The increasing trend of 3D integration in the electronic and opto-electronic devices calls for new tools and platforms for their fatigue analysis and reliability assessments. Due to the complexity of the problem arising from small-scale samples and the need for integration of samples in the test platform and the relevant measurement requirements and monitoring of damage development, there is still no established method available for stress testing of micro- and nano-structures. In this paper, we propose a two-port send and receive surface acoustic wave (SAW) device for stress loading in the ultra-high-cycle fatigue (UHCF) regime of microstructures that can potentially be fabricated on the device surface. The SAWs propagate on the surface of a bridge, which provide a secondary MEMS resonator. The pair of the SAW transducers, fabricated on the two ends of the bridge, have dual function. One of them loads the structure under test and the other monitors damage development within the sample, which manifests itself as a phase shift in the SAWs propagating on the bridge. This stress-testing platform consists of an AlN piezoelectric layer on top of a Silicon substrate, which is, via MEMS processing, etched to release the movable bridge. This paper evaluates the properties of the designed platform via simulation and measurement.

This paper reports a new design of a fiber optic sensor probe for minimally invasive pressure and temperature measurement. The presented concept enables the integration of multiple sensing points into a medical diagnostic probe for spatially distributed and simultaneous pressure sensing. A sensing point consists of a Fiber Bragg Grating (FBG), which is locally covered by a glass capillary. A side wall hole in the capillary transfers pressure into bending of the fiber. Asymmetric tapering of the fiber cladding along the FBG enables the strain of the fiber core. This structuring is necessary in order to shift the neutral axis of the fiber whereby bending results in measurable strain of the FBG. An outer sensing point diameter of $500 \mu \mathrm{m}$ enables the probe's transfer through catheters to reach the place of targeted diagnostics inside the vascular system. The novel measurement system consisting out of a structured glass fiber and glass capillaries was fabricated and tested.

In this paper, a simple yet effective model order reduction technique for modeling arbitrary piezoelectric component using the finite element method (FEM), is developed and tested. The reduced order model (ROM) is derived from well known and efficient reducing order modeling techniques. The mechanical part of the coupled electro-mechanical system is reduced using the modal superposition technique. Then, the inner nodes of the electric parts are reduced using static condensation and the electrode nodes a boundled to form only one degree of freedom per electrode. The reduced model is tested on the model of a piezoelectric cantilever with one electrode, in harmonic and transient analysis, with different modes of excitation, namely external force excitation, voltage excitation and base acceleration. Additionally it could be shown, that the ROM can be improved for small mode bases by extending the mode base with an orthogonalized static mode.

In this paper we present an experimental study of a laser optical distance sensors for the use in respiration sensing. In different scenarios like sleeping apnea, desk situation, car driving situation the breathing rate measurement behavior of this contactless method is characterized with respect to a temperature sensorbased reference method with direct contact to the nose. A signal processing method based on B-spline fitting was developed and we found good agreement with the reference measurements. Hence, we were able to show that within a distance of 120 cm it is possible to use a optical distance sensor which is designed for focusing purposes in dark light conditions as a medical sensor to determine the respiration rate.

Silicon (Si)-based, multiple Fourier-horn ultrasonic nebulizer (MFHUN) was fabricated through femtosecond laser cutting of Si to reduce the preparation time of samples and to study the effectiveness of this manufacturing process for producing Si-resonating nebulizers. The geometrical characterization of the structures showed tolerances in the dimensions. These tolerances affected the efficient positioning of the liquid at the tip of the horn. Furthermore, the effect of the dimensional variations on the mechanical functionality increased with minimizing the size of the resonator. By managing the flow rate of the liquid fed to the nebulizer and adjusting the frequency of the structure when in contact with the liquid, atomization occurs.

Ultrasonic nebulizers have the ability to break liquid medicine into aerosols by generating standing waves at the surface of the liquid. Multi Fourier-horn ultrasonic nebulizer (MFHUN) was employed to atomize liquid by ultrasonic oscillation. UV femtosecond laser was used to structure the resonator layout on silicon wafer in order to fabricate MFHUN with reduced fabrication time and complexity. Piezoelectric transducer was manually placed on the resonator to excite longitudinal oscillation. The samples were characterized to investigate the effect of the fabrication process and the piezoelectric transducer placement tolerances on the ability of MFHUN to atomize liquid. The results showed that placing the piezoelectric transducer closer to the center of the drive section is required to increase the amplitude of the oscillation. The thickness of the adhesive layer beneath the piezoelectric transducer should not exceed 30 mu m. Structures which showed amplitudes higher than the instability threshold atomized deionized water successfully.

