This contribution describes an micro-opto-electro-mechanical system transducer with a well defined inherent non-linear transfer behavior and its impact on the quantification of static and dynamic displacements in a vibrating measurement mode. The transducer's output signal is proportional to a light-flux that is modulated by two overlapping aperture arrays. One of these arrays is deposited on a fixed glass cover while the other one is etched into a moveable seismic mass of a silicon micro-electro-mechanical chip. The non-linear transfer characteristic is achieved by pairing triangularly shaped apertures with rectangular ones. The seismic mass is actuated by a mechanical shaker unit and the resulting first and second harmonics of the output signal are recorded with lock-in amplifiers. These harmonics contain information about both the static displacement and the vibration amplitude of the seismic mass. The presented method was tested with a proof-of -concept device and first measurement results exhibit a static displacement resolution of 3.67 nm which is a slight improvement compared to DC measurement approaches exhibiting a resolution of 5.39 nm. Furthermore, a inclination sensor was built employing this vibrating measurement approach showing that the resolution was improved at least by an factor of three. i3/4 (C) 2017 Elsevier B.V. All rights reserved.

This contribution describes an opto-mechanical transducer with a non-linear transfer behaviour and its impact on the quantification of static and dynamic displacements in a vibrating measurement mode. The device's output signal is proportional to a lightflux that is modulated by two overlapping gratings. One of the gratings is deposited on a fixed glass cover while the other one is etched into a moveable seismic mass of a Si MEMS chip. The non-linear transfer characteristic is achieved by paring a triangular grating with a rectangular one. The mass is actuated by a mechanical shaker unit and the resulting 1st and 2nd harmonic of the output signal are recorded with Lock-In amplifiers. These harmonics contain information about the static displacement and the vibration amplitude of the mass. The presented method allows for a precise measerement of the static displacement with an error of ±0.017% compared to DC measurements exhibiting an error of ±0.066%.

In the past years, researches demonstrated the great potential of novel MOEMS vibration sensors regarding their displacement resolution and sensitivity. The authors show that it is possible to further enhance the dynamic range of these sensors. This is achieved by utilizing feedback mechanisms such as electrostatic actuation without any crosstalk to the optical readout. Furthermore, this allows for canceling out unwanted ringing. The discussed proof of concept prototypes incorporate two electrostatic comb-drive actuators. They enable the seismic mass to reset along the main oscillation axes over a path of several microns and up to the resonance frequency of 400 Hz. It was proven that there is no unwanted crosstalk between the actuation and the position readout. The MOEMS readout features a sensitivity of approximately 200 mV/μm with a noise equivalent displacement of 35 pm/√Hz.

This contribution describes a novel magnetic field transducer based on a MOEMS (micro-opto-electo-mechanical-system) readout. The silicon structure is deflected in a static magnetic field due to the Lorentz force This deflection is measured with the mechano-optical transducer [1]. The transduction method is based on the modulation of a perpendicularly introduced light flux. The modulation is achieved by one movable optical grating on a suspended structure and a second grating that is fixed to the foundation of the system. The proof-of-concept device was characterized at ambient pressure exhibiting a sensitivity of 200 mV/T. The noise equivalent magnetic resolution limit is 1.5 T/vHz which results mainly from the opto-electrical evaluation circuit. By introducing advanced opto-electronics and using improved MEMS devices it is feasible to reduce this value down to 1 nT/vHz which is equivalent to the fundamental mechanical Brownian noise limit. (C) 2016 The Authors. Published by Elsevier Ltd.

Key aspects of piezoelectric actuation of circular-crested guided elastic waves (ccGEW) in homogeneous plates are investigated experimentally and studied with finite element analysis (FEA). The specific implementation of fiber-optic strain transduction presented offers virtually distortion-free conversion of radial GEW displacements with a flat transfer characteristic and negligible interference with the wave to be studied. Due to a concentric arrangement of actuator disc, fiber-optic transducer and circular plate, a shuttling GEW pulse packet can be retained over an exceptionally long period of time. Hence accurate long term measurements of the excited surface strain in response to piezoelectrical actuation becomes feasible for specific GEW modes. Presumably, traveling-wave-like behavior of compressional ccGEW pulses including the transition of converging into expanding wave packets around the symmetry axis is observed for the first time. Minor deviations between FEA predictions and measurement results can be traced back to imperfections of the experimental setup or inaccurate material data. The presented approach may be used for thorough characterization of piezoelectric disc actuators and studies of ccGEW propagation in various homogeneous materials. (C) 2016 Elsevier B.V. All rights reserved.

