Elliptical, interdigital transducer

An elliptical, interdigital transducer comprising a plurality of concentric, elliptically shaped conductive fingers situated within one quadrant of an ellipse and mounted on a piezoelectric material, said fingers having a width and a spacing along the minor axis of said ellipse substantially equal to each other, said fingers having a width and a spacing along the major axis of said ellipse substantially equal to each other, and said width and spacing of said fingers, respectively, along said major axis being substantially twice the width and spacing of said fingers, respectively, along said minor axis, whereby upon the application of an exitation frequency f.sub.1 to said transducer, a low frequency surface wave of frequency f.sub.1 will propagate along the major axis toward the focus, and upon application of an exitation of frequency f.sub.2 with f.sub.2 >

• f.sub.1, a high frequency surface wave of frequency f.sub.2 will propagate along the minor axis toward the focus, and upon application of exitation frequency f with f.sub.1 .ltoreq. f .ltoreq. f.sub.2, a resonance will occur at some point, d.sub.e, on a line through the ellipse and the focus such that d.sub.e = V/4f, where V is the characteristic velocity of acoustic waves in said piezoelectric material.