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We present a concept for autonomous, long-term and high-pressure fluid transport on disposable microfluidic chips, which are fully bio-compatible and compostable. The actuation principle is based on ethanol fermentation, a well-known biological process in which yeast cells convert molecules like sucrose into cellular energy and thereby produce ethanol and carbon dioxide (CO 2 ) as metabolic waste products. A two-chamber fluidic system separated by a flexible membrane is suggested for active fluid transport utilizing a bio-reactor. One chamber, connected to the outside via a pressure-sensitive valve, contains the fluid to be actuated, the other one the culture medium for the yeast cells. Once the yeast cells are injected into the culture medium, ethanol fermentation and thus the production of CO 2 starts, which builds up pressure on the membrane and hence also on the fluid chamber. As soon as the switching point of the pressure sensitive valve is reached, fluid transport at a predefined and constant flow rate starts.

We study the fluid dynamics of polar high-k fluids immersed in non-polar insulating fluids, excited by electrowetting-on-dielectric (EWOD) forces inside a tube with pressure compensation channels. The fluids are set in motion using the electrowetting effect resulting in a pressure difference inside the tube. A model of the pressure field for various viscosities of the surrounding fluid is obtained by finite element analysis of the Navier-Stokes equation. From the time dependent pressure response and the associated viscous damping, a correlation with the fluid's dynamic viscosity is obtained. In the next step, we study the pressure evolution after driving the polar fluid in one direction and stopping it rapidly at the edge of the driving electrode. The decay time of the pressure induced height difference inside the compensation channels can also be related to the surrounding non-polar fluid's viscosity. Subsequently, a cheap alternative fabrication process of an EWOD stack will be shown and used to build a tube oscillator simulated in the steps before.

An efficient semi-numeric boundary element method for the calculation of the response of interdigitated touch sensors is introduced and used to demonstrate interesting properties of embedded printed capacitive touch sensors on steel substrates. The strength of the method is that layer compositions with finite conductivity and arbitrary sequence of layer permittivities can be calculated efficiently for all aspect ratios. The method is used to further investigate previous findings, where we have shown, that measuring the coupling capacitance between the interdigitated fingers at low frequencies is the most sensitive approach.

We present a measurement system where a spherical permanent magnet is levitated in an actively controlled magnetic field. The sensor system measuring viscosity and density independently. In operation mode, the magnet is held in a constant levitation position. Due to a special actuation scheme, the magnet rotates around its vertical axis. Using this setup and immersing the magnet in a fluid, it is possible to analyze viscosity and density of all kinds of fluids, except ferrofluids. The magnetic levitation system avoids any connection penetrating the walls of the measurement chamber; only the spherical permanent magnet measurement body is in contact with the sample fluid. Due to this, the measurement procedure is reproducible, repeatable and resource saving.

Acoustic streaming is a promising way for transporting fluid or particles suspended in a fluid in lab-on-a-chip devices and microfluidics in general. In literature usually water is considered as the working medium. In this contribution we present a framework based on perturbation theory, which implements viscoelastic fluid behavior to the acoustic streaming effect expanding the applicability beyond simple Newtonian fluids. Numerical simulations were carried out by finite element analysis. As an example we consider the steady flow generated in a channel by acoustic streaming using the upper-convected Maxwell (UCM) model to describe the viscoelastic behavior.

In this work we present the fabrication and experimental characterization of an optimized vertical-cavity enhanced resonant thermal emitter (VERTE) for vertical emission at a wavelength of 4.26 pm. Our results show that such structure allows for a four time enhancement of the emission around the design wavelength when compared to out of band emission.

In recent years, the implementation of printed strain gauges as cost-effective alternatives to conventional glued strain gauges was investigated. Printed strain gauges are, in general, not temperature compensated due to the lacking availability of appropriate materials. Their accuracy (and applicability) therefore is strongly affected by temperature drifts. In this contribution, we propose a concept for temperature compensated strain measurement with printed strain gauges based on two nested, meander shaped strain gauges consisting of different materials. Due to the proximity of the sensors, they are both affected by the same strain and the same local temperature. It is shown that, by measurement of the resistance of both strain gauges, the strain applied to the strain gauges can accurately be determined even if the sensors are subject to temperature fluctuations.

