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A new concept for designing an integrated chemical multisensor with only two ports based on surface acoustic waves is presented. Following a principle from antenna theory an acoustic group antenna is assembled consisting of a number of... more
A new concept for designing an integrated chemical multisensor with only two ports based on surface acoustic waves is presented. Following a principle from antenna theory an acoustic group antenna is assembled consisting of a number of identical interdigital transducers that are fed with currents of equal amplitude, but with a phase difference between neighbors. The propagation of the wave launched by such an antenna is investigated through simulation of the associated surface potential. In order to validate the concept and the simulation arrays with up to ten element-IDTs are built and the distribution of the periodic displacement of the substrate surface is observed by laser interferometry.
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On June 16th and 17th, 2016, the highly successful lecture series on measurement and sensor technologies as part of the IEEE Workshop at the Institute for Measurement and Sensor Technology at the University of Applied Sciences Ruhr West... more
On June 16th and 17th, 2016, the highly successful lecture series on measurement and sensor technologies as part of the IEEE Workshop at the Institute for Measurement and Sensor Technology at the University of Applied Sciences Ruhr West (HRW) was continued in collaboration with the Institute of Thermodynamics at the University of Siegen, the Chair of Measurement and Sensor Technology at the Technical University of Chemnitz and the ITMO National Research University of Information Technologies, Mechanics and Optics in St. Petersburg, Russia. This time the event featured an even more international orientation by linking it with the Russian SENSORICA. The topics of the 36 contributions to the workshop covered sensor technology in vehicles as well as industrial and medical measurement technology. Eight topics were chosen for this special issue. One half of them are focused on the field of medical measurement techniques such as magnetic resonance imaging, optical tracking for minimal-invasive surgery, exact preoperative planning in hip surgery and an approach for a telemetric multi-sensor system. The other half addresses the field of optical measurement systems applied to engine testing, LIBS for elemental analysis, IR-based quantitative measurement of complex substances in liquids and the analysis of wavefront structures of diode lasers. Our workshop again offered a platform for knowledge transfer between industry and public as well as commercial research institutions in the area of measurement technology.
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Planar interdigital capacitors (IDC) covered with a thin Cr 2 O 3 layer and a zeolite thick film are known to act as gas sensors. Until now, their impedance behavior has been modeled by equivalent circuits involving constant-phase... more
Planar interdigital capacitors (IDC) covered with a thin Cr 2 O 3 layer and a zeolite thick film are known to act as gas sensors. Until now, their impedance behavior has been modeled by equivalent circuits involving constant-phase elements (CPE) with a poor physical justification. We present a physical model for the sensor impedance which is based on the underlying atomistic processes.
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ABSTRACT The authors discuss the compensation of second-order effects of a filter structure which provides different transfer functions by operating two or more transducers in parallel, thereby adding or subtracting the respective... more
ABSTRACT The authors discuss the compensation of second-order effects of a filter structure which provides different transfer functions by operating two or more transducers in parallel, thereby adding or subtracting the respective transmissions in order to obtain the desired functions. For each resulting transfer function, the diffraction and the circuit effects are compensated. The various possibilities of designing this switchable filter are discussed, and a comparison between analysis and measurement of a compensated structure is presented
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ABSTRACT In this contribution, we describe a novel temperature-compensated SAW strain sensor for remote sensing. Temperature is the most important disturbance variable in SAW sensors, and this motivates the search for methods to suppress... more
ABSTRACT In this contribution, we describe a novel temperature-compensated SAW strain sensor for remote sensing. Temperature is the most important disturbance variable in SAW sensors, and this motivates the search for methods to suppress the temperature influence. The sensor design proposed consists of two SAW structures each comparable to a delay line and exploits electrical loading and multiple-transit signals. The interdigital transducers (IDTs) are connected in a way that leads to a sensor signal with a frequency spectrum showing a certain number of minima depending on the distances between the IDTs. The frequencies of these minima are influenced by both strain and temperature. Their evaluation allows to extract a temperature compensated strain signal with a resolution of about 10 ppm.
