Elastic surface wave device

Abstract

In an elastic surface wave device comprising a piezoelectric substrate, a first transducer group, and a second transducer group or groups located on one or both sides of the first transducer group to exchange elastic surface waves with the first transducer group, the second transducer group comprises a plurality of transducers sharing the same elastic surface wave propagation path. The geometrical central positions of the individual transducers making up the second transducer group are located symmetrically about the geometrical central position (0--0') of the entire second transducer group, with each pair of such symmetrically located transducers incorporating the same number of pairs. The delay time, that is, the time taken by elastic surface waves propagating between the centers of every two adjoining transducers, excluding the two outermost transducers, is constant (.tau.). The distance between the center of each of the two outermost transducers and that of the transducer adjoining the outermost transducer is determined such that the delay time taken between the two transducers is, if the number of pairs incorporated in the outermost transducer is an integer, equal to an odd-number multiple of one-half of the above-mentioned constant delay time (.tau.), or, if the number of pairs incorporated in the outermost transducer is not an integer, equal to an odd-number multiple of one-half of the above-mentioned constant delay time (.tau.), plus or minus a quater wavelength time.