Acoustic touch position sensor using shear wave propagation

• US 5,177,327 A
• Filed: 11/16/1990
• Issued: 01/05/1993
• Est. Priority Date: 11/16/1990
• Status: Expired due to Term

• Current Assignee: The Whitaker Corporation (Meggitt PLC)
• Original Assignee: Exzec Incorporated
• Inventors: Knowles, Terence J.
• Primary Examiner(s): SCHREYER, STAFFORD
• Application Number:
  US07/615,030
• Time in Patent Office: 781 Days
• Field of Search: 178/18, 178/19, 340/706, 340/712, 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
• CPC Class Codes: Y10S 367/907 Coordinate determination

Abstract

An acoustic touch position sensor is shown in which a transducer coupled to a side of a substrate imparts a shear wave into the substrate for propagation along a first axis. A reflective array is disposed along the first axis to reflect portions of the shear wave along a plurality of parallel paths extending across a touch surface of the substrate to a second reflective array the axis of which is parallel to the axis of the first reflective array. The second reflective array reflects the shear waves incident thereto to a transducer mounted on the side of the substrate and responsive to shear waves propagated thereto for providing a signal representative of these shear waves. A touch on the substrate results in a partial absorption of the energy in the shear wave so as to produce a perturbation therein which is sensed to determine the axial position of the touch on the substrate. In a second embodiment a single transducer and reflective array is provided for each axis, a coordinate on which is to be determined. In a third embodiment of the present invention, a single transducer is provided to transmit and receive shear waves propagating along perpendicular parallel paths.

Claims

1. A touch position sensor comprising:

a substrate capable of propagating a shear wave, said substrate having at least one touch surface;

means for propagating a shear wave in said substrate along a plurality of paths of differing lengths and differing positions, a touch on said substrate touch surface forming a perturbation in said shear wave; and

means for sensing the time of occurrence of said perturbation to determine the position of said touch.

2. A touch position sensor as recited in claim 1 wherein the thickness of said substrate is less than two times the wavelength of said shear wave.

3. A touch position sensor as recited in claim 1 wherein the thickness of said substrate is less than one-half times the wavelength of said shear wave.

4. A touch position sensor as recited in claim 1 wherein said substrate is formed of plastic.

5. A touch position sensor as recited in claim 1 wherein said substrate is formed of glass.

6. A touch position sensor as recited in claim 5 wherein said substrate is formed of plastic.

7. A touch position sensor as recited in claim 6 wherein said substrate includes a plastic material having an optical coating to substantially eliminate reflection, said plastic material being laminated to a surface of said glass.

8. A touch position sensor as recited in claim 5 wherein said glass is frosted.

9. A touch position sensor as recited in claim 5 wherein said substrate is formed of metal.

10. A touch position sensor as recited in claim 1 wherein said substrate is formed of a ceramic.

11. A touch position sensor as recited in claim 1 wherein said substrate is curved.

12. A touch position sensor as recited in claim 1 wherein said propagating means includes a first piezoelectric transducer bonded on a first edge of said substrate.

13. A touch position sensor as recited in claim 12 wherein said propagating means includes a conductive frit for bonding said first transducer to said first edge.

14. A touch position sensor as recited in claim 13 further including a second transducer bonded on a second edge of said substrate, said second edge being adjacent to said first edge wherein said conductive frit for bonding said first transducer extends to said second edge to bond said second transducer to said second edge.

15. A touch position sensor as recited in claim 12 wherein the height of said transducer is equal to the thickness of said substrate.

16. A touch position sensor as recited in claim 1 wherein said propagating means propagates a zeroth order horizontally polarized shear wave.

17. A touch position sensor as recited in claim 1 wherein said propagating means includes:

means for generating a drive signal; and

a transducer coupled to a first edge of said substrate and responsive to said drive signal for inducing a zeroth order horizontally polarized shear wave in said substrate for propagation along said paths in a first direction.

18. A touch position sensor as recited in claim 17 wherein said substrate has a second edge for reflecting said shear wave along at least a portion of said paths in a second direction opposite to said first direction and back to said transducer said transducer sensing a shear wave reflected back thereto to provide a signal representative of the sensed shear wave.

19. A touch position sensor as recited in claim 18 wherein said second edge is machined so as to be reflective.

20. A touch position sensor as recited in claim 17 wherein said propagating means includes an array of spaced reflectors of variable height.

