Dielectric composite and a method of manufacturing a dielectric composite

• US 20080226878A1
• Filed: 10/31/2007
• Published: 09/18/2008
• Est. Priority Date: 11/03/2006
• Status: Active Grant

• Current Assignee: Danfoss A/S
• Original Assignee: Danfoss A/S
• Inventors: Benslimane, Mohamed Yahia, Gravesen, Peter
• Granted Patent: US 7,880,371 B2
• Time in Patent Office: Days
• US Class Current: 428/174
• CPC Class Codes: H10N 30/05 Manufacture of multilayered piezoelectric or electrostrictive devices, or parts thereof, e.g. by stacking piezoelectric bodies and electrodes
• CPC Class Codes: H10N 30/084 by moulding or extrusion
• CPC Class Codes: H10N 30/098 Forming organic materials
• CPC Class Codes: H10N 30/206 using only longitudinal or thickness displacement, e.g. d33 or d31 type devices
• CPC Class Codes: H10N 30/50 having a stacked or multilayer structure
• CPC Class Codes: H10N 30/506 having a cylindrical shape and having stacking in the radial direction, e.g. coaxial or spiral type rolls
• CPC Class Codes: H10N 30/871 Single-layered electrodes of multilayer piezoelectric or electrostrictive devices, e.g. internal electrodes
• CPC Class Codes: Y10S 310/80 Piezoelectric polymers, e.g. PVDF
• CPC Class Codes: Y10T 428/24628 Nonplanar uniform thickness material

Abstract

A composite for a transducer facilitates an increased actuation force as compared to similar prior art composites for transducers. The composite facilitates increased compliance of the transducer in one direction, an improved reaction time as compared to similar prior art composites for transducers, and provides an increased lifetime of the transducer in which it is applied.

Claims

1. A composite comprising:

a film made of a dielectric material and having a first surface and second surface, at least the first surface comprising a surface pattern of raised and depressed surface portions, and

a first electrically conductive layer being deposited onto the surface pattern, the electrically conductive layer having a corrugated shape which is formed by the surface pattern of the film,

wherein the raised and depressed surface portions have a shape and/or size which varies periodically along at least one direction of the first surface.

2. The composite according to claim 1, wherein the electrically conductive layer has a modulus of elasticity being higher than a modulus of elasticity of the film.

3. The composite according to claim 1, provided as a web of potentially unlimited length.

4. The composite according to claim 1, wherein the dielectric material is a polymer material.

5. The composite according to claim 1, wherein the dielectric material has properties similar to an elastomer.

6. The composite according to claim 1, wherein the film has a largest thickness which is less than 110 percent of an average thickness of the film.

7. The composite according to claim 1, wherein the film has a smallest thickness which is at least 90 percent of an average thickness of the film.

8. The composite according to claim 1, wherein the first electrically conductive layer has a largest thickness which is less than 110 percent of an average thickness of the first electrically conductive layer.

9. The composite according to claim 1, wherein the first electrically conductive layer has a smallest thickness which is at least 90 percent of an average thickness of the first electrically conductive layer.

10. The composite according to claim 1, wherein the surface pattern comprises waves forming troughs and crests extending in essentially one common direction, each wave defining a height being a shortest distance between a crest and neighbouring troughs.

11. The composite according to claim 10, wherein the waves have a shape which is periodically repeated.

12. The composite according to claim 10, wherein an average height of the waves is between ⅓

and 20 μ

m.

13. The composite according to claim 12, wherein each wave defines, a largest wave having a height of at most 110 percent of the average wave height.

14. The composite according to claim 12, wherein each wave defines a smallest wave having a height of at least 90 percent of the average wave height.

15. The composite according to claim 10, wherein the film has an average thickness being between 10 and 200 μ

m.

16. The composite according to claim 10, wherein a ratio between an average height of the waves and an average thickness of the film is between 1/50 and ½

.

17. The composite according to claim 10, wherein the waves have a wavelength defined as the shortest distance between two crests, and wherein a ratio between an average height of the waves and an average wavelength is between 1/30 and 2.

18. The composite according to claim 10, wherein a ratio between an average thickness of the first electrically conductive layer and an average height of the waves is between 1/1000 and 1/50.

19. The composite according to claim 1, wherein the first electrically conductive layer has a thickness in the range of 0.01-0.1 μ

m.

20. The composite according to claim 1 and being substantially longer in a lengthwise direction than in a perpendicular crosswise direction.

21. The composite according to claim 20, wherein the surface pattern defines a compliance direction in which the composite is mostly compliant, wherein the compliance direction forms an angle between 0 and 90 degrees to the lengthwise direction.

22. The composite according to claim 21, wherein the composite has a compliance in the compliance direction which is at least 50 times larger than its compliance in a direction being at least substantially perpendicular to the compliance direction.

23. The composite according to claim 20, wherein the surface pattern forms wave crests and troughs extending essentially in the lengthwise direction.

24. The composite according to claim 20, wherein the surface pattern forms wave crests and troughs extending essentially in the crosswise direction.

25. The composite according to claim 1, wherein the surface pattern comprises a plurality of identical sub patterns

26. The composite according to claim 1, wherein the film has a surface with a shape which is essentially unaffected by its contact with the first electrically conductive layer.

