Concerning practical implementation the sensor mounting and the stability of the polyethylene foil, currently used as membrane material, are investigated. The sensor is based on two opposed membranes vibrating in parallel where a sample liquid is enclosed between the membranes. The excitation and read-out mechanisms of the membrane vibration are based on Lorentz forces induced in a static magnetic field. Each membrane carries three conductive paths for excitation, which can be separately connected to the excitation currents. This allows the excitation of the first and second modes of vibration and enables prestressing the second mode of oscillation. Analyzing the material-stability of the used polyethylene foil shows a strong long-term drift of the modulus of elasticity and an increase of internal damping with increasing temperature. Comparing the resonance frequency of the fundamental mode with earlier measurements achieved with the second mode of resonance indicates an increased sensitivity to density featuring a reasonably sustained quality factor for high viscosities. Thereby, the sensitivity can be adjusted by varying the distance between the membranes.

Description: In this work we present near-field wireless sensing of single and multiple open-ended micro coils using an electrically small loop antenna. Wirelessly characterized parameters of open-ended micro coils include its resonance frequency, quality factor and inductance. Moreover a wireless frequency-dependent analytical model was developed. Micro coil inductance was extracted from the wirelessly measured signal using a constraint-based least-squares approach. Wireless measurements and analytical fit of micro coils are in strong agreement which validates the analytical model. Finite element method (FEM) simulations of the coupled system were done in COMSOL Multiphysics.

Description: In this work dynamic variation of gate bias is used on a gas-sensitive SiC field effect transistor ("GasFET") to optimize its sensitivity and increase its selectivity. Gate bias ramps introduce strong hysteresis in the sensor signal. The shape of this hysteresis is shown to be an appropriate feature both for the discrimination of various gases (ammonia, carbon monoxide, nitrogen monoxide and methane) as well as for different gas concentrations (250 and 500 ppm). The shape is very sensitive to ambient conditions as well as to the bias sweep rate. Thus, the influences of oxygen concentration, relative humidity, sensor temperature and cycle duration, i.e., sweep rate, are investigated and reasons for the observed signal changes, most importantly the existence of at least two different and competing processes taking place simultaneously, are discussed. Furthermore, it is shown that even for very fast cycles, in the range of seconds, the gas-induced shape change in the signal is strong enough to achieve a reliable separation of gases using gate bias cycled operation and linear discriminant analysis (LDA) making this approach suitable for practical application.

Description: Surface acoustic wave (SAW) resonators electrically behave like LCR circuits, their frequency can be influenced by temperature, pressure and torque. When they are used for passive wireless sensing on rotating machinery, they can also be influenced by the angular variations of the coupling between the coupler elements and the receiving coupler element impedance. This parasitic frequency shift is known as the "pulling effect". In this paper, we present a capacitive coupler based on open coplanar strip lines for physical measurements on a small diameter rotating shaft. This approach allows a single 434 MHz resonator angular frequency pulling lower than 200 Hz (0.46 ppm) and 100 Hz (0.23 ppm) in a differential configuration. This is more than 10 times lower compared to frequency pulling obtained using couplers based on circular and electrically shorted transmission lines. RADAR-based interrogation, finite element method (FEM) simulation, coupler parameters and frequency pulling measurements results are presented to demonstrate the performances of the complete system.

Description: Sulfonated single-walled carbon nanotubes have been used in an integrated electrode structure for the detection of carbon monoxide. The sensor responds to 0.5 ppm of CO in air at room temperature. All eight sensors with this material in a 32-sensor array showed good repeatability and reproducibility, with response and recovery times of about 10 s. Pristine nanotubes generally do not respond to carbon monoxide and the results here confirm sulfonated nanotubes to be a potential candidate for the construction of an electronic nose that requires at least a few materials for the selective detection of CO.

Description: A new induction-heated fixed-point device was developed for calibration of temperature measurement devices typically used in laser heat treatment for the temperature range 1000–1500 °C. To define the requirements for the calibration method, selected measurement setups were compared as well as process data and results of industrial processes were analyzed. Computer simulation with finite element method (FEM) and finite difference method (FDM) was used to optimize the system components and processing parameters of the induction heating of fixed-point cells. The prototype of the fixed-point device was tested successfully, and the first measuring results are presented here. The new calibration method is expected to improve the quality and reproducibility of industrial heat treatment processes with temperature control.

