Surface acoustic wave device for sensing a touch-position

• US 5,767,608 A
• Filed: 03/06/1997
• Issued: 06/16/1998
• 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:
  US08/812,704
• Time in Patent Office: 467 Days
• Field of Search: 310/322, 310/313 R, 310/365, 310/313 B, 310/313 D, 333/193, 73/597
• 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 (SAW) position-sensing device comprising a piezoelectric substrate, an input interdigital transducer (IDT) T formed on an upper end surface of the piezoelectric substrate, and an output IDT R formed on the upper end surface of the piezoelectric substrate such that the finger direction of the IDT R is slanting to that of the IDT T by an angle α. The thickness d of the piezoelectric substrate is larger than three times an interdigital periodicity P of the IDT T. An interdigital periodicity P_N along the vertical direction to the finger direction of the IDT R is equal to the product of the interdigital periodicity P and cos α. An overlap length L_P along the finger direction of the IDT R is equal to the product of an overlap length L of the T and sec α. When an electric signal is applied to the IDT T, the SAW is excited on the upper end surface of the piezoelectric substrate, and is transducer to electric signals E_j with phases θ_j by the IDT R, the phases θ_j corresponding to positions F_j. The total phase Σθ_j made by the phases θ_j, and the total electric signal ΣE_j made by the electric signals E_j are zero. The IDT T and R form minute propagation lanes Z_j, corresponding to the positions F_j, of the SAW on the upper end surface of the piezoelectric substrate. If touching a position F_x on a minute propagation lane Z_x, an electric signal E with a phase θ is delivered from the IDT R. The position F_x corresponds to an electric signal E_x with a phase θ_x, the electric signal ΣE_j minus the electric signal E_x being equal to the electric signal E, the phase Σθ_j minus the phase θ_x being equal to the phase θ.

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 direction of the thickness d thereof;

an input interdigital transducer T formed on said upper end surface of said piezoelectric substrate, said thickness d being larger than three times an interdigital periodicity P of said interdigital transducer T; and

an output interdigital transducer R formed on said upper end surface of said piezoelectric substrate such that the finger direction of said interdigital transducer R is slanting to that of said interdigital transducer T by an angle α

, an interdigital periodicity P_N along the vertical direction to the finger direction of said interdigital transducer R being equal to the product of said interdigital periodicity P and cos α

,

said interdigital transducer T receiving an electric signal with a frequency approximately corresponding to said interdigital periodicity P, and exciting a surface acoustic wave on said upper end surface of said piezoelectric substrate, said surface acoustic wave having the wavelength approximately equal to said interdigital periodicity P,

said interdigital transducer R transducing said surface acoustic wave 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 piezoelectric substrate, 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 said interdigital transducer R,

said interdigital transducers T and R forming minute propagation lanes Z_j (j=1, 2, . . . , χ

) of the surface acoustic wave on said upper end surface of said piezoelectric substrate, said minute propagation lanes Z_j corresponding to said positions F_j,

said interdigital transducer R delivering an electric signal E with a phase θ

only when touching with a finger or others on 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

.

2. A surface acoustic wave position-sensing device as defined in claim 1, wherein an overlap length L_P along the finger direction of said interdigital transducer R is equal to the product of an overlap length L of said interdigital transducer T and sec α

.

3. 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.

4. A surface acoustic wave position-sensing device comprising:

a piezoelectric substrate 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 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, said thickness d being larger than three times an interdigital periodicity P of said interdigital transducers T_o, T_i and R_o, 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

; 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, and exciting a surface acoustic wave on said upper end surface of said piezoelectric substrate, said surface acoustic wave having the wavelength approximately equal to said interdigital periodicity P,

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 piezoelectric substrate, 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 interdigital transducers T_i and R_i1 forming N propagation lanes D_i1 (i=1, 2,. . . , N) of the surface acoustic wave on said upper end surface of said piezoelectric substrate, 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 R_i2 forming N propagation lanes D_i2 (i=1, 2, . . . , N) of the surface acoustic wave on said upper end surface of said piezoelectric substrate, 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_i1, and by evaluating a difference between said phases θ and

θ

_base.

5. A surface acoustic wave position-sensing device as defined in claim 4 further comprising:

N switches W_i (i=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 Q₁,

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.

6. A surface acoustic wave position-sensing device as defined in claim 4, 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

.

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

8. A surface acoustic wave position-sensing device as defined in claim 4, 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.

9. A surface acoustic wave position-sensing device as defined in claim 4 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 of 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.

10. A surface acoustic wave position-sensing device as defined in claim 4, wherein said piezoelectric substrate is made of a piezoelectric ceramic, the polarization axis thereof being parallel to the thickness direction thereof.