Gentle-bevel flat acoustic wave touch sensor

• US 5,739,479 A
• Filed: 03/04/1996
• Issued: 04/14/1998
• Est. Priority Date: 03/04/1996
• Status: Expired due to Term

• Current Assignee: Elo Touch Solutions, Inc.
• Original Assignee: Elo Touchsystems Incorporated (Elo Touch Solutions, Inc.)
• Inventors: Scharff, Daniel H., Kent, Joel Christopher, Gomes, Paulo Irulegui, Lewis, Michael LeRoy, De Renzi, Robert, Ocampo, Michelle, Davis-Cannon, Marcia M.
• Primary Examiner(s): Kuntz, Curtis
• Assistant Examiner(s): Shankar, Vijay
• Application Number:
  US08/610,260
• Time in Patent Office: 771 Days
• Field of Search: 178/18, 178/19, 345/173, 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

An acoustic wave touch sensor comprising an acoustic wave transducer, for transducing an acoustic wave; a substrate, having a front surface. A surface bound acoustic wave interface, having at one least bevel edge, is provided, having an transmitted acoustic wave signal attenuation of less than about 3 dB. The acoustic wave transducer is mounted to transmit the acoustic wave through the interface into the substrate, so that the energy of the acoustic wave appears at the surface. The acoustic wave transducer is mounted on a beveled region of the substrate, inclined to the front surface. The beveled edge has an effective radius which is small as compared to the wavelength and a bevel angle such that the acoustic wave is attenuated by less than about 3 dB on transmission across the edge. In this manner, means are provided to recess transducers for improved product robustness and compactness of design.

Claims

1. An acoustic wave touch sensor comprising:

a substrate, having a front surface, and a bevel having an edge and an angle with respect to said front surface; and

an acoustic wave transducer, mounted to said substrate to electrically transduce an acoustic wave, having a wavelength and traveling in said substrate,

said edge having an effective radius which is small as compared to said wavelength and a bevel angle such that a portion of said acoustic wave is attenuated by less than about 3 dB on transmission through a region of said substrate proximate to and crossing said edge.

2. The acoustic sensor according to claim 1, wherein said bevel has an angle less than +25°

with respect to said front surface.

3. The acoustic sensor according to claim 1, wherein said bevel has an angle of about +16°

with respect to said front surface.

4. The acoustic sensor according to claim 1, wherein said bevel has an angle of between about +6°

and +20°

with respect to said front surface.

5. The acoustic sensor according to claim 1, wherein said bevel angle is negative.

6. The acoustic sensor according to claim 1, wherein said bevel has a negative angle of magnitude less than 25°

with respect to said front surface.

7. The acoustic sensor according to claim 1, wherein said acoustic wave transducer comprises a piezoelectric element mounted on a wedge, said wedge being mounted on said bevel, said acoustic wave being a surface bound acoustic wave.

8. The acoustic sensor according to claim 1, wherein said substrate is formed of glass.

9. The acoustic sensor according to claim 1, wherein said substrate is formed of borosilicate glass.

10. The acoustic sensor according to claim 1, wherein said substrate is a glass sheet having a thickness of about 0.5 inches.

11. The acoustic sensor according to claim 1, wherein said substrate is formed of aluminum.

12. The acoustic sensor according to claim 1, wherein said front surface has a perimeter edge having a length, said bevel being approximately parallel to and adjacent said perimeter edge, having approximately the same length as said perimeter edge.

13. The acoustic sensor according to claim 12, further comprising an electrical wire connected to said acoustic wave transducer, said wire being disposed adjacent to said bevel.

14. The acoustic sensor according to claim 1, wherein said bevel is a positive bevel, said acoustic wave transducer is disposed on said bevel, behind said front surface.

15. The acoustic sensor according to claim 1, wherein said substrate has an outer boundary, said acoustic wave transducer being situated within said outer boundary of said substrate.

16. The acoustic sensor according to claim 1, further comprising a reflective array, said reflective array redirecting portions of said acoustic wave across said front surface.

17. The acoustic sensor according to claim 16, wherein both said reflective array and said acoustic wave transducer are disposed on said bevel, said reflective array redirecting portions of said acoustic wave across said edge to said front surface.

18. The acoustic sensor according to claim 16, wherein said acoustic wave transducer is disposed on said bevel, said reflecting array being disposed on said front surface and redirecting portions of said acoustic wave across said front surface.

19. The acoustic sensor according to claim 16, wherein a touch on said front surface perturbs said acoustic wave, said acoustic wave transducer receiving said perturbed acoustic wave.

20. The acoustic sensor according to claim 1, further comprising a coversheet, parallel to said front surface, fastened proximate to said bevel.

21. The acoustic sensor according to claim 1, wherein said bevel comprises a lateral edge having a substantial thickness with respect to said substrate.

