Scientific Contributions

JOURNAL PAPERS

How stable and unstable states of Coulomb-actuated microbeams can be successfully simulated by combining FEM with arc-length method? Both approaches confirm that the shape of the bending profile of a Coulomb-activated prismatic microbeam, clamped at both ends, is almost identical to the shape of the Euler-Bernoulli zero-mode. The observation paves the way for lumped-parameter models of high accuracy that only use a single spatial degree of freedom, amenable to direct physical interpretation. The fruit of this research work is a surprisingly accurate zero-mode approximation that has numerous applications in the modeling of the physics of electrostatic MEMS actuators.

Coulomb-actuated microbeams revisited: experimental and numerical modal decomposition of the saddle-node bifurcation

MEMS-based micro speakers are used as sound transducers for smart devices such as hearables. Such devices require high sound pressure levels (SPL), low harmonic distortion (THD) and low power consumption for industrial, consumer and medical applications. Several important advantages of the concept comprise CMOS compatibility including integration capabilities with microelectronic circuitry, scalable mass productions, low unit cost, small foot print for high sound quality and very low power consumption. The novel micro speaker concept based on nanoscopic electrostatic actuation presented in this paper essentially involves in-plane electrostatic bending actuators and uses the chip volume rather than its surface for sound generation. The research paper describes the principle, design, fabrication and initial characterisation results.

Concept and proof for an all-silicon MEMS micro speaker utilizing air chambers

In this research paper, we present an electrostatic actuator principle, fabricated in a CMOS-compatible process, which allows high deflections with small electrode separation. The concept presented makes the huge electrostatic forces within nanometre small electrode separation accessible for large deflections. Electrostatic actuations that are larger than the electrode separation were measured. The driving concept enables the investigation and development of micro systems with a high potential for improved device and system performance. A solution is demonstrated to prevent or reduce the occurrence of pull-in related failure mechanisms of MEMS actuators and sensors. 

A small-gap electrostatic micro-actuator for large deflections

CONFERENCE PAPERS

This paper for the 23rd International Congress on Acoustics presents the acoustic properties of an electroacoustic MEMS transducer. The transducer is based on electrostatic bending actuators with lateral deflection. The actuators are arranged between a vented handle and cover wafer and are designed to emit sound in the audible frequency range. The results of acoustic measurements are discussed demonstrating audio reproduction capabilities for in-ear audio applications.

Electrostatic all silicon MEMS speakers for in-ear audio applications – acoustic measurements and modelling approach

At DAGA 2018, our electrostatic MEMS micro speakers were introduced for the first time, whereby no membrane but the wafer volume is used to generate sound. The article explains the groupwise counter-phase movement of the bending transducers, whereby vibration-free sound transmitters are possible. With the lateral arrangement of air inlets and outlets, several chips can be stacked and electronics for control as well as further MEMS sensor technology can be monolithically integrated.

CMOS-compatible MEMS loudspeaker for in-ear applications
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