Karin Bauer

Resonant accelerometer with self-test

A new resonant accelerometer is presented consisting of a doubly clamped beam coupled to a seismic mass. The beam is thermally excited by an implanted resistor and its vibration is sensed piezoresistively. An acceleration which deflects the seismic mass leads to characteristic strains inside the resonator, shifting its resonance frequency. We studied the oscillation characteristics of the resonant beam. The non-linearity at high excitation amplitudes is treated theoretically and experimentally. Further, it is shown that the electrical and thermal cross-talk can be eliminated. The resonant sensing principle ensures a quasi-digital output signal, high sensitivity and a mechanical integrity test. Advanced automotive safety systems and x-by wire applications require a high reliability of the employed sensors. The sensor presented here allows an on-going self-test without any constructive changes of the sensor element. The self-test concept, we developed also finds applications in other sensors with resonant structures.

Silicon angular rate sensor for automotive applications with piezoelectric drive and piezoresistive read-out

In this work a silicon angular rate sensor for automotive applications with a new architecture is presented. It is based on the vibrating tuning fork principle with excitation direction of the tines perpendicular to the wafer surface. This arrangement allows the design of tines with significant inertial masses which lead to substantial signal. The oscillation of the tines is excited by a piezoelectric drive using an AlN thin film layer. The angular rate to be measured causes a torsional oscillation of the stem. The torsional amplitude is proportional to the angular rate and is measured by a piezoresistive read-out structure. We use silicon bulk micromachining based on a new twofold SOI-technique.

A novel PDMS based capacitive pressure sensor

In this paper, a capacitive pressure sensor for aeronautical applications is presented. The sensor mainly consists of a thin structured layer of Polydimethylsiloxane (PDMS) that is embedded between two metal films. In this application the structured PDMS layer is used as dielectric and as spring element. The optimal design of the sensor was determined using a finite element analysis. The technological implementation of the first test samples using microtechnology is shown. The static and dynamic characterization of the pressure sensor validates the high sensitivity and temporal resolution of the sensor.

Robust superelastic, metallic amplification unit for piezoelectric microactuators

In this work, a robust metallic amplification unit for piezoelectric microactuators is presented. The mechanism which is implemented with a sliced membrane structure made from a superelastic nickel titanium alloy is based on a mechanical lever in order to amplify the small piezoelectrically induced deformation. Therefore, increased stroke can be provided up to high frequencies. The fabrication process using laser ablation, the assembly process, the static and dynamic simulations and experimental measurements are reported. An amplification factor of 9 has been achieved for a specific load transmission point position. The dynamic response shows a quality factor of 25 at 11.97 kHz for the first mode. Compared to silicon, nickel titanium shows enhanced properties against failure and facilitates the integration process.

Numerical modeling of a MEMS actuator considering several magnetic force calculation methods

Purpose – The purpose of this paper is to investigate the accuracy of different force calculation methods and their impact on mechanical deformations. For this purpose, a micrometer scaled actuator is considered, which consists of a micro‐coil and of a permanent magnet (PM) embedded in a deformable elastomeric layer.Design/methodology/approach – For the magnetic field evaluation a hybrid numerical approach (finite element method/boundary element method (FEM/BEM) coupling and a FEM/BEM/Biot‐Savart approach) is used, whereas FEM is implemented for the mechanical deformation analysis. Furthermore, for the magneto‐mechanical coupling several force calculation methods, namely the Maxwell stress tensor, the virtual work approach and the equivalent magnetic sources methods, are considered and compared to each other and to laboratory measurements.Findings – The numerically evaluated magnetic forces and the measured ones are in good accordance with each other with respect to the normal force acting on the PM. Neve...

Tunable Membrane for Electromagnetic Devices Using Dielectric Elastomers

The amplitudes of miniaturized electromagnetic actuators are clearly enhanced if the eigenfrequencies of the membrane are used for actuation. However, the bandwidth for such operation is very limited. This can be overcome to some extent by the employment of membranes with electrically tunable stiffness. In this context we investigated membranes of dielectric elastomer materials and present experimental results on the ability to change their pre-strain to shift the eigenmodes to lower frequencies upon activation. Furthermore, the viscoelastic properties of an acrylic and a silicone membrane are investigated and compared to dynamic experiments. The parameters for the stiffness and viscoelasticity are derived from the experimental creep data and incorporated in a hyperelastic material model. Using this adapted stress-strain relationship the membrane behavior over time can be evaluated for different loading as well as pre-strain conditions.

Aerospace applications of mass market MEMS products

Aerospace applications of MEMS products, originally developed for automotive mass markets, are discussed. Various sensor examples with a high dual use potential are presented: inertial sensing, flow and gas sensing, robust micro sensors including SiC- and GaN-based devices, as well as first approaches towards flexible and distributed microsystems. In Europe the automotive industry is one of the main MEMS market drivers, simply because of the sheer size of this market and Europes strong position in this industrial field. Main MEMS activities are development and integration of vehicle dynamics sensing systems, passenger safety and navigation systems, air and fuel intake systems, as well as sensor systems for exhaust gas after treatment and climate control. Benefits on the customer side are increased safety, passenger comfort and reduced fuel consumption. Benefits on the manufacturers side are increased sub-system integration, modularity and reduced production cost. In the future the aerospace industry is likely to benefit from the introduction of micro-systems for the same reasons as the automotive industry. Interests of the aerospace industry are increasing safety and reliability of airplane operation, health and state monitoring of fuselage and airplane subsystems as well as improving service and maintenance procedures. In comparison to automotive applications, the numbers of devices needed is likely to be much smaller, however, new challenges arise in so far as distributed sensing and actuating microsystems will be needed. The idea is to identify and to exploit synergies between automotive mass market MEMS applications and lower-volume aerospace ones. The effort necessary to meet aerospace requirements and the extent of necessary trade-offs in customizing automotive MEMS is addressed considering the above-mentioned examples.