22. The acoustic sensor according to claim 1, further comprising an outer edge surface, said bevel being formed between said outer edge surface and said front surface, said outer edge surface being substantially perpendicular to said front surface.

23. The acoustic sensor according to claim 1, said bevel being a positive bevel, further comprising a lateral wall of said bevel, said lateral wall, with said bevel, forming a trench in said substrate.

24. The acoustic sensor according to claim 1, wherein said acoustic wave transducer comprises an electro-acoustic device mounted on said beveled portion of said substrate, said acoustic wave transducer being for propagating a surface acoustic wave on said front surface.

25. The acoustic sensor according to claim 1, wherein said front surface is non-planar.

26. The acoustic sensor according to claim 1, wherein said substrate comprises a second edge in said region forming a pair of edges including said edge, said pair of edges being spaced from said edge to cause destructive interference of a reflected portion of said acoustic wave from each of said edges, said second edge having an effective radius which is small as compared to said wavelength and each edge having a respective angle such that said acoustic wave is attenuated by less than about 3 dB on transmission across said pair of edges.

27. The acoustic sensor according to claim 1, wherein said substrate comprises a plurality of edges, including said edge, in said region, each of said edges being spaced to produce reflections which sum to effectively destructively interfere, said plurality of edges each having an effective radius which is small as compared to said wavelength and angles such that said acoustic wave is attenuated by less than about 3 dB on transmission across said plurality of edges.

28. The acoustic sensor according to claim 1, wherein said substrate comprises a plurality of edges, a net attenuation of said acoustic wave across said plurality of edges being less than an acoustic loss across an edge having a largest attenuation loss.

29. The acoustic sensor according to claim 1, wherein said acoustic wave, when crossing said region, is a quasi-Rayleigh wave.

30. The acoustic sensor according to claim 1, wherein said acoustic wave, when crossing said region, is a surface bound wave for which the root-mean-square depth of the acoustic power is less than half of the surface bound wave'"'"'s wavelength.

31. The acoustic sensor according to claim 1, wherein said acoustic wave, when crossing said region, is a surface bound wave whose root-mean-square power-density depth times 25 divided by half the wavelength is less than about the angle of said edge.

32. The acoustic sensor according to claim 31, wherein said surface-bound wave is a Love wave.

33. The acoustic sensor according to claim 1, wherein said substrate is brittle and has an outer boundary adapted to resist fracture.

34. The acoustic sensor according to claim 1, wherein said substrate is brittle and has a minimum thickness of about 0.020 inches.

35. The acoustic sensor according to claim 1, wherein said effective radius of said edge provides causes an abrupt acoustic impedance change of said substrate for said acoustic wave traveling is said substrate in proximity to said edge.

36. The acoustic touch sensor according to claim 1, wherein said edge is associated with phase incoherence in a wave-function overlap integral between an incident portion and a transmitted portion of said acoustic wave.

37. The acoustic touch sensor according to claim 1, wherein said edge forms an acoustic transmission discontinuity for said acoustic wave.

38. The acoustic touch sensor according to claim 1 wherein said edge is unblended.

39. The acoustic touch sensor according to claim 1 wherein said edge forms a sharp angle.

40. The acoustic sensor according to claim 1, wherein said substrate comprises a touch region, said acoustic wave transducer being mounted across said edge from said touch region.

41. The acoustic sensor according to claim 1, wherein said substrate has a thickness which decreases lateral to said edge.

42. The acoustic sensor according to claim 1, wherein said acoustic wave transducer has an acoustic axis which intersects said edge.

43. The acoustic sensor according to claim 1, wherein said acoustic wave transducer has an acoustic axis which does not intersect said edge, further comprising an acoustically reflective array disposed along said acoustic axis.

44. The acoustic sensor according to claim 1, further comprising means for sensing a perturbation of said acoustic wave propagating in said substrate.

45. The acoustic sensor according to claim 1, further comprising an electronic analyzer circuit receiving a signal from said acoustic wave transducer corresponding to an acoustic signal propagating in said substrate.

46. The acoustic sensor according to claim 1, further comprising an electric signal generator exciting said acoustic wave transducer to generate said acoustic wave.

47. The acoustic sensor according to claim 1, wherein:

at least a portion of said acoustic wave intersects said edge, said edge having a bevel angle such that said acoustic wave transducer is displaced from said front surface.

48. An acoustic wave device comprising:

a substrate, having two adjoining mutually inclined surfaces and a boundary therebetween; and

an electroacoustic transducer mounted to said substrate on one of said surfaces and being displaced from a plane of said adjoining surface, said electroacoustic transducer interacting with an acoustic wave traveling in said substrate, at least a portion of said acoustic wave having a path in said substrate underlying both of said adjoining surfaces, and being attenuated by less than about 3 dB on transmission across said boundary and being associated with a distinct reflected subportion.