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We demonstrate the utilization of the fundamental principle of nonlinear dynamics, namely, the Liénard-type representations of ordinary differential equations, also referred to as fast-slow systems, to describe and understand relaxation oscillations in electronic circuits. Relaxation oscillations are characterized by periods of slow signal changes followed by fast, sudden transitions. They are generated either intentionally by means of usually simple circuits or often occur unintentionally where they would not have been expected, such as in circuits with only one dominant energy storage device. The second energy storage required to promote oscillatory solutions of the governing equations can also be provided by spurious elements or mechanisms. The conditions that distinguish harmonic from (anharmonic) relaxation oscillations are discussed by considering the underlying eigenvalues of the system. Subsequently, we show how to intuitively understand relaxation oscillations through analyses of the phase diagram based on the fast-slow system representation of the nonlinear differential equation. Practical examples of oscillators including $RC$ and $LR$ op-amp circuits and the so-called “Joule thief” circuit are discussed to illustrate this principle. The applicability of the method is not limited to electrical circuits, but extends to a variety of disciplines, such as chemistry, biology, geology, meteorology, and social sciences.

A modular microfluidic system can be used to quickly set up an individually adaptable microfluidic network by linking and delinking different functional building blocks. We present a convenient and reliable connection technology, which is based on magnets and casted O-ring-like structures leading to a sealed connection without the need of additional sealing materials. Based on an improved, previously presented fabrication technology, modular microfluidic polydimethylsiloxane (PDMS) blocks using a polyurethane (PU) mold, 3D printed acrylonitrile butadiene styrene (ABS) channel structures and a magnetic connection system in combination with a casted O-ring link, featuring various integration technologies have now been designed and experimentally evaluated. In particular, this paper will address the realization of directional valves, reciprocating pumps, finger pumps, directly-cast check- and Tesla-valves, fluidic flow sensors, fluidic mixers, commercial valves, and various sensors. By using different measurement setups, the feasibility of these devices is demonstrated. Moreover, limitations and issues encountered during fabrication as well as future work are discussed.

We report highly selective resonant emission from an aperiodic Tamm plasmon-polariton (TP) emitter featuring a targeted mid infrared emission wavelength in the region of 4.26 μm. This spectral region is of high interest in context with integrated CO2 absorption sensing. To the best of our knowledge, the measured thermal emission at peak temperatures up to 500 °C of TP emitters featuring a half-wavelength cavity have never been related to simulations in a satisfactory manner in terms of peak position, emission intensity and temperature behavior. The layer thicknesses quantified via scanning electron microscope (SEM) featured deviations from the targeted periodic configuration due to statistical variation of deposition and etching process. Simulations using the Transfer-Matrix Method suggested a higher Q-factor and higher peak emission associated with the obtained aperiodic configurations compared to the target periodic configuration featuring a quarter-wave stack (QWS). Although the improved spectral features of the aperiodic stack could not quite be resolved, the spectral position, the qualitative temperature behavior and the angular emission pattern in the range of 0° to 10° could be confirmed by Fourier-transform infrared (FTIR) spectroscopy.

Here we present an alternative technological approach to paper-based microfluidics that, to the best of our knowledge, has not been reported so far. Instead of defining fluid conducting paths by cutting fluidic structures, or by printing hydrophobic substances on paper, we prepare cellulose/polymer composites that can be printed additively on, in principle, arbitrarily shaped substrates and surfaces. In this way, with respect to geometry and properties, well defined fluid conducting structures based on cellulose can be realized, that can additionally be fully embedded in an organic surface coating. Moreover, the composite can, prior to the printing step, be doped with a functional component, which facilitates the realization of printed analytical devices using just a single base material and process technology. In this sense, the proposed technology can be seen as an alternative pathway to paper-based microfluidics, that may be attractive for specific niche-applications such as, for example, bio-chemical assays embedded in the surface of everyday necessities or commodities. Especially lateral flow immunoassays, pandemic-driven needed in large quantities, may embody a future application field of the presented technology.