We designed, simulated and experimentally characterized thin silver microheater structures placed on a dielectric multilayer membrane, which represent the concept of vertical-cavity enhanced resonant thermal emission (VERTE). This concept has the goal to achieve selective and coherent thermal emission on the backside of the multilayer membrane. The dielectric stack also is responsible for the thermal insulation, i.e. is preventing heat to be conducted away into the silicon substrate. However, the large fractions of silver demanded by the VERTE concept seem to contradict the goal of high thermal insulation for efficient heating. Here, we focus on microheater structures with high fractions of silver on the area of the membrane. We show that target operation temperatures up to 800 K (suitable for mid IR region) could be reached in finite-element simulations and experiments with reasonable amounts of electric power supply, despite conduction losses into the substrate. Sample devices featuring the multilayers were fabricated using PECVD and dry etching. The multilayer membranes showed remarkable mechanical and thermal stability, making the structures suitable for a source for optical on-a-chip mid-infrared sensing.

In this paper we present a new balanced flowthrough viscosity sensor working with a torsionally resonating pipe. The whole system is machined in aluminum and is designed to be placed in the pipes of a chemical production plant. The quality factor Q and the resonance frequency fr are used as measures for the viscosity and density. We describe the sensor setup, its working principle for different resonant modes, the actuation and the readout of the sensor and present first measurement results for liquids featuring different viscosities.

Acoustic streaming effects are usually treated using perturbation theory by writing the field variables as perturbation expansions utilizing a small scale parameter and solving the ensuing equation systems. When conducting numerical simulations, this approach can help reducing the computational effort drastically. In most cases, the zero-order velocity is assumed to be zero, which is an applicable assumption, if the fluid is considered to be at rest in the unperturbed state. If this assumption is not fulfilled, the zero-order velocity has to be taken into account in the calculation. In this contribution we investigate the influence of such a background velocity field on the resulting acoustic streaming flow by finite element analysis. The zero-order velocity is therefore included in a numerical simulation scheme, which is based on perturbation theory. The impact of the zero-order velocity is investigated in two examples taken from literature.

This work reports on the hysteresis behavior and an initial baseline drift of printed strain gauges embedded in organic coating layers on sheet steel that we recently introduced. We subsequently investigated the performance over an extended period of time, which revealed interesting and partially unexpected material properties of printed strain gauges made from silver and carbon. Both silver- and carbon-based strain gauges show a hysteresis behavior of the gauge factor and non-negligible nonlinear characteristics. Furthermore, the carbon-based sensors show a strong initial base line drift within the first 50–100 cycles. All three effects, namely hysteresis, nonlinear gauge factor and initial base line drift, are confirmed within their respective standard deviations.

The paper reports on temperature behavior of strain sensitivity of recently introduced screen printing technology facilitating the realization of silver and carbon black piezoresistors embedded in organic coatings. Piezoresistive layers were prepared by screen printing directly on the top of the organic coating. Since no glue or carrying substrates are between the sensitive element and the device under test, the coupling factor is high and the strain is efficiently transferred to the sensing element. The strain induced changes in resistance (piezoresistive effect) are generally lower compared to the changes induced by temperature. The temperature dependence of the sensitivity to strain was investigated utilizing both single element piezoresistors and piezoresistors connected to a Wheatstone bridge. The study analyzes strain-gauges under longitudinal tensile and compressive strain and temperatures up to 80 °C. Screen printed strain gauges can provide reliable and robust strain measurements for coated metallic substrates, the sensor performance is comparable to the conventional solution with glued sensors.

A piezoelectric tuning fork sensor is evaluated as a physical excitation and sensing device aiming at the detection of crystals and their nucleation behavior in joint fluids, as observed in gout. This device allows to study the crystallization tendency at varying temperatures or at increased uric acid concentrations as predominant in real human joints. In this work, a tuning fork resonator is characterized to enable spatially resolved viscosity and density measurements by calculating the mode shape of the vibration from resonance frequency measurements when immersed in test liquids.

