MICROMACHINABLE ULTRASONIC LEAKY-WAVE AIR TRANSDUCERS

Ultrasonic air transducers using leaky waves on thin membranes are ana lyzed using perturbation and normal mode approaches. The transducers u tilize the efficient coupling of ultrasonic energy to air through radi ation of these leaky wave modes when their phase velocity is close to the sound speed in air. Theoretical results on optimum transducer dime nsions and bandwidth estimation show that a minimum conversion loss of 8.7 dB with a 78% fractional bandwidth is possible. Common micromachi ning materials are shown to be suitable transducer materials and resul t in feasible devices. This is demonstrated by fabricating a 580 kHz t ransducer using a silicon membrane bonded to a ring of PZT-SH. With th is configuration the transducer is self line focusing. Results of thro ugh transmission experiments on silicon and transmission images on pap er are reported. (C) 1988 American Institute of Physics.