We present an automated, contactless method to map thin film thickness and stress across microelectromechanical systems (MEMS) wafers. Using white light interferometry on cantilevers and step profiles, we extract both mean and gradient stress with orientation sensitivity. Applied to six thin films, the approach reveals process-dependent variations, offering a reliable tool for evaluating and comparing MEMS materials and fabrication methods.

Bistability is a mechanical phenomenon resulting in two stable, switchable states similar to a light switch. Micromachined piezoelectric bistable loudspeakers can utilize this effect to generate ultrasonic pulses with substantial loudness for applications such as distance measurements. In this work, we study different aspects of such a micromachined ultrasonic loudspeaker and demonstrate that such a device is feasible for ranging applications.

Photo-thermal actuation and laser Doppler vibrometry enable fast, contactless characterization of MEMS (microelectromechanical system) resonators already before electrical connections are made. This paper details a tailored setup combining a precision stage, vacuum chamber, laser diode, and vibrometer to analyze silicon MEMS devices on a wafer level. Tests reveal how silicon device layer thickness affects resonance frequency and identify dominant loss mechanisms in different vibrational modes.

A new method for water detection in lubricated rail components is presented. It is based on a robust humidity sensor combined with robust data evaluation to determine the water content of greases. Based on a laboratory evaluation in the relevant environment, the presented approach offers an online monitoring tool to predict the water content of grease-lubricated rail parts, thereby enhancing the reliability and safety while reducing the maintenance costs and downtime of railway wagons.