21. A touch position sensor as recited in claim 17 wherein said transducer is coupled to said substrate by a flexible connector capable of transmitting a shear wave to said substrate to allow said transducer to be positioned remote from said substrate.

22. A touch position sensor as recited in claim 21 wherein said flexible connector is formed of a metal strip.

23. A touch position sensor as recited in claim 22 wherein said metal strip has a variable thickness, the thickness of said strip adjacent to said plate being equal to the thickness of said plate.

24. A touch position sensor as recited in claim 22 including a sheathing for said metal strip.

25. A touch position sensor as recited in claim 24 wherein said sheathing is plastic.

26. A touch position sensor comprising:

a substrate capable of propagating a shear wave, said substrate having at least one touch surface;

means for reflecting portions of a shear wave along paths of differing lengths, said means being disposed along an axis of said substrate and each of said path lengths being associated with a different position along an axis parallel to the axis of said reflecting means;

means for generating a zeroth order horizontally polarized shear wave propagating in said substrate in a direction along the axis of said reflecting means, a touch on said substrate touch surface forming a perturbation in said shear wave; and

means for sensing the time of occurrence of a perturbation to determine the axial position of said touch.

27. A touch position sensor as recited in claim 26 wherein the thickness of said substrate is less than two times the wavelength of said shear wave.

28. A touch position sensor as recited in claim 26 wherein the thickness of said substrate is less than one-half of a wavelength of said shear wave.

29. A touch position sensor as recited in claim 26 wherein said substrate is formed of a plastic plate.

30. A touch position sensor as recited in claim 26 wherein said substrate is formed of a glass plate.

31. A touch position sensor as recited in claim 30 wherein said glass is tempered.

32. A touch position sensor as recited in claim 30 wherein said glass is frosted.

33. A touch position sensor as recited in claim 26 wherein said substrate is formed of a metal plate.

34. A touch position sensor as recited in claim 26 wherein said substrate is formed of a ceramic plate.

35. A touch position sensor as recited in claim 26 wherein said substrate is curved.

36. A touch position sensor as recited in claim 26 wherein said propagating means includes a first transducer bonded on a first edge of said substrate.

37. A touch position sensor as recited in claim 36 wherein said propagating means includes a conductive frit for bonding said transducer to said first edge.

38. A touch position sensor as recited in claim 37 further including a second transducer bonded on a second edge of said substrate, said second edge being adjacent to said first edge wherein said conductive frit for bonding said first transducer extends to said second edge to bond said second transducer to said second edge.

39. A touch position sensor as recited in claim 36 wherein the height of said transducer is equal to the thickness of the substrate.

40. A touch position sensor as recited in claim 26 wherein said propagating means propagates a zeroth order horizontally polarized shear wave.

41. A touch position sensor comprising:

a substrate capable of propagating a shear wave, said substrate having at least one touch surface;

first means for reflecting portions of a shear wave along first paths of differing lengths, at least a portion of said first paths being substantially in parallel and axially spaced;

second means for reflecting portions of a shear wave along second paths of different lengths, at least a portion of said second paths being substantially in parallel, axially spaced and generally perpendicular to said first parallel path portions;

means for propagating a shear wave along said first and second paths, a touch on said substrate touch surface forming a perturbation in a shear wave propagating along first and second paths intersecting the position of the touch; and

means for sensing the occurrence of a perturbation in a shear wave propagated along said first path and the occurrence of a perturbation in a shear wave propagating along said second path to determine the position of a touch on said touch surface.

42. A touch position sensor as recited in claim 41 wherein said propagating means includes a first transducer coupled to said substrate to impart a first shear wave into said substrate for travel along said first paths and a second transducer coupled to said substrate to impart a second shear wave into said substrate for travel along said second paths.

43. A touch position sensor as recited in claim 42 further including a third transducer coupled to said substrate to sense shear waves propagating along said first paths and to provide a signal representative thereof and a fourth transducer coupled to said substrate to sense shear waves propagating along said second paths and to provide a signal representative thereof.

44. A touch position sensor as recited in claim 43 wherein said first reflecting means includes:

a first reflective array disposed on said substrate and a second reflective array disposed on said substrate parallel to and spaced from said first reflective array, said first transducer imparting a shear wave to said first reflective array, said first reflective array reflecting said shear wave along said first path portions to said second reflective array and said second reflective array reflecting said shear wave to said third transducer; and

a third reflective array disposed on said substrate and a fourth reflective array disposed on said substrate in parallel to and spaced from said third reflective array, said second transducer imparting a shear wave to said third reflective array, said third reflective array reflecting said shear wave along said second path portions to said fourth reflective array and said fourth reflective array reflecting said shear wave to said fourth transducer.

