Abstract A body of piezoelectric material propagates acoustic surface waves. Coupled to a surface of the body is a first transducer that launches the waves. Spaced on the same surface from the first device is a second transducer that responds to the launched waves. In order to reduce interference from reflections and increase efficiency, an end surface of the body is selectively located with respect to the adjacent transducer and is formed to define a particular angle with respect to the wave propagating surface. With the transducer elements in the form of interleaved combs of electrodes, absorption of reflections from an end surface is increased by effectively locating the end surface a precise fraction of an acoustic wavelength from the nearest comb electrode or tooth. Moreover, the response of the combined apparatus to signals being transmitted may be altered by changing either the angle that the end surface forms with respect to the propagating surface or by changing the spacing of the end surface from the transducer. The response also may be altered by depositing a different material on the wave propagating surface.
In an acoustic filter having an acoustic-wave-propagating substrate and a surface-wave transducer actively coupled to a propagating surface of that substrate for interacting with surface waves propagating on a predetermined portion of the substrate, said transducer including an array of interleaved combs of conductive electrodes defining a pattern of spaced interdigital teeth, the improvement in which the end surface of said substrate on the side of said transducer opposite said predetermined portion is effectively located midway between an actual one of said teeth and an adjacent virtual image of said one tooth.
Claim 2
Dependent Claim
92 words
In an acoustic filter having an acoustic-wave-propagating substrate and a surface-wave transducer actively coupled to a propagating surface of that substrate for interacting with surface waves propagating on a predetermined portion of the substrate, said transducer including an array of interleaved combs of conductive electrodes defining a pattern of spaced interdigital teeth, the improvement in which the end surface of said substrate on the side of said transducer opposite said predetermined portion is effectively located midway between an actual one of said teeth and an adjacent virtual image of said one tooth.