Surface acoustic wave touch-position sensing device

• US 5,852,261 A
• Filed: 08/09/1996
• Issued: 12/22/1998
• Est. Priority Date: 08/09/1996
• Status: Expired due to Term

• Current Assignee: Toda, Kohji
• Original Assignee: Toda, Kohji
• Inventors: Toda, Kohji
• Primary Examiner(s): Shankar, Vijay
• Application Number:
  US08/694,983
• Time in Patent Office: 865 Days
• Field of Search: 178/18, 178/19, 178/20, 178/18.01, 178/18.04, 178/19.02, 345/173, 345/176, 345/177, 367/907
• US Class Current: 178/18.04
• 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 touch-position sensing device comprising at least two surface acoustic wave-transducing units X and Y having N propagation lanes U_Xi (i=1, 2, . . . , N) and U_Yi (i=1, 2, . . . , N), respectively, a nonpiezoelectric plate, and a controlling system connected with the units X and Y. Each unit includes a piezoelectric substrate P_T, a piezoelectric substrate P_R, at least an input interdigital transducer formed on one end surface of the piezoelectric substrate P_T, and at least an output interdigital transducer formed on one end surface of the piezoelectric substrate P_R. The piezoelectric substrates P_T and P_R are mounted on an upper end surface of the nonpiezoelectric plate. When an electric signal E_T is applied to the input interdigital transducer, a surface acoustic wave is excited in the piezoelectric substrate P_T. The surface acoustic wave is transmitted to the piezoelectric substrate P_R through the upper end surface of the nonpiezoelectric plate, and is transduced to an electric signal E_R. If touching a crossing point of the lanes U_Xi and U_Yi on the upper end surface of the nonpiezoelectric plate, the surface acoustic wave is intercepted at the crossing point. Therefore, the magnitude of the electric signal E_R corresponding to the crossing point decrease or disappearance. Thus, it is possible to specify the crossing point.

Claims

1. A surface acoustic wave touch-position sensing device comprising:

at least two surface acoustic wave transducing units X and Y, each thereof consisting of

a piezoelectric substrate P_T having two end surfaces running perpendicular to the direction of the thickness d thereof,

a piezoelectric substrate P_R having two end surfaces running perpendicular to the direction of the thickness d thereof,

N interdigital transducers I_Ti (i=1, 2, . . . , N) formed on one end surface of said piezoelectric substrate P_T, said thickness d of said piezoelectric substrate P_T being smaller than an interdigital periodicity p of each interdigital transducer I_Ti,

an interdigital transducer I_R formed on one end surface of said piezoelectric substrate P_R and having an interdigital periodicity equal to said interdigital periodicity p, said thickness d of said piezoelectric substrate P_R being smaller than said interdigital periodicity p, and

N switches C_i (i=1, 2, . . . , N), an output terminal of each thereof being connected with an input terminal of each of said interdigital transducers I_Ti ;

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 P_T and P_R 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,

said interdigital transducer I_Ti receiving an electric signal E_T with a frequency approximately corresponding to said interdigital periodicity p, exciting the surface acoustic wave of the first mode and the higher order modes in said piezoelectric substrate P_T, and transmitting said surface acoustic wave having the wavelength approximately equal to said interdigital periodicity p to said piezoelectric substrate P_R 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 I_R transducing said surface acoustic wave in said piezoelectric substrate P_R to an electric signal E_R with a frequency approximately corresponding to said interdigital periodicity p,

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 P_T and P_R alone,

said controlling system turning on and off said switches C_i with a fixed period in turn, keeping a check on a magnitude of said electric signal E_R, sensing a touch with a finger or others on said upper end surface of said nonpiezoelectric plate by a decrease or a disappearance in magnitude of said electric signal E_R, picking out one of said switches C_i turned on when said decrease or said disappearance in magnitude of said electric signal E_R happens,

said surface acoustic wave transducing unit X having N propagation lanes U_Xi (i=1, 2, . . . , N) of said surface acoustic wave between said interdigital transducers I_Ti and I_R, two neighbors of said propagation lanes U_Xi being closed or partially overlapping each other,

said surface acoustic wave transducing unit Y having N propagation lanes U_Yi (i=1, 2, . . . , N) of said surface acoustic wave between said interdigital transducers I_Ti and I_R, two neighbors of said propagation lanes U_Yi being closed or partially overlapping each other, said propagation lanes U_Xi being vertical to said propagation lanes U_Yi.