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Zusammenfassung Planare Chemosensoren bestehen häufig aus Interdigitalelektroden (IDE), die auf einem Substrat aufgebracht und in mehrere Schichten von Funktionsmaterialien wie Metalloxiden oder Ionenleitern eingebettet wurden. Die... more
Zusammenfassung Planare Chemosensoren bestehen häufig aus Interdigitalelektroden (IDE), die auf einem Substrat aufgebracht und in mehrere Schichten von Funktionsmaterialien wie Metalloxiden oder Ionenleitern eingebettet wurden. Die Impedanzen solcher Sensoren weisen untereinander ähnliche, charakteristische Spektren auf, was auf ein gemeinsames zugrunde liegendes Funktionsprinzip hindeutet. Zur quantitativen Erfassung der Sensorimpedanz bedarf es daher eines physikalischen Modells, das den Zusammenhang zwischen der Sensorimpedanz und den Materialparametern der eingesetzten Schichten, der Geometrie und der Betriebstemperatur beschreibt. Ausgehend von den Methoden der klassischen Halbleitertheorie wird in der vorgestellten Arbeit der durch den Sensor tretende Strom berechnet. Dabei wird der Einfluss eventuell vorhandener beweglicher Ionen durch eine elektrostatische Näherung beschrieben. Aus den ersten Harmonischen der zeitvariablen Bauteilspannung und des Bauteilstromes lässt sich da...
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In electrical capacitance tomography (ECT), the resolution of the reconstructed permittivity distribution improves with the number of electrodes used whereas the number of capacitance measurements and the measurement time increases with... more
In electrical capacitance tomography (ECT), the resolution of the reconstructed permittivity distribution improves with the number of electrodes used whereas the number of capacitance measurements and the measurement time increases with the number of electrodes. To cope with this tradeoff, we present a phantom-dependent adaptation scheme in which coarse measurements are performed with terminal electrodes interconnected to form a synthetic electrode ring with fewer but larger electrodes. The concept was tested by observing the sloshing of water inside a pipe. We compare the reconstructed results based on eight synthetic electrodes, on 16 elementary electrodes, and on the adaptation scheme involving both the eight synthetic electrodes and some of the elementary capacitances. The reconstruction used the projected Landweber algorithm for capacitances determined by a finite-element simulation and for measured capacitances. The results contain artefacts attributed to the influence of the ...
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This paper discusses impedance spectroscopy as a method to characterize different types of quartz sand, chromite sand, and mixtures of sand. Based on two types of measurement cells, the impedance spectra for various dry sands were... more
This paper discusses impedance spectroscopy as a method to characterize different types of quartz sand, chromite sand, and mixtures of sand. Based on two types of measurement cells, the impedance spectra for various dry sands were measured. The spectra differ enough to allow the sands to be distinguished. The results were validated by extracting the relative permittivity from the impedance and comparing it to literature data. After that, the method could be applied with confidence to other material systems. The influence of moisture was investigated with two types of quartz sand, and typical mixtures of form sand, chromite sand, and regenerated (quartz) sand were studied. In each case, the sand composition had a distinct influence on the Nyquist plot of the impedance spectrum. Compared to results from a laboratory foundry system, the new method exhibits a much more systematic dependence on the sand composition. If one succeeds in describing the impedance spectra with an equivalent c...
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This Technical Note contains a study of advanced sensor technologies for a cryogenic benchmark experiment. The benchmark experiment is a redesign of baseline experiment 2 presented in Technical Note 4 of the activity, with... more
This Technical Note contains a study of advanced sensor technologies for a cryogenic benchmark experiment. The benchmark experiment is a redesign of baseline experiment 2 presented in Technical Note 4 of the activity, with state-of-the-art ‘conventional’ sensor technologies now replaced by alternative measurement methods. In a comprehensive study different technologies are first described, then evaluated in terms of application potential and specifically adapted TRL scale. This includes: Particle Velocimetry, Ultrasound Tomography, specialised ultrasound methods (Lamb-Waves, Quasi-Scholten-Waves), Electrical Capacitance Tomography, Optical Tomography, Time of Flight Cameras, Wire-Mesh Sensors and Microwave/RF-methods. The intended application in this Note is the detection of free surface topologies of cryogenic liquids (fill level, dynamics due to external acceleration, boiling at the free surface). Recommendations regarding required experimental test to increase technology readines...
