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Die Überwachung des Motorölzustandes in Kraftfahrzeugen erlaubt die Realisierung vergrößerter Ölwechselintervalle. Dies bringt sowohl ökonomische als auch ökologische Vorteile. Überdies kann man durch die direkte Überwachung des Ölzustandes Rückschlüsse auf den momentanen Zustand des Motors ziehen, was die frühzeitige Erkennung von möglichen Motorschäden unterstützt. In diesem Beitrag präsentieren wir einen multifunktionalen Ölzustandssensor, welcher sich für als Geber in einem Motorölmanagementsystem eignet.

A method of analysis for electromagnetic wave phenomena in multilaiyered media consisting of bianisotropic slabs with periodically inhomogeneous material parameters is presented. The analysis relies on a transformation of Maxwell's equations into an equivalent eigenoperator equation for the transverse components of the field vectors, which is Fourier transformed into an algebraic eigenvalue equation in spectral domain. The fields in the inhalmogeneous layers are then expressed in terms of eigenmodes, where the expansion coefficients are determined by imposing internal and external boundary conditions. The proposed method lis verified by comparing numerical results for ordinary isotropic-media problems with corresponding results obtained previously by different methods. The applicability and convergence behavior of the approach is illustrated for typical sample applications involving scattering- and guided-wave problems.

Closed form time-harmonic Green dyadics are constructed for a special class of homogeneous gyrotropic bianisotropic materials. First the spatial Fourier transform of these Green dyadics with respect to the preferential direction of the material is calculated and then a closed form inverse Fourier transform is performed. The results in the paper are a generalisation of known Green dyadics for specific uniaxial bianisotropic media and uniform isotropic media.

In this contribution two different types of resonating sensors for the viscosity of fluids with adjustable resonance frequencies in the range of 1 kHz to 10 kHz are presented. Analytical models relating measurement data to the viscosity of the examined liquid and measurement results are presented and the benefits of the discussed sensor designs in terms of high tunability and their sensitivity to viscosity are discussed.

In this contribution a macroscopic double membrane rheometer presented earlier is modified to a single membrane configuration in order to study further characteristics of driving modes and material properties. Excitation and read- out of the membrane vibration are based on Lorentz forces induced in a static magnetic field. First, the possibility to influence on the excited vibration mode by pre-stressing the membrane is studied. It results that pre-stressing slightly increases the frequency of the resonance peaks and furthermore enables the excitation of lower order vibration modes at lower frequencies. By changing the pre-stress, the induced vibration modes and consequently the sensitivity range of the sensor can be altered. A second focus of the present work was to study the robustness of the Poly-Ethylene material and the resulting change of the vibration behavior with respect to temperature and aging. It was found that heating of the material increases the internal friction and decreases frequency and quality factor of the eigenmode. Furthermore, aging results in a considerable increase of the polymer stiffness leading to an increase of the eigenfrequency.

A sensor suitable for online monitoring of viscosity and density of glycerol–water mixtures is presented. The device is based on Lorentz force excitation and features an integrated piezoresistive readout. The core sensing element is a rectangular vibrating plate suspended by four beam springs. Two of the plate-carrying springs comprise piezoresistors. With two additional resistors on the silicon rim they form a half Wheatstone-bridge. Through the conductive layer of the beam springs a sinusoidal excitation current is driven. In the field of a permanent magnet, the Lorentz force excites plate vibrations resulting in a bridge unbalance. We recorded both the frequency response of the amplitude and the phase of the bridge output. By evaluating the properties of the resonant system, it is possible to extract the glycerol percentage and, hence, the viscosity and the mass density of the mixtures.

Miniaturized resonating viscosity sensors operating at frequencies in the low KHz-range offer portability and results comparable to existing lab viscometers. In this paper we will briefly describe a viscosity measurement cell based on a concept that we proposed earlier utilizing electrodynamic-acoustic resonator sensors with a design based on interchangeable resonator cards, which allow for ease of maintenance of the device and provides higher measurement repeatability. Experimental results obtained with the new resonator cards show the clear dependence of the resonance frequency and Q factor on viscosity. In addition, an experimental approach is taken to study the effects of magnetic field variations on the Q factor of the investigated resonators which are suspended by S-shaped (meander) beams and operating either in air or liquids.