This paper reports a fiber-optic pressure sensor probe with multiple measuring points for simultaneous time and location resolved pressure sensing.Two different measurement principles were combined to a hybrid sensor which allows sensing before, along and after stenosis at the same time.At the tip a Fabry-Pérot-Interferometer is formed by a reflective multilayer membrane of a pressure sensor chip and an optical fiber.The sealed cavity provides absolute pressure sensing.20 millimeter below the fiber tip, six Fiber Bragg Gratings are integrated.The first Fiber Bragg Grating is reinforced for additional temperature sensing.The five following Fiber Bragg Gratings act as sensing array for continuous pressure monitoring.The sensing components are coated with a silicone mantle of 1.5 mm diameter.The complete signal evaluation is done with a Fiber Bragg Grating interrogation device.The in-vivo trial with a pig allowed the determination of pressure relations and pulse wave velocity in the lumbar spinal canal.A stenosis was simulated by inflating a balloon inserted in parallel to the probe.For the first time, lumbar spinal stenosis was diagnosed by the measurement technique of the presented probe.This is a new diagnostic approach to verify the indication for surgery.First, mechanical structure aspects and the evaluation technique of our probe is described.Then, experimental results of the in-vivo trial are presented.From these results the possibility of implementing a new diagnostic method for the frequent lumbar spinal stenosis disease with claudication using to our sensing system could be derived.

This paper reports a Silicon (Si)-based, multiple Fourier-horn ultrasonic nebulizer (MFHUN) which was fabricated through femtosecond laser structuring of Si to reduce sample preparation time and study the effectiveness of this manufacturing process for Si-resonating structures. The system showed better transfer characteristics than what is reported in literature, giving the presented nebulizer the advantage of higher power efficiency and lower individual sample preparation costs.

Electrowetting on Dielectrics (EWOD) is an important method of manipulating discrete fluid droplets in digital microfluidic systems. In this paper, a simply implemented low cost EWOD system based on printed circuit board was built and tested. The form of the triple contact line (TCL) connecting the droplet with solid surface and ambient surrounding was simulated using a numerical simulation tool called Surface Evolver (SE). Different electrode patterns and sizes were designed and measurements were conducted using deionized (DI) water mixed with Sodium Chloride (NaCl) as fluidic samples. Polytetrafluoroethylene (PTFE), Parylene C and Parafilm were used as dielectric layers separating microfluidic droplets from the electrodes surface. In addition, these materials provided a hydrophobic surface leading to an increase in the initial contact angle of the droplets. The actuation voltage of the system varied between 40 V and 183 V depending on the electrodes pattern and size and the volume of the droplets. The smoothness and regularity of the PCB and hydrophobic surfaces had a major effect on decreasing the actuation voltage of the system.

This paper introduces a pressure sensor catheter with two different measurement principles. A Fabry-Perot- Interferometer at the fiber tip is formed by a reflective multilayer membrane of a pressure sensor chip. The cavity provides absolute pressure sensing. 20 millimeter before the fiber tip a Fiber Bragg Grating is integrated for additional temperature sensing. The sensing components are completely coated with a silicone mantle of 2 mm diameter. The signal evaluation is both done with a Fiber Bragg Grating interrogation device. First, mechanical structure aspects of the manufactured fiber-optic hybrid sensor as well as the sensing principle is described. Then, experimental results, including quantification and separation of pressure and temperature sensitivity are presented. Out of these characteristics the possibility for absolute pressure sensing with temperature compensation for the application as a pressure sensor catheter is confirmed.

This paper introduces an absolute pressure sensor based on an extrinsic fiber-optic Fabry-Perot-Interferometer molded into a silicone catheter. The interferometer principle is formed between the tip of an optical fiber and a reflective multilayer membrane containing aluminum nitride. The signal analysis is done by a Fiber Bragg Grating interrogation device. First, the optical sensing principle as pressure sensor in an invasive catheter with a diameter of 1 mm is described. Then, the dependence of the optical signal on changes of hydrostatic pressure and ambient temperature is shown. Out of these characteristics it was possible to evaluate the pressure sensor catheter for potential application in the human vascular system.

The mechanics of medical endoscopes have not fundamentally changed over the last 40 years. Most endoscopes are manually operated through Bowden cables to control the head of the device, which is known to have major limitations. We propose a shape memory alloy actuated setup to enable computer-aided control. Before a complex manufacturing of porotypes is established, the design needs to be evaluated for feasibility. In this work, an efficient design approach is highlighted, where the thermal properties for an asymmetric cross-section of the endoscope is modeled with finite elements in the transient elecfro-thermo-mechanical domain and the results are then transferred to a network model to efficiently evaluate operation procedures. With the proposed model approach, a fast but detailed description is established which focuses on the optimization of dimensional and material parameters and models efficiently the impact of complex dynamic operating regimes.

