A SAW Filter consists of two interdigital transducers (IDTs) on a piezoelectric crystal substrate . The IDTs consist of interleaved metal electrodes which are used to launch and receive the waves, so that an electrical signal is converted to an acoustic wave and then back to an electrical signal.An impulse voltage applied to the transducer generates, due to piezoelectricity, mechanical displacements in the crystal between electrodes (or fingers) of opposite polarity. These crystal displacements propagate and create a wave at the surface of the crystal perpendicular to the electrodes. The inverse phenomenon occurs when this acoustic wave travels under another transducer: it in turn creates an electromagnetic output signal. The characteristic of frequency depends on the pattern of electrodes.