Ultrasonic touch-position sensitive device

An ultrasonic touch-position sensing device comprising:

• a piezoelectric substrate having an upper- and a lower end surfaces running perpendicular to the thickness direction thereof;
• a nonpiezoelectric plate having an upper- and a lower end surfaces running perpendicular to the direction of the thickness d thereof;
• a surface acoustic wave transducing unit X consisting of
• an input interdigital transducer T.sub.X formed on said upper end surface of said piezoelectric substrate and having an interdigital periodicity P.sub.X and an overlap length L.sub.X, the thickness of said piezoelectric substrate being larger than three times said interdigital periodicity P.sub.X, said thickness d of said nonpiezoelectric plate being smaller than said interdigital periodicity P.sub.X,
• an output interdigital transducer R.sub.X opposed to said interdigital transducer T.sub.X on said upper end surface of said piezoelectric substrate and placed such that the finger direction of said interdigital transducer R.sub.X is slanting to that of said interdigital transducer T.sub.X by an angle .alpha., an interdigital periodicity P.sub.N along the vertical direction to the finger direction of said interdigital transducer R.sub.X being equal to the product of said interdigital periodicity P.sub.X and cos .alpha., an overlap length L.sub.P along the finger direction of said interdigital transducer R.sub.X being equal to the product of said overlap length L.sub.X and sec .alpha. as well as the product of N times (N=1, 2, . . . , n) said interdigital periodicity P.sub.X and cosec .alpha., and
• an amplifier A.sub.X, an output terminal of said interdigital transducer R.sub.X being connected with an input terminal of said interdigital transducer T.sub.X via said amplifier A.sub.X ;
• a surface acoustic wave transducing unit Y consisting of
• an input interdigital transducer T.sub.Y formed on said upper end surface of said piezoelectric substrate and having an interdigital periodicity P.sub.Y and an overlap length L.sub.Y, the thickness of said piezoelectric substrate being larger than three times said interdigital periodicity P.sub.Y, said thickness d of said nonpiezoelectric plate being smaller than said interdigital periodicity P.sub.Y,
• an output interdigital transducer R.sub.Y opposed to said interdigital transducer T.sub.Y on said upper end surface of said piezoelectric substrate and placed such that the finger direction of said interdigital transducer R.sub.Y is slanting to that of said interdigital transducer T.sub.Y by an angle .alpha., an interdigital periodicity P.sub.N along the vertical direction to the finger direction of said interdigital transducer R.sub.Y being equal to the product of said interdigital periodicity P.sub.Y and cos .alpha., an overlap length L.sub.P along the finger direction of said interdigital transducer R.sub.Y being equal to the product of said overlap length L.sub.Y and sec .alpha. as well as the product of N times (N=1, 2, . . . , n) said interdigital periodicity P.sub.Y and cosec .alpha., said lower end surface of said nonpiezoelectric plate being cemented on said upper end surface of said piezoelectric substrate through said interdigital transducers T.sub.X, R.sub.X, T.sub.Y and R.sub.Y, and
• an amplifier A.sub.Y, an output terminal of said interdigital transducer R.sub.Y being connected with an input terminal of said interdigital transducer T.sub.Y via said amplifier A.sub.Y ;
• and
• a controlling system comprising a signal controller and being connected with said surface acoustic wave transducing units X and Y,
• said interdigital transducer T.sub.X receiving an electric signal with a frequency approximately corresponding to said interdigital periodicity P.sub.X, exciting a surface acoustic wave of the zeroth mode and the higher order modes on an area, in contact with said interdigital transducer T.sub.X, of said upper end surface of said piezoelectric substrate, and transmitting said surface acoustic wave having the wavelength approximately equal to said interdigital periodicity P.sub.X to an area, in contact with said interdigital transducer R.sub.X, of said upper end surface of said piezoelectric substrate, through said nonpiezoelectric plate, the phase velocity of said surface acoustic wave of said zeroth mode being approximately equal to the phase velocity of the Rayleigh wave traveling on said piezoelectric substrate alone under the electrically shorted condition, the phase velocity of said surface acoustic wave of said higher order modes being approximately equal to the phase velocity of the Rayleigh wave traveling on said piezoelectric substrate alone under the electrically opened condition,