In recent years, there has been a significant increase in research into silicon-based on-chip sensing. In this paper, a coupled cavity waveguide (CCW) based on a slab photonic crystal structure was designed for use as a label-free biosensor. The photonic crystal consisted of holes arranged in a triangular lattice. The incorporation of defects can be used to design sensor devices, which are highly sensitive to even slight alterations in the refractive index with a small quantity of analyte. The plane wave expansion method (PWE) was used to study the dispersion and profile of the CCW modes, and the finite difference time domain (FDTD) technique was used to study the transmission spectrum, quality factor, and sensitivity. We present an analysis of adiabatically coupling light into a coupled cavity waveguide. The results of the simulation indicated that a sensitivity of 203 nm/RIU and a quality factor of 13,360 could be achieved when the refractive indices were in the range of 1.33 to 1.55.

Concentration gradient generators are common components of microfluidic devices when specified mixing ratios have to be acquired. However, depending on their complexity, the creation of a suitable design is an elaborate task. Although approaches exist that derive such a design, they suffer from low flexibility and usability, which is why most concentration gradient generators are still mainly designed manually thus far—a time-consuming and error-prone task. To tackle this problem, we propose a method for the automatic design of tree-shaped concentration gradient generators and introduce a publicly available online tool that automatically generates a suitable design by adjusting the hydrodynamic resistances within the network. Moreover, the proposed tool is not only able to generate designs complying with user-defined requirements, such as mixing ratios, flow rates, and channel widths but also works for any number of outlets. Simulations using a Computational Fluid Dynamics (CFD) tool as well as evaluations on fabricated designs confirm the quality of the results obtained by the proposed tool.

This paper investigates the use of a miniaturized filter based on a triangular lattice of holes in a photonic crystal (PhC) slab. The plane wave expansion method (PWE) and finite-difference time-domain (FDTD) techniques were utilized to analyze the dispersion and transmission spectrum, as well as the quality factor and free spectral range (FSR) of the filter. A 3D simulation has demonstrated that for the designed filter, an FSR of more than 550 nm and a quality factor of 873 can be attained by adiabatically coupling light from a slab waveguide into a PhC waveguide. This work designs a filter structure that is implemented into the waveguide and is suitable for a fully integrated sensor. The small size of the device provides a strong potential for the realization of large arrays of independent filters on a single chip. The fully integrated character of this filter has further advantages such as reducing power loss in coupling light from sources to filters and also from filters to waveguides. The ease of fabrication is another benefit of completely integrating the filter.

Non-dispersive infrared (NDIR) absorption spectroscopy is a widespread approach to gas sensing due to its selectivity and conceptual simplicity. One of the main challenges towards the development of fully integrated NDIR sensors is the design and fabrication of microstructures, typically waveguides, that can combine high sensitivity with the ease of integrability of other sensor elements (sources, filters, detectors). Here, we investigate theoretically and experimentally a class of coupled strip-array (CSA) waveguides realized on a SiO2/Si3N4 platform with mass semiconductor fabrication processes. We demonstrate that this class of waveguides shows comparable sensitivity for a wide range of presented geometries, making it a very promising platform for satisfying multiple sensor and fabrication requirements without loss of performance.

In this work, we investigated the optimization of a plasmonic slot waveguide (PSWG) in the mid-IR region particularly for a representative wavelength of 4.26 µm, which is the absorption line of CO2 and thus particularly relevant for applications. We analysed the mode features associated with metal-dielectric-metal (MDM), dielectric-metal-dielectric (DMD), and truncated metal film (TMF) structures with respect to the considered PSWG. Subsequently, the mode features of the PSWG were considered based on what we outlined for MDM, DMD, and TMF structures. Furthermore, as confinement factor and propagation length are two crucial parameters for absorption sensing applications, we optimized the PSWG based on a figure of merit (FOM) defined as the product of the aforementioned quantities. To characterize the propagation length, the imaginary part of the effective mode index of a guided mode was considered, leading to a dimensionless FOM. Finally, we investigated the PSWG also for other wavelengths and identified particularly attractive wavelengths and geometries maximizing the FOM.

