ALBERT

Description: The impact of a hexamethyldisiloxane (HMDSO) treatment on the response of doped SnO2 sensors is investigated for acetone, carbon monoxide and hydrogen. The sensor was operated in temperature cycles based on the DSR concept (differential surface reduction). According to this concept, the rate constants for the reduction and oxidation of the surface after fast temperature changes can be evaluated and used for quantification of reducing gases as well as quantification and compensation of sensor poisoning by siloxanes, which is shown in this work. Increasing HMDSO exposure reduces the rate constants and therefore the sensitivity of the sensor more and more for all processes. On the other hand, while the rate constants for acetone and carbon monoxide are reduced nearly to zero already for short treatments, the hydrogen sensitivity remains fairly stable, which greatly increases the selectivity. During repeated HMDSO treatment the quasistatic sensitivity, i.e. equilibrium sensitivity at one point during the temperature cycle, rises at first for all gases but then drops rapidly for acetone and carbon monoxide, which can also be explained by reduced rate constants for oxygen chemisorption on the sensor surface when considering the generation of surface charge.

Description: Ensuring the highest quality standards at competitive prices is one of the greatest challenges in the manufacture of electronic products. The identification of flaws has the uppermost priority in the field of automotive electronics, particularly as a failure within this field can result in damages and fatalities. During assembling and soldering of printed circuit boards (PCBs) the circuit carriers can be subject to errors. Hence, automatic optical inspection (AOI) systems are used for real-time detection of visible flaws and defects in production. This article introduces an application strategy for combining a deep learning concept with an optical inspection system based on image processing. Above all, the target is to reduce the risk of error slip through a second inspection. The concept is to have the inspection results additionally evaluated by a convolutional neural network. For this purpose, different training datasets for the deep learning procedures are examined and their effects on the classification accuracy for defect identification are assessed. Furthermore, a suitable compilation of image datasets is elaborated, which ensures the best possible error identification on solder joints of electrical assemblies. With the help of the results, convolutional neural networks can achieve a good recognition performance, so that these can support the automatic optical inspection in a profitable manner. Further research aims at integrating the concept in a fully automated way into the production process in order to decide on the product quality autonomously without human interference.

Description: State determination of catalytic converters based on an ultra-wideband communication system Journal of Sensors and Sensor Systems, 4, 255-262, 2015 Author(s): I. Motroniuk, R. Stöber, and G. Fischerauer A novel microwave-based approach for monitoring the state of aftertreatment systems such as diesel particulate filters (DPFs), three-way catalytic converters (TWCs), and selective catalytic reduction (SCR) catalysts is proposed. The volume inside the metallic housing of the DPF, TWC, or SCR is considered as a wireless communication channel between two terminals of a communication system. It is shown that, depending on the transmission channel characteristics, the properties of the catalyst, such as the catalyst state, can be inferred. This is done by means of an ultra-wideband (UWB) measurement and the subsequent evaluation and processing of the waveform in the time and frequency domains.

Description: On the use of electrochemical multi-sensors in biologically charged media Journal of Sensors and Sensor Systems, 4, 295-303, 2015 Author(s): S. Sachse, A. Bockisch, U. Enseleit, F. Gerlach, K. Ahlborn, T. Kuhnke, U. Rother, E. Kielhorn, P. Neubauer, S. Junne, and W. Vonau For the investigation and characterisation of liquid media with microorganisms, electrochemical sensors are typically used. Usually the microorganisms are part of the process or cannot be excluded for different reasons. This paper describes the application of various electrodes, which are partly miniaturised and combined with multi-sensor systems for several applications in processes containing microorganisms. The application in industrial bioprocesses like beer brewing and biogas production, and in paper manufacturing, is described. The performance of the multi-sensor systems, and thus their suitability for a contribution to improved process monitoring, is evaluated. The multi-sensor systems represent an interesting tool to enhance monitoring capacities at installed systems without the necessity for huge port installations and offer the possibility to monitor the spatial distribution of gradients. The developed systems presented here allow location-independent measurements in process plants with a variable positioning of the sensors in the industrial reactors.