Electromechanical resonators are sensitive to the material parameters of a surrounding medium and therefore can be used as sensors for viscoelastic properties and density. In our recent work, we presented a metallic plate resonator excited by Lorentz forces in a permanent magnetic field. We improved the interface circuitry by using signal transformers, so that it is now possible to make accurate measurements using a commonly available low-cost audio- interface. Beside that, the necessary sample volume is reduced to a maximum of 50μl, so that a drop of liquid covers the sensitive area. Using a reflector parallel to the oscillation plane, standing waves in the gap could be generated. A desirable feature of resonator sensors is tunability over a significant frequency range. We investigated mechanisms to change the resonance frequency, e.g. an electric current that induces thermal stress. These advancements pave the way for a versatile low-cost, easy-to-use solution to measure viscoelastic properties in numerous applications.

Miniaturized physical sensors for precise density and viscosity analysis are required as supplement or replacement for complex and expensive laboratory instruments. Utilizing miniature mechanical resonators as transducers, one can greatly reduce the necessary liquid volume, measurement time, and complexity of the experimental setup. In this contribution, we describe the development of a miniature, modular measurement setup for a large viscosity range. We devised and fabricated an inexpensive flow-through cell using milling technology of multiple PCB layers and Parafilm sealing for easy assembly and disassembly. The mechanical resonator is designed as a suspended plate using Lorentz force excitation and movement induction detection. The Qfactor of the resonator is evaluated and related to the density-viscosity product of different test liquids at multiple resonant modes of vibration at low operating frequencies for over a wide range of different viscosities.

The frequency response of resonant structures immersed in liquid media allows the derivation of the physical properties of the fluid. We present a novel class of non-piezoelectric metallic shear mode resonators with Lorentz force actuation, which are read out by a motion-induced voltage. The fluid–structure interaction mechanism is dominated by decaying shear waves excited near the oscillating surfaces. The response is thus comparable to that of quartz thickness shear mode (TSM) resonators. However, the comparably low resonance frequency qualifies the presented principle for the rheological analysis of complex structured liquids like suspensions, emulsions, or polymer solutions, where quartz TSM sensors fail due to their high oscillation frequency and the associated small penetration depth. Measurements verify the fluid–structure interaction model and demonstrate the applicability to selected examples of complex liquids.

Interdigitated electrodes represent a commonly used planar structure when it comes to implementing capacitive sensors. The electric field decays strongly in the surface normal direction of the electrode arrangement. This can be used to estimate the thickness of dielectric films residing on the electrodes. A simple example for an application would be the detection of the build-up of biofilms. The exact expressions for the capacitance are relatively complex and can be provided in closed form only for the case without a cover layer. In this contribution we present an efficient modeling approach based on a physically motivated approximation of the charge distribution on the electrodes. Establishing a closed-form spectral domain representation of the associated electric potential distribution allows a numerically highly efficient calculation of the capacitance utilizing the FFT algorithm. In contrast to previous works, additional cover layers can be easily included in the model, which allows studying the aforementioned sensing effect.

Miniaturized viscosity sensors are attractive devices for condition monitoring applications involving fluid media. Most recently introduced devices utilize vibrating resonant mechanical structures interacting with the fluid where the resonance frequency and the quality factor are affected by the fluid's viscosity. The viscosity of a liquid shows a significant dependence on temperature. Thus, besides a precise determination of the liquid's temperature, the temperature dependence and stability of the sensor's resonance characteristics and a thorough understanding and knowledge of the latter are prerequisite for accurate viscosity measurement. This contribution discusses different design approaches with respect to temperature-stable resonators.

A recently introduced membrane rheometer consisting of a sample cell covered with two Lorentz force actuated membranes is modeled using a spectral Fourier transform method yielding a semi-numerical solution. This solution presented here efficiently delivers valuable properties like frequency responses, penetration depths of shear waves, and power dissipation regimes. Furthermore this novel concept enables the designer to simulate the behavior of the system under varying setup parameters in order to obtain an optimum setup for the given measurement problem.

Many sensor signals are afflicted with unwanted components induced by parasitic but well known sensor effects. With utilization of digitizing interface circuits the suppression of these components is typically performed in the digital domain. Hence the effective resolution of the system is reduced, especially when unwanted signal components are dominating the signal’s magnitude. In this contribution, a method of parasitic signal compensation as implemented in an impedance analyzer circuit for a quartz crystal resonating sensor is presented.

By measuring modulus and phase of either impedance Z or reflection coefficient S 11 of differently shaped electrodes which were in defined contact with a biological sample, we showed that electrical parameters may be utilized to assess biological functions on a three-dimensional (3D) in-vitro system. Using the example of a human hepatic 3D cell model we showed that certain frequency domains in the impedance or reflection coefficient spectra may be assigned to specific biological functions, which would possibly enable the investigation of preclinical drug metabolism and toxicity testing in-vitro . Furthermore, we comment on assets and drawbacks of the electrode designs for the use as a measurement probe in biological studies.