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This Technical Note presents the results of cryogenic sensor validation experiments in liquid nitrogen/liquid hydrogen and proposes upgrades to the measurement technologies. Electrical capacitance tomography and Ultrasound Tomography are... more
This Technical Note presents the results of cryogenic sensor validation experiments in liquid nitrogen/liquid hydrogen and proposes upgrades to the measurement technologies. Electrical capacitance tomography and Ultrasound Tomography are for the first time introduced in cryogenic conditions. Functionality and performance for the detection of liquid levels and bubbles in liquid nitrogen (77K) are assessed. Sensor application and feed-through techniques are established. Fibre-optic temperature sensors are used to measure high resolution temperature profiles in the liquid and gas phase of nitrogen. The performance of three different fibre coatings is investigated and optimised. Finally, the sensor is used for vertical temperature profile measurements in the liquid and gas phase of hydrogen (20K). In the domain of fibre-optic technologies, fibre optic bundles used as image and light guides are tested in cryogenic conditions. They are operable in the cold gas phase above liquid nitrogen ...
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It would be very advantageous if the condition of molding materials (sand-binder systems) in regen-erator units used in foundries could be monitored in real-time. This work presents the results of inves-tigations in this direction. It is... more
It would be very advantageous if the condition of molding materials (sand-binder systems) in regen-erator units used in foundries could be monitored in real-time. This work presents the results of inves-tigations in this direction. It is shown that the condition monitoring can possibly be based on imped-ance spectroscopy because the resulting curves are characteristic of the material used. New and used sands as well as two-component mixtures of sands and binders showed a systematic behavior, which allows the sand or the composition of the mixture to be identified (classified) in the future.
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This Technical Note contains the design of a cryogenic benchmark experiment, introducing alternate measurement methods such as ultrasound tomography or electric capacitance tomography. The benchmark experiment is a redesign of baseline... more
This Technical Note contains the design of a cryogenic benchmark experiment, introducing alternate measurement methods such as ultrasound tomography or electric capacitance tomography. The benchmark experiment is a redesign of baseline experiment 1 presented in Technical Note 1 of the activity, with state-of-the-art "conventional" sensor technologies now replaced by alternative measurement methods. In a comprehensive study different technologies are first described, then evaluated in terms of application potential and specifically adapted TRL scale. This includes: Ultrasound Tomography, Electrical Resistance Tomography, Electrical Capacitance Tomography, Optical Tomography, Time of Flight Cameras, Nuclear Magnetic Resonance Tomography, Wire-Mesh Sensors, Computed X-Ray Tomography and Neutron Absorption. The intended application in this Note is the detection of gas bubbles within cryogenic liquids. After assessment of parasitic heating, microgravity compatibility and cryoge...
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Sensors for various fluid physical quantities play a vital role in the management of cryogenic liquid propellants (hydrogen, oxygen, methane), used worldwide in launchers such as the European Ariane rockets. In addition, measurement... more
Sensors for various fluid physical quantities play a vital role in the management of cryogenic liquid propellants (hydrogen, oxygen, methane), used worldwide in launchers such as the European Ariane rockets. In addition, measurement devices are particularly central in all basic scientific fluid experimentation, investigating for instance liquid sloshing, free liquid surface movement, boiling or bubble formation. The results of these experiments in microgravity and on ground enable the efficient design of present-day cryogenic launcher (upper) stages and (as possible future applications) of long-term orbital propellant storage facilities, in-orbit refuelling stations and interplanetary cryogenic propulsion. These utilizations call for sensor technology to efficiently perform propellant mass gauging, determine fill-levels, temperature fields, phase change quantities and bubble formation in a nonintrusive fashion. An overview of various candidate cryogenic sensor technologies currently...
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Zusammenfassung Verlustbehaftete Kapazitäten sind für kommerzielle Kapazitätssensoren, die nur einen Kapazitätswert ausgeben, problematisch: der parasitäre ohmsche Widerstand parallel zur Kapazität verfälscht das Messergebnis. Bei... more
Zusammenfassung Verlustbehaftete Kapazitäten sind für kommerzielle Kapazitätssensoren, die nur einen Kapazitätswert ausgeben, problematisch: der parasitäre ohmsche Widerstand parallel zur Kapazität verfälscht das Messergebnis. Bei Messungen an Flüssigkeiten im Rahmen der elektrischen Kapazitätstomographie (ECT) kann der Einfluss gravierend werden. Mit erhöhtem Messaufwand könnte man die ECT zur elektrischen Impedanztomographie (EIT) erweitern und damit sowohl die Kapazität als auch den Widerstand der verlustbehafteten Kapazität messen. Als aufwandsarme Alternative stellen wir hier einen modellbasierten De-Embedding-Ansatz vor. Er ertüchtigt kommerzielle Kapazitätssensoren, die die Kapazität über die Messung einer Entladezeitkonstante bestimmen, auch mit stärker verlustbehafteten Kapazitäten zurechtzukommen. Der Ansatz beruht auf dem Ersatzschaltbild der realen Messsituation, dessen zugehörige Differentialgleichung im Zeitbereich gelöst wird. Durch Variation der gesuchten Kapazität u...