Description: Self-sufficient sensor for oxygen detection in packaging via radio-frequency identification Journal of Sensors and Sensor Systems, 4, 179-186, 2015 Author(s): C. Weigel, M. Schneider, J. Schmitt, M. Hoffmann, S. Kahl, and R. Jurisch A new disposable radio-frequency identification (RFID) sensor for detecting oxygen in packages with a protective atmosphere is presented. For safety reasons and system costs in consumer packages, no battery or energy harvesting devices can be used. Each part of a package, especially in food packaging, must be completely safe even if it is swallowed. Several materials have been investigated that safely react with oxygen and thus change electrical parameters without the need of an additional energy supply. In particular linseed oil was tested, because it is known to react in oxygen-containing atmosphere from liquid to solid. Linseed oil is used not only as food but also as a key part in ecological paint coatings. A significant relative change of capacity was observed during linseed oil drying, which results in −20% after 5 h and −38% after 30 h at an oxygen concentration of 20.5 and 50% relative humidity, respectively. Pure unsaturated fatty acids were also tested in an oxygen-containing atmosphere and showed similar behaviour. The reaction speed is partially dependent on the level of unsaturation of fatty acids. The oxygen sensor is coupled with an RFID front end with an internal charge time measurement unit for capacity determination. The combination of sensor element, sensitive material and RFID allows for biocompatible and save systems that indicate the presence of oxygen within a package.

Description: Increasing the sensitivity of electrical impedance to piezoelectric material parameters with non-uniform electrical excitation Journal of Sensors and Sensor Systems, 4, 217-227, 2015 Author(s): K. Kulshreshtha, B. Jurgelucks, F. Bause, J. Rautenberg, and C. Unverzagt To increase the robustness and functionality of piezoceramic ultrasonic sensors, e.g. for flow, material concentration or non-destructive testing, their development is often supported by computer simulations. The results of such finite-element-based simulations are dependent on correct simulation parameters, especially the material data set of the modelled piezoceramic. In recent years several well-known methods for estimation of such parameters have been developed that require knowledge of the sensitivity of a measured behaviour of the material with respect to the parameter set. One such measurable quantity is the electrical impedance of the ceramic. Previous studies for radially symmetric sensors with holohedral electrode setups have shown that the impedance shows little or no sensitivity to certain parameters and simulations reflect this behaviour making parameter estimation difficult. In this paper we have used simulations with special ring-shaped electrode geometry and non-uniform electrical excitation in order to find electrode geometries, with which the computed impedance displays a higher sensitivity to the changes in the parameter set. We find that many such electrode geometries exist in simulations and formulate an optimisation problem to find the local maxima of the sensitivities. Such configurations can be used to conduct experiments and solve the parameter estimation problem more efficiently.

Description: Simulation model for the evaluation and design of miniaturized non-resonant photoacoustic gas sensors Jochen Huber, Katrin Schmitt, and Jürgen Wöllenstein J. Sens. Sens. Syst., 5, 293-299, doi:10.5194/jsss-5-293-2016, 2016 A simulation model to predict system behaviour of photoacoustic CO 2 sensors is presented. The sensor output signal that depends on the CO 2 concentration can be simulated if the boundary conditions of the system are known. A comparison of simulated values with experimental results is made. There is good accordance between simulation and experiments. Photoacoustic gas sensors offer great potential for miniaturized gas sensors. The simulation model is an effective tool for further developments.

Description: Microfluidic measurement of cell motility in response to applied non-homogeneous DC electric fields Marisa Rio, Sharanya Bola, Richard H. W. Funk, and Gerald Gerlach J. Sens. Sens. Syst., 5, 237-243, doi:10.5194/jsss-5-237-2016, 2016 Endogeneous electric fields (EFs) affect a wide range of cellular functions such as migration, wound healing and regeneration. Similar results were observed when external EFs are applied. To date, the phenomenon of electrotaxis has been studied only in homogeneous EF environments. Here, we report on the construction and fabrication of a microfluidic biochip as well as first results for stimulation of cells with stationary, non-homogeneous EFs.

Description: Gas sensors based on plasma-electrochemically oxidized titanium foils Mhamed El Achhab and Klaus Schierbaum J. Sens. Sens. Syst., 5, 273-281, doi:10.5194/jsss-5-273-2016, 2016 We have developed a preparation technique to form graphite/TiO 2 /Ti and platinum-graphite/TiO 2 /Ti solid-state sensors based on plasma electrolytic oxidation (PEO) of titanium foils, whereby a porous titanium oxide layer is formed with well-defined phase composition and a reproducible microstructure. A printing method is used to deposit graphite or catalytically active graphite-platinum electrodes. Our design enables the application of many different detection principles such as calorimetry.

Description: Ultrafast imaging Raman spectroscopy of large-area samples without stepwise scanning Elmar Schmälzlin, Benito Moralejo, Daniel Bodenmüller, Maxim E. Darvin, Gisela Thiede, and Martin M. Roth J. Sens. Sens. Syst., 5, 261-271, doi:10.5194/jsss-5-261-2016, 2016 Imaging astronomy spectrographs are designed for recording thousands of spatially resolved spectra of a two-dimensional image field within one single exposure. Transferring this technology to imaging Raman spectroscopy allows a considerably faster acquisition of chemical maps. Within the scope of a research project, this method is refined for medical diagnostics, e.g., the identification of potentially cancerous abnormalities of skin tissue.