Surface acoustic wave device for sensing a touch-position

• US 5,798,597 A
• Filed: 03/06/1997
• Issued: 08/25/1998
• Est. Priority Date: 03/06/1997
• Status: Expired due to Term

• Current Assignee: Toda, Kohji
• Original Assignee: Toda, Kohji
• Inventors: Toda, Kohji
• Primary Examiner(s): Budd, Mark O.
• Assistant Examiner(s): WILLIAMS, TIMOTHY A J
• Application Number:
  US08/812,706
• Time in Patent Office: 537 Days
• Field of Search: 310/313 R, 310/313 B, 310/313 D, 333/193, 333/194, 333/195, 333/196, 73/632
• US Class Current: 310/313.00R
• CPC Class Codes: G06F 3/0436 in which generating transducers and detecting transducers are attached to a single acoustic waves transmission substrate

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.

Claims

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 of

an input interdigital transducer T_o formed on said upper end surface of said piezoelectric substrate,

N input interdigital transducers T_i (i=1, 2, . . . , N) formed on said upper end surface of said piezoelectric substrate,

an output interdigital transducer R_o opposed to said interdigital transducer T_o on said upper end surface of said piezoelectric substrate and placed such that the finger direction of said interdigital transducer R_o runs parallel with that of said interdigital transducer T_o,the thickness of said piezoelectric substrate being larger than three times an interdigital periodicity P of said interdigital transducers T_o, T_i and R_o, said thickness d of said nonpiezoelectric plate being smaller than said interdigital periodicity P, and

at least two output interdigital transducers R_i1 and R_i2 (i=1, 2, . . . , N) opposed to each interdigital transducer T_i on said upper end surface of said piezoelectric substrate and placed such that the finger direction of said interdigital transducers R_i1 and R_i2 is slanting to that of said interdigital transducer T_i by an angle α

, respectively, an interdigital periodicity P_N along the vertical direction to the finger direction of said interdigital transducers R_i1 and R_i2 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 T_o,T_i, R_o, R_i1 and R_i2 ; and

a controlling system connected with said surface acoustic wave transducing units X and Y,

each of said interdigital transducers T_o and T_i 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 T_o and T_i, 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 R_o, R_i1 and R_i2, 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_o transducing said surface acoustic wave excited by said interdigital transducer T_o to an electric signal with a phase θ

_base and delivering said electric signal,

each of said interdigital transducers R_i1 and R_i2 transducing said surface acoustic wave excited by each interdigital transducer T_i to electric signals E_j (j=1, 2, . . . , χ

) with phases θ

_j (j=1, 2, . . . , χ

), respectively, said phases θ

_j corresponding to positions F_j (j=1, 2, . . . , χ

) on said upper end surface of said nonpiezoelectric plate, respectively, each electric signal E_j 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

E_j made by said electric signals E_j being zero and not able to be detected at each of said interdigital transducers R_i1 and R_i2,

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_i and R_i1 forming N propagation lanes D_i1 (j=1, 2, . . . , N) of the surface acoustic wave on said upper end surface of said nonpiezoelectric plate, each propagation lane D_i1 consisting of minute propagation lanes Z_j (j=1, 2, . . . , χ

) corresponding to said positions F_j,

said interdigital transducers T_i and Ri₂ forming N propagation lanes D_i2 (j=1, 2, . . . , N) of the surface acoustic wave on said upper end surface of said nonpiezoelectric plate, each propagation lane D_i2 consisting of minute propagation lanes Z_j (j=1, 2, . . . , χ

) corresponding to said positions F_j,

one of said interdigital transducers R_i1 and R_i2 delivering an electric signal E with a phase θ

only when touching a position F_x, out of said positions F_j, on a minute propagation lane Z_X out of said minute propagation lanes Z_j, said position F_x corresponding to an electric signal E_x with a phase θ

_x, said total electric signal Σ

E _j minus said electric signal E_x 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 F_X by an appearance of said electric signal E at said one of said interdigital transducers R_i1 and R_i2, and finding said position F_X by detecting said one, delivering said electric signal E, of said interdigital transducers R_i1 and R_i2, and by evaluating a difference between said phases θ and

θ

_base.

2. A surface acoustic wave position-sensing device as defined in claim 1 further comprising:

N switches W_i (j=1, 2, . . . , N) corresponding to said interdigital transducers T_i, an output terminal of each switch W_i being connected with an input terminal of each interdigital transducer T_i,

output terminals of said interdigital transducers R_i1 being connected with each other at an output point Q_i,

output terminals of said interdigital transducers R_i2 being connected with each other at an output point Q₂,

said controlling system turning on and off said switches W_i with a fixed period in turn, sensing a touch on said position F_x by an appearance of said electric signal E at one of said output points Q₁ and Q₂, and finding said position F_x by detecting said one, delivering said electric signal E, of said output points Q₁ and Q₂, by choosing a closed one out of said switches W_i when said electric signal E appears, and by evaluating said difference between said phases θ and

θ

_base.

3. A surface acoustic wave position-sensing device as defined in claim 1, wherein the sum of an overlap length L_p along the finger direction of said interdigital transducer R_i1 and that of said interdigital transducer R_i2 is approximately equal to the product of an overlap length L of said interdigital transducer T_i and sec α

.

4. A surface acoustic wave position-sensing device as defined in claim 1, wherein two neighbors of said propagation lanes D_i1 and D_i2 are closed or partially overlapping each other.

5. A surface acoustic wave position-sensing device as defined in claim 1, wherein said propagation lanes D_i1 and D_i2 of said surface acoustic wave transducing unit X and that of said surface acoustic wave transducing unit Y are vertical to each other.

6. A surface acoustic wave position-sensing device as defined in claim 1 further comprising:

an amplifier A_x, an input terminal of said interdigital transducer R_o of said surface acoustic wave transducing unit X being connected with each input terminal of said interdigital transducer T_o of said surface acoustic wave transducing units X and Y via said amplifier A_x,

said interdigital transducers T_o and R_o in said surface acoustic wave transducing unit X, a propagation lane of a surface acoustic wave between said interdigital transducers T_o and R_o in said surface acoustic wave transducing unit X, and said amplifier A_x forming an oscillator.

7. A surface acoustic wave position-sensing device as defined in claim 1, wherein said piezoelectric substrate is made of a piezoelectric ceramic, the polarization axis thereof being parallel to the thickness direction thereof.

8. A surface acoustic wave position-sensing device as defined in claim 1 further comprising a supporting board cemented to said lower end surface of said piezoelectric substrate.