Abstract
A phased array measurement technique is proposed for high resolution and ghost-suppressive measurement based on a synthesized directivity pattern using multiple frequencies. Tunable resonant-type piezoelectric ultrasonic microsensors have been developed for the measurement technique. The ultrasonic sensor consists of a silicon-micromachined diaphragm structure and a piezoelectric PZT (Pb(Zr,Ti)O3) capacitor on it. The capacitor has inner and outer top electrodes; the inner electrode for ultrasonic sensing, and the outer electrode for resonant frequency tuning through converse-piezoelectrically induced stress by applying external dc voltage. Two kinds of fabrication process have been developed to make flat and deflected diaphragms. Resonant frequency has increased nearly twice on the flat diaphragm and decreased to a half on the deflected diaphragm under a bias voltage application in the range of ±8 V.
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