Grating transducer for acoustic touchscreens

A substrate for an acoustic sensing device, having a region, and a surface, comprising:

• (a) an acoustic transducer, coupling to a bulk wave in said substrate having an axis of propagation intersecting said surface;
• (b) a diffractive acoustic wave mode coupling structure, formed proximate to said surface, adapted to convert acoustic wave energy of the bulk wave to a wave propagating along an axis parallel to said surface;
• and
• (c) means for detecting acoustic converted acoustic wave energy in a manner adapted for determining a position of a perturbation thereof.

A method of sensing touch on a substrate having a surface, comprising the steps of:

• transducing a bulk wave in the substrate propagating through said substrate along an axis intersecting the surface;
• diffractively coupling energy of the bulk wave to a wave having a converted wave mode with appreciable energy at the surface and propagating along an axis parallel to the surface;
• and
• detecting a perturbation of the wave having a converted wave mode.