Surface-wave distributed acoustic reflection transducer and filter including such a transducer

A surface-acoustic-wave transducer operating at a predetermined frequency for coupling electrical energy into acoustic energy on a substrate, said transducer comprising:

• a substrate which supports propagation of surface-acoustic waves;
• a plurality of interdigitated electrodes oriented on said substrate to convert input electrical energy into propagating surface-acoustic-waves on said substrate;
• a first plurality of said electrodes being irregularly placed in at least one region of the transducer so as to enhance the reflection of acoustic energy in one direction, and a second plurality of said electrodes being irregularly placed in at least one further region of the transducer so as to enhance the reflection of acoustic energy in the opposite direction thereby resulting in local acoustic resonances within the transducer which serve to increase the coupling of the transducer over a limited range of frequencies, the position of said first and second plurality of irregularly placed electrodes being a function of a desired resonance frequency wherein said desired resonance frequency is said predetermined frequency,
• said electrodes being asymmetrically arranged whereby the acoustic energy is radiated from the transducer predominantly in a preferred direction.