Surface acoustic wave device for sensing a touch-position
First Claim
1. A surface acoustic wave 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;
two surface acoustic wave transducing units X and Y, each thereof consisting ofan input interdigital transducer To formed on said upper end surface of said piezoelectric substrate,N input interdigital transducers Ti (i=1, 2, . . . , N) formed on said upper end surface of said piezoelectric substrate,an output interdigital transducer Ro opposed to said interdigital transducer To on said upper end surface of said piezoelectric substrate and placed such that the finger direction of said interdigital transducer Ro runs parallel with that of said interdigital transducer To,the thickness of said piezoelectric substrate being larger than three times an interdigital periodicity P of said interdigital transducers To, Ti and Ro, said thickness d of said nonpiezoelectric plate being smaller than said interdigital periodicity P, andat least two output interdigital transducers Ri1 and Ri2 (i=1, 2, . . . , N) opposed to each interdigital transducer Ti on said upper end surface of said piezoelectric substrate and placed 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
, said lower end surface of said nonpiezoelectric plate being cemented on said upper end surface of said piezoelectric substrate through said interdigital transducers To,Ti, Ro, Ri1 and Ri2 ; 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 zeroth mode and the higher order modes on an area, in contact with said interdigital transducers To and Ti, 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 to an area, in contact with said interdigital transducers Ro, Ri1 and Ri2, 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 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, . . . , χ
) with phases θ
j (j=1, 2, . . . , χ
), respectively, said phases θ
j corresponding to positions Fj (j=1, 2, . . . , χ
) 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 lower than that traveling on said piezoelectric substrate alone,said interdigital transducers Ti and Ri1 forming N propagation lanes Di1 (j=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, . . . , χ
) corresponding to said positions Fj,said interdigital transducers Ti and Ri2 forming N propagation lanes Di2 (j=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, . . . , 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
E j 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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Abstract
A surface acoustic wave position-sensing device comprising a piezoelectric substrate, a nonpiezoelectric plate, two surface acoustic wave transducing units and a controlling system connected with the units. Each unit consists of interdigital transducers (IDTs). The thickness of the piezoelectric substrate is larger than three time an interdigital periodicity of the IDTs. The thickness of the nonpiezoelectric plate is smaller than the interdigital periodicity. Each of the IDTs is placed such that the finger direction thereof is slanting to that of the IDTs by an angle α. When an electric signal is applied to each of the IDTs a SAW is excited on an area, and transmitted to an area, in contact with the IDTs of the upper end surface of the piezoelectric substrate through the nonpiezoelectric plate. The controlling system senses a touch with a finger by the generation of the electric signal at one of the interdigital transducers.
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Citations
8 Claims
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1. A surface acoustic wave position-sensing device comprising:
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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; two surface acoustic wave transducing units X and Y, each thereof consisting of an input interdigital transducer To formed on said upper end surface of said piezoelectric substrate, N input interdigital transducers Ti (i=1, 2, . . . , N) formed on said upper end surface of said piezoelectric substrate, an output interdigital transducer Ro opposed to said interdigital transducer To on said upper end surface of said piezoelectric substrate and placed such that the finger direction of said interdigital transducer Ro runs parallel with that of said interdigital transducer To,the thickness of said piezoelectric substrate being larger than three times an interdigital periodicity P of said interdigital transducers To, Ti and Ro, said thickness d of said nonpiezoelectric plate being smaller than said interdigital periodicity P, and at least two output interdigital transducers Ri1 and Ri2 (i=1, 2, . . . , N) opposed to each interdigital transducer Ti on said upper end surface of said piezoelectric substrate and placed 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
, said lower end surface of said nonpiezoelectric plate being cemented on said upper end surface of said piezoelectric substrate through said interdigital transducers To,Ti, Ro, Ri1 and Ri2 ; anda 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 zeroth mode and the higher order modes on an area, in contact with said interdigital transducers To and Ti, 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 to an area, in contact with said interdigital transducers Ro, Ri1 and Ri2, 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 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, . . . , χ
) with phases θ
j (j=1, 2, . . . , χ
), respectively, said phases θ
j corresponding to positions Fj (j=1, 2, . . . , χ
) 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 lower than that traveling on said piezoelectric substrate alone, said interdigital transducers Ti and Ri1 forming N propagation lanes Di1 (j=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, . . . , χ
) corresponding to said positions Fj,said interdigital transducers Ti and Ri2 forming N propagation lanes Di2 (j=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, . . . , 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
E j 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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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Specification