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ZusammenfassungIn der elektrischen Kapazitätstomografie (ECT) verbessert sich die Auflösung der rekonstruierten Permittivitätsverteilung mit der Elektrodenanzahl, wohingegen die Anzahl der Kapazitätsmessungen und die Messzeit steigt und... more
ZusammenfassungIn der elektrischen Kapazitätstomografie (ECT) verbessert sich die Auflösung der rekonstruierten Permittivitätsverteilung mit der Elektrodenanzahl, wohingegen die Anzahl der Kapazitätsmessungen und die Messzeit steigt und das Signal-Rausch-Verhältnis sinkt. Um einen Kompromiss zwischen Elektrodenanzahl und Auflösung zu finden, haben wir ein phantomabhängiges Adaptionsverfahren untersucht, in dem grobe Messungen mit verbundenen Einzelelektroden, die quasi synthetische größere Elektroden darstellen, durchgeführt werden. Das Verfahren wurde anhand eines Kunststoffzylinders im Erfassungsbereich im Inneren eines Rohres getestet. Wir vergleichen die rekonstruierten Ergebnisse basierend auf den Kapazitäten zwischen sechs synthetischen Elektroden und zwölf elementaren Elektroden sowie mit dem Adaptionsverfahren, das sowohl die Kapazitäten zwischen den sechs synthetischen Elektroden als auch zwischen einigen der elementaren Kapazitäten auswertet. Die Permittivitätsverteilung w...
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ZusammenfassungDie Ober- und Hauptstufen von Trägerraketen werden oftmals mit kryogenen Flüssigkeiten betrieben. Im Besonderen ist es für eine Zündung des Triebwerkes in der Schwerelosigkeit wichtig, das
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The investigation of fluid phenomena is of high interest in the management of cryogenic liquid propellants used in space launch vehicles. In order to efficiently design cryogenic propulsion systems or orbital cryogenic propellant storage... more
The investigation of fluid phenomena is of high interest in the management of cryogenic liquid propellants used in space launch vehicles. In order to efficiently design cryogenic propulsion systems or orbital cryogenic propellant storage facilities, experiments concerning fill-levels, bubble formations and boiling have to be conducted in microgravity and on earth. Thus measurement devices are needed that can give insight into the spatial distribution and the behavior of the fluids inside the cryogenic system. One possibility to observe liquids inside a given volume without intruding into the system and thereby disturbing the flow characteristics is to use a capacitive system with electrodes embedded into the walls of the vessel. In this paper experiments with such a system at cryogenic temperatures are presented. To simulate the behavior of rocket fuel in space a cryostat was filled with liquid nitrogen and by way of controlling the pressure inside or locally heating the liquid, bubbles were created. Two capacitive measurement systems have been submerged into the cryogenic liquid to monitor the location and size of bubbles inside the liquid and to observe the state of the liquid/gas interface. One system consisted of a cylindrical polycarbonate ring with four embedded electrodes and a polycarbonate lid at the top carrying one ring-shaped electrode. Many small bubbles thus could be trapped and coalesced in this half closed cylinder (bubble trap) forming a big single gas volume. The other system was a polycarbonate ring with 16 electrodes arranged along its circumference. The task of these systems was to measure the filling level inside the cylindrical bubble trap and to detect and quantify rising bubbles inside the cryostat by measuring the mutual capacitances of selected electrode pairs. To interpret the measurement results, FEM simulation results were used to generate a characteristic curve for the relationship between filling level and measured capacitances. To validate the results, two cameras were mounted inside the cryostat which allowed the simultaneous recording of the filling level and the existence of bubbles and bubble streams. We observed a good agreement between measurement and simulation. Overall the suitability of the system for cryogenic applications has been successfully demonstrated.
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For accclcrator vacuum chambers especially in cooling rings the rf characteristic is of high importance. Within a certain rf frequency range for example a certain wave attenu-at,ion is required to decouple cooling antennas and kickers... more
For accclcrator vacuum chambers especially in cooling rings the rf characteristic is of high importance. Within a certain rf frequency range for example a certain wave attenu-at,ion is required to decouple cooling antennas and kickers from each other. A general purpose 2d-wave analysis program is prc-s~nt,rul which can calculate wave propagation characteristics in arbitrary shaped chambers. The inside of the chamber may have an arbitrary distribution of permittivc and/or permeable mate-rial. Losses are treated by solving Maxwell's equations with truly comples field vcY+ors.
