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Surface acoustic wave device for sensing a touch-position

  • US 5,838,088 A
  • Filed: 03/06/1997
  • Issued: 11/17/1998
  • Est. Priority Date: 03/06/1997
  • Status: Expired due to Term
First Claim
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1. A surface acoustic wave position-sensing device comprising:

  • two surface acoustic 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 To 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 Ro opposed to said interdigital transducer To, said interdigital transducer Ro being formed on one end surface of said piezoelectric substrate PR and placed such that the finger direction of said interdigital transducer Ro runs parallel with that of said interdigital transducer To, said thickness d of said piezoelectric substrates PT and PR being smaller than an interdigital periodicity P of said interdigital transducers To, Ti and Ro, andat least two output interdigital transducers Ri1 and Ri2 (i=1, 2, . . . , N) opposed to each interdigital transducer Ti, said interdigital transducers Ri1 and Ri2 being formed 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 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 PT and PR being mounted on said upper end surface of said nonpiezoelectric plate; and

    a controlling system connected with said surface acoustic wave transducing units X and Y,each of said interdigital transducers To and Ti receiving an electric signal with a frequency approximately corresponding to said interdigital periodicity P, exciting a surface acoustic wave of the first mode and the higher order modes in said piezoelectric substrate PT, and transmitting said surface acoustic wave having the wavelength approximately equal to said interdigital periodicity P to said piezoelectric substrate PR 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,said interdigital transducer Ro transducing said surface acoustic wave excited by said interdigital transducer To to an electric signal with a phase θ

    base and delivering said electric signal,each of said interdigital transducers Ri1 and Ri2 transducing said surface acoustic wave excited by each interdigital transducer Ti to electric signals Ej (j=1, 2, . . . , X) with phases θ

    j (j=1, 2, . . . , X), respectively, said phases θ

    j corresponding to positions Fj (j=1, 2, . . . , X) on said upper end surface of said nonpiezoelectric plate, respectively, 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 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 PT and PR alone,said interdigital transducers Ti and Ri1 forming N propagation lanes Di1 (i=1, 2, . . . , N) of the surface acoustic wave on said upper end surface of said nonpiezoelectric plate, each propagation lane Di1 consisting of minute propagation lanes Zj (j=1, 2, . . . , X) corresponding to said positions Fj,said interdigital transducers Ti and Ri2 forming N propagation lanes Di2 (i=1, 2, . . . , N) of the surface acoustic wave on said upper end surface of said nonpiezoelectric plate, each propagation lane Di2 consisting of minute propagation lanes Zj (j=1, 2, . . . , X) 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 R12, and by evaluating a difference between said phases θ and

    θ

    base.

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