Description: In this paper, a new acoustic sensor principle for coating detection within liquid-filled tubes and containers based on mode conversion of leaky Lamb waves is introduced. Leaky Lamb waves are excited and detected by single-phase transducers, which are attached on the outer side of a tube or container. By transmission time and amplitude measurements, coating formation within the liquid-filled tube and container is detected non-invasively. This new sensor principle is subdivided into the separate considerations of Lamb wave excitation, mode conversion and inverse mode conversion. The Lamb wave excitation by a single-phase transducer is visualized by scanning laser Doppler vibrometer imaging. The mode conversion process of leaky Lamb waves is measured by membrane hydrophone measurements and Schlieren visualization; afterwards, the measured emission angles are compared with the theoretical one. The inverse mode conversion process of pressure waves back to leaky Lamb waves is visualized by Schlieren images. By merging the results of Lamb wave excitation, mode conversion and inverse mode conversion, the new sensor concept is explained. Theoretical considerations and measurement results of adhesive tape coating inside a liquid-filled plastic tube and a liquid-filled stainless steel container verify the new acoustic sensor principle. Finally the measuring sensitivity and the technical realization are discussed.

Description: Palladium platinum (PdPt) has been intensively studied these last decades due to high conversion rate in hydrogen oxidation at room temperature with significant exothermic effects. These remarkable properties have been studied by measuring the temperature variations of alumina (Al2O3) supported nanosized PdPt nanoparticles exposed to different hydrogen concentrations in dry air. This catalyst is expected to be used as a sensing material for stable and reversible ultrasensitive hydrogen sensors working at room temperature (low power consumption). Structural and gas sensing characterisations and catalytic activity of PdPt / Al2O3 systems synthesised by co-impregnation will be presented. Catalytic characterisations show that the system is already active at room temperature and that this activity sharply increases with rise in temperature. Moreover, the increase of the PdPt proportion in the co-impregnation process improves the activity, and very high conversion can be reached even at room temperature. The thermal response (about 3 °C) of only 1 mg of PdPt / Al2O3 is reversible, and the time response is about 5 s. The integration of PdPt / Al2O3 powder on a flat substrate has been realised by the deposition onto the powder of a thin porous hydrophobic layer of parylene. The possibility of using PdPt in gas sensors will be discussed.

Description: Optimum detergent dosage during a washing process depends on water quality, degree of pollution and quantity of laundry. Particularly, water quality is an important factor. Other parameters like carbonate- or non-carbonate hardness and calcium / magnesium (Ca / Mg) ratio in addition to total hardness of water have an impact on the amount of detergent. This work discusses the possibilities realizing a detergent sensor that measures important parameters for the washing process and assess the ideal necessary amount of detergent during the washing process. The approach is to combine impedance spectroscopy with cyclic voltammetry in order to determine both water quality and concentration of detergent in the suds which build up the basis for an optimum detergent dosage. The results of cyclic voltammetry show that it is possible to identify the Ca / Mg ratio and the carbonate hardness separately, which is necessary for the optimization of the washing process. Impedance measurements identify total hardness and detergent concentrations.

Description: The usage of mobile sensor platforms arose in research a few decades ago. Since the beginning of satellite sensing, measurement principles and analysing methods have become widely implemented for aerial and ground vehicles. Mainly in Europe, the United States and Australia, sensor platforms in precision farming are used for surveying, monitoring and scouting tasks. This review gives an overview of available sensor platforms used in recent agricultural and related research projects. A general categorisation tree for platforms is outlined in this work. Working in manual, automatic or autonomous ways, these ground platforms and unmanned aircraft systems (UAS) with an agricultural scope are presented with their sensor equipment and the possible architectural models. Thanks to advances in highly powerful electronics, smaller devices mounted on platforms have become economically feasible for many applications. Designed to work automatically or autonomously, they will be able to interact in intelligent swarms. Sensor platforms can fulfil the need for developing, testing and optimising new applications in precision farming like weed control or pest management. Furthermore, commercial suppliers of platform hardware used in sensing tasks are listed.

Description: This paper presents a sensor system to predict behavior patterns that occur when patients leave their beds. We originally developed plate-shaped sensors using piezoelectric elements. Existing sensors such as clip sensors and mat sensors require restraint of patients. Moreover, these sensors present privacy problems. The features of our sensors are that they require no power supply or patient restraint. We evaluated our system using a basic experiment to predict seven behavior patterns. We obtained a result of predicted behavior patterns related to bed-leaving using only six sensors installed under a bed. Especially, our system can correctly detect behavior patterns of lateral sitting, which is a position that occurs when a patient tries to leave from the bed, and terminal sitting, which is the position immediately before bed-leaving. They were discerned from other behavior patterns.