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

an amplifier A_X, an input terminal of said switch C_i in said surface acoustic wave transducing unit Y being connected with an output terminal of said interdigital transducer I_R in said surface acoustic wave transducing unit X via said amplifier A_X ; and

an amplifier A_Y, an input terminal of said switch C_i in said surface acoustic wave transducing unit X being connected with an output terminal of said interdigital transducer I_R in said surface acoustic wave transducing unit Y via said amplifier A_Y,

said switches C_i in said surface acoustic wave transducing unit X, said propagation lanes U_Xi as delay elements, said amplifier A_X, said switches C_i, in said surface acoustic wave transducing unit Y, said propagation lanes U_Yi as delay elements, and said amplifier A_Y forming N oscillators H_i (i=1, 2, . . . , N).

3. A surface acoustic wave touch-position sensing device as defined in claim 1 further comprising a supporting board cemented to said lower end surface of said nonpiezoelectric plate.

4. A surface acoustic wave touch-position sensing device as defined in claim 1, wherein each of said piezoelectric substrates P_T and P_R is made of a piezoelectric ceramic, the polarization axis thereof being parallel to the thickness direction thereof.

5. A surface acoustic wave touch-position sensing device as defined in claim 1, wherein each of said piezoelectric substrates P_T and P_R is made of a piezoelectric polymer.

6. A surface acoustic wave touch-position sensing device comprising:

at least two surface acoustic wave transducing units X and Y, each thereof consisting of

a piezoelectric substrate P_T having an upper- and a lower end surfaces running perpendicular to the direction of the thickness d thereof,

a piezoelectric substrate P_R having an upper- and a lower end surfaces running perpendicular to the direction of the thickness d thereof,

N interdigital transducers T_i (i=1, 2, . . . , N) formed on said upper end surface of said piezoelectric substrate P_T, each interdigital transducer T_i consisting of two electrodes T_i-1 and T_i-2 and having two kinds of distances between one electrode finger of said electrode T_i-1 and two neighboring electrode fingers of said electrode T_i-2, said thickness d of said piezoelectric substrate P_T being smaller than an interdigital periodicity p of said interdigital transducer T_i,

an interdigital transducer R, formed on said upper end surface of said piezoelectric substrate P_R, consisting of two electrodes R_-1, and R_-2, having two kinds of distances between one electrode finger of said electrode R_-1 and two neighboring electrode fingers of said electrode R_-2, and having an interdigital periodicity equal to said interdigital periodicity p, said thickness d of said piezoelectric substrate P_R being smaller than said interdigital periodicity p,

N earth electrodes G_Ti (i=1, 2, . . . , N) formed on said lower end surface of said piezoelectric substrate P_T,

an earth electrode G_R formed on said lower end surface of said piezoelectric substrate P_R,

a phase shifter S_T including at least a coil L₁,

a phase shifter S_R including at least a coil L₂, and

N pairs of switches W_i (i=1, 2,. . . , N), each pair of switches W_i consisting of two switches W_i-1 and W_i-2, output terminals of said switches W_i-1 and W_i-2 being connected with input terminals of said electrodes T_i-1 and T_i-2, respectively;

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 P_T and P_R being mounted on said upper end surface of said nonpiezoelectric plate through said earth electrodes G_Ti and G_R, respectively; and

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

said interdigital transducer T_i and said earth electrode G_Ti receiving an electric signal E_T1 between said electrode T_i-1 and said earth electrode G_Ti, and an electric signal E_T2 between said electrode T_i-2 and said earth electrode G_Ti via said phase shifter S_T, exciting a surface acoustic wave of the first mode and the higher order modes in said piezoelectric substrate P_T, and transmitting said surface acoustic wave having the wavelength approximately equal to said interdigital periodicity p to said piezoelectric substrate P_R 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, each of said electric signals E_T1 and E_T2 having a frequency approximately corresponding to said interdigital periodicity p, the phase difference between said electric signals E_T1 and E_T2 being 2 π

y,

said interdigital transducer R and said earth electrode G_R transducing said surface acoustic wave in said piezoelectric substrate P_R, with wavelength approximately equal to said interdigital periodicity p, to an electric signal E_R1, between said electrode R_-1, and said earth electrode G_R, and an electric signal E_R2 between said electrode R_-2 and said earth electrode G_R, each of said electric signals E_R1 and E_R2 having a frequency approximately corresponding to said interdigital periodicity p, the phase difference between said electric signals E_R1 and E_R2 being 2 π

y,

said phase shifter S_R combining said electric signals E_R1 and E_R2, and delivering a combined electric signal E_R,

