Touch panel for an acoustic touch position sensor

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The touch position sensor of the present invention includes a substrate 10 that is capable of propagating a shear wave 12 as shown in FIG.
2A.
The substrate 10 may be formed of tempered or frosted glass, plastic, metal or ceramic.
The substrate 10 may further be formed as a flat plate as shown or the substrate may be curved.
In order to induce a shear wave propagating in the X direction, a piezoelectric transducer 14 is bonded on to an edge of the substrate perpendicular to the axis of propagation, X.
The transducer 14 is responsive to a drive signal for vibrating along the Y axis wherein a horizontal shear wave 12 is induced in the transducer 14 and coupled thereby directly to the substrate 10.
As shown in FIG.
2B, the shear wave 12 imparted into the substrate 10 is not confined to a single surface of the substrate 10, but extends throughout the entire thickness of the substrate 10.
The particles of the shear wave move only in the Y direction.
It is noted that shear waves may be symmetric or anti-symmetric about the median plane.
In the preferred embodiment of the present invention a non-dispersive shear wave is employed.
More particularly, this non-dispersive mode is the zeroth order of the following plate solution for a wave traveling in the X direction.
##EQU1## where Ux, Uy, Uz are displacement components in the x, y and z directions respectively, A is a constant, .
lambda.
is the wavelength, and f is the number of cycles per second.
This shear wave is designated herein as the zeroth order horizontally polarized shear wave or Zohps wave.
(See Physical Acoustics, Ed.
W.
P.
Mason, Voll-Part A P120, Academic Press 1964, New York and London).
A touch position sensor 16 in accordance with a first embodiment of the present invention is shown in FIG.
3 having a pair of transmitting and receiving transducers 18, 20 and 22, 24 associated with each axis for which a coordinate is desired to be determined.
Although the touch position sensor 16 has four transducers 18, 20 and 22, 24 respectively associated with the X axis and Y axis so that both X and Y coordinates of a touch may be determined, if only a single coordinate is desired, for example a coordinate along the X axis, then the transducers 22 and 24 associated with the Y axis may be eliminated