An ultrasonic sensor for in-air applications has been fabricated using ferroelectric polymer technology. The proximity sensor, designed to be incorporated into a multiple sensing robotic gripper, consists of two unimodal transducers, a transmitter, and a receiver and is obtained by curving a strip of 40- mu m-thick polyvinylidene fluoride. The transducers have a resonance frequency of 63.5 kHz, a quality factor Q approximately equal to 12 and a transverse piezoelectric coupling coefficient k/sub 31/ of 0.29. The maximum detectable distance is 300 mm, with an axial resolution of about 3 mm. Furthermore transducers resonating at 380 kHz, which operate at a maximum distance of 100 mm with a resolution of 2 mm can be fabricated by using the same technique. Features and performance of both transmitter and receiver are discussed, together with the echo acquisition and the preprocessing electronic unit.
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