Surface acoustic wave position-sensing device

• US 5,723,934 A
• Filed: 08/09/1996
• Issued: 03/03/1998
• 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): Budd, Mark O.
• Application Number:
  US08/694,981
• Time in Patent Office: 571 Days
• Field of Search: 310/313 R, 310/313 A, 310/313 B, 310/313 D, 333/150-155, 333/193-196, 178/18, 178/19
• 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
• CPC Class Codes: G06K 19/063 the carrier being marginally punched or notched, e.g. having elongated slots
• CPC Class Codes: G06K 19/0675 the resonating marks being of the surface acoustic wave [SAW] kind SAW devices per se H03H9/64
• CPC Class Codes: G06K 19/07749 the record carrier being capable of non-contact communication, e.g. constructional details of the antenna of a non-contact smart card

Abstract

A surface acoustic wave position-sensing device comprising a piezoelectric substrate, a nonpiezoelectric plate, 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, and a controlling system connected with the units X and Y. Each unit includes input and output interdigital transducers formed on the upper end surface of the piezoelectric substrate. One end surface of the nonpiezoelectric plate is mounted on the upper end surface of the piezoelectric substrate through the interdigital transducers. When an electric signal E_T is applied to the input interdigital transducer, a surface acoustic wave is excited on an area, in contact with the input interdigital transducer, of the upper end surface of the piezoelectric substrate. The surface acoustic wave is transmitted to an area, in contact with the output interdigital transducer, of the upper end surface of the piezoelectric substrate, through 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 n 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 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;

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

N interdigital transducers T_i (i=1, 2, ...... , N) formed on said upper end surface of said piezoelectric substrate, the thickness of said piezoelectric substrate being larger than approximately three times an interdigital periodicity p of said interdigital transducer T_i, said thickness of d of said nonpiezoelectric plate being smaller than said interdigital periodicity p,

an interdigital transducer R formed on said upper end surface of said piezoelectric substrate and having an interdigital periodicity equal to said interdigital periodicity p, said lower end surface of said nonpiezoelectric plate being mounted on said upper end surface of said piezoelectric substrate through said interdigital transducers T_i and R, and

N switches W_i (i=1, 2, ...... , N), output terminals thereof being connected with input terminals of said interdigital transducers T_i, respectively; and

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

said interdigital transducer T_i receiving an electric signal E_T 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 transducer 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 transducer R, 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 transducing said surface acoustic wave transmitted to said area, in contact with said interdigital transducer R, of said upper end surface of said piezoelectric substrate, 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 lower than that traveling on said piezoelectric substrate alone,

said controlling system turning on and off said 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 one of said 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 lane U_X being vertical to said propagation lane U_Yi.

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

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

said switches W_i in said surface acoustic wave transducing unit X, said propagation lanes U_Xi as delay elements, said amplifier A_X, said switches W_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 position-sensing device as defined in claim 1 further comprising a supporting board cemented to said lower end surface of said piezoelectric substrate.

4. 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.

5. 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;

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

an interdigital transducer T formed on said upper end surface of said piezoelectric substrate, the thickness of said piezoelectric substrate being larger than approximately three times an interdigital periodicity p of said interdigital transducer T, said thickness d of said nonpiezoelectric plate being smaller than said interdigital periodicity p, and

N interdigital transducers R_i (i=1, 2, ...... , N) formed on said upper end surface of said piezoelectric substrate and having an interdigital periodicity equal to said interdigital periodicity p, said lower end surface of said nonpiezoelectric plate being mounted on said upper end surface of said piezoelectric substrate through said interdigital transducers T and R_i ; and

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

said interdigital transducer T receiving an electric signal E_T 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 transducer T, 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_i, 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 transducers R_i transducing said surface acoustic wave transmitted to said area, in contact with said interdigital transducers R_i, of said upper end surface of said piezoelectric substrate, to electric signals E_Ri (i=1, 2, ...... , N), said electric 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 lower than that traveling on said piezoelectric substrate 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 said upper 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 lane U_Xi being vertical to said propagation lane U_Yi.

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

an amplifier AMP, an output terminal of the interdigital transducer R₁ of said interdigital transducers R_i in said surface acoustic wave transducing unit Y being connected with an input terminal of said interdigital transducer T in said surface acoustic wave transducing units X and Y, respectively,

said interdigital transducer T in said surface acoustic wave transducing unit Y, the propagation lane U_Y1 as a delay element, said interdigital transducer R_R1 in said surface acoustic wave transducing unit Y, and said amplifier AMP forming an oscillator H₁.

7. A surface acoustic wave position-sensing device as defined in claim 5 further comprising a supporting board cemented to said lower end surface of said piezoelectric substrate.

8. A surface acoustic wave position-sensing device as defined in claim 5, wherein said piezoelectric substrate is made of a piezoelectric ceramic, the polarization axis thereof being parallel to the thickness direction thereof.