In this work, we present and analyze a design of an absorber–waveguide system combining a highly sensitive waveguide array concept with a resonant selective absorber. The waveguide part is composed of an array of coupled strip waveguides and is therefore called a coupled strip array (CSA). The CSA is then coupled to the end of a slab Tamm plasmon (STP-) resonator, which is composed of a quasicrystal-like reflector formed by the patterning of a silicon slab and an interfacing tungsten slab. The concept describes an emitter–waveguide or waveguide–detector system featuring selective plasmon-enhanced resonant absorption or emission. These are crucial properties for corresponding optical on-chip integrated devices in context with evanescent field absorption sensing in fluids or gases, for example. Thus, the concept comprises a valuable and more cost-effective alternative to quantum cascade lasers. We designed the lateral dimensions of the STP resonator via a simple quasi-crystal approach and achieved strong narrowband resonances (emittance and Q-factors up to 85% and 88, respectively) for different silicon thicknesses and substrate materials (air and silicon oxide). Moreover, we analyze and discuss the sensitivity of the complete emitter–waveguide system in dependence on the slab thickness. This reveals the crucial correlation between the expected sensitivity assigned to the absorber–waveguide system and field confinement within the silicon.

Photonic sensors that operate in the mid-infrared spectral range are an emerging field for photonic microsystems. In this paper, we present a photonic gas sensor concept based on silicon waveguides using infrared evanescent field absorption. The waveguides were specifically designed for CO2 sensing at a wavelength of λ = 4.26μm as possible application for the proposed sensor platform. The waveguide cross section as well as the substructure were investigated using finite-element simulations and the devised structures were fabricated using mass fabrication processes exclusively. In order to evaluate the potential for long interaction path lengths using polysilicon strip waveguides, a study on the intrinsic losses of polysilicon waveguides was conducted. The lowest intrinsic damping that was obtained for polysilicon strip waveguides was 3.98 dB/cm. Furthermore, the sensing capability of the devised waveguides was tested with quantitative CO2 measurements down to a concentration of 500 ppm CO2. From the quantitative measurements, the evanescent field ratio was estimated and was in the range between η = 14%-16%.

In this study, we investigate the potential of one-dimensional plasmonic grating structures to serve as a platform for, e.g., sensitive refractive index sensing. This is achieved by comparing numerical simulations to experimental results with respect to the excitation of surface plasmon polaritons (SPPs) in the mid-infrared region. The samples, silver-coated poly-silicon gratings, cover different grating depths in the range of 50 nm–375 nm. This variation of the depth, at a fixed grating geometry, allows the active tuning of the bandwidth of the SPP resonance according to the requirements of particular applications. The experimental setup employs a tunable quantum cascade laser (QCL) and allows the retrieval of angle-resolved experimental wavelength spectra to characterize the wavelength and angle dependence of the SPP resonance of the specular reflectance. The experimental results are in good agreement with the simulations. As a tendency, shallower gratings reveal narrower SPP resonances in reflection. In particular, we report on 2.9 nm full width at half maximum (FWHM) at a wavelength of 4.12 µm and a signal attenuation of 21%. According to a numerical investigation with respect to a change of the refractive index of the dielectric above the grating structure, a spectral shift of 4122nmRIU can be expected, which translates to a figure of merit (FOM) of about 1421 RIU−1. The fabrication of the suggested structures is performed on eight-inch silicon substrates, entirely accomplished within an industrial fabrication environment using standard microfabrication processes. This in turn represents a decisive step towards plasmonic sensor technologies suitable for semiconductor mass-production.