In this work we present the realization of a fully spray processed embedded temperature sensor. The sensing element is a thermocouple made of conductive materials which are high temperature stable polymer based paints with organic or metallic filler particles. The thermocouple is embedded in an organic paint layer which shows, besides good high temperature properties up to 250 °C, excellent mechanical and chemical stability. The manufactured thermocouples are tested up to a junction temperature of 250 °C, first without and afterwards with an encapsulation layer. The measured output voltage for a terminal temperature of 25 °C and a junction temperature of 250 °C is in the region of 4.23 mV before and after top coating. Finally, a layer analysis of the encapsulated device is made using a cross-section polish.

Sensing of gases is a promising area for applications of photonic systems operating in the mid-infrared spectral range. We present an infrared evanescent-field absorption gas sensor based on a silicon strip waveguide, which was specifically designed for CO2 sensing. We discuss finite element simulations that were used to design the strip waveguide and furthermore present experimental data of quantitative CO2 measurements with the devised structures. The first demonstrator device detects concentrations down to 5000 ppm CO2 which is the workplace exposure limit in most jurisdictions.

We introduce an analysis platform for the viscoelastic properties of biological fluids such as the synovia found in articular joints. Small sample volumes are available for diagnostic purpose. Our approach uses a thickness shear mode quartz crystal integrated in an electrodynamically actuated spring structure. This combines the sensitivity of the quartz resonator operating at several overtones in the MHz range with previously introduced low kHz frequency multimode resonators. The latter is not only advantageous for characterizing viscoelastic fluids but is also used as an acoustic streaming actuator. Particulate matter in the sample thus can be resuspended and their settling is observed by tracking the resonance frequencies and Q-factors of both the quartz and electrodynamic resonator sensors.

The mid-infrared region is prominent for gas sensing due to the unique footprint of various volatile organic compounds. We investigated the intrinsic damping in silicon slab waveguides in the mid-infrared region in order to provide a platform for evanescent-Qeld sensing using silicon waveguides.

We evaluate a recently devised design of vertical-cavity enhanced resonant thermal emitter (VERTE) regarding stability to fabrication tolerances of PVD layer deposition techniques. Such an emitter achieves narrowband and coherent thermal emission and is composed of an multilayer stack of dielectric layers (silicon and silica) on top of a reflective metal (silver) structure. The silica layer above the metal acts as a vertical cavity enhancing the electromagnetic field between the reflective metal and the dielectric stack forming a Bragg mirror (1-D photonic crystal). In our previous work, we identified several suitable five-layer-stack configurations, which considered several features and limitations of a real-world device, such as temperature dependence of the materials, fabrication constraints or unwanted emission modes. However, the emission characteristics are very sensitive to the geometrical and optical properties of the material. In order to examine this behaviour, a Monte-Carlo algorithm was used to apply a Gauss-distributed error in depth (relative the unperturbed layer thickness) for every individual layer. The robustness of the emission properties against fabrication errors were evaluated and analyzed by significant statistical quantities. As expected, the main issue compromising the emission properties is a deviation of the resonance wavelength in relation to the initial target resonance wavelength of the unperturbed configuration. Interestingly, configurations with larger average layer thicknesses and therefore with larger absolute thickness deviations did not exhibit a larger variance of the emission wavelength. Instead, the variance slightly decreased or remained constant. A similar result was obtained for increasing the number of dielectric layers. In contrast, the peak emissivity (at normal incidence) was significantly influenced by the average layer depth of a configuration. Also, the effect of broadening of the spectral emittance curve due to random thickness fluctuations was evaluated. It was found that the broadening due to relative thickness errors can be considered as negligible for most configurations.

