Coded grating transducer

Claim 1

A coded, acoustic, surface-wave, device having a high input impedance, comprising: a substrate; an input transducer disposed upon the substrate, which comprises: a plurality of N linear, parallel, equally-spaced electrodes disposed upon the substrate; the two end electrodes being connectable to an input electrical signal, which causes the propagation of an acoustic signal across the surface of the substrate, the acoustic signal comprising two components, an upper component propagating in an upper propagation channel, and a lower component propagating in a lower propagation channel; a plurality of N-1 sets of linear, parallel, electrodes, shorter in length than the first-named plurality of longer electrodes, and interposed between, parallel to, and equally spaced between, the longer electrodes, each set including at least one short electrode; the shorter electrodes being disposed at one or the other end of the longer electrodes, in either the upper or lower propagation channel; the combination of placements forming a code; two adjacent electrodes, whether long or short, being spaced the same distance apart; the surface-wave device further comprising an output transducer disposed upon the substrate, which comprises; a longer electrode, spaced a distance apart from, and parallel to the electrodes of, the input transducer, which first intercepts the propagating acoustic wave; a pair of sets of shorter electrodes, of substantially the same length as the first-named shorter electrodes, the number of electrodes in each pair being equal to the number of electrodes in tHe first-named set of shorter electrodes, one set of the pair being disposed at each end of, and parallel to, the longer electrode, one set in each of the two propagation channels; and a pair of output electrodes, approximately equal in length to either of the other named shorter electrodes, for providing a transduced electrical output signal.