Low-cost facile interferometer for displacement mapping of harmonically excited MEMS

In this work, we present a simple, assembled from readily available components, low cost, imaging vibrometer based on a Twyman-Green interferometer with digital interferogram acquisition, allowing to map displacement contour levels of a harmonically excited piezoelectric membrane, on the principle of exposure integration. We experimentally demonstrate the capabilities of our setup on imaging the 4th mechanical mode of vibration of a 200 micrometer radius piezoelectric micromachined ultrasonic transducer membrane vibrating at 842 kHz, with an out-of-plane amplitude of 475 nm. Our results allow a direct visualization of the influence of etching trenches onto the vibrating membrane, in excellent agreement with FEM simulations.