In this work we present a design to enhance absorption of infrared light by a fluid analyte being in contact with a slot photonic crystal ring resonator (slot-PCRR). For this purpose, we propose a new PCRR design facilitating higher interaction between guided mode and analyte. These types of PCRRs are based on two-dimensional photonic crystals, which consist of an array of holes in a silicon slab being arranged in a hexagonal lattice. The holes will be filled with liquid analyte. A slot is embedded in this hexagonal ring cavity to create a slot-PCRR. The strong confinement of light in the low index region, occupied by the analyte, is the key advantage of the slot- PCRR. We also calculate the relative intensity change in the transmission spectrum due to the absorption in the analyte. The maximum change obtained is given by a mode which has most of the electromagnetic field energy in the region the region filled with the analyte. Furthermore, this mode is well separated from neighboring bands, which has the advantage that impinging light with specified frequency is less likely to spuriously couple to other modes with the same frequency, which would decrease the amount of energy coupled to desired mode. The slot-PCRR yields a higher relative change due to absorption compared to the PCRR without a slot. In this work, the radii of six rods at the outer PhC were tuned to enhance the quality factor of slot-PCRR. Using these optimum values of radii, the Q-factor rises up to 80000.

A design for a high Q factor photonic crystal ring resonator (PCRR) is presented. The PCRR is based on 2D pillar type photonic crystals, which consist of a hexagonal array of silicon rods. The cavity is created by removing elements from the regular PhC grid. Achieving strong confinement of light intensity in the low index region (filled with the gaseous analyte) is the advantage of this PCRR. In that manner, the interaction of light and analyte, which can be a liquid or a gas, will be enhanced. The high quality factor of the cavity (Q=1.2×104 ), along with strong overlap between the field of the resonant mode and the analyte as well as the low group velocity of PCRR modes yield enhanced light-matter interaction. An enhancement factor of 1.149×105 compared to the bulk light absorption in a homogenous material provides the potential for highly sensitive gas detection with a photonic crystal ring resonator.

Electrochemical impedance spectroscopy (EIS) was used to detect and investigate nucleation in silicalite-1 clear solutions. Although zeolite nucleation was previously assumed to be a step event, inducing a sharp discontinuity around a Si/OH– ratio of 1, complex bulk conductivity measurements at elevated temperatures reveal a gradual decay of conductivity with increased silicon concentrations. Inverse Laplace transformation of the complex conductivity allows the observation of the chemical exchange phenomena governing nanoaggregate formation. At low temperatures, the fast exchange between dissociated ions and ion pairs leads to a gradual decay of conductivity with an increasing silicon content. Upon heating, the exchange rate is slower and the residence time of ion pairs inside of the nanoaggregates is increasing, facilitating the crystallization process. This results in a bilinear chemical exchange and gives rise to the discontinuity at the Si/OH– ratio of 1, as observed by Fedeyko et al. EIS allows the o...

A generalized reduced order model for resonant viscosity and mass density sensors is presented and experimentally verified. Thereduced expressions for the resonance frequency and quality factor, respectively, are mathematically valid for in-plane oscillatingplates, oscillating spheres and laterally oscillating cylinders. However, as shown for measurements obtained with a tuning forkresonator with rectangular cross-section, the model can also be applied for resonating structures, for which closed form solutionsof the fluid structure interaction are not available. Benefits of the presented model are amongst others first, its simplicity, whichrequires no more than three calibration measurements for parameter identification and second, its general applicability for resonantmass density and viscosity sensors which furthermore facilitates the comparison of dierent resonant mass density and viscositysensors in terms of sensitivity and measurement noise propagation.