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Zusammenfassung Es wird ein neues Verfahren zur interferometrischen Erfassung von akustischen Oberflächenwellen vorgestellt. Die beschriebene Methode erlaubt die Extraktion der absoluten Amplitude und der Phase einer hochfrequenten... more
Zusammenfassung Es wird ein neues Verfahren zur interferometrischen Erfassung von akustischen Oberflächenwellen vorgestellt. Die beschriebene Methode erlaubt die Extraktion der absoluten Amplitude und der Phase einer hochfrequenten Schwingung, unabhängig von Oberflächenreflexionsfaktoren, Variationen der Laserleistung oder Sensitivität des Interferometers. Ermöglicht wird dies durch die synchrone Erfassung des Messsignals mittels eines vektoriellen Netzwerkanalysators und eines digitalen Speicheroszilloskops. Die anschließende digitale Signalverarbeitung extrahiert die gewünschte Information aus den Messdaten. Zur Verifikation wurden Simulationen der Anregung akustischer Wellen mit dem Deltafunktionsmodell durchgeführt und mit den Messdaten verglichen. Anhand der Messdaten wird schließlich die anisotrope Slowness-Kurve konstruiert. Diese Information kann zur Bestimmung der Materialparameter von Dünnschichten verwendet werden.
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It is well known that miniaturized gas sensors can be obtained by coating a planar interdigital capacitor with a sensitive layer and exploiting the impedance changes induced by analyte incorporation. Commonly, one assumes that the sensor... more
It is well known that miniaturized gas sensors can be obtained by coating a planar interdigital capacitor with a sensitive layer and exploiting the impedance changes induced by analyte incorporation. Commonly, one assumes that the sensor characteristics only depend on the sensitive layer but not on the substrate carrying the interdigital capacitor. However, in many cases, the sensor has to
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ABSTRACT Measuring mechanical strain with high resolution always makes it necessary to also monitor temperature and even humidity of the sensors environment. In this contribution, a novel highly sensitive strain sensor with inbuilt... more
ABSTRACT Measuring mechanical strain with high resolution always makes it necessary to also monitor temperature and even humidity of the sensors environment. In this contribution, a novel highly sensitive strain sensor with inbuilt temperature measurement already proposed by the authors is thoroughly investigated with regard to the influence of temperature and humidity on its transfer function. Not only the static influence of the temperature on the strained device, but also the dynamic effects of temperature changes have been studied.
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A numerical approach for the solution of Maxwell's equation is presented. Based on a finite difference Yee lattice the method transforms each of the four Maxwell equations into an equivalent matrix expression that can be subsequently... more
A numerical approach for the solution of Maxwell's equation is presented. Based on a finite difference Yee lattice the method transforms each of the four Maxwell equations into an equivalent matrix expression that can be subsequently treated by matrix mathematics and suitable numerical methods for solving matrix problems. The algorithm, although derived from integral equations, can be considered to be a special case of finite difference formalisms
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ABSTRACT Planar interdigital capacitors (IDC) covered with a thin Cr2O3 layer and a thick film of platinum-doped Na-ZSM-5 zeolite, are known to act as very selective impedometric hydrocarbon gas sensors. In this contribution, the... more
ABSTRACT Planar interdigital capacitors (IDC) covered with a thin Cr2O3 layer and a thick film of platinum-doped Na-ZSM-5 zeolite, are known to act as very selective impedometric hydrocarbon gas sensors. In this contribution, the impedance spectra are calculated taking into account the ionic conductivity of the zeolite and the p-type semiconductor properties of Cr2O3 as well as the blocking electrode characteristics of the zeolite/Cr2O3 interface. A simplified differential equation for the charge velocity in the zeolite is derived and solved for a driving sinusoidal voltage. Thus, the time-dependent current through the zeolite and the Cr2O3 is obtained. By Fourier transforming the current, the IDC impedance spectrum is calculated. Since the ambient hydrocarbon concentration influences the charge carrier density in the Cr2O3 film, the calculated sensor current responds to the concentration change, accordingly leading to a good agreement between measured and calculated impedance spectra.