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 P_T and P_R alone,

said controlling system turning on and off said pairs of switches W_i with a fixed period in turn, keeping a check on a magnitude of said electric signal E_R, sensing a touch with a finger or others on said upper end surface of said nonpiezoelectric plate by a decrease or a disappearance in magnitude of said electric signal E_R, picking out said pair of switches W_i turned on when said decrease or said disappearance in magnitude of said electric signal E_R happens,

said surface acoustic wave transducing unit X having N propagation lanes U_Xi (i=1, 2, . . . , N) of said surface acoustic wave between said interdigital transducers T_i and R, two neighbors of said propagation lanes U_Xi being closed or partially overlapping each other,

said surface acoustic wave transducing unit Y having N propagation lanes U_Yi (i=1, 2, . . . , N) of said surface acoustic wave between said interdigital transducers T_i and R, two neighbors of said propagation lanes U_Yi being closed or partially overlapping each other, said propagation lanes U_Xi being vertical to said propagation lanes U_Yi.

7. A surface acoustic wave touch-position sensing device as defined in claim 6, wherein x<

1/2 in a shorter distance xp of said two kinds of distances between one electrode finger of said electrode T_i-1 and two neighboring electrode fingers of said electrode T_i-2, x<

1/2 in a shorter distance xp of said two kinds of distances between one electrode finger of said electrode R_-1 and two neighboring electrode fingers of said electrode R_-2, x+y=±

1/2 in said phase difference 2 π

y between said electric signals E_T1 and E_T2, and x+y=+±

1/2 in said phase difference 2 π

y between said electric signals E_R1 and E_R2.

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

an amplifier A_X, an input terminal of said phase shifter S_T in said surface acoustic wave transducing unit Y being connected with an output terminal of said phase shifter S_R in said surface acoustic wave transducing unit X via said amplifier A_X ; and

an amplifier A_Y, an input terminal of said phase shifter S_T in said surface acoustic wave transducing unit X being connected with an output terminal of said phase shifter S_R in said surface acoustic wave transducing unit Y via said amplifier A_Y,

said phase shifter S_T in said surface acoustic wave transducing unit X, said pairs of switches W_i in said surface acoustic wave transducing unit X, said propagation lanes U_Xi as delay elements, said phase shifter S_R in said surface acoustic wave transducing unit X, said amplifier A_X, said phase shifter S_T in said surface acoustic wave transducing unit Y, said pairs of switches W_i in said surface acoustic wave transducing unit Y, said propagation lanes U_Yi as delay elements, said phase shifter S_R in said surface acoustic wave transducing unit Y, and said amplifier A_Y forming N oscillators H_i (i=1, 2, . . . , N).

9. A surface acoustic wave touch-position sensing device as defined in claim 6 further comprising a supporting board cemented to said lower end surface of said nonpiezoelectric plate.

10. A surface acoustic wave touch-position sensing device as defined in claim 6, wherein each of said piezoelectric substrates P_T and P_R is made of a piezoelectric ceramic, the polarization axis thereof being parallel to the thickness direction thereof.

11. A surface acoustic wave touch-position sensing device as defined in claim 6, wherein each of said piezoelectric substrates P_T and P_R is made of a piezoelectric polymer.