We present the theoretical background of a previously introduced viscosity measurement system based on a principle similar to that of the well-known falling ball viscometer. Even though the falling ball viscometer does not allow a viscosity measurement at defined shear rates, it has been established as frequently used referenced method in the chemical industry and is still widely used today. We modified the mode of operation to permit continuous measurements by building an orbiting sphere viscometer, where a sphere mounted on a spring wire performs steady motions on a circular path. The movements are electromagnetically excited in a contactless manner such that the actuator does not have to be placed within the fluid. The readout can be performed by piezoelectric sensors (as described below) and alternatively also by means of inductive sensing. Classical rheometer principles (such as rotating cylinders or plate-cone arrangements) often involve precision drives and bearings which in our case were completely avoided. Both readout methods avoid also mechanical feedthroughs (e.g., in terms of a rotating shaft) where the inductive method additionally avoids electrical contacts in the measurement chamber. This is an important feature for process automation in the chemical industry, just as the possibility of continuous measurements, which allows uninterrupted control of the viscosity during a production process. Due to the easy scalability of the system it is applicable in a wide range of viscosities. Various operating modes are possible and allow different physical parameters to be sensed. In this paper, we describe those modes mathematically and compare them to the results of a finite element simulation. We furthermore analyze various spurious effects and studied the influences of geometrical design parameters associated with an experimental prototype.

A resonant sensor for a fluid's viscosity and mass density, employing an out-of-plane vibrating U-shaped tungsten wire is presented. The motivation for such a design is based on four major aspects, which are: operation in the low kilohertz range, circular cross-section of the resonator, electrodynamic actuation and read-out by means of Lorentz forces and low cross-sensitivity of the device's resonance frequency to temperature. The setup is described in detail, an analytical model is presented and results from experiments using acetone–isopropanol and DI-water–glycerol solutions are discussed to show the sensor's performance.

As alternative to established thermal substrates and thin membranes, we have investigated fully porous silicon substrates as highly insulating material for thermal devices. Exhibiting a thermal conductivity similar to silica glass and considerably lower than silicon nitride due to increased phonon scattering, thick mesoporous silicon also offers improved thermal and mechanical stability. Our work has focused on full wafer thickness porosification as a not extensively documented use of porous silicon and its application to thermal devices. Here we present measurement and finite element simulation results for our latest generation thin film microheaters on fully porous silicon substrates as proof of concept devices. Porosity, mass density, and specific heat capacity of porous silicon are deduced from fabrication parameters, thermal conductivity is determined by the so-called 3ω-measurement method, and all material properties are validated by fitting measurement data to our finite element models. For thick fully porous domains we estimated a thermal conductivity of ≈0.9 W/m/K, as well as a density of ≈1200 kg/m3, a specific heat capacity of ≈780 J/kg/K and a corresponding volumetric porosity of ≈50%. Thin film fabrication of nitride passivation and molybdenum meander microheaters on fully porous domains allowed characterization of thermal performance and insulation. For 10 mm2 microheaters we measured a power efficiency of 0.40 K/mW stable up to a maximum temperature of 475 °C, compared to 0.37 K/mW stable up to 440 °C on silica glass. Both static and dynamic heater measurements show superior performance of fully porous silicon substrates compared to reference samples on thin silica glass substrates.

For thermal sensors and devices, porous silicon is a comparably novel alternative to standard materials such as thin glass substrates or silicon nitride membranes. These materials are primarily characterized by their thermal conductivity and heat capacity, as well as temperature stability and mechanical fragility. In this paper, we present details of the porous silicon technology for full wafer porosification as well as static and dynamic device and material characterization. The reduction of thermal conductivity is estimated with the dynamic 3ω technique and compared with pure silicon and silica glass wafers. Thin film microheaters have been deposited on the samples as proof of concept for the characterization and comparison of thermal insulation, heat capacity, as well as thermal and mechanical stability.