We report on a novel imaging system for large depth of field photoacoustic scanning macroscopy. Instead of commonly used piezoelectric transducers, fiber-optic based ultrasound detection is applied. The optical fibers are shaped into rings and mainly receive ultrasonic signals stemming from the ring symmetry axes. Four concentric fiber-optic rings with varying diameters are used in order to increase the image quality. Imaging artifacts, originating from the off-axis sensitivity of the rings, are reduced by coherence weighting. We discuss the working principle of the system and present experimental results on tissue mimicking phantoms. The lateral resolution is estimated to be below 200 μm at a depth of 1.5 cm and below 230 μm at a depth of 4.5 cm. The minimum detectable pressure is in the order of 3 Pa. The introduced method has the potential to provide larger imaging depths than acoustic resolution photoacoustic microscopy and an imaging resolution similar to that of photoacoustic computed tomography.

Plasmonic slot waveguides have attracted much attention due to the possibility of high light confinement, although they suffer from relatively high propagation loss originating from the presence of a metal. Although the tightly confined light in a small gap leads to a high confinement factor, which is crucial for sensing applications, the use of plasmonic guiding at the same time results in a low propagation length. Therefore, the consideration of a trade-off between the confinement factor and the propagation length is essential to optimize the waveguide geometries. Using silicon nitride as a platform as one of the most common material systems, we have investigated free-standing and asymmetric gold-based plasmonic slot waveguides designed for sensing applications. A new figure of merit (FOM) is introduced to optimize the waveguide geometries for a wavelength of 4.26 µm corresponding to the absorption peak of CO2, aiming at the enhancement of the confinement factor and propagation length simultaneously. For the free-standing structure, the achieved FOM is 274.6 corresponding to approximately 42% and 868 µm for confinement factor and propagation length, respectively. The FOM for the asymmetric structure shows a value of 70.1 which corresponds to 36% and 264 µm for confinement factor and propagation length, respectively.

The design and modeling of a curved shape photonic crystal taper consisting of Si rods integrated with a photonic crystal waveguide are presented. The waveguide is composed of a hexagonal lattice of Si rods and optimized for CO2 sensing based on absorption spectroscopy. We investigated two different approaches to design a taper for a photonic crystal waveguide in a hexagonal lattice of silicon rods. For the first approach (type 1), the taper consists of a square lattice taper followed by a lattice composed of a smooth transition from a square to a hexagonal lattice. In the second approach (type 2), the taper consists of a distorted hexagonal lattice. Different shapes, such as convex, concave, and linear, for the curvature of the taper were considered and investigated. The structure of the taper was improved to enhance the coupling efficiency up to 96% at a short taper length of 25 lattice periods. The finite-difference time-domain (FDTD) technique was used to study the transmission spectrum and the group index. The study proves the improvement of coupling using a curved shape taper. Controlling the group index along the taper could be further improved to enhance the coupling efficiency in a wider spectral range.

We investigate the concept of slab Tamm plasmons (STP) in regard to their properties as resonant absorber or emitter structures in the mid-infrared spectral region. In particular, we compare the selective absorption characteristics resulting from different choices of absorbing material, namely Ag, W, Mo or highly doped Si. We devised a simplified optimization procedure using finite element simulations for the calculation of the absorption together with the application of micro-genetic algorithm (GA) optimization. As characteristic for plasmonic structures, the specific choice of the metallic absorber material strongly determines the achievable quality factor (Q). We show that STP absorbers are able to mitigate the degradation of Q for less reflective metals or even non-metals such as doped silicon as plasmonic absorber material. Moreover, our results strongly indicate that the maximum achievable plasmon-enhanced absorption does not depend on the choice of the plasmonic material presuming an optimized configuration is obtained via the GA process. As a result, absorptances in the order of 50–80% could be achieved for any absorber material depending on the slab thickness (up to 1.1 µm) and a target resonance wavelength of 4.26 µm (CO2 absorption line). The proposed structures are compatible with modern semiconductor mass fabrication processes. At the same time, the optimization procedure allows us to choose the best plasmonic material for the corresponding application of the STP structure. Therefore, we believe that our results represent crucial advances towards corresponding integrated resonant absorber and thermal emitter components.

