Dennis Hohlfeld

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A recently introduced set up of capacitive micromachined ultrasonic transducers (cMUT) combines a conductive membrane above a structured sacrificial layer. All previous approaches either require an additional metallic electrode or do not possess a structured sacrificial layer and, consequently, may make exact adjustment of the membrane dimensions difficult.(More)
In this paper we present a new possibility to determine unknown material thermal properties based on experimental measurements. We use a parametrized finite element (FE) model and fit it to a measured transient curve. Using brute force, this process requires an extensive computational time. However, it is possible to speed it up significantly by using model(More)
In this contribution we present system-level modeling and simulation results for an electrostatic energy harvester with electrically adjustable operation frequency. The device is able to convert mechanical energy present in ambient vibrations into electrical energy. The energy is stored by charging a capacitor and available at constant voltage. The lumped(More)
In this paper we present a novel approach to determine material thermal properties of thin film materials. As a testcase we have chosen silicon nitride employed in a micro-hotplate structure. We use ANSYS to build a three-dimensional finite element (FE) model of the test structure, which considers heat conduction and convection effects. It is further(More)
This paper proposes a novel modeling methodology for MEMS-based piezoelectric vibration energy harvesting systems. The approach is based on coupling of the reduced order model and the power circuitry. A numerically accurate reduced order model of the harvester was connected to a synchronized switch harvesting on inductor scheme and optimized subsequently.(More)
This work presents an optimization strategy towards extending the operational frequency range of piezoelectric MEMS energy harvesting devices. We propose to use coupled micromechanical resonators to enable efficient energy harvesting at multiple frequencies with a single device. The proposed design, obtained by optimization algorithms, exhibits closely(More)
In this paper we demonstrate a system-level simulation of a temperature controlled microsystem which is based on a reduced order model of a micro hotplate. Together with the electro-thermal microstructure we have implemented a control scheme, which allows the hotplate to operate either at a defined setpoint independent of ambient temperature or to follow(More)