12. A surface acoustic wave touch-position sensing device comprising:

at least two surface acoustic wave transducing units X and Y, each thereof consisting of

a piezoelectric substrate P_T having an upper- and a lower end surfaces running perpendicular to the direction of the thickness d thereof,

a piezoelectric substrate P_R having an upper- and a lower end surfaces running perpendicular to the direction of the thickness d thereof,

an interdigital transducer T, formed on said upper end surface of said piezoelectric substrate P_T, consisting of two electrodes T_-1 and T_-2 and having two kinds of distances between one electrode finger of said electrode T_-1 and two neighboring electrode fingers of said electrode T_-2, said thickness d of said piezoelectric substrate P_T being smaller than an interdigital periodicity p of said interdigital transducer T,

N interdigital transducers R_i (i=1, 2. . . , N) formed on said upper end surface of said piezoelectric substrate P_R, each interdigital transducer R_i having an interdigital periodicity equal to said interdigital periodicity p, said thickness d of said piezoelectric substrate P_R being smaller than said interdigital periodicity p, and

an earth electrode G_T formed on said lower end surface of said piezoelectric substrate P_T ;

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 P_T and P_R being mounted on said upper end surface of said nonpiezoelectric plate through said lower end surfaces of said piezoelectric substrates P_T and P_R, respectively;

a phase shifter S_T including at least a coil L₁ ; and

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

said interdigital transducer T and said earth electrode G_T receiving an electric signal E_T1 between said electrode T_-1 and said earth electrode G_T, and an electric signal E_T2 between said electrode T_-2 and said earth electrode G_T via said phase shifter S_T, exciting a surface acoustic wave of the first mode and the higher order modes in said piezoelectric substrate P_T, and transmitting said surface acoustic wave having the wavelength approximately equal to said interdigital periodicity p to said piezoelectric substrate P_R 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, each of said electric signals E_T1 and E_T2 having a frequency approximately corresponding to said interdigital periodicity p, the phase difference between said electric signals E_T1 and E_T2 being 2 π

y,

said interdigital transducer R_i transducing said surface acoustic wave in said piezoelectric substrate P_R, with wavelength approximately equal to said interdigital periodicity p, to electric signals E_Ri (i=1, 2,. . . , N), said signal E_Ri having a frequency approximately corresponding to said interdigital periodicity p,

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 P_T and P_R alone,

said controlling system keeping a check on a magnitude of said electric signals E_Ri, sensing a touch with a finger or others on the other end surface of said nonpiezoelectric plate by a decrease or a disappearance in magnitude of said electric signals E_Ri, picking out at least one of said interdigital transducers R_i corresponding to said decrease or said disappearance in magnitude of said electric signals E_Ri,

said surface acoustic wave transducing unit X having N propagation lanes U_Xi (i=1, 2, . . . , N) of said surface acoustic wave between said interdigital transducers T and R_i, two neighbors of said propagation lanes U_Xi being closed or partially overlapping each other,

said surface acoustic wave transducing unit Y having N propagation lanes U_Yi (i=1, 2, . . . , N) of said surface acoustic wave between said interdigital transducers T and R_i, two neighbors of said propagation lanes U_Yi being closed or partially overlapping each other, said propagation lanes U_Xi being vertical to said propagation lanes U_Yi.

13. A surface acoustic wave touch-position sensing device as defined in claim 12, wherein x<

1/2 in a shorter distance xp of said two kinds of distances between one electrode finger of said electrode T_-1 and two neighboring electrode fingers of said electrode T_-2, and x+y=±

1/2 in said phase difference 2 π

y between said electric signals E_T1 and E_T2.

14. A surface acoustic wave touch-position sensing device as defined in claim 12 further comprising

an amplifier AMP, two output terminals of said phase shifter S_T being connected with input terminals of said electrodes T_-1, and T_-2, respectively, an input terminal of said phase shifter S_T being connected with an interdigital transducers R₁ of said interdigital transducers R_i in said surface acoustic wave transducing unit Y, via said amplifier AMP,

said interdigital transducer T in said surface acoustic wave transducing unit Y, a propagation lane U_Yi, as a delay element, of said surface acoustic wave between said interdigital transducers T and R₁ in said surface acoustic wave transducing unit Y, said interdigital transducer R₁, said amplifier AMP and said phase shifter S_T forming an oscillator H₁.

15. A surface acoustic wave touch-position sensing device as defined in claim 12 further comprising a supporting board cemented to said lower end surface of said nonpiezoelectric plate.

16. A surface acoustic wave touch-position sensing device as defined in claim 12, wherein each of said piezoelectric substrates P_T and P_R is made of a piezoelectric ceramic, the polarization axis thereof being parallel to the thickness direction thereof.

17. A surface acoustic wave touch-position sensing device as defined in claim 12, wherein each of said piezoelectric substrates P_T and P_R is made of a piezoelectric polymer.