Hybrid systems consisting of a quantum emitter coupled to a mechanical oscillator are receiving increasing attention for fundamental science and potential applications in quantum technologies. In contrast to most of the presented works in this field, in which the oscillator eigenfrequencies are irreversibly determined by the fabrication process, we present here a simple approach to obtain frequency-tunable mechanical resonators based on suspended nanomembranes. The method relies on a micromachined piezoelectric actuator, which we use both to drive resonant oscillations of a suspended Ga(Al)As membrane with embedded quantum dots and to fine-tune their mechanical eigenfrequencies. Specifically, we excite oscillations with frequencies of at least 60 MHz by applying an AC voltage to the actuator and tune the eigenfrequencies by at least 25 times their linewidth by continuously varying the elastic stress state in the membranes through a DC voltage. The light emitted by optically excited quantum dots is used as a sensitive local strain gauge to monitor the oscillation frequency and amplitude. We expect that our method has the potential to be applicable to other optomechanical systems based on dielectric and semiconductor membranes possibly operating in the quantum regime., This work was supported by the FWF (P 29603), the Linz Institute of Technology (LIT), the LIT Secure and Correct Systems Lab funded by the state of Upper Austria, the EU project HANAS (No. 601126210), AWS Austria Wirtschaftsservice (PRIZE Programme, Grant No. P1308457), the European Research council (ERC) under the European Union's Horizon 2020 Research and Innovation Programme (SPQRel, Grant Agreement No. 679183), and the German Excellence Initiative via the Cluster of Excellence Nanosystems Initiative Munich (NIM). X. Yuan acknowledges support of the China Scholarship Council (CSC, No. 201306090010). Y. Huo thanks support of NSFC (No. 11774326) and STCSM (Nos. 17ZR1443900 and 17PJ1409900). J.M.-S. acknowledges support through the Clarín Programme from the Government of the Principality of Asturias and a Marie Curie-COFUND European grant (No. PA-18-ACB17-29).

The performance of a recently introduced method to estimate the resonance parameters from complex spectral data and the error propagation for viscosity and density parameters of liquids are examined. The method is known to produce excellent results when used for piezoelectric and Lorentz force actuated sensors for single port or two-port devices. The method is also suited for very low quality factors (< 10) which extends the usable measurement range of many sensor concepts, especially for fluid sensing applications. Generally valid expressions for the measurement accuracy are stated and compared to measurement results obtained with a piezoelectric tuning fork and a Lorentz force actuated and inductively read out platelet sensor.

Most recently introduced viscosity and mass density sensors utilize vibrating resonant mechanical structures interacting with the sample fluid where the resonance frequency and the quality factor are affected by both, the fluid's viscosity and its mass density. Unlike singly clamped beams, straight, doubly clamped structures are advantageous when using electromagnetic excitation and read-out based on Lorentz forces which allow high excitation forces and read-out signals. However, classical straight beams such as bridges are subjected to high cross-sensitivities of their resonance frequencies to ambient temperature. To overcome high spurious temperature dependencies but to benefit from the straight doubly clamped approach, a spiral spring resonator applicable as viscosity and mass density sensor has been designed.

The introduction of electric polarization and magnetization—the density of electric and magnetic dipole moments respectively—into Maxwell's equations requires establishing their respective relation to polarization charges and magnetization currents. Using a method introduced by Feynman in his famous lectures on physics and considering statistically distributed dipoles on the microscopic scale, the desired relations can be established in a manner that may be more intuitive to undergraduate students.

The principle of using steel tuning forks for viscosity and mass density measurements is investigated. From recorded frequency responses of fully immersed tuning forks, resonance frequencies and quality factors are evaluated and related to the liquids mass densities and viscosities. The benefit of these resonators is their mechanical rigidity which allows the application in harsh environments and mechanical cleaning processes without detuning or damaging the device. The setup was particularly devised that only the resonator itself but no excitation or read-out mechanisms get wetted by the sample liquid. The results obtained with a circular cross-sectioned tuning fork in different liquids are shown and discussed.

In this contribution we discuss a generalized, reduced order model for resonant viscosity and mass density sensors which considers also the devices’ cross sensitivities to temperature. The applicability of the model is substantiated by experimental results from measurements obtained with a circular steel tuning fork in various liquids and temperatures. Advantages of this model are its simplicity, its general applicability for resonant mass density and viscosity sensors which furthermore facilitates the comparison of different sensors.

