Patent ID: 6060812
Filing Date: 2000-05-09
Classification: G06F

Abstract:
An ultrasonic touch-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 at the middle of said lower end surface of said piezoelectric substrate, the polarization axis of said piezoelectric substrate being parallel to the finger direction of said interdigital transducer T, said interdigital transducer T having an interdigital periodicity P and an overlap length L, the thickness d of said piezoelectric substrate being smaller than said interdigital periodicity P;two output interdigital transducers R.sub.1 and R.sub.2, formed at one edge of said lower end surface of said piezoelectric substrate and opposed to said interdigital transducer T;two output interdigital transducers R.sub.3 and R.sub.4, formed at the other edge of said lower end surface of said piezoelectric substrate and opposed to said interdigital transducer T, each of said interdigital transducers R.sub.1, R.sub.2, R.sub.3 and R.sub.4, being placed such that the finger direction thereof is slanting to that of said interdigital transducer T by an angle .alpha., an interdigital periodicity P.sub.N along the vertical direction to the finger direction of each of said interdigital transducers R.sub.1, R.sub.2, R.sub.3 and R.sub.4, being equal to the product of said interdigital periodicity P and cos .alpha., an overlap length L.sub.P along the finger direction of each of said interdigital transducers R.sub.1, R.sub.2, R.sub.3 and R.sub.4, being equal to the product of at most half said overlap length L and sec .alpha.;a nonpiezoelectric plate having an upper- and a lower end surfaces running perpendicular to the thickness direction thereof, said lower end surface thereof being cemented on said upper end surface of said piezoelectric substrate, said upper end surface of said piezoelectric substrate being under electrically opened condition, said upper end surface of said nonpiezoelectric plate consisting of a first area S.sub.1 between said interdigital transducers T and R.sub.1, a second area S.sub.2 between said interdigital transducers T and R.sub.2, a third area S.sub.3 between said interdigital transducers T and R.sub.3, and a fourth area S.sub.4 between said interdigital transducers T and R.sub.4 ; anda signal controller, output terminals of said interdigital transducers R.sub.1, R.sub.2, R.sub.3 and R.sub.4, being connected with said signal controller;said piezoelectric substrate and said nonpiezoelectric plate forming a bilayer assembly;said interdigital transducer T receiving an electric signal with a frequency approximately corresponding to said interdigital periodicity P, and exciting an SH wave of the zeroth mode and the higher order modes in said bilayer assembly, said SH wave having the wavelength approximately equal to said interdigital periodicity P, the phase velocity of said SH wave being approximately equal to the average value between the shear wave velocity traveling on said nonpiezoelectric plate alone and that traveling on said piezoelectric substrate alone;said interdigital transducer R.sub.1 transducing said SH wave to an electric signal E.sub.1 and delivering said electric signal E.sub.1 only when touching on said area S.sub.1 ;said interdigital transducer R.sub.2 transducing said SH wave to an electric signal E.sub.2 and delivering said electric signal E.sub.2 only when touching on said area S.sub.2 ;said interdigital transducer R.sub.3 transducing said SH wave to an electric signal E.sub.3 and delivering said electric signal E.sub.3 only when touching on said area S.sub.3 ;said interdigital transducer R.sub.4 transducing said SH wave to an electric signal E.sub.4 and delivering said electric signal E.sub.4 only when touching on said area S.sub.4 ;said signal controller sensing a touch with a finger or others on said area S.sub.1, S.sub.2, S.sub.3, or S.sub.4 by an appearance of said electric signal E.sub.1, E.sub.2, E.sub.3 or E.sub.4 at said interdigital transducer R.sub.1, R.sub.2, R.sub.3 or R.sub.4, respectively, and moving an image on a display panel connected with an output terminal of said signal controller along a touching direction from one to the other of said areas S.sub.1, S.sub.2, S.sub.3 and S.sub.4.