Slotted beam piezoelectric composite

• US 20070114890A1
• Filed: 11/24/2006
• Published: 05/24/2007
• Est. Priority Date: 11/23/2005
• Status: Active Grant

• Current Assignee: Hottinger Bruel & Kjaer Incorporated
• Original Assignee: MicroStrain, Inc. (Spectris PLC)
• Inventors: Churchill, David, Arms, Steven
• Granted Patent: US 7,692,365 B2
• Time in Patent Office: Days
• US Class Current: 310/339
• CPC Class Codes: H02N 2/188 adapted for resonant operation
• CPC Class Codes: H10N 30/306 Cantilevers

Abstract

One aspect of the present patent application is an energy harvesting device comprising a composite structure including a base spring and a piezoelectric structure. The base spring has a base spring surface having elevated portions separated by a recessed portion. The piezoelectric structure substantially crosses the recessed portion. In one aspect the piezoelectric structure includes a piezoelectric element that is bonded to the elevated portions. In another aspect, the base spring has a base spring stiffness. The piezoelectric element has a piezoelectric element stiffness. The base spring stiffness is less than the piezoelectric element stiffness. In another aspect, the composite structure has a natural frequency of vibration, and this natural frequency of vibration of the composite structure is automatically adjustable. In another aspect, the piezoelectric elements are stacked. In another aspect, the piezoelectric structure is located in the recessed portion.

Claims

1. An energy harvesting device, comprising a composite structure including a base spring and a piezoelectric structure, wherein said base spring has a base spring surface having elevated portions separated by a recessed portion, wherein said piezoelectric structure substantially crosses said recessed portion.

2. An energy harvesting device as recited in claim 1, wherein said base spring includes a taper.

3. An energy harvesting device as recited in claim 1, wherein said piezoelectric structure includes a piezoelectric element bonded to said elevated portions.

4. An energy harvesting device as recited in claim 3, wherein said base spring surface has a plurality of said recessed portions, wherein an elevated portion is located on both sides of each said recessed portion.

5. An energy harvesting device as recited in claim 4, wherein said piezoelectric element extends across each of said recessed portions and is bonded to each of said elevated portions.

6. An energy harvesting device as recited in claim 5, wherein said base spring has a lower stiffness than said piezoelectric element.

7. An energy harvesting device as recited in claim 4, wherein said base spring includes a long axis, wherein said recessed portions are arranged perpendicular to said long axis.

8. An energy harvesting device as recited in claim 3, wherein said composite structure includes a plurality of said piezoelectric elements.

9. An energy harvesting device as recited in claim 3, wherein one said piezoelectric element is located on a first side of said base spring and a second said piezoelectric element is located on a second side of said base spring.

10. An energy harvesting device as recited in claim 9, wherein two said piezoelectric elements are located on a first side of said base spring and two said piezoelectric elements are located on a second side of said base spring.

11. An energy harvesting device as recited in claim 10, wherein said two piezoelectric elements located on said first side of said base spring are stacked and wherein said two piezoelectric elements located on said second side of said base spring are stacked.

12. An energy harvesting device as recited in claim 8, wherein said plurality of piezoelectric elements are stacked.

13. An energy harvesting device as recited in claim 8, further comprising a plurality of rectifier bridges, wherein each said plurality of piezoelectric elements is connected to a different one of said rectifier bridges.

14. An energy harvesting device as recited in claim 1, wherein a low stiffness material is located within said recessed portion, wherein said piezoelectric element is bonded to said low stiffness material.

15. An energy harvesting device as recited in claim 1, wherein said base spring has a damping characteristic about equal to that of a base spring without said recessed portion.

16. An energy harvesting device as recited in claim 1, wherein said piezoelectric structure is located in said recessed portion.

17. An energy harvesting device as recited in claim 16, wherein said piezoelectric structure includes a bulk piezoelectric material.

18. An energy harvesting device as recited in claim 17, wherein said bulk piezoelectric material includes a single crystal piezoelectric material.

19. An energy harvesting device as recited in claim 16, further comprising a flex circuit having wiring, wherein said piezoelectric structure contacts said wiring within said recessed portion.

20. An energy harvesting device as recited in claim 19, wherein said flex circuit extends along an edge of said base spring.

21. An energy harvesting device as recited in claim 16, wherein said base spring surface has an elevated portion defining a level, wherein a portion of said bulk piezoelectric structure is located at said level.

22. An energy harvesting device as recited in claim 1, wherein said base spring is fabricated of metal.

23. An energy harvesting device as recited in claim 22, wherein said metal includes a superelestic nickel titanium material.

24. An energy harvesting device as recited in claim 1, wherein said composite structure further includes a mass, wherein said mass is mounted on said base spring.