Liquid condition monitoring is applied to monitor the state of a liquid which itself is constituent of a product in a production process (e.g., in food industry) or which is an indicator for the state of a machine or plant (e.g., lubrication oil). In this contribution, selected physical sensor principles are reviewed and the relevance of the associated measurement domain as well as the influence of the liquid's microstructure is highlighted.

Electromechanical resonators are sensitive to the properties of the surrounding medium due to interaction forces onto the surface caused by motions in the medium. In the present contribution, fully metallic Lorentz force resonators exhibiting in-plane oscillation are used to excite shear waves to measure the linear viscoelastic storage and loss-moduli at specific frequencies in the kHz range of complex fluids (e.g. aqueous polymeric solutions). Reflected shear waves in a well defined gap are employed to extend the measurement range as well as the capability to measure at multiple frequencies. Numerical methods and reduced order models are employed to solve for the velocity field and interaction forces to determine the required quantities from the measured frequency response.

In this contribution, we present a symmetric arrangement of resonating plates for viscosity and mass density measurement. Regarding the oscillation mode, the design resembles that of micro machined tuning forks and is based on previously introduced resonating plate designs. It exhibits similar sensitivity to viscosity and mass density as the single plate resonators while having a lower damping when operated in the tuning fork mode. In this contribution we introduce the new design, present the results of FE simulations in order to determine the associated eigenmodes and examine the effects of the used actuation method on the sensor. Measurement results are presented which show the general dependence of the tuning fork design on viscosity and mass density as well as the differences exhibited by different modes, particularly the in phase and out of phase vibration modes of the plates.

We report on a novel method to determine the thermal conductivity, thermal diffusivity, and average emissivity of a thin-film diaphragm embedded in a MEMS multi-parameter wind sensor. Compared to other measurement techniques for thermal thin-film parameters, our method does not require fabrication of custom specimens. The results can be obtained from frequency response measurements directly carried out on the wind sensor. We describe the theoretical background of this method, provide an efficient analytical model (validated by FEM simulations) for the parameter extraction from the raw measurement data, and demonstrate its application by sample measurements performed on multi-layer Si x N y -SiO2 thin-film diaphragms.

Quartz crystal tuning fork resonators are suitable sensors for separable, simultaneous measurement of the density and the viscosity of a surrounding fluid. In this contribution we present the application of a frequency tracking interface for measurement of gas density and viscosity with a single quartz crystal tuning fork resonator. By frequency tracking, we obtain equal accuracy for the density and viscosity estimation as by evaluation of the admittance spectrum in the vicinity of the resonance frequency (which is typically used) but with a significantly reduced measurement time (one measurement per second compared to about 50 seconds per admittance spectrum). Furthermore, sophisticated fitting algorithms are not required.

We introduce a wide channel, micro-fluidic device for the transfer of particles and cells between different fluidic media, for example from a sample liquid to water, based on acoustophoresis (AP) as well as negative dielectrophoresis (nDEP). Rapid prototyping was used in order to determine the dimensions of the microfluidic channels and FE (finite element) simulations were performed to derive the optimal nDEP electrodes geometries. We chose to combine nDEP and AP because of the selective nature of DEP and the high throughput possibilities that the AP offers as well as the AP independence from the dielectric properties of the used media.

A semianalytical approach for the determination of the singular behaviour of electromagnetic fields near a perfectly (electrically and/or magnetically) conducting wedge is presented. The surrounding medium is assumed to consist of several general bianisotropic wedges. Explicit formulas are provided and the numerical implementation is outlined. The applicability of the method is demonstrated with sample results.

Due to unique features, micromachined thermal sensors are an interesting alternative to classical macroscopic apparatuses for the determination of thermal conductivities. A typical drawback of sophisticated miniaturized sensing elements is the fact that for most devices no analytical solution of the heat conduction equation can be obtained and thus a numerical model has to be implemented to determine the thermal parameter(s) of interest. In this contribution, an analytical model of a micromachined sensor for measuring the thermal conductivity and diffusivity of different liquids is presented. The model not only accounts for the unique sensor geometry but also for additional spurious effects associated with the devices membrane

In the present contribution we study the decomposition of a source into transverse electric (TE) and transverse magnetic (TM) parts in general uniaxial, bianisotropic media. We use a spatial Fourier transform with respect to the axial direction to derive the decomposition in the Fourier domain first. In a next step an analytical inverse transform is performed to obtain the space-domain result. It is shown that in general the decomposition of a source that occupies a finite region fills up the whole space. It is further shown that our results contain the previously published results for uniaxial anisotropic materials as special cases. © 1995 John Wiley & Sons, Inc.

