Model for s.a.w. scattering by i.d.t. and its application to s.a.w. track changer

A superposition model for surface-acoustic-wave (s.a.w.) scattering by an interdigital transducer (i.d.t.) has been developed. In essence, it consists of two steps, (a) The incident s.a.w. induces a voltage across the i.d.t. (b) The bidirectionally radiated s.a.w., due to this induced voltage, is superposed with the incident s.a.w. to yield the scattered s.a.w. field. It is shown to considerably simplify the s.a.w. scattering parameter calculations for i.d.t. The results agree with earlier observations. Scattering parameter calculations of nonuniformly illuminated, resonantly loaded hybrid-junction i.d.t.s (r.l.h.i.d.t.) show that (i) s.a.w.s are unidirectionally radiated over the unilluminated part of the h.i.d.t. and (ii) it is described by a (track-changing) transfer function of bandpass type, with flat bandwidths up to 20% of nearly 0 dB loss, under appropriate conditions. The r.l.h.i.d.t. track changer should, therefore, be useful in realising long delay lines. The attractive feature of the r.l.h.i.d.t. as an s.a.w. track changer is that its implementation is practically feasible even on a low piezoelectric-coupling substrate like ST quartz. However, its main disadvantages are the requirement of (a) multilevel high-resolution lithography and (b) the additional high-Q tuning inductors for resonant loading.