Cost-effective system for the characterization of microstructure vibrating in out-of-plane modes

A cost-effective system for the dynamic characterization of microstructures driven to vibrate in out-of-plane modes is presented. The proposed solution provides swept-frequency excitation of the microstructure under test and detects the corresponding displacement by a single-point optical triangulator interfaced to a tailored conditioning circuitry. By taking advantage of the forced excitation of the microstructure, the system performs synchronous undersampling of the signal from the triangulator to measure the frequency response of the microstructure. The proposed method is equivalent to coherent demodulation with lock-in detection, therefore inherently offers good signal-to-noise performances. The system has been prototyped making use of a PC-based data acquisition board and tested on different microstructures, such as a piezoelectric bimorph cantilever, a MEMS accelerometer, and a SOI microresonator with off-chip excitation.