The typical transducer considered consists of a piezoelectric film, and associated.electrodes, connected to one gate of a dual-gate field-effect transistor in the silicon wafer on which the piezoelectric film is situated. An individual transducer responds to various modes of excitation (flexural, surface, bulk) at frequencies which may range from far below one Hertz to hundreds of megahertz. The second gate of the field-effect transistor can be used for electrical amplitude control or for mixing purposes, Connection of a number of these small transducers together to form arrays permits realizing ultrasonic receiving devices having variable directivity, and progammable surface-wave signal processors