Description: CHAMP has so far been the most successful magnetic field mission. For achieving that, special effort had to be invested in building a magnetically clean spacecraft. The magnetic moment of the spacecraft is about 1 Am2. In this article we introduce a new method that allows the determination of the magnetic moment during the mission from the average current strength of the magneto-torquers. In order to achieve precise field vector data, the readings of the fluxgate magnetometer are routinely calibrated against the absolute Overhauser measurements. A reanalysis of all the magnetic field data is performed which takes also into account small disturbances from the power system. Uncertainties of the final magnetic field data are estimated to be of the order of 0.1 nT.

Description: "Faster, safer, more accurately and more flexibly'' is the title of the "manufacturing metrology roadmap'' issued by the VDI/VDE Society for Measurement and Automatic Control (http://www.vdi.de/gma). The document presents a view of the development of metrology for industrial production over the next ten years and was drawn up by a German group of experts from research and industry. The following paper summarizes the content of the roadmap and explains the individual concepts of "Faster, safer, more accurately and more flexibly'' with the aid of examples.

Description: In measurement science and engineering, the method of compensation plays a decisive role and is widely used in practical applications, in particular for sensors and measurement systems, where high accuracy is required. However, a general theoretical system description of this method with particular respect to figures of merit in sensor technology does not exist yet. Nevertheless, this is important for a real understanding of the system's structure and its properties and would facilitate prospective sensor design. Within this work, we provide a general system-based description and comparison of both the compensation and the deflection method. Based on a general sensor model and selected transfer functions, which cover most sensor types, important sensor properties like static deviations in sensitivity, long-term drift effects, response time, output signal characteristics as well as nonlinearities and hysteresis are studied in a systematic fashion for both measurement methods. In the case of a compensation method, the core sensor element is part of a controlled closed-loop system, leading to different system properties compared to an open-loop sensor operated in deflection method. The influence of linear standard controllers, which are widely used in industrial measurement and control systems, is studied with respect to the sensor properties. In the conclusions we will summarize which controller type is appropriate for the attainment of a specifically targeted sensor behavior.

Description: Particle emission from traffic, power plants or, increasingly, stoves and fireplaces poses a serious risk for human health. The harmfulness of the particles depends not only on their size and shape but also on adsorbates. Particle detectors for size and concentration are available on the market; however, determining content and adsorbents is still a challenge. In this work, a measurement setup for the characterization of dust and ash particle content with regard to their adsorbates is presented. For the proof of concept, ammonia-contaminated fly ash samples from a coal-fired power plant equipped with a selective non-catalytic reduction (SNCR) system were used. The fly ash sample was placed on top of a heater substrate situated in a test chamber and heated up to several hundred degrees. A silicon carbide field-effect transistor (SiC-FET) gas sensor was used to detect desorbing species by transporting the headspace above the heater to the gas sensor with a small gas flow. Accumulation of desorbing species in the heater chamber followed by transfer to the gas sensor is also possible. A mass spectrometer was placed downstream of the sensor as a reference. A clear correlation between the SiC-FET response and the ammonia spectra of the mass spectrometer was observed. In addition, different levels of contamination can be distinguished. Thus, with the presented setup, chemical characterization of particles, especially of adsorbates which contribute significantly to the harmfulness of the particles, is possible.

Description: Tungsten oxide nanoneedles (NNs) functionalised with gold nanoparticles (NPs) have been integrated with alumina gas-sensor platforms using a simple and effective co-deposition method via aerosol-assisted chemical vapour deposition (AACVD) utilising a novel gold precursor, (NH4)AuCl4. The gas-sensing results show that gold NP functionalisation of tungsten oxide NNs improves the sensitivity of response to ethanol, with sensitivity increasing and response time decreasing with increasing amount of gold.

Description: In a previous work (Marek et al., 2013) a time-monitoring oxygen sensor was proposed. This sensor is based on a diffusion-controlled oxygen reaction of the indicator system methylene blue (MB)/leuco methylene blue (LMB) and riboflavin embedded in a water-loaded poly(vinyl alcohol) (PVA) matrix. It can be used in packaging, sensors, and biotechnology applications. Since the oxygen diffusion coefficient in the PVA matrix strongly depends on temperature and humidity, two different approaches were developed within this work to compensate for these two effects. To compensate for faster oxygen diffusion at higher temperatures, iron particles were added to the PVA matrix, resulting in a novel PVA/iron composite matrix. Adding silicone particles allows compensating the influence of humidity. Both temperature and humidity compensation were modeled using the finite-element method in good accordance with the experimental data. This allows tuning the sensor for application at different conditions of temperature and humidity and therewith in different environments.

