Surface acoustic wave touch-position sensing device

A surface acoustic wave touch-position sensing device comprising:

• at least two surface acoustic wave transducing units X and Y, each thereof consisting of
• a piezoelectric substrate P.sub.T having an upper- and a lower end surfaces running perpendicular to the direction of the thickness d thereof,
• a piezoelectric substrate P.sub.R having an upper- and a lower end surfaces running perpendicular to the direction of the thickness d thereof,
• N interdigital transducers T.sub.i (i=1, 2, . . . , N) formed on said upper end surface of said piezoelectric substrate P.sub.T, each interdigital transducer 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 smaller than an interdigital periodicity p of said interdigital transducer T.sub.i,
• an interdigital transducer R, formed on said upper end surface of said piezoelectric substrate P.sub.R, consisting of two electrodes R.sub.-1, and R.sub.-2, 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, and having an interdigital periodicity equal to said interdigital periodicity p, said thickness d of said piezoelectric substrate P.sub.R being smaller than said interdigital periodicity p,
• N earth electrodes G.sub.Ti (i=1, 2, . . . , N) formed on said lower end surface of said piezoelectric substrate P.sub.T,
• an earth electrode G.sub.R formed on said lower 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, 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 an upper- and a lower end surfaces running perpendicular to the thickness direction thereof, the thickness of said nonpiezoelectric plate being larger than three times said interdigital periodicity p, said piezoelectric substrates P.sub.T and P.sub.R being mounted on said upper end surface of said nonpiezoelectric plate through said earth electrodes G.sub.Ti and G.sub.R, respectively;
• and
• a controlling system connected with said surface acoustic wave transducing units X and Y,
• 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 a surface acoustic wave of the first mode and the higher order modes in said piezoelectric substrate P.sub.T, and transmitting said surface acoustic wave having the wavelength approximately equal to said interdigital periodicity p to said piezoelectric substrate P.sub.R through said upper end surface of said nonpiezoelectric plate, the phase velocity of said surface acoustic wave of said first mode and said higher order modes being approximately equal to the phase velocity of the Rayleigh wave traveling on said nonpiezoelectric plate alone, each of said electric signals E.sub.T1 and E.sub.T2 having a frequency approximately corresponding to said interdigital periodicity p, the phase difference between said electric signals E.sub.T1 and E.sub.T2 being 2 .pi.y,
• said interdigital transducer R and said earth electrode G.sub.R transducing said surface acoustic wave in said piezoelectric substrate P.sub.R, with wavelength approximately equal to said interdigital periodicity p, 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, 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 surface acoustic wave traveling on said nonpiezoelectric plate alone is higher than that traveling on 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 on said upper 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,
• said surface acoustic wave transducing unit X having N propagation lanes U.sub.Xi (i=1, 2, . . . , N) of said surface acoustic wave between said interdigital transducers T.sub.i and R, two neighbors of said propagation lanes U.sub.Xi being closed or partially overlapping each other,
• said surface acoustic wave transducing unit Y having N propagation lanes U.sub.Yi (i=1, 2, . . . , N) of said surface acoustic wave between said interdigital transducers T.sub.i and R, two neighbors of said propagation lanes U.sub.Yi being closed or partially overlapping each other, said propagation lanes U.sub.Xi being vertical to said propagation lanes U.sub.Yi.

A surface acoustic wave touch-position sensing device comprising:

• at least two surface acoustic wave transducing units X and Y, each thereof consisting of
• a piezoelectric substrate P.sub.T having an upper- and a lower end surfaces running perpendicular to the direction of the thickness d thereof,
• a piezoelectric substrate P.sub.R having an upper- and a lower end surfaces running perpendicular to the direction of the thickness d thereof,
• an interdigital transducer T, formed on said upper end surface of said piezoelectric substrate P.sub.T, consisting of two electrodes T.sub.-1 and T.sub.-2 and having two kinds of distances between one electrode finger of said electrode T.sub.-1 and two neighboring electrode fingers of said electrode T.sub.-2, said thickness d of said piezoelectric substrate P.sub.T being smaller than an interdigital periodicity p of said interdigital transducer T,
• N interdigital transducers R.sub.i (i=1, 2. . . , N) formed on said upper end surface of said piezoelectric substrate P.sub.R, each interdigital transducer R.sub.i having an interdigital periodicity equal to said interdigital periodicity p, said thickness d of said piezoelectric substrate P.sub.R being smaller than said interdigital periodicity p, and
• an earth electrode G.sub.T formed on said lower end surface of said piezoelectric substrate P.sub.T ;
• a nonpiezoelectric plate having an upper- and a lower end surfaces running perpendicular to the thickness direction thereof, the thickness of said nonpiezoelectric plate being larger than three times said interdigital periodicity p, said piezoelectric substrates P.sub.T and P.sub.R being mounted on said upper end surface of said nonpiezoelectric plate through said lower end surfaces of said piezoelectric substrates P.sub.T and P.sub.R, respectively;
• a phase shifter S.sub.T including at least a coil L.sub.1 ;
• and
• a controlling system connected with said two surface acoustic wave transducing units X and Y,
• said interdigital transducer T and said earth electrode G.sub.T receiving an electric signal E.sub.T1 between said electrode T.sub.-1 and said earth electrode G.sub.T, and an electric signal E.sub.T2 between said electrode T.sub.-2 and said earth electrode G.sub.T via said phase shifter S.sub.T, exciting a surface acoustic wave of the first mode and the higher order modes in said piezoelectric substrate P.sub.T, and transmitting said surface acoustic wave having the wavelength approximately equal to said interdigital periodicity p to said piezoelectric substrate P.sub.R through said upper end surface of said nonpiezoelectric plate, the phase velocity of said surface acoustic wave of said first mode and said higher order modes being approximately equal to the phase velocity of the Rayleigh wave traveling on said nonpiezoelectric plate alone, each of said electric signals E.sub.T1 and E.sub.T2 having a frequency approximately corresponding to said interdigital periodicity p, the phase difference between said electric signals E.sub.T1 and E.sub.T2 being 2 .pi.y,
• said interdigital transducer R.sub.i transducing said surface acoustic wave in said piezoelectric substrate P.sub.R, with wavelength approximately equal to said interdigital periodicity p, to electric signals E.sub.Ri (i=1, 2,. . . , N), said signal E.sub.Ri having a frequency approximately corresponding to said interdigital periodicity p,
• said nonpiezoelectric plate being made of a material such that the phase velocity of the surface acoustic wave traveling on said nonpiezoelectric plate alone is higher than that traveling on said piezoelectric substrates P.sub.T and P.sub.R alone,
• said controlling system keeping a check on a magnitude of said electric signals E.sub.Ri, sensing a touch with a finger or others on the other end surface of said nonpiezoelectric plate by a decrease or a disappearance in magnitude of said electric signals E.sub.Ri, picking out at least one of said interdigital transducers R.sub.i corresponding to said decrease or said disappearance in magnitude of said electric signals E.sub.Ri,
• said surface acoustic wave transducing unit X having N propagation lanes U.sub.Xi (i=1, 2, . . . , N) of said surface acoustic wave between said interdigital transducers T and R.sub.i, two neighbors of said propagation lanes U.sub.Xi being closed or partially overlapping each other,
• said surface acoustic wave transducing unit Y having N propagation lanes U.sub.Yi (i=1, 2, . . . , N) of said surface acoustic wave between said interdigital transducers T and R.sub.i, two neighbors of said propagation lanes U.sub.Yi being closed or partially overlapping each other, said propagation lanes U.sub.Xi being vertical to said propagation lanes U.sub.Yi.