This paper analyzes wavelength drifts of a Fiber Bragg Grating interrogation device due to variations in different environmental conditions. First, the thermal induced wavelength shifts of the Fiber Bragg Gratings were abstracted. Then, it was possible to investigate the correlations between wavelength drifts and A) temperature of the interrogation device, B) air pressure, and C) static inclination of the interrogation device. Out of these three factors, unsteady temperature of the interrogation device proved to be the main reason for wavelength drift in our setup. Variations in air pressure were the second most important factor, whereas the static inclination of the interrogation device showed the least but still considerable effect on wavelength drifts. A temperature stabilization of the device housing temperature is introduced and a software-based offsetting of the air pressure is discussed.

We investigate the influence of parametric excitations on MEMS vibration energy harvesters for energy autonomous sensor systems. In Industry 4.0 (or Industrial IoT) applications, interconnected sensors provide a means of data acquisition for automated control of the manufacturing process. Ensuring a continuous energy supply to the sensors is essential for their reliable operation. Manufacturing machines usually display a wide spectrum of vibration frequencies which needs to be covered by an array of harvester substructures in order to maintain the desired output level. We show that mechanical structures designed to implement a Helmholtz-Duffing oscillator have an increased bandwidth by exploiting several orders of parametric resonances. In contrast to concepts implementing parametric amplification in a multi-mode scenario, our concept is based on a single mechanical mode. Therefore, it is more robust against fabrication tolerances as the relevant multi-mode resonance conditions do not need to be matched on the level of single chips. Using exact transient simulations and semi-analytic models to showcase the relation of the Helmholtz-Duffing oscillator to the damped and driven Mathieu equation, we show that parametric resonances highly increase the bandwidth of the output power whenever high Helmholtz nonlinearities are present. To achieve the required nonlinearities, we suggest nonlinear stress-strain curves and we propose to achieve such nonlinearities through field-induced striction by magneto- or electrostriction. In contrast to existing approaches, where external fields are harvested using strictive effects, we employ external fields that manipulate the effective Young's modulus to achieve parametric excitations in a mechanical oscillator. Thus, we are able to propose a novel energy harvester concept incorporating strictive materials that exploits the effects of parametric excitations to achieve broadband vibrational energy harvesting. (C) 2020 Elsevier Ltd. All rights reserved.

Thin metal layers, especially those made of copper, are omnipresent in today’s packaging applications as e.g. RDL structures, conductor traces on flexible and stretchable substrates, chip finishes or terminal metallisation, serving electrical, thermal or mechanical purposes. As Cu is very process and size dependent, especially thin layers will display residual stresses, textures, inhomogeneity or damage, all of which determine its properties as e.g. elastic and (visco-)plastic behaviour, fatigue resistance etc. As thin layers are extremely difficult to handle, a characterisation method to examine thermo-mechanical properties of thin metal films within a specimen centred approach (no transfer, no clamping of samples, customised testing equipment) is proposed based on dynamic thin film membrane excitation and resonance spectrum analysis by a simple, fast and low cost method involving electrodynamic excitation. The method produces very good accuracy when benchmarked against scanning laser Doppler vibrometry.

Sensors and actuators based on resonant microelectromechanical systems (MEMS), such as scanning micromirrors, are well established in automotive and consumer products. As the areas of application broaden toward highly automated driving and augmented reality, the performance requirements for the MEMS are also increasing. Devices outside of the performance specifications have to be rejected, which is costly due to the high processing times of MEMS technologies. In particular, nonlinear system behavior is often found to cause unexpected device failure or performance issues. Thus, accurate simulation or rather system models, which account for nonlinear sensor dynamics, can not only increase process yield, but, more importantly, also lead to a comprehensive understanding of the underlying physics and, consequently, to improved MEMS design. In a recent work by Nabholz et al. “Spontaneous parametric down-conversion induced by non-degenerate three-wave mixing in a scanning MEMS micro mirror” (Sci. Rep., vol. 9, 2019, Art. no. 3997), we have studied the possibility of a rather drastic device failure induced by nonlinearities on the example of a resonant scanning MEMS micromirror. On the level of a few selected chips, we have carefully measured the complex nonlinear system behavior and modeled it by a nonlinear mode-coupling phenomenon known as spontaneous parametric downconversion (SPDC). The most intriguing feature of SPDC is the sudden change from a rather linear to a highly nonlinear system behavior at the threshold or rather critical oscillation amplitude of the mirror. However, the threshold only lies within the range of the mirror's operational amplitude if certain frequency resonance conditions regarding the modes of the mechanical structure are met. As a direct consequence, the critical amplitude strongly depends on the frequency spectrum of the MEMS design, which, in turn, is largely influenced by fabrication imperfections. In this letter, we validate the dependence of the critical amplitude on the resonance condition by measuring it for over 600 micromirrors on wafer level. Our work does not only validate the theory of SPDC with measurements on such a large scale but also demonstrates modeling strategies, which are essential for MEMS product design.