Air conditioning systems need permanent monitoring of the mass and energy flows in air ducts to assess their proper operation and detect and correct changes that may occur with time. This is a prerequisite for optimization in terms of energy efficiency. Such distributed monitoring systems require low-cost and robust flow sensors that must not be extremely precise, but give a good indication of the flow distribution within the air conditioning system. In this paper we present a novel flow sensor based on thick-film thermopiles deposited by silk-screen-printing on a plastic carrier. The flexible printed thermopile transducer was characterised in a flow channel to demonstrate the feasibility of the technology for air conditioning systems. The transducer exhibits a strictly increasing behaviour with increasing flow velocity, which is in good agreement to FEM simulations.

Measurement of air flows is an important task in many process monitoring systems. In applications like control of ventilation and air conditioning systems, robustness, ease of use, and cost are important issues calling for simple and effective sensor design. This paper investigates the use of commercial-off-the-shelf printed circuit board technologies for the fabrication of calorimetric flow sensors. Such sensors are known to be sensitive when being implemented using thin-film technology. The paper reviews the operation principle of thermal flow sensors and their performance in micromachined silicon technology for comparison. Subsequently, a similar design is introduced where heating and temperature sensing elements are made from standard copper traces on a flexible PCB substrate. Simulation studies demonstrate the basic viability of this approach, even if it might entail some performance penalties. First experimental data of sensor prototypes show that the repeatability of the PCB manufacturing processes is basically sufficient for using copper traces as sensors, but leaves also room for future improvement in both technology and sensor design.

Inclination sensors are essential elements in many different fields of application such as navigation, metrology, geodetics, geoscience, as well as in the consumer market. In general, for high precision navigation. The sensor's resolution is one of the key parameters to improve the performance and to open up new areas of applications. The implementation of a miniaturized optical readout is one of the most promising ways to accomplish this goal. This paper discusses the principle of a novel inclination sensor along with obtained measurements of two prototypes with different mechanical parameters. The achieved sensitivity is 0.044 V/° resulting in an angular resolution of 0.0051°.

The majority of MEMS vibration sensors requires relatively high resonance frequencies of several kilohertz to avoid mechanical contact of moving parts such as electrode plates. In contrast to that, our hybrid micro-opto-electro- mechanical system (MOEMS) enables sensor applications at low frequencies. This work describes a distinct MOEMS featuring extremely low resonance frequencies of below 200Hz. It is operated ambient air without closed loop feed- back, extensive electronics and cooling. Due to the soft suspension of the micro-mechanical sub-system the funda- mental limit, the Brownian noise floor, is reached. The resulting noise equivalent displacement for frequencies above the resonance is 1.9 pm/ √Hz, which is equivalent to 0.29μg/ √Hz below the resonance. We describe the design space for sensors with further enhanced sensitivity and resonance frequencies far below 100Hz.

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

The majority of MEMS vibration sensors requires relatively high resonance frequencies of several kHz to avoid mechanical contact of moving parts such as plates or electrodes. In contrast to that, the presented hybrid micro-opto-electro-mechanical system (MOEMS) principle enables displacement sensors applicable at low frequencies. This work describes a distinct MOEMS featuring extremely low resonance frequencies of below 200 Hz. The discussed sensor operates in ambient air without closed loop feedback, extensive electronics, or cooling. Due to the soft suspension of the micro-mechanical sub-system, the fundamental limit, i.e., the Brownian noise floor, is reached for frequencies below the resonance frequency. The related noise equivalent displacement is 1.9 pm/√Hz. Above resonance, the measured noise of 0.86 pm/√Hz, which is equivalent to 0.29 μg/√Hz is dominated by the noise of the electrical components. Also a discussion about feasible improvements regarding the sensitivity and pushing the mechanical resonance frequency below 100 Hz is given.