The design and modeling of a highly sensitive sensor based on a slot photonic crystal waveguide (slot-PCWG) is presented. The structure consists of cylindrical air rods drilled in a dielectric slab on a triangular lattice, which are filled with SiO2. The waveguide is formed by removing elements from the regular photonic crystal grid in a row, and embedding a slot in the center position. This concept allows for a vast enhancement of the evanescent field ratio, leading to a strong overlap between the field of the waveguide mode and the analyte. In the present work, we show that the sensitivity at the constant slab thickness of the slot-PCWG modes is greatly enhanced, up to a factor of 7.6 compared with the corresponding PCWG modes or Si-slab WGs. The finite-difference time-domain (FDTD) technique and plane wave expansion (PWE) methods were used to study the dispersion and profile of the PCWG mode. The simulation results show the potential of this design, which will be fabricated and tested in the following steps of the project.

Advanced fluid models relating viscosity and density to resonance frequency and quality factor of vibrating structures immersed in fluids are presented. The numerous established models which are ultimately all based on the same approximation are refined, such that the measurement range for viscosity can be extended. Based on the simple case of a vibrating cylinder and dimensional analysis, general models for arbitrary order of approximation are derived. Furthermore, methods for model parameter calibration and the inversion of the models to determine viscosity and/or density from measured resonance parameters are shown. One of the two presented fluid models is a viscosity-only model, where the parameters of it can be calibrated without knowledge of the fluid density. The models are demonstrated for a tuning fork-based commercial instrument, where maximum deviations between measured and reference viscosities of approximately ±0.5% in the viscosity range from 1.3 to 243 mPas could be achieved. It is demonstrated that these results show a clear improvement over the existing models.

A simple setup, which is suitable for parallel deposition of homogenous liquids with a precise volume (dosage), is presented. First, liquid is dispensed as an array of droplets onto a superhydrophobic dosage plate, featuring a 3 × 3 array of holes. The droplets rest on these holes and evaporate with time until they are small enough to pass through them to be used on the final target, where a precise amount of liquid is required. The system can be fabricated easily and operates in a highly parallel manner. The design of the superhydrophobic dosage plate can be adjusted, in terms of the hole positions and sizes, in order to meet different specifications. This makes the proposed system extremely flexible. The initial dispensed droplet mass is not significant, as the dosing takes place during the evaporation process, where the dosage is determined by the hole diameter. In order to speed up the evaporation process, microheaters are screen printed on the back side of the dosage plate. To characterize the temperature distribution caused by the microheaters, temperature sensors are screen printed on the top side of the dosage plate as well. Experimental data regarding the temperature sensors, the microheaters, and the performance of the setup are presented, and the improvement due to the heating of the dosage plate is assessed. A significant reduction of the total evaporation time due to the microheaters was observed. The improvement caused by the temperature increase was found to follow a power law. At a substrate temperature of 80 °C, the total evaporation time was reduced by about 79%.

We provide an overview of recent achievements using quartz tuning forks for sensing liquid viscosity and density. The benefits of using quartz crystal tuning forks (QTFs) over other sensors are discussed on the basis of physical arguments and issues arising in real world applications. The path to highly accurate and robust measurement systems is described and a recently devised system considering these findings is presented. The performance of the system is analyzed for applications such as the mixing ratio measurement of fuels, diesel-soot contamination for engine oil condition monitoring, and particle size characterization in suspensions. It is concluded that using properly designed systems enables a variety of applications in industry and research.

The detection of infrared radiation is of great interest for a wide range of applications, such as absorption sensing in the infrared spectral range. In this work, we present a CMOS compatible pyroelectric detector which was devised as a mid-infrared detector, comprising aluminium nitride (AlN) as the pyroelectric material and fabricated using semiconductor mass fabrication processes. To ensure thermal decoupling of the detector, the detectors are realized on a Si3N4/SiO2 membrane. The detectors have been tested at a wavelength close to the CO2 absorption region in the mid-infrared. Devices with various detector and membrane sizes were fabricated and the influence of these dimensions on the performance was investigated. The noise equivalent power of the first demonstrator devices connected to a readout circuit was measured to be as low as 5.3 × 10 − 9 W / Hz .

