1. An amplifier comprising a substrate member of piezoelectric material having a propagation surface adapted to permit the propagation of acoustic surface waves therealong, an electromagnetic wave to acoustic surface wave input transducer, disposed on said propagation surface, modulator means for modulating acoustic surface waves operably engaged to said propagation surface at A point substantially coinciding with the first power density minimum of an acoustic surface wave fundamental propagating from said input transducer, and demodulator means for demodulating acoustic surface waves operably engaged to said propagation surface at a point substantially coinciding with the first power density maximum of said surface wave fundamental beyond said modulator means.

4. The method of fabricating an amplifier comprising the steps of rendering one surface of a piezoelectric substrate member suitable for the propagation of acoustic surface waves, affixing an electromagnetic wave to acoustic surface wave input transducer to said surface, applying an electromagnetic wave input signal of a given frequency to said input transducer, measuring and recording the power densities of the acoustic surface wave fundamental responsive to said electromagnetic wave input signal propagating along said substrate member, affixing acoustic wave modulating means to said substrate member propagation surface at a point substantially coinciding with the first power density minimum of said acoustic surface wave fundamental, and affixing an acoustic wave demodulator to said substrate member propagation surface at a point substantially coinciding with the first power density maximum of said surface wave fundamental beyond said modulating means.