We present a feasibility study aiming at the detection of silica nanoparticles (NPs) in human intestinal epithelial cells. Caco-2 cells were maintained in cell culture medium (Dulbecco's Modified Eagle's Medium, DMEM) and differentiated for 21 days. To study the effect of silica NPs on the differentiated Caco-2 cell, cells were treated for 24 h with different doses. We measured the serum-free culture medium first, which was supplemented with different doses of silica NPs using a parallel-plate capacitor principle to demonstrate the sensitivity of the sensing principle to the particle concentration. In a next step we treated Caco-2 cells with serum-free culture medium containing silica NPs. After 24 h incubation time, culture medium was removed and cells were washed with PBS, so that topical adherent NPs should have been removed. We finally present the use of a second coplanar electrode design with eight single electrodes connectable in arbitrary combination to detect the silica NPs in cells.

Functional materials such as piezoelectric and pyroelectric polymers or organic photodiodes are promising candidates for flexible sensor surfaces; combining thin films of these materials with large-area resistive electrodes leads to position-sensitivity for passive touch- or light-point localization, respectively. However, this type of large-area sensors for passive stimulus-localization lacks a general theoretical description, which is necessary to understand the physics underlying the sensor concept. To this end we present a one-dimensional, theoretical model for these sensors; the model is based on the solutions of the telegrapher's equations under the appropriate boundary conditions. We specify the applied boundary conditions, list approximate solutions for certain parameter ranges and present two model-based normalization procedures. These normalization procedures allow for stimulus localization independently of its magnitude and significantly increase the quality of the measurement signals. Experimental results agree well with theoretical findings, proving the suitability of the presented theoretical models.

A resonating sensor to measure liquid density and viscosity is investigated. The sensor consists of a sample cell sealed by two polymer membranes carrying conductive paths for Lorentz force excitation and inductive readout. The setup is modeled by a semi-numeric method in the spectral domain. The model is used to reproduce and to explain experimentally demonstrated and previously published results. From the verified numerical model, simpler approximate equations are derived using energy methods. Furthermore, adverse effects which can impair the proper operation are discussed.

We present the design and fabrication of a single-mode slab waveguide structure for mid-infrared spectroscopy optimized for broadband coupling. The sensor uses grating couplers for robust off-axis coupling and a silicon nitride guiding layer for mechanical robustness. An external cavity quantum cascade laser-based transmission method is introduced for characterizing the structure’s broadband coupling behavior. Light from an external cavity quantum cascade laser with a spectral range of 0.5 μm around 6 μm was coupled into the waveguide without the need for moving parts. First spectra taken with this sensor are presented.

Considering the total force on matter in a dynamic electromagnetic field yields that, in contrast to the static case, the rate of change of mechanical momentum is not directly related to the integration of the Maxwell stress tensor but an additional term occurs, which can be interpreted as the rate of change of ?electromagnetic momentum?. For beginners, the latter concept is hard to grasp in terms of a field theory. However, the electromagnetic momentum can readily be interpreted as the momentum of the photons associated with the electromagnetic field as presented in this paper. Even though the notion of photons is not required or included in Maxwellian electrodynamics, this relation may help students to get a better grip on the interpretation of momentum conservation in electrodynamics.

Miniaturized resonating viscosity sensors operating at frequencies in the low KHz-range, offer portability and measurement results comparable to existing lab viscometers. In this paper, we present a viscosity measurement cell, based on a concept that we proposed earlier utilizing electrodynamic-acoustic resonator sensors, with a novel design based on interchangeable resonator cards. Experimental results obtained with the new resonator cards show the dependence of the resonance frequency and Q-factor on viscosity. We obtained repeatability errors in the order of a few percent for a range of Newtonian liquids. We discuss the related errors in viscosity measurement based on deviations in the determination of the Q-factor and resonance frequency. In addition, experiments were made aiming at increasing the initial Q-factor of the sensor by varying the distance separating the two magnets of the viscosity measurement cell and investigating different bonding techniques of the resonator card. Based on these results, design rules for the magnetic circuit and the mounting are derived.

We present the application of diamagnetic levitation of a small floater magnet for the realization of a magnetically actuated membrane actuator in polymer composite technology. Following this approach the neutral position of the actuating membrane can be adjusted by diamagnetically stabilized levitation and the actuation of the membrane is induced by an integrated coil which is driven by an ac-signal. This setup holds the advantage that the neutral position of the flexible membrane can be stabilized with no external energy input, and the separation of the off-position from the driving mechanism allows for many possible applications of the device in, for instance, microfluidic systems.