Description: At the German Aerospace Center (DLR), capacitive humidity sensors are used to measure relative humidity in experiments under extreme atmospheric conditions such as on Mars or in the coldest regions on Earth. This raises the question whether such experiments can be performed using low-cost humidity sensors with a tolerable measurement uncertainty. As part of the standardizing project SMADLUSEA (project no. SF11021A), nine capacitive humidity sensors (Sensirion SHT75) were investigated for pressure ranging from 10 to 1000 hPa (low vacuum) and temperatures from −70 to 25 °C. It has been shown that these sensors worked reliably and with reproducibly measured values over the entire investigated pressure and temperature range. There was no aging of the sensors observable. In addition to the known strong temperature dependency, the SHT75 also shows a pressure dependency below −10 °C. A characteristic curve for the SHT75 was calculated with an expanded uncertainty of 7% of the measured values. In conclusion, low-cost capacitive humidity sensors offer the option to obtain reliably measured values even under extreme conditions with comparatively little effort.

Description: In the present study, Au-surfactant core-shell colloidal nanoparticles (NPs) with controlled dimension and composition were synthesized by sacrificial anode electrolysis. Transmission electron microscopy (TEM) revealed that Au NPs core diameter is between 8 and 12 nm, as a function of the electrosynthesis conditions. Moreover, surface spectroscopic characterization by X-ray photoelectron spectroscopy (XPS) analysis confirmed the presence of nanosized gold phase. Controlled amounts of Au NPs were then deposited electrophoretically on carbon nanotube (CNT) networked films. The resulting hybrid materials were morphologically and chemically characterized using TEM, SEM (scanning electron microscopy) and XPS analyses, which revealed the presence of nanoscale gold, and its successful deposition on CNTs. Au NP/CNT networked films were tested as active layers in a two-pole resistive NO2 sensor for sub-ppm detection in the temperature range of 100–200 °C. Au NP/CNT exhibited a p-type response with a decrease in the electrical resistance upon exposure to oxidizing NO2 gas and an increase in resistance upon exposure to reducing gases (e.g. NH3). It was also demonstrated that the sensitivity of the Au NP/CNT-based sensors depends on Au loading; therefore, the impact of the Au loading on gas sensing performance was investigated as a function of the working temperature, gas concentration and interfering gases.

Description: A highly miniaturized piezoresistive humidity sensor has been developed. The starting point of the development was a 1 × 1 mm2 piezoresistive pressure sensor chip. As sensing material, a polyimide was used that swells with increasing adsorption of water molecules. To convert the swelling into an electrical signal, a thin layer of the polyimide was deposited onto the bending plate of the pressure sensor. The humidity sensor was characterized in a climate chamber. The measurements show a sensitivity of 0.25 mV per percent relative humidity (%RH) and a non-linearity of 3.1% full scale (FS) in the range of 30–80% RH. A high cross-sensitivity to temperature of around 0.5 mV °C−1 was measured, so temperature compensation is necessary. For stress-free packaging of the sensor chip, a novel packaging technology was developed.

Description: Rising demand and increasing cost pressure for lightweight materials – such as sandwich structures – drives the manufacturing industry to improve automation in production and quality inspection. Quality inspection of honeycomb sandwich components with infrared (IR) thermography can be automated using image classification algorithms. This paper shows how principal component analysis (PCA) via singular value decomposition (SVD) is applied to compress data in an IR-video sequence in order to save processing time in the subsequent step of image classification. According to PCA theory, an orthogonal transformation can project data into a lower dimensional subspace with linearly uncorrelated principal components preserving all original information. The effect of data reduction is confirmed with experimental data from IR-video sequences of simple square-pulsed thermal loadings on aramid honeycomb-sandwich components with CFRP/GFRP (carbon-/glass-fiber-reinforced plastic) facings and GFRP inserts. Hence, processing time for image classification can be saved by reducing the dimension of information used by the classification algorithm without losing accuracy.

Description: Today, the assembly of laser systems requires a large share of manual operations due to its complexity regarding the optimal alignment of optics. Although the feasibility of automated alignment of laser optics has been shown in research labs, the development effort for the automation of assembly does not meet economic requirements – especially for low-volume laser production. This paper presents a model-based and sensor-integrated assembly execution approach for flexible assembly cells consisting of a macro-positioner covering a large workspace and a compact micromanipulator with camera attached to the positioner. In order to make full use of available models from computer-aided design (CAD) and optical simulation, sensor systems at different levels of accuracy are used for matching perceived information with model data. This approach is named "chain of refined perception", and it allows for automated planning of complex assembly tasks along all major phases of assembly such as collision-free path planning, part feeding, and active and passive alignment. The focus of the paper is put on the in-process image-based metrology and information extraction used for identifying and calibrating local coordinate systems as well as the exploitation of that information for a part feeding process for micro-optics. Results will be presented regarding the processes of automated calibration of the robot camera as well as the local coordinate systems of part feeding area and robot base.

