Elastic wave position-sensing device

An elastic wave position-sensing device comprising:

• at least two elastic wave transducing units X and Y, each thereof consisting of
• a piezoelectric substrate P.sub.T having two end surfaces running perpendicular to the direction of the thickness D thereof, and comprising N piezoelectric parts P.sub.Ti (i=1, 2, . . . , N),
• a piezoelectric substrate P.sub.R having two end surfaces running perpendicular to the direction of the thickness D thereof,
• N interdigital transducers T.sub.i (i=1, 2, . . . , N), each thereof being formed on one end surface of each of said piezoelectric parts P.sub.Ti, each of said interdigital transducers T.sub.i consisting of two electrodes T.sub.i-1 and T.sub.i-2 and having two kinds of distances between one electrode finger of said electrode T.sub.i-1 and two neighboring electrode fingers of said electrode T.sub.i-2, said thickness D of said piezoelectric substrate P.sub.T being approximately equal to or smaller than an interdigital periodicity p of said interdigital transducer T.sub.i,
• an interdigital transducer R formed on one end surface of said piezoelectric substrate P.sub.R, consisting of two electrodes R.sub.-1 and R.sub.-2, and having two kinds of distances between one electrode finger of said electrode R.sub.-1 and two neighboring electrode fingers of said electrode R.sub.-2, said thickness D of said piezoelectric substrate P.sub.R being approximately equal to or smaller than an interdigital periodicity p of said interdigital transducer R,
• N earth electrodes G.sub.Ti (i=1, 2, . . . , N), each thereof being formed on the other end surface of each of said piezoelectric parts P.sub.Ti,
• an earth electrode G.sub.R formed on the other end surface of said piezoelectric substrate P.sub.R,
• a phase shifter S.sub.T including at least a coil L.sub.1,
• a phase shifter S.sub.R including at least a coil L.sub.2, and
• N pairs of switches W.sub.i (i=1, 2, . . . , N), each pair of switches W.sub.i consisting of two switches W.sub.i-1 and W.sub.i-2, and output terminals of said switches W.sub.i-1 and W.sub.i-2 being connected with input terminals of said electrodes T.sub.i-1 and T.sub.i-2, respectively;
• a nonpiezoelectric plate having two end surfaces, the thickness of said nonpiezoelectric plate being equal to or smaller than said thickness D of said piezoelectric substrates P.sub.T and P.sub.R, said piezoelectric substrates P.sub.T and P.sub.R being mounted on one or the other end surface of said nonpiezoelectric plate through said earth electrodes G.sub.Ti and G.sub.R, respectively, said nonpiezoelectric plate comprising N nonpiezoelectric parts .sub.Ti (i=1, 2, . . . , N) adjacent to said piezoelectric parts P.sub.Ti, a nonpiezoelectric part .sub.R adjacent to said piezoelectric substrate P.sub.R, and the remaining nonpiezoelectric part;
• a display panel, mounted on said one end surface of said nonpiezoelectric plate;
• and
• a controlling system connected with said two elastic wave transducing units X and Y, and said display panel,
• said piezoelectric substrates P.sub.T and P.sub.R, and said nonpiezoelectric plate forming
• N bilayer zones L.sub.Ti (i=1, 2, . . . , N) consisting of said piezoelectric parts P.sub.Ti and said nonpiezoelectric parts .sub.Ti,
• a bilayer zone L.sub.R consisting of said piezoelectric substrate P.sub.R and said nonpiezoelectric part .sub.R, and
• a monolayer zone between said bilayer zones L.sub.Ti and said bilayer zone L.sub.R, and consisting of said remaining nonpiezoelectric part,
• said interdigital transducer T.sub.i and said earth electrode G.sub.Ti receiving an electric signal E.sub.T1 between said electrode T.sub.i-1 and said earth electrode G.sub.Ti, and an electric signal E.sub.T2 between said electrode T.sub.i-2 and said earth electrode G.sub.Ti via said phase shifter S.sub.T, exciting an elastic wave of the S.sub.o mode and the higher order modes in said bilayer zone L.sub.Ti, and transmitting said elastic wave, having the wavelength approximately equal to said interdigital periodicity p of said interdigital transducer T.sub.i, to said bilayer zone L.sub.R through said monolayer zone, each of said electric signals E.sub.T1 and E.sub.T2 having a frequency approximately corresponding to said interdigital periodicity p of said interdigital transducer T.sub.i, the phase difference between said electric signals E.sub.T1 and E.sub.T2 being 2.pi.y, the phase velocity of said elastic wave being approximately equal to the phase velocity V.sub.fd=0, of the S.sub.o mode elastic wave, corresponding to a condition that the product FD of the frequency F of said elastic wave and said thickness D of said piezoelectric substrate P.sub.T is zero,
• said interdigital transducer R and said earth electrode G.sub.R transducing said elastic wave in said bilayer zone L.sub.R, with wavelength approximately equal to said interdigital periodicity p of said interdigital transducer R, to an electric signal E.sub.R1 between said electrode R.sub.-1 and said earth electrode G.sub.R, and an electric signal E.sub.R2 between said electrode R.sub.-2 and said earth electrode G.sub.R, each of said electric signals E.sub.R1 and E.sub.R2 having a frequency approximately corresponding to said interdigital periodicity p of said interdigital transducer R, the phase difference between said electric signals E.sub.R1 and E.sub.R2 being 2.pi.y,
• said phase shifter S.sub.R combining said electric signals E.sub.R1 and E.sub.R2, and delivering a combined electric signal E.sub.R,
• said nonpiezoelectric plate being made of a material such that the phase velocity of the elastic wave in said nonpiezoelectric plate alone is approximately equal to that in said piezoelectric substrates P.sub.T and P.sub.R alone,
• said controlling system turning on and off said pairs of switches W.sub.i with a fixed period in turn, keeping a check on a magnitude of said electric signal E.sub.R, sensing a touch with a finger or others under a fixed or more pressure on the other end surface of said nonpiezoelectric plate by a decrease or a disappearance in magnitude of said electric signal E.sub.R, picking out said pair of switches W.sub.i turned on when said decrease or said disappearance in magnitude of said electric signal E.sub.R happens, specifying a touch-position corresponding with the picked out pair of switches W.sub.i, and producing an image corresponding to said touch-position on said display panel,
• said elastic wave transducing unit X having N propagation lanes U.sub.Xi (i=1, 2, . . . , N) of the elastic wave in said monolayer zone between said bilayer zones L.sub.Ti and L.sub.R in said elastic wave transducing unit X, two neighbors of said propagation lanes U.sub.Xi being closed or partially overlapping each other,
• said elastic wave transducing unit Y having N propagation lanes U.sub.Yi (i=1, 2, . . . , N) of the elastic wave in said monolayer zone between said bilayer zones L.sub.Ti and L.sub.R in said elastic wave transducing unit Y, two neighbors of said propagation lanes U.sub.Yi being closed or partially overlapping each other, said propagation lane U.sub.Xi being vertical to said propagation lane U.sub.Yi.