• said interdigital transducer T.sub.Y receiving an electric signal with a frequency approximately corresponding to said interdigital periodicity P.sub.Y, exciting a surface acoustic wave of the zeroth mode and the higher order modes on an area, in contact with said interdigital transducer T.sub.Y, of said upper end surface of said piezoelectric substrate, and transmitting said surface acoustic wave having the wavelength approximately equal to said interdigital periodicity P.sub.Y to an area, in contact with said interdigital transducer R.sub.Y, of said upper end surface of said piezoelectric substrate, through said nonpiezoelectric plate, the phase velocity of said surface acoustic wave of said zeroth mode being approximately equal to the phase velocity of the Rayleigh wave traveling on said piezoelectric substrate alone under the electrically shorted condition, the phase velocity of said surface acoustic wave of said higher order modes being approximately equal to the phase velocity of the Rayleigh wave traveling on said piezoelectric substrate alone under the electrically opened condition,
• said interdigital transducer R.sub.X transducing said surface acoustic wave excited by said interdigital transducer T.sub.X to electric signals E.sub.Xi (i=x, . . . , 2, 1, 0, -1, -2, . . . , -x) with frequencies f.sub.Xi (i=x, . . . , 2, 1, 0, -1, -2, . . . , -x) respectively, the total electric signal .SIGMA.E.sub.Xi made by said electric signals E.sub.xi being zero and not able to be detected at said interdigital transducer R.sub.X,
• said interdigital transducer R.sub.Y transducing said surface acoustic wave excited by said interdigital transducer T.sub.Y to electric signals E.sub.Yj (j=y, . . . , 2, 1, 0, -1, -2, . . . , -y) with frequencies f.sub.Yj (j=y, . . . , 2, 1, 0, -1, -2, . . . , -y) respectively, the total electric signal .SIGMA.E.sub.Yj made by said electric signals E.sub.Yj being zero and not able to be detected at said interdigital transducer R.sub.Y,
• 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 lower than that traveling on said piezoelectric substrate alone,
• said interdigital transducers T.sub.X and R.sub.X forming propagation lanes Z.sub.Xi (i=x, . . . , 2, 1, 0, -1, -2, . . . , -x) of the surface acoustic wave on said upper end surface of said nonpiezoelectric plate, a propagation lane Z.sub.XO existing on the line not only vertical to the finger direction of said interdigital transducer T.sub.X but also dividing the overlap length L.sub.X of said interdigital transducer T.sub.X into two halves, said propagation lanes Z.sub.Xi corresponding to positions F.sub.Xi (i=x, . . . , 2, 1, 0, -1, -2, . . . , -x) on said upper end surface of said nonpiezoelectric plate,
• said interdigital transducers T.sub.Y and R.sub.Y forming propagation lanes Z.sub.Yj (j=y, . . . , 2, 1, 0, -1, -2, . . . -y) of the surface acoustic wave on said upper end surface of said nonpiezoelectric plate, a propagation lane Z.sub.YO existing on the line not only vertical to the finger direction of said interdigital transducer T.sub.Y but also dividing the overlap length L.sub.Y of said interdigital transducer T.sub.Y into two halves, said propagation lanes Z.sub.Yj corresponding to positions F.sub.Yj (j=y, . . . , 2, 1, 0, -1, -2, . . . , -y) on said upper end surface of said nonpiezoelectric plate,
• said controlling system sensing a touch with a finger or others on a crossing point made from a position F.sub.Xx and a position F.sub.Yy by an appearance of an electric signal E.sub.X-x at said interdigital transducer R.sub.X and an appearance of an electric signal E.sub.Y-y at said interdigital transducer R.sub.Y, finding said crossing point by detecting the frequency f.sub.X-x of said electric signal E.sub.X-x and the frequency f.sub.Y-y of said electric signal E.sub.Y-y, and producing an image on a position, corresponding to said crossing point, on a display panel receiving said electric signal E.sub.X-x and said electric signal E.sub.Y-y.