Description: In this paper an electrochemical endotoxin biosensor consisting of an immobilized lipopolysaccharide (LPS) ligand, polymyxin B (PmB), is presented. Several parameters involved both in the device fabrication and in the detection process were analyzed to optimize the ligand immobilization and the interaction between PmB and LPS, aiming at increasing the sensitivity of the sensor. Different electrochemical pre-treatment procedures as well as the functionalization methods were studied and evaluated. The use of a SAM (self-assembled monolayer) to immobilize PmB and the quantification of the interactions via cyclic voltammetry allowed the development of a robust and simple device for in situ detection of LPS. Thus, the biosensor proposed in this work intends an approach to the demanding needs of the market for an integrated, portable and simple instrument for endotoxin detection.

Description: Active long-path differential optical absorption spectroscopy (LP-DOAS) has been an effective tool for measuring atmospheric trace gases for several decades. However, instruments were large, heavy and power-inefficient, making their application to remote environments extremely challenging. Recent developments in fibre-coupling telescope technology and the availability of ultraviolet light emitting diodes (UV-LEDS) have now allowed us to design and construct a lightweight, portable, low-power LP-DOAS instrument for use at remote locations and specifically for measuring degassing from active volcanic systems. The LP-DOAS was used to measure sulfur dioxide (SO2) emissions from La Fossa crater, Vulcano, Italy, where column densities of up to 1.2 × 1018 molec cm−2 (~ 500 ppmm) were detected along open paths of up to 400 m in total length. The instrument's SO2 detection limit was determined to be 2 × 1016 molec cm−2 (~ 8 ppmm), thereby making quantitative detection of even trace amounts of SO2 possible. The instrument is capable of measuring other volcanic volatile species as well. Though the spectral evaluation of the recorded data showed that chlorine monoxide (ClO) and carbon disulfide (CS2) were both below the instrument's detection limits during the experiment, the upper limits for the X / SO2 ratio (X = ClO, CS2) could be derived, and yielded 2 × 10−3 and 0.1, respectively. The robust design and versatility of the instrument make it a promising tool for monitoring of volcanic degassing and understanding processes in a range of volcanic systems.

Description: The carbon monoxide (CO) gas sensing properties of low-resistance heavily Ga-doped ZnO thin films were evaluated. The ZnO films with a thickness of 50 nm were deposited at 200 °C by ion plating. The electrical properties of the ZnO films were controlled by varying the oxygen assist gas flow rate during deposition. The CO gas sensitivity of ZnO films with Au electrodes was investigated in nitrogen gas at a temperature of 230 to 330 °C. CO gas concentration was varied in the range of 0.6–2.4% in nitrogen gas. Upon exposure to CO gas, the current flowing through the film was found to decrease. This response occurred even at the lowest temperature of 230 °C, and is thought to be the result of a mechanism different than the previously reported chemical reaction.

Description: The gas sensing properties of resistive gas sensors of BaFe0.7Ta0.3O3-δ (BFT30) prepared by the so-called aerosol deposition method, a method to manufacture dense ceramic films at room temperature, were investigated. The electrical response of the films was investigated first under various oxygen concentrations and in a wide temperature range between 350 and 900 °C. Between 700 and 900 °C, the conductivity of BaFe0.7Ta0.3O3-δ (BFT30) depends on the oxygen concentration with a slope of almost 1/4 in the double-logarithmic plot vs. oxygen partial pressure. In addition, the sensor response is temperature independent. BFT30 responds fast and reproducibly to changing oxygen partial pressures even at 350 °C. The cross-sensitivity has been investigated in environments with various gases (C3H8, NO, NO2, H2, CO, CO2, and H2O) in synthetic air between 350 and 800 °C. BFT30 exhibits good sensing properties to NO between 350 and 400 °C in the range from 1.5 to 2000 ppm with a high selectivity to the other investigated gas species. Thus this semiconducting ceramic material is a good candidate for a temperature-independent oxygen sensor at high temperatures with the application in exhausts and for a selective nitrogen monoxide (NO) sensor at low temperatures for air quality monitoring.