Experimental methodology to measure damping in microstructures by using the actuation force hysteresis curve

The study of damping in MEMS (micro electro-mechanical systems) is crucial for dynamic response prediction and functional parameters estimation as switch and release time, resonance and quality factor. Geometrical features (borders, perforations, anchors, etc.) complicate the airflow and impose to validate the results calculated or simulated with models. Fluid damping is the dominant dissipation source, accompanied by structural dissipations, thermo-elastic damping, anchor losses, surface effects and electric losses. In literature, the damping coefficient of MEMS is generally derived from the peaks of the structural frequency response function (FRF) by the half power method. Despite the wide usage of this approach, it is affected by two main drawbacks: highly precise and automated detection instruments are needed, and it is applicable only in resonance conditions. The method presented here is based on the measurement of damping from the hysteresis cycle of the actuation force; it applies in the time domain and works at any frequency and vibration amplitude. The effectiveness of this methodology on MEMS is proved by comparing the damping results with those provided at resonance conditions by the half power method. The samples, designed by the authors, are gold microplates with square holes and elastic springs. The measurements are conducted by the laser vibrometer Polytech MSA500. The comparison shows very good agreement with the damping coefficients calculated with the traditional approach (differences within 2% at resonance).