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Elastic wave device for sensing a touch-position

  • US 5,767,604 A
  • Filed: 03/06/1997
  • Issued: 06/16/1998
  • Est. Priority Date: 03/06/1997
  • Status: Expired due to Term
First Claim
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1. An elastic wave position-sensing device comprising:

  • two elastic wave transducing units X and Y, each thereof consisting ofa piezoelectric substrate PT having two end surfaces running perpendicular to the direction of the thickness d thereof,a piezoelectric substrate PR having two end surfaces running perpendicular to the direction of the thickness d thereof,an input interdigital transducer T0 formed on one end surface of said piezoelectric substrate PT,N input interdigital transducers Ti (i=1, 2, . . . , N) formed on said one end surface of said piezoelectric substrate PT,an output interdigital transducer R0 opposed to said interdigital transducer T0 and placed on one end surface of said piezoelectric substrate PR such that the finger direction of said interdigital transducer R0 runs parallel with that of said interdigital transducer T0, said thickness d of said piezoelectric substrates PT and PR being smaller than an interdigital periodicity P of said interdigital transducers T0, Ti and R0, andat least two output interdigital transducers Ri1 and Ri2 (i=1, 2, . . . , N) opposed to each interdigital transducer Ti and placed on said one end surface of said piezoelectric substrate PR such that the finger direction of said interdigital transducers Ri1 and Ri2 is slanting to that of said interdigital transducer Ti by an angle α

    , respectively, an interdigital periodicity PN along the vertical direction to the finger direction of said interdigital transducers Ri1 and Ri2 being equal to the product of said interdigital periodicity P and cos α

    ;

    a nonpiezoelectric plate having two end surfaces, the thickness of said nonpiezoelectric plate being smaller than two times said thickness d, said piezoelectric substrates PT and PR being mounted on one end surface of said nonpiezoelectric plate; and

    a controlling system connected with said elastic wave transducing units X and Y,a part, adjacent to said piezoelectric substrate PT, of said nonpiezoelectric plate, and said piezoelectric substrate PT forming a bilayer zone BT,a part, adjacent to said piezoelectric substrate PR, of said nonpiezoelectric plate, and said piezoelectric substrate PR forming a bilayer zone BR,the remaining part, between said bilayer zones BT and BR, of said nonpiezoelectric plate consisting of a monolayer zone,each of said interdigital transducers T0 and Ti receiving an electric signal with a frequency approximately corresponding to said interdigital periodicity P, exciting an elastic wave of the S0 mode and the higher order modes in said bilayer zone BT, and transmitting said elastic wave, having the wavelength approximately equal to said interdigital periodicity P, to said bilayer zone BR through said monolayer zone, the phase velocity of said elastic wave being approximately equal to the phase velocity Vfd=0, of the S0 mode elastic wave, corresponding to a condition that the product fd of the frequency f of said elastic wave and said thickness d is zero,said interdigital transducer R0 transducing said elastic wave excited by said interdigital transducer T0 to an electric signal with a phase θ

    base and delivering said electric signal,each of said interdigital transducers Ri1 and Ri2 transducing said elastic wave excited by each interdigital transducer Ti to electric signals Ej (j=1, 2, . . . , χ

    ) with phases θ

    j (j=1, 2, . . . , χ

    ), respectively, said phases θ

    j corresponding to positions Fj (j=1, 2, . . . , χ

    ) on one or the other end surface of said monolayer zone, each electric signal Ej having a frequency approximately corresponding to said interdigital periodicity P, the total phase Σ

    θ

    j made by said phases θ

    j being zero, the total electric signal Σ

    Ej made by said electric signals Ej being zero and not able to be detected at each of said interdigital transducers Ri1 and Ri2,said interdigital transducers Ti and Ri1 forming N propagation lanes Di1 (i=1, 2, . . . , N) of the elastic wave in said monolayer zone, each propagation lane Di1 consisting of minute propagation lanes Zj (j=1, 2, . . . , χ

    ) corresponding to said positions Fj,said interdigital transducers Ti and Ri2 forming N propagation lanes Di2 (i=1, 2, . . . , N) of the elastic wave in said monolayer zone, each propagation lane Di2 consisting of minute propagation lanes Zj (j=1, 2, . . . , χ

    ) corresponding to said positions Fj,one of said interdigital transducers Ri1 and Ri2 delivering an electric signal E with a phase θ

    only when touching a position FX, out of said positions Fj, on a minute propagation lane ZX out of said minute propagation lanes Zj, said position FX corresponding to an electric signal EX with a phase θ

    X, said total electric signal Σ

    Ej minus said electric signal EX being equal to said electric signal E, said total phase Σ

    θ

    j minus said phase θ

    X being equal to said phase θ

    ,said controlling system sensing a touch with a finger or others on said position FX by an appearance of said electric signal E at said one of said interdigital transducers Ri1 and Ri2, and finding said position FX by detecting said one, delivering said electric signal E, of said interdigital transducers Ri1 and Ri2, and by evaluating a difference between said phases θ and

    θ

    base.

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