The performance of our previously devised thermal multi-parameter wind sensor for gaseous fluids is noticeably influenced by the thermal heat shunt induced by the thin-film membrane where heating and temperature sensing elements are embedded. Consequently, reliable values for the thermal parameters of the thin-film membrane are mandatory for their design and characterization. We present a new method to determine the thermal conductivity, thermal diffusivity, and average spectral emissivity of the thin-film membrane. Compared to commonly used measurement techniques for these thermal thin-film parameters, our method does not require custom-built specimens, i. e., the results can be obtained from transient excess temperature measurements carried out directly on the wind sensor device. We describe the theoretical background of this method, provide an efficient analytical model for the data evaluation including its validation by computer numerical analyses, and showcase sample measurements on multi-layer SixNy-SiO2 thin films.

We present a development study of a robust inter-ferometric transducer for elastic deformations excited by mechanical vibrations. In contrast to known methods using piezoelectric, fiber Bragg grating and Fabry-Perot interferometer sensors, we deal with pronounced spatially distributed transduction based on arbitrary shaped fiber segments like fiber optic coils. This approach allows, e.g., an omnidirectional sensitivity characteristic in case of circular shaped fiber segments, and offers a high immunity against electromagnetic interferences. Omnidirectional transducer characteristics are beneficial for vibration detection on complex shaped bodies. A finite element model simulation (FEM) is used to demonstrate the detection capacity for Lamb waves propagating in a carbon fiber reinforced polymer (CFRP) matrix.

Light flux modulators based on micro-opto-electro-mechanical systems (MOEMS) enable high resolution displacement based inertial sensors. The three major noise sources for such devices are the Brownian noise originating from the surrounding air, the noise emerging from the optoelectronic detector and the noise contributed by the amplifier circuit. To unveil the resolution limiting mechanisms, we investigated the performance of a transimpedance amplifier in relation to opto-electrical receivers. To verify this approach, a SPICE simulation model including all noise sources was set up and compared with measurements. The experimental data suggest that the noise of the utilized transimpedance amplifier can be optimized for a given dynamic resistance and noise current of a given photoreceiver.

An often reported problem during production and operation of silicon MEMS is stiction. It describes the sticking of movable MEMS parts to surrounding structures. The probability of the occurrence of stiction is linked to the surface energy of the MEMS. Self assembling monolayers can be used to reduce the surface energy and therefore the probability of stiction. These monolayers have to resist high temperatures up to 400°C to be compatible with various micro-production processes, e.g., eutectic bonding. Several groups tried to coat such monolayers with different success and results. One problem is the instability of the coating method due to water contaminations of the coating solution. To circumvent this error source, an experimental setup was designed and built up to minimize the water content of the monolayer solvent and ensures reproducible conditions during the coating process. The required set of liquids is piped through a system of valves and tubes to rinse a trench with a silicon die. To avoid contamination of the liquids with water, the setup is partly placed in a box flushed with nitrogen. With this experimental setup, the surface energy γs of the MEMS structures had been reduced from 18.1 mJ/m2 to 33.1 μJ/m2 and 36.6 μJ/m2 for FDTS and DDMS, respectively.

In this work a competitive OMEMS (optical micro electromechanical system) readout for displacement is presented. Congruent positioned gratings modulate the light flux caused by a relative in-plane displacement. As demonstrator, an inertial sensor is used. Consisting of a Si-chip bearing a perforated and spring suspended MEMS structure (seismic mass), which is bonded with SU8 to a glass chip featuring vapor deposited Cr-pattern. Both form a partially transparent sandwich structure where the transmittance depends on the position of the suspended Si mass. The modulated light flux is generated and detected by an SMD-LED and a phototransistor at the top and bottom side of the sandwich structure, respectively. First results show a high sensitivity of 21 mV/nm displacement of the seismic mass featuring a noise level of about 200 pm/√Hz.