27. The composite according to claim 26, wherein the composite has a shape which is essentially unaffected by an elastic modulus of the first electrically conductive layer.

28. The composite according to claim 26, wherein the film has a surface with a shape which is essentially unaffected by the thickness of the first electrically conductive layer.

29. The composite according to claim 1, wherein the film has a surface with a shape which is essentially unaffected by an elastic modulus of the film.

30. The composite according to claim 29, wherein the film has a surface with a shape which is essentially unaffected by the thickness of the film.

31. The composite according to claim 1 comprising a second electrically conductive layer arranged on an opposite surface of the film relative to the first electrically conductive layer to form an electroactive composite.

32. The composite according to claim 1, wherein the second surface comprises a surface pattern covered by an electrically conductive layer.

33. The composite according to claim 1, wherein the second surface is substantially flat.

34. The composite according to claim 1, wherein a resistivity of the dielectric material is larger than 10¹⁰Ω

·

cm.

35. The composite according to claim 1, wherein a resistivity of the electrically conductive material is less than 10⁻

4Ω

·

cm.

63. A transducer comprising a composite according to claim 1.

36. A multilayer composite comprising at least two layers of composite, each composite layer comprising:

a film made of a dielectric material and having a front surface and rear surface, the front surface comprising a surface pattern of raised and depressed surface portions, and

a first electrically conductive layer being deposited onto the surface pattern, the electrically conductive layer having a corrugated shape which is formed by the surface pattern of the film.

37. The multilayer composite according to claim 36, wherein the raised and depressed surface portions of the surface pattern of the film of each composite layer have a shape and/or a size which varies periodically along at least one direction of the front surface.

38. The multilayer composite according to claim 36, wherein the composite layers are arranged with the rear surfaces towards each other.

39. The multilayer composite according to claim 36, wherein the composite layers are adhesively bonded to each other.

40. The multilayer composite according to any claim 36, wherein the film of each composite layer comprises waves forming crests and troughs extending in one common direction.

41. The multilayer composite according to claim 40, wherein composite layers are arranged relative to each other to provide a shortest possible distance between crests of one layer and crests of another layer.

42. The multilayer composite according to claim 40, wherein the composite layers are arranged relative to each other to provide a longest possible distance between crests of one layer and crests of another layer.

64. A transducer comprising a multilayer composite according to claim 36.

43. A method of making a polymeric composite, the method comprising:

providing a shape defining element having a surface pattern of raised and depressed surface portions,

providing a liquid polymer composition onto the surface pattern,

curing the liquid polymer to form a polymeric film having a surface with a replicated pattern of raised and depressed surface portions in such a manner that the raised and depressed surface portions obtain a shape and/or size which varies periodically along at least one direction of the surface, and

depositing a first electrically conductive layer onto the replicated surface pattern so that the electrically conductive layer is shaped by the replicated pattern.

44. The method according to claim 43, wherein the step of coating the film with a first electrically conductive layer comprises the step of using a shape of the polymeric film to shape the electrically conductive layer.

45. The method according to claim 43, wherein the electrically conductive layer is deposited on the film in a physical vapour deposition process.

46. The method according to claim 43, wherein the electrically conductive layer is deposited onto the film in a thickness of 0.1-0.01 micrometer.

47. The method according to claim 46, wherein the thickness is controlled by quartz crystal micro balance.

48. The method according to claim 46, wherein the electrically conductive layer is made in a sputtering process.

49. The method according to claim 46, wherein the electrically conductive layer is made in an electron beam process.

50. The method according to claim 43, wherein the step of depositing an electrically conductive layer comprises depositing a first electrically conductive layer and depositing a second electrically conductive layer on top of the first electrically conductive layer.

51. The method according to claim 50, wherein the step of depositing the first electrically conductive layer and the step of depositing a second electrically conductive layer are performed at different depositing rates.

52. The method according to claim 50, wherein the step of depositing a first electrically conductive layer comprises depositing a first material, and the step of depositing a second electrically conductive layer comprises depositing a second material.

53. The method according to claim 43, wherein the film is provided by use of a liquid polymer and a reverse roll process.

54. The method according to claim 43, wherein the film is provided by use of a liquid polymer and a gravure roll process.

55. The method according to claim 43, wherein the film is provided by use of a liquid polymer and a slot die coating process.

56. The method according to claim 53, wherein the liquid polymer comprises a solvent.

57. The method according to claim 43, wherein the film is exposed to heat or ultraviolet light to initiate cross-linking.

58. The method according to claim 43, wherein the film is treated with a plasma to improve adhesion of the electrically conductive layer.

59. The method according to claim 58, wherein the treatment is conducted with a glow discharge which is known to generate mild plasma.

60. The method according to claim 58, wherein an adhesion promoter is applied to at least said portion of the film after the step of plasma treating and before the step of depositing the electrically conductive layer thereon.

61. The method according to claim 60, wherein the adhesion promoter is provided by applying a layer of chromium or titanium between the film and the electrically conductive layer.

62. The method according to claim 60, wherein the adhesion promoter is applied to the film of the dielectric material in a physical vapour deposition process.