25. An energy harvesting device as recited in claim 24, wherein said mass is movable on said base spring.

26. An energy harvesting device as recited in claim 24, wherein said composite structure has a natural frequency of vibration, wherein said composite structure is mounted on a substrate subject to vibration at a substrate frequency, wherein said substrate frequency is variable, wherein said natural vibration frequency of said composite structure is adjustable to match variation in said substrate vibration frequency.

27. An energy harvesting device as recited in claim 26, further comprising a controller, wherein a feedback signal from said piezoelectric element is used by said controller to automatically adjust said natural vibration frequency of said composite structure.

28. An energy harvesting device as recited in claim 27, wherein said controller automatically adjusts said natural vibration frequency to about equal said substrate vibration frequency.

29. An energy harvesting device as recited in claim 27, wherein said controller automatically adjusts position of said mass on said base spring to provide said composite structure with a natural frequency of vibration about equal to said substrate vibration frequency.

30. An energy harvesting device as recited in claim 24, wherein said composite structure has a natural frequency of vibration, wherein said composite structure further includes a second element coupled to said base spring, wherein varying a parameter of said second element varies said natural frequency of vibration.

31. An energy harvesting device as recited in claim 30, wherein said second element includes a spring.

32. An energy harvesting device as recited in claim 30, wherein said second element includes a magnet.

33. An energy harvesting device, comprising a composite structure including a base spring and a piezoelectric structure, said piezoelectric structure bonded to said base spring, wherein said base spring has a base spring stiffness and said piezoelectric structure has a piezoelectric structure stiffness, wherein said base spring stifffiess is less than said piezoelectric structure stiffness.

34. An energy harvesting device as recited in claim 33, wherein said base spring includes a taper.

35. An energy harvesting device as recited in claim 33, wherein said base spring has a first side and a second side opposite said first side, wherein said piezoelectric structure includes a first piezoelectric element mounted on said first side and a second piezoelectric element mounted on said second side.

36. An energy harvesting device as recited in claim 35, wherein said first side has a first side surface, wherein said first side surface includes elevated portions and a recessed portion, wherein said elevated portions are on opposite sides of said recessed portion, wherein said first piezoelectric element extends across said recessed portion and is bonded to said elevated portions.

37. An energy harvesting device, comprising a composite structure including a base spring, a piezoelectric structure, and a proof mass, wherein said composite structure has a natural frequency of vibration, wherein said natural frequency of vibration is automatically adjustable.

38. An energy harvesting device as recited in claim 37, wherein said composite structure is for mounting on a substrate having a substrate vibration frequency, wherein said natural frequency vibration is automatically adjustable to tune said composite structure to a natural frequency about equal to said substrate vibration frequency.

39. An energy harvesting device as recited in claim 38, wherein position of said proof mass on said base spring is automatically adjustable to provide said composite structure with a natural frequency of vibration about equal to said substrate vibration frequency.

40. An energy harvesting device as recited in claim 37, further comprising a second element coupled to said base spring, wherein varying a parameter of said second element varies said natural frequency of vibration of said composite structure.

41. An energy harvesting device as recited in claim 40, wherein said second element includes a spring.

42. An energy harvesting device as recited in claim 40, wherein said second element includes a magnet.

43. An energy harvesting device, comprising a composite structure including a base spring and a piezoelectric structure, said base spring having a base spring effective thickness, said piezoelectric structure having a piezoelectric structure effective thickness, wherein said piezoelectric structure effective thickness is greater than said base spring effective thickness.

44. An energy harvesting device as recited in claim 43, wherein said base spring has a first side and a second side opposite said first side, wherein said piezoelectric structure includes a first piezoelectric element mounted on said first side and a second piezoelectric element mounted on said second side, wherein said piezoelectric structure effective thickness is about equal to a spacing between said first piezoelectric element and said second piezoelectric element.

45. An energy harvesting device as recited in claim 44, wherein said first side has a first side surface having elevated portions and a recessed portion, wherein said first piezoelectric element is bonded to said elevated portions.

49. An energy harvesting device as recited in claim 45, further comprising a second piezoelectric element mounted on said base spring, wherein said second piezoelectric element has a second piezoelectric element thickness, wherein said base spring maximum thickness is greater than said second piezoelectric element thickness.

50. An energy harvesting device as recited in claim 45, wherein said base spring has a second side, wherein said second side is opposite said first side, wherein said second piezoelectric element is mounted on said second side.

46. An energy harvesting device, comprising a composite structure including a base structure and stacked piezoelectric elements, wherein said stacked piezoelectric elements are mounted to said base structure.

47. An energy harvesting device as recited in claim 46, further comprising a plurality of rectifier bridges, wherein each said stacked piezoelectric elements is connected to a different one of said rectifier bridges.

48. An energy harvesting device, comprising a composite structure including a base spring and a first piezoelectric element, wherein said base spring includes a first side wherein said base spring has