Scanning micro-mirror actuators are silicon-based oscillatory micro-electro-mechanical systems (MEMS). They enable laser distance measurements for automotive LIDAR applications as well as projection modules for the consumer market. For MEMS applications, the geometric structure is typically designed to serve a number of functional requirements. Most importantly, the mode spectrum contains a single high-Q mode, the drive mode, which per design is expected to yield the only resonantly excited geometric motion during operation. Yet here, we report on the observation of a resonant three-mode excitation via a process known as spontaneous parametric down-conversion. We show that this phenomenon, most extensively studied in the field of nonlinear optics, originates from three-wave coupling induced by geometric nonlinearities. In combination with further Duffing-type nonlinearities, the micro mirror displays a variety of nonlinear dynamical behaviour ranging from stationary state bifurcations to dynamical instabilities observable via amplitude modulations. We are able to explain and emulate all experimental observations using a single fundamental model. In particular, our analysis allows us to understand the conditions for the onset of three-wave down-conversion which if not accounted for in the design of the MEMS structure, can have drastic impact on its functionality even leading to fracture.

This article presents an accurate, automated and general method for reduced order modeling (ROM) of squeeze film damping including frequency depending mode-interaction effects for arbitrary plate geometries. The method is based on several subspace projection steps using a non-orthogonal vector basis of the Reynolds equation, so-called non-orthogonal subspace projection approach. The resulting model is compatible with any model of mechanical MEMS structure projected onto modal subspace. The interaction between mechanical modes due to i.e. asymmetric gaps or package warping is automatically included in this method.

The requirements pertaining to the reliability and accuracy of micro-electromechanical gyroscopic sensors are increasing, as systems for vehicle localization emerge as an enabling factor for autonomous driving. Since micro-electromechanical systems (MEMS) became a mature technology, the modelling techniques used for predicting their behaviour expanded from mostly linear approaches to include nonlinear dynamic effects. This leads to an increased understanding of the various nonlinear phenomena that limit the performance of MEMS sensors. In this work, we develop a model of two nonlinearly coupled mechanical modes and employ it to explain measured drive mode instabilities in MEMS gyroscopes. Due to 3:1 internal resonance between the drive mode and a parasitic mode, energy transfer within the conservative system occurs. From measurements of amplitude response curves showing hysteresis effects, we extract all nonlinear system parameters and conclude that the steady-state model needs to be expanded by a transient simulation in order to fully explain the measured system behaviour.

Sensors and actuators based on resonant micro-electro-mechanical systems (MEMS), such as scanning micro mirrors, are well-established in automotive and consumer products. As the areas of application broaden towards highly automated driving and augmented reality, the performance requirements for the MEMS are also increasing. In particular, nonlinear system behavior is often found to cause unexpected performance issues. Thus, accurate system models which account for nonlinear sensor dynamics can not only increase process yield, but more importantly, lead to a comprehensive understanding of the underlying physics and consequently to improved MEMS design. In a recent work (1, see comments below), we have studied the possibility of a rather drastic device failure induced by nonlinearities on the example of a resonant scanning MEMS micro mirror. On the level of a few selected chips, we have carefully measured the complex nonlinear system behavior and modeled it by a mode-coupling phenomenon known as spontaneous parametric down-conversion (SPDC). The most intriguing feature of SPDC is the sudden change from a rather linear to a highly nonlinear system behavior at the critical oscillation amplitude of the mirror. However, the threshold only lies within the range of the mirrors operational amplitude, if certain frequency resonance conditions regarding the modes of the mechanical structure are met. As a direct consequence, the critical amplitude strongly depends on the frequency spectrum of the MEMS design which in turn is largely influenced by fabrication imperfections. In this work, we validate the dependence of the critical amplitude on the resonance condition by measuring it for over 600 micro mirrors on wafer-level. Our work does not only validate the theory of SPDC with measurements on such a large scale, but also demonstrates modeling strategies which are essential for MEMS product design.