In this work we present the experimental characterization of a vertical-cavity enhanced resonant detector (VERD) optimized for detection in the mid-infrared. We demonstrate that the VERD shows a 7.1 times higher absorption and responsivity at 4.26 µm compared to a bare metal absorber. As such this design can be easily optimized and integrated to specifically enhance the absorption around the design wavelength.

Thermocouples classically consist of two metals or semiconductor components that are joined at one end, where temperature is measured. Carbon black is a low-cost semiconductor with a Seebeck coefficient that depends on the structure of the carbon particles. Different carbon black screen-printing inks generally exhibit different Seebeck coefficients, and two can therefore be combined to realize a thermocouple. In this work, we used a set of four different commercially available carbon-black screen-printing inks to print all-carbon-black thermocouples. The outputs of these thermocouples were characterized and their Seebeck coefficients determined. We found that the outputs of pure carbon-black thermocouples are reasonably stable, linear, and quantitatively comparable to those of commercially available R- or S-type thermocouples. It is thus possible to fabricate thermocouples by an easily scalable, cost-efficient process that combines two low-cost materials.

There is an increasing need for embedded sensors integrated into parts and mechanical components, which are often polymer based. We investigated a solution to print capacitive sensors onto elastic polymer sheets to monitor the physical contact with other adjacent components. The capacitive sensors are oriented in an array across the surface of said sheet to monitor the contact and the distance to a neighboring electrically conductive object. In the particularly investigated setup, the sheet is embedded between to metallic (aluminum) plates and the capacitance of the sensor is changed due to the compression of the dielectric material between the interdigital fingers constituting the sensor.

Integrated silicon photonics in the mid-infrared is a promising platform for cheap and miniaturized chemical sensors, including gas and/or liquid sensors for environmental monitoring and the consumer electronics market. One major challenge in integrated photonics is the design of an integrated detector sensitive enough to detect minimal changes in light intensity resulting from, for example, the absorption by the analyte. Further complexity arises from the need to fabricate such detectors at a high throughput with high requirements on fabrication tolerances. Here we analyze and compare the sensitivity of three different chip-integrated detectors at a wavelength of 4.17 µm, namely a resistance temperature detector (RTD), a diode and a vertical-cavity enhanced resonant detector (VERD).

Mid-infrared (MIR) on-chip sensing on Si has been a progressive topic of research in the recent years due to excitation of vibrational and rotational bands specific to materials in this range and their immunity against visible light and electromagnetic interferences. For on-chip applications, integration of all the optical components including the MIR source is crucial. In this work, we introduce a slab photonic crystal (PhC) thermal source where the birthplace and the filtering of the photons occur in the same region. Due to the forbidden frequency bands and high density of states in the band edge, it provides electric efficiency and filtering performance.

We present a valveless microfluidic pump utilizing an oscillating membrane made from a flexible printed circuit board. The microfluidic channel is fabricated by a 3D printing process and features diffuser/nozzle structures to obtain a directed flow; the flexible membrane is bonded to the channel. The membrane is actuated via Lorentz forces to accomplish out-of-plane motions and push the fluid through the channel. A permanent magnet provides the static magnetic field required for the actuation. The simple fabrication method can potentially be used for inexpensive mass fabrication for disposable devices.

Sensing of gases is a promising area for applications of photonic sensor devices that operate in the mid-infrared spectral range. We present a numerical investigation of slot waveguides for evanescent field sensing of CO2. The sensor platform is a poly-silicon slot waveguide on silicon dioxide, where both layers are deposited on a standard silicon substrate. The evanescent field ratio, which is a crucial parameter for the sensing performance of the waveguides, was determined and values as high as 42% were obtained.

