Two-frequency combination in ultrasonic measurement on a sparse phased array using tunable microsensors

Two-frequency combination technique can effectively decreases sidelobes in ultrasonic measurement on a sparse phased array. Tunable resonant-type ultrasonic microsensors have been fabricated for the measurement technique by switching the resonant frequency to the two frequencies. The ultrasonic sensor consists of a piezoelectric lead-zirconate-titanate (PZT) capacitor on a silicon-micromachined thin diaphragm structure. The piezoelectric capacitor has two kinds of electrode for ultrasonic sensing and for frequency tuning by applying a dc bias voltage. The resonant frequency has been tuned from a base frequency down to a sub-frequency which has -47% lower than the base frequency. The two-frequency measurement at the base and sub-frequencies achieves ghost suppression by decreasing sidelobes down to -17dB.