Vibration modes in impulse response of piezoelectric diaphragms for ultrasonic microsensors

Diaphragm structures of piezoelectric ultrasonic microsensors were fabricated and their vibration modes responding to an ultrasound pulse were investigated. A vibrating piezoelectric diaphragm has an inhomogeneous polarization distribution and its electrode is designed to avoid cancellation of positive and negative polarizations in the fundamental vibration mode. However, a short ultrasound pulse used for ultrasonic measurement has components of higher frequencies than the fundamental one and might cause higher order vibration modes according to the diaphragm shape. Square and circular diaphragms with flat or buckled profiles were fabricated in this work and evaluated with a scanning laser Doppler vibrometer. The circular buckled diaphragm shape was the most suitable among them on centrosymmetric vibration modes which influence to piezoelectric output and sensitivity.