45. A touch position sensor as recited in claim 43 wherein said first reflecting means includes:

a first reflective edge of said substrate;

a second reflective edge of said substrate, said second reflective edge being disposed parallel to said first reflective edge and spaced therefrom;

a first array of reflective elements positioned adjacent said first reflective edge; and

a second array of reflective elements positioned adjacent said second reflective edge, said first transducer imparting a shear wave to said first array, said first array reflecting said shear wave to said second edge, said first edge reflecting said shear wave to said second edge, said second edge reflecting said shear wave to said second reflecting array and said second reflecting array reflecting said shear wave to said third transducer.

46. A touch position sensor as recited in claim 43 wherein said second reflecting means includes:

a first reflective edge of said substrate;

a second reflective edge of said substrate, said second reflective edge being disposed parallel to said first reflective edge and spaced therefrom;

a first array of reflective elements positioned adjacent said first reflective edge; and

a second array of reflective elements positioned adjacent said second reflective edge, said first transducer imparting a shear wave to said first array, said first array reflecting said shear wave to said second edge, said first edge reflecting said shear wave to said second edge, said second edge reflecting said shear wave to said second reflecting array and said second reflecting array reflecting said shear wave to said fourth transducer.

47. A touch position sensor as recited in claim 45 further including absorbing strips between said first reflective array and said first edge and between said second reflective array and said second edge.

48. A touch position sensor as recited in claim 41 wherein said propagating means including a first transducer coupled to said substrate to impart a first shear wave into said substrate for travel along said first paths in one direction, said first transducer receiving a shear wave propagating along said first paths in a direction opposite to said one direction and providing a first signal representative of a received shear wave to which said sensing means is responsive.

49. A touch position sensor as recited in claim 48 wherein said propagating means including a second transducer coupled to said substrate to impart a second shear wave into said substrate for travel along said second paths in one direction, said second transducer receiving a shear wave propagating along said second paths in a direction opposite to said one direction and providing a second signal representative of a received shear wave to which said sensing means is responsive.

50. A touch position sensor as recited in claim 49 including means for generating a drive signal and means for controlling the application of said drive signal to said first and second transducers during respective first and second non-overlapping time periods wherein said first transducer receives shear waves imparted in said substrate in said first time period during said first time period and said second transducer receives shear waves imparted in said substrate in said second time period during said second time period.

51. A touch position sensor as recited in claim 50 including means for coupling said first transducer to said drive signal generating means during a first portion of said first time period, said coupling means coupling said first transducer to said sensing means during a second portion of said first time period.

52. A touch position sensor as recited in claim 50 including means for coupling said second transducer to said drive signal generating means during a first portion of said second time period, said coupling means coupling said second transducer to said sensing means during a second portion of said second time period.

53. A touch position sensor as recited in claim 49 wherein said first reflecting means includes an array of reflective elements disposed along an axis and a reflective edge disposed on said substrate generally opposite to said array, said array of reflective elements reflecting portions of a shear wave imparted by said first transducer to said reflective edge and said reflective edge reflecting said shear wave portions back to said reflective array for reflection back to said first transducer.

54. A touch position sensor as recited in claim 49 wherein said second reflecting means includes an array of reflective elements disposed along an axis and a reflective edge disposed on said substrate generally opposite to said array, said array of reflective elements reflecting portions of a shear wave imparted by said first transducer to said reflective edge and said reflective edge reflecting said shear wave portions back to said reflective array for reflection back to said second transducer.

55. A touch position sensor as recited in claim 41 wherein said propagating means includes a signal transducer to impart a shear wave into a substrate for travel along said first paths and second paths.

56. A touch position sensor as recited in claim 55 wherein said propagating means includes means for coupling a shear wave from said transducer to said second reflecting means.

57. A touch position sensor as recited in claim 56 wherein said first reflecting means includes a first array of reflective elements disposed along a first axis of said substrate and means disposed along a second axis of said substrate generally parallel to said first axis and spaced therefrom for reflecting shear waves received from said first array back to said first array, said second reflecting means including a second array of reflective elements disposed along a third axis of said substrate and means disposed along a fourth axis of said substrate generally parallel to said third axis and spaced therefrom for reflecting shear waves received from said second array back to said second array.

58. A touch position sensor as recited in claim 57 wherein said first axis is adjacent to said third axis and said coupling means includes a reflective edge intersecting said first and third axis.