In this paper, a hybrid optical guiding system based on low group velocity offered by photonic crystal (PhC) waveguides and vertical confinement as well as high field enhancement of. Surface lasmon polaritons (SPP) is proposed. We show that for efficient sensing, conventional two-dimensional PhC waveguides with finite height require a high aspect ratio in the order of 30 in order to efficiently confine the guiding mode. The fabrication of devices with such a high aspect ratio is considered too challenging and inefficient for mass production. By combining a PhC waveguide and SPPs, the proposed system efficiently confines the optical mode vertically while benefiting from the lateral confinement enabled by PhC structures. As a result, the required aspect ratio drops to about 4 making the fabrication in large scale feasible. This design provides strong light-matter interaction within small dimensions, which is beneficial for miniaturizing on-chip photonic sensors.

In this work we propose and evaluate a concept for a selective thermal emitter suitable for monolithic on-chip integration suitable for fabrication by conventional CMOS-compatible processes. The concept is based on our recently presented work on vertical-cavity enhanced resonant thermal emission (VERTE). Here we present the application of this concept to a slab waveguide structure, instead of depositing extended dielectric layers forming a one-dimensional photonic crystal. We optimize the dimension by certain design considerations and geneticalgorithm optimization and demonstrate effective absorbing/emitting properties (depending on different slab heights) of such a low-cost structure by exciting so-called optical Tamm-states on the metal-dielectric interface.

This work presents a thermocouple that is fully screen printed and consists exclusively of carbon black conductors. Two different carbon black inks were printed to form a thermocouple, which has been characterized regarding its output voltage. For reference, each of the carbon black inks was used in combination with gold to form two further thermocouples. These have also been characterized and the output voltage used to predict the output of the associated thermocouple consisting of pure carbon black conductors. The results have been compared with the measurement results and show that the output of the pure carbon black thermocouple is roughly 10% lower than expected.

This work deals with the realization of a fully printed thermocouple-array on a flexible substrate for condition monitoring applications. The thermocouple-array consisting of carbon black and silver was fabricated on PET-foil in a screen printing process and characterized up to a junction temperature of 150 °C. To ensure that no spurious voltages of the thermocouple occur due to deformations of the flexible substrate, the cross-sensitivity to deformation of the foil was investigated as well. Finally, as a test case, the temperature gradient of a plastic bar heated on a single end was measured with the thermocouple-array.

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.

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.

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.

In this work we investigate the coupling of radiation originating from a vertical-cavity enhanced thermal emitter (VERTE) into an optical waveguide, which can, for instance, act as a sensing element. We present full wave modelling results demonstrating highly efficient emitter-to-waveguide diffraction coupling at multiple angles using the previously designed VERTE together with a shallow blazed grating. It is shown that the coherent and dispersive thermal emission of the VERTE concept is well suited to achieve highly efficient and integrated mode coupling in the mid IR region.

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.

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.

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.

Electrowetting-on-Dielectrics (EWOD) can be used to build a device, where a polar fluid droplet gets actuated between two EWOD electrodes. In our setup, each electrode is located between a laser diode and an oppositely arranged photo diode. In that manner, the presence of a fluid droplet located above one certain electrode can be optically detected by means of this transmission setup. The droplet’s viscosity dependent switching time, i.e., the time it takes to move the droplet between these two electrodes can be obtained by a time difference measurement of both transmission signals. CFD simulations of the switching time, which depends on the droplet’s viscosity, and furthermore absorption simulations according to the Beer Lambert law have been carried out with DI water as a sample fluid. A low-cost and rapid fabrication method of the so called absorption EWOD (aEWOD) switch is reported and the fabricated EWOD stack is characterized with the aid of surface profilometry.

The last years showed an increased request for miniaturised, CMOS-compatible gas detectors. In contrast to sensors utilizing metal-oxide chemical interfaces, optical strategies are potentially faster and more robust. Recently we demonstrated CO2 detection by evanescent-wave absorption in the mid-infrared using a combination of an external laser source and silicon waveguides based on CMOS technology. We now go one step further and demonstrate the feasibility of detection of CO2 down to a concentration of 3% with a low-cost integrated thermal source. These results are promising for further technological developments towards on-chip mid-infrared photonic gas sensors, and new designs are currently devised to increase the yet relatively low sensitivity.