Regarding analog design [ultrasonic ranging system]

An ultrasonic ranging system requires at least one ultrasonic transducer, a device to convert electrical energy to acoustic and acoustic energy back to electrical. In the automotive safety system we describe, a set of three transducers is employed. Two transducers are directed at /spl plusmn/120 degrees with respect to a central axis of a vehicle and are used for relatively short range detection. The third is directed along the central axis of the vehicle and is used for longer range detection.