Electrowetting on dielectrics is an established actuation principle in digital microfluidics. The Lippmann-Young equation describes the dependence of the contact angle to applied voltages. At high voltages the changes of the contact angle diminish and the contact angle saturates. Several theories try to explain that phenomenon. Amongst others, trapped charges and leak currents were proposed as the mechanisms behind the contact angle saturation. In this paper, we will combine these two theories to a common one and show that leak current and dielectric breakdown causes trapped charges and leads to a deviation of the Lippmann-Young equation and to a non-constant but oscillating contact angle at increasing voltages.The thermodynamic derivation takes into account the electrostatic energy of a perfect capacitor, consisting of a homogeneous or a layered dielectric isolation. In our contribution, we show that isolation layers consisting of real materials with non-zero conductivities and, especially in the case of dielectric breakdown in one of these layers, display electrostatic energies different from that of an ideal capacitor. Thus, the contribution to the surface energies changes and the wetting contact angle differs from the Lippmann-Young prediction. It turns out, that the change of the surface energy of a solid to liquid interface differs depending on the order of the applied dielectric layers.

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.

Silicon-based MEMS technology has furthered the introduction of sensors and actuators in many applications. Particularly in inertial sensing, where no contact with a medium to be sensed is required, highly reliable and cost-effective solutions have been developed. For application in fluidic environments, special demands regarding the interaction can occur. Also, silicon-based technology is not cost-effective in low-volume applications.In our recent work, we thus consider hybrid technologies and concentrate on physical sensor principles, which often provide more robustness in process control and condition monitoring than dedicated chemical sensors featuring chemical reactions with the environment by means of specific chemical interfaces. The latter are frequently prone to reliability issues, e.g. due to poisoning, drift, etc. Examples for physical parameters are thermal and electrical conductivity, permittivity, viscosity, speed of sound, and density. In this contribution, sensing concepts addressing these target parameters are reviewed.

In this work we report on the integration of all-printed multi-layer ferroelectric sensor stacks into organic coatings on metallic surfaces like sheet steel. Manufacturing techniques for realizing thin film sensor layers on top of organic coatings using screen printing are presented. Results for the piezo/pyroelectric sensor layer with variable printing parameters are then analysed and compared.

The response to extensional deformation of aqueous polymeric solutions depends strongly on the molecular weight and concentration of the solute. The molecular weight of hyaluronic acid in the synovial fluid is a critical parameter for its physiological condition. We propose a novel method for the characterization of these kinds of fluids using a fluidic two-phase system where a dispensed droplet is elongated by electrostatic forces from a voltage source of up to two kilovolts. This way a filament is formed comparable to laboratory capillary breakup extensional rheometers. High-speed imaging is used to investigate the rapid deformation process. Using a mathematical model for the dynamics of the filament evolution, the fluid parameters like the shear viscosity and elastic modulus are derived. The deformation rate can be controlled over a wide range by the magnitude and slope of the applied voltage.

We present a sensor setup based on acoustic pressure waves allowing the determination of the acoustic viscosity and sound velocity of liquids. Compared to previously presented planar transducer based approaches, the proposed setup does not require the correction of spurious diffraction effects. Beside the basic sensor setup, a 1D-model and experimental data obtained with a first prototype device are discussed.

We present a special operation mode of a levitating sphere viscometer which allows steady rotations of a levitated magnet around its vertical axis. In contrast to miniaturized oscillatory viscosity sensors, this mode of operation allows to obtain viscosity measurements more comparable to standard laboratory viscometers. Moreover, the measurement range is increased to higher viscosities, where no resonance peak is detectable in with oscillatory sensors. Using electromagnetical actuation and the readout, all fluids except ferrofluids are measurable. Due to the levitation and the contactless readout, only the measurement body has to be in contact with the fluid, all readout and actuation parts can be placed outside the measurement cell, which makes the setup particularly useful for, e.g., sterile, toxic or poisonous fluids.