59. A touch position sensor as recited in claim 55 wherein said propagating means includes means for generating a drive signal and means for coupling said transducer to said drive signal generating means during a first time period and to said sensing means during a second time period.

60. A touch position sensor as recited in claim 41 wherein the thickness of said substrate is less than two times the wavelength of said shear wave.

61. A touch position sensor as recited in claim 41 wherein the thickness of said substrate is less than one-half of a wavelength of said shear wave.

62. A touch position sensor as recited in claim 41 wherein said substrate is formed of plastic.

63. A touch position sensor as recited in claim 41 wherein said substrate is formed of glass.

64. A touch position sensor as recited in claim 63 wherein said glass is tempered.

65. A touch position sensor as recited in claim 63 wherein said glass is frosted.

66. A touch position sensor as recited in claim 41 wherein said substrate is formed of metal.

67. A touch position sensor as recited in claim 41 wherein said substrate is formed of a ceramic.

68. A touch position sensor as recited in claim 41 wherein said substrate is curved.

69. A touch position sensor as recited in claim 41 wherein said propagating means includes a first transducer bonded on a first edge of said substrate.

70. A touch position sensor as recited in claim 69 wherein said propagating means includes a conductive frit for bonding said transducer to said edge.

71. A touch position sensor as recited in claim 70 further including a second transducer bonded on a second edge of said substrate, said second edge being adjacent to said first edge wherein said conductive frit for bonding said first transducer extends to said second edge to bond said second transducer to said second edge.

72. A touch position sensor as recited in claim 41 wherein the height of said transducer is equal to the thickness of the substrate.

73. A touch position sensor as recited in claim 41 wherein said propagating means propagates a zeroth order horizontally polarized shear wave.

74. A touch position as recited in claim 41 including means for reducing the effects of Lamb Waves propagating in said substrate.

75. A touch position sensor as recited in claim 74 wherein each of said first and second reflecting means includes at least one array of reflective elements and said interference reducing means includes spurious mode suppressor reflectors disposed adjacent each of said arrays.

76. A touch position sensor as recited in claim 74 wherein each of said first and second reflecting means includes at least one array of reflective elements and said interference reducing means includes an absorbing medium disposed on the surface of said substrate adjacent to each array to absorb Lamb Wave energy.

77. A touch position sensor as recited in claim 76 wherein said substrate is a plate having a top touch surface and a bottom surface, said absorbing medium being disposed on both said top and said bottom surface.

78. A touch position sensor comprising:

a substrate capable of propagating a shear wave, said substrate having first and second generally parallel sides, third and fourth generally parallel sides and a top touch surface;

a first transmitting transducer coupled to said first side of said substrate and responsive to a drive signal for imparting a shear wave into said substrate, said shear wave propagating along a first axis perpendicular to said first side;

a first receiving transducer coupled to said first side of said substrate spaced from said first transmitting transducer and responsive to a received shear wave for generating a signal representative thereof;

a first array of reflective elements disposed along said first axis, said reflective elements being spaced to reflect portions of said shear wave along first, substantially parallel spaced paths, a touch on said substrate touch surface forming a perturbation in a shear wave propagating along a first path intersecting the position of the touch;

a second array of reflective elements disposed along a second axis parallel to and spaced from said first axis, said reflective elements being spaced to reflect shear waves propagating along said first, substantially parallel paths to said first receiving transducer;

means coupled to said first transmitting transducer for generating a drive signal; and

means coupled to said first receiving transducer and responsive to said shear wave signal for determining the position of a touch relative to said first axis.

79. A touch position sensor as recited in claim 78 including:

means for storing the time at which said first transmitting transducer imparts a shear wave into said substrate;

means for storing the time at which a shear wave reflected by the first reflective elements in said first and second arrays is received by said first receiving means; and

means for calculating the distance traveled by the shear wave reflected by said first reflective elements of said first and second arrays to determine a first dimension of said touch surface.

80. A touch position sensor as recited in claim 79 further including means for storing the time at which a shear wave reflected by the last reflective elements in said first and second arrays is received by said first receiving means, said calculating means calculating the distance traveled by the shear wave reflected by said last reflective elements of said first and second arrays to determine a second dimension of said touch surface.

81. A touch position sensor as recited in claim 80 further including means responsive to said calculating means for automatically justifying the coordinates of a touch surface.