In this contribution, we describe a novel electronic readout circuit for TSM resonators, which can be used, e.g., for viscosity sensing in liquids. In contrast to conventionally utilized oscillator circuits, the present circuit eliminates the disturbing influence of the static capacitance of the sensor by means of a synchronous detector. The sensor is externally fed by a voltage controlled oscillator, which is tuned to the fundamental resonance frequency by means of a control circuit utilizing a frequency modulation of the VCO signal. When the control loop has settled, either the obtained resonance frequency or the damping of the sensor can be used as output signals providing a measure for the viscosity.

Probing nucleation and growth of porous crystals at a molecular level remains a cumbersome experimental endeavour due to the complexity of the synthesis media involved. In particular, the study of zeolite formation is hindered as these typically form in multiphasic synthesis media, which restricts experimental access to crystallisation processes. Zeolite formation from single phasic hydrated silicate ionic liquids (HSiL) opens new possibilities. In this work, HSiL zeolite crystallisation is investigated in situ using a specifically designed conductivity measurement set-up yielding access to crystallisation kinetics. Based on the conductivity data and final yields, a crystallisation model explaining the results based on a surface growth mechanism was derived. The excellent agreement between experiment and theory indicates zeolite crystallisation from highly ionic media proceeds via a multi-step mechanism, involving an initial reversible surface condensation of a growth unit, followed by incorporation of that unit into the growing crystal. The first step is governed by the liquid phase concentration and surface energy, while the final step shows a correlation to the mobility of the cation involved. ispartof: Faraday Discussions vol:235 issue:0 pages:162-182 ispartof: location:England status: published

In recent years, sensors and sensor systems have gained increasing importance for automotive electronics. In this paper, the suitability and the perspectives in the application of microacoustic sensors in the fields of angular rate sensors, pressure sensors, wireless sensor readout and liquid sensors are discussed.

A method of analysis for electromagnetic wave phenomena in multilayered media and waveguides consisting of inhomogeneous and bianisotropic materials is presented. Both imposed and eigenstate problems are addressed. Particular emphasis is placed on numerical results concerning Brillouin diagrams and Green's functions associated with corrugated structures. >

Microemulsions are gaining increasing importance, e.g., in food industry and as systems providing microdomains for chemical reactions. For both, the research on and the preparation of microemulsions, monitoring the phase state is a crucial issue. We report on the utilization of permittivity and miniaturized viscosity sensors for this purpose.

The excitation of acoustic resonators is traditionally based on the piezoelectric effect. The alternative magnetic direct generation of acoustic waves is the basic operation principle of electromagnetic acoustic transducers (EMATs). For sensor applications this method can be applied to a mechanical resonator, thus enhancing the rather poor transduction efficiency by the high acoustic Q-factors. This principle has been theoretically investigated in FEM and PSpice simulations and practically applied to high-Q silicon membranes. The advantages of this non-piezoelectric sensor showing strong resonances with Q-factors up to 105 have been demonstrated. Sensor response to mass loading shows a Sauerbrey-like behavior suitable for sensing purposes.

Die vorliegende Dissertation fasst die rezenten Forschungsergebnisse des Verfassers im Bereich mechanischerResonatoren für Viskositäts- und Dichtesensorik zusammen, welche zwischen 2010 und 2015 imRahmen eines international joint doctorate programs am Institut für Mikroelektronik und Mikrosensorikder Johannes Kepler Universität Linz, sowie am Laboratoire de l’Intégration du Matériau auSystème der Université de Bordeaux erreicht wurden. In den Vorarbeiten von Arbeitsgruppen beiderInstitute wurden bereits Konzepte für elektrisch angeregte und ausgelesene mechanische Resonatorenzur Bestimmung von Viskosität und Dichte von Flüssigkeiten erarbeitet und umgesetzt. Hierbei konntegezeigt werden, dass die Resonanzfrequenz und Güte eingetauchter Resonatoren abhängig sindvon Viskosität und Dichte der jeweiligen Flüssigkeiten. Die dabei untersuchten Konzepte beinhaltetenstrukturierte Polymerfolien, nass-chemisch geätzte Neusilberbleche, mikromechanisch hergestellte Siliziumstrukturen,sowie siebgedruckte PZT Resonatoren.Die Motivation zur Untersuchung und Entwicklung solcher miniaturisierter Resonatoren resultiert unteranderem aus deren Anwendbarkeit für Inline-, Insitu- und Handgeräte für Labor- bzw. industrielle Anwendungen.Besonders für Letztere sind Robustheit, Langzeitstabilität und Zuverlässigkeit, aber auchpräzise Messergebnisse Grundvoraussetzung. Um den Anforderungen der Ergebnisse und Erkenntnisseder zuvor genannten Arbeiten gerecht zu werden, wurden folgende Ziele für diese Dissertationdefiniert. Erstens, die Entwicklung robuster, langzeitstabiler Messaufbauten zur Erreichung präziserMessergebnisse, wodurch eine geringe Temperaturquerempfindichkeit als weitere Bedingung aufgestelltwurde. Zweitens sollte untersucht werden ob und mit welcher Genauigkeit sowohl Viskosität als auchDichte mit einem einzigen Instrument gemessen werden können. Drittens, sollte einerseits das Verhaltenverschiedener Viskositäts- und Dichtesensoren modelliert bzw. deren Vergleich ermöglicht werden.Basierend auf einer vorwiegend experimentellen Herangehensweise und unter Miteinbeziehung der zugrundeliegendenTheorien von Strömungs- und Strukturmechanik sowie der Elektrodynamik, konntendie o.g. Anforderungen erfüllt werden. [...], This thesis summarizes the author’s recent work on the topic of mechanical resonators for liquidviscosity and mass density sensing, which were achieved between 2010 and 2015 in the course of aninternational joint doctorate program performed at the Institute for Microelectronics and Microsensorsat the Johannes Kepler University Linz, Austria and the Laboratoire de l’Intégration du Matériau auSystème in Bordeaux, France. In previous studies performed by work groups of both laboratories,the concept of using electrically actuated and read-out mechanical resonators for the determination ofliquids’ viscosities and mass densities has been established and elaborated. These works showed that theresonance frequencies and quality factors of immersed resonators are affected by the liquids’ viscositiesand mass densities, respectively. The investigated concepts included devices using structured polymeror wet-etched new silver sheets as well as micro-machined silicon and screen-printed PZT resonators.The motivation for investigating and developing such miniaturized resonators was formed, amongstothers, by their capability for in-line, in-situ and handheld-devices for laboratory as well as for industrialapplications. Especially for the latter, physical robustness, long-term stability and reliability,as well as accurate measurement results are basic requirements. To satisfy these requirements andconsidering the results and insights of earlier works, the objectives of this thesis were first, implementingrobust measuring setups featuring long-term stability and high measurement accuracy, where thelatter furthermore requires low cross-sensitivity to temperature. Second, investigating the capabilityof measuring both, a liquid’s mass density and viscosity with a single device as well as providing anestimate of achievable measurement accuracies for both quantities. And third, enabling the modelingof the performance of different viscosity and mass density sensors on the one side and their comparisonon the other side. These three specifications were accomplished by following mainly experimental approachesand investigations but also by elaborating the underlying theory of hydrodynamics, structuralmechanics, and electrodynamics. [...], Cette thèse synthétise les travaux récents de l’auteur sur l’utilisation de résonateurs mécaniques pour la détermination simultanée de la viscosité et de la masse volumique de liquides. Ces travaux ont été réalisés entre 2010 et 2015 dans le cadre d’une thèse en cotutelle entre l’Institut de Microélectronique et des Microcapteurs de l’Université Johannes Kepler à Linz en Autriche et le Laboratoire de l’Intégration du Matériau au Système de l’Université de Bordeaux en France. Dans des études précédentes effectuées sur ce sujet par les groupes des deux laboratoires, le concept de l’utilisation de résonateurs mécaniques actionnés et mesurés électriquement pour la détermination de la viscosité et de la masse volumique deliquide avait été établi et validé. Ces travaux antérieurs ont montré que la fréquence de résonance et le facteur de qualité de résonateurs immergés dépendent à la fois de la viscosité et de la masse volumique du fluide environnant.L’intérêt d’utiliser de tels microcapteurs résonants vient du fait qu’il est possible de les utiliser in-situ,notamment pour des applications industrielles. Pour ce type d’applications, il est important que les capteurs aient entre autre une bonne résistance physique, une bonne stabilité à long terme, une bonne fiabilité, ainsi qu’une bonne précision de mesure. Pour satisfaire ces exigences et compte tenu des résultats des travaux antérieurs, les objectifs principaux de cette thèse étaient (1) la mise en oeuvre de configurations de mesure robustes offrant une bonne stabilité à long terme et une bonne précision de mesure, ce qui nécessite une faible sensibilité à la température, (2) la mesure simultanée de la viscosité et de la masse volumique avec un seul capteur et (3) la modélisation et la comparaison des performances des différents dispositifs mis au point et testés. Ces trois objectifs ont été atteints en combinant des approches expérimentales et théoriques (hydrodynamique, mécanique du solide et électrodynamique). [...]