82. A touch position sensor as recited in claim 78 further including

a second transmitting transducer coupled to said third side of said substrate and coupled to said drive signal generating means, said second transmitting transducer being responsive to a drive signal for imparting a shear wave into said substrate, said shear wave propagating along a third axis perpendicular to said third side;

a second receiving transducer coupled to said third side of said substrate and spaced from said second transducer and responsive to a received shear wave for generating a signal representative thereof;

a third array of reflective elements disposed along said third axis, said reflective elements being spaced to reflect portions of said shear wave along second, substantially parallel spaced paths, a touch on said substrate touch surface forming a perturbation in a shear wave propagating along a second path intersecting the position of a touch; and

a fourth array of reflective elements disposed along a fourth axis parallel to and spaced from said third axis, said reflective elements being spaced to reflect shear waves propagating along said second, substantially parallel paths to said second receiving transducer to generate a signal representative of said received waves, said determining means being coupled to said second receiving transducer for determining the position of a touch relative to said third axis.

83. A touch position sensor as recited in claim 82 wherein each of said transducer is bonded to said substrate by a conductive frit.

84. A touch position sensor as recited in claim 83 wherein at least two of said transducers are bonded to said substrate by a conductive frit that extends from one side of said substrate to another side of said substrate.

85. A touch position sensor as recited in claim 82 including means positioned adjacent to each array of reflective elements to reduce the effects of Lamb Waves if any propagating in said substrate.

86. A touch position sensor as recited in claim 85 wherein said reducing means includes spurious mode suppressor reflectors disposed adjacent to each array of reflective elements.

87. A touch position sensor as recited in claim 85 wherein said reducing means includes an absorbing medium disposed on said substrate adjacent to each array of reflective elements.

88. A touch position sensor as recited in claim 85 wherein said reducing means includes an absorbing medium disposed on the top and bottom surfaces of said substrate adjacent to each array of reflective elements.

89. A touch position sensor as recited in claim 82 wherein each of said transducers is coupled to said substrate by a flexible connector capable of transmitting a shear wave to said substrate to allow said transducers to be positioned remote from said substrate.

90. A touch position sensor as recited in claim 89 wherein said flexible connector is formed of a metal strip.

91. A touch position sensor as recited in claim 90 wherein said metal strip has a variable thickness, the thickness of said strip adjacent to said plate being equal to the thickness of said plate.

92. A touch position sensor as recited in claim 90 including a sheathing for said metal strip.

93. A touch position sensor as recited in claim 92 wherein said sheathing is plastic.

94. A touch position sensor as recited in claim 78 wherein the thickness of said substrate is less than two wavelengths of said shear wave.

95. A touch position sensor as recited in claim 78 wherein said propagating means propagates a zeroth order horizontally polarized shear wave.

96. A touch position sensor as recited in claim 78 wherein said substrate is curved.

97. A touch position sensor as recited in claim 78 wherein said substrate has a bottom touch surface.

98. A touch position sensor comprising:

a substrate capable of propagating a shear wave, said substrate having first and second generally parallel sides, third and fourth generally parallel sides and a top touch surface;

a first transducer coupled to said first side of said substrate and responsive to a drive signal for imparting a shear wave into said substrate, said shear wave propagating along a first axis perpendicular to said first side and a touch on said substrate touch surface forming a perturbation in said shear wave and said transducer being responsive to a shear wave sensed thereby to provide a first signal representative thereof;

a first array of reflective elements disposed along said first axis, said shear wave along first, substantially parallel paths to a side of said substrate opposite said first array, said third side being reflective to reflect shear waves back along said first substantially parallel paths to said first array, said first array reflecting shear waves from said opposite side to said first transducer;

means for generating drive signals coupled to said first transducer; and

means responsive to said first transducer signal for determining the position of a touch relative to said first axis.

99. A touch position sensor as recited in claim 98 further including a second transducer coupled to said third side or said fourth side of said substrate and responsive to a drive signal for imparting a shear wave into said substrate, said shear wave propagating along a second axis perpendicular to said third and fourth sides, said second transducer being responsive to a shear wave sensed thereby to provide a second signal representative thereof;

a second array of reflective elements disposed along said second axis, said reflective elements being spaced to reflect positions of said shear wave along second, substantially parallel second paths across said substrate touch surface, to a side opposite said second array wherein a touch on said substrate touch surface forms a perturbation in a shear wave propagating along a path intersecting the position of the touch, said opposite side being reflective to reflect shear waves back along said second substantially parallel paths to said second array, said second array reflecting shear waves from said opposite side to said second transducer, said determining means being coupled to said second transducer and responsive to a second signal for determining the position of a touch relative to said second axis.

100. A touch position sensor as recited in claim 99 wherein each of said transducers is bonded to said substrate by a conductive frit.

101. A touch position sensor as recited in claim 99 including means positioned adjacent to each array of reflective elements to reduce the effects of Lamb Waves if any propagating in said substrate.

102. A touch position sensor as recited in claim 101 wherein said reducing means includes spurious mode suppressor reflectors disposed adjacent to each array of reflective elements.

103. A touch position sensor as recited in claim 101 wherein said reducing means includes an absorbing medium disposed on said substrate adjacent to each array of reflective elements.

104. A touch position sensor as recited in claim 101 wherein said reducing means includes an absorbing medium disposed on the top and bottom surfaces of said substrate adjacent to each array of reflective elements.

105. A touch position sensor as recited in claim 101 wherein each of said transducers is coupled to said substrate by a flexible connector capable of transmitting a shear wave to said substrate to allow said transducers to be positioned remote from said substrate.

106. A touch position sensor as recited in claim 105 wherein said flexible connector is formed of a metal strip.

107. A touch position sensor as recited in claim 106 wherein said metal strip has a variable thickness, the thickness of said strip adjacent to said plate being equal to the thickness of said plate.

108. A touch position sensor as recited in claim 106 including a sheathing for said metal strip.

109. A touch position sensor as recited in claim 108 wherein said sheathing is plastic.

110. A touch position sensor as recited in claim 99 wherein the thickness of said substrate is less than one-half of a wavelength of said shear wave.

111. A touch position sensor as recited in claim 99 wherein said propagating means propagates a zeroth order horizontally polarized shear wave.

112. A touch position sensor as recited in claim 99 wherein said substrate is curved.

113. A touch position sensor as recited in claim 99 wherein said substrate has a bottom touch surface.

114. A touch position sensor as recited in claim 99 wherein said third side is machined to provide a reflective edge.

115. A touch position sensor as recited in claim 98 further including:

means intersecting said first axis and a second axis for reflecting a shear wave propagating along said first axis to said second axis and for reflecting a shear wave propagating along said second axis to said first axis;

a second array of reflective elements disposed along said second axis, said reflective elements of said second array being spaced to reflect portions of a shear wave along second substantially parallel paths to a side opposite said second array, said side opposite to said second array being reflective to reflect shear waves back along said second substantially parallel paths to said second array, said second array reflecting shear waves from said second parallel paths to said reflecting means for reflection back to said transducer.

116. A touch position sensor as recited in claim 115 wherein said third side is machined to provide a reflective edge.

117. A touch position sensor as recited in claim 115 wherein each of said transducers is bonded to said substrate by a conductive frit.

118. A touch position sensor as recited in claim 115 including means positioned adjacent to each array of reflective elements to reduce the effects of Lamb Waves if any propagating in said substrate.

119. A touch position sensor as recited in claim 118 wherein said reducing means includes spurious mode suppressor reflectors disposed adjacent to each array of reflective elements.

120. A touch position sensor as recited in claim 118 wherein said reducing means includes an absorbing medium disposed on said substrate adjacent to each array of reflective elements.

121. A touch position sensor as recited in claim 118 wherein said reducing means includes an absorbing medium disposed on the top and bottom surfaces of said substrate adjacent to each array of reflective elements.

122. A touch position sensor as recited in claim 115 wherein each of said transducers is coupled to said substrate by a flexible connector capable of transmitting a shear wave to said substrate to allow said transducers to be positioned remote from said substrate.

123. A touch position sensor as recited in claim 122 wherein said flexible connector is formed of a metal strip.

124. A touch position sensor as recited in claim 123 wherein said metal strip has a variable thickness, the thickness of said strip adjacent to said plate being equal to the thickness of said plate.

125. A touch position sensor as recited in claim 123 including a sheathing for said metal strip.

126. A touch position sensor as recited in claim 125 wherein said sheathing is plastic.

127. A touch position sensor as recited in claim 115 wherein the thickness of said substrate is less than one-half of a wavelength of said shear wave.

128. A touch position sensor as recited in claim 115 wherein said propagating means propagates a zeroth order horizontally polarized shear wave.

129. A touch position sensor as recited in claim 115 wherein said substrate is curved.

130. A touch position sensor as recited in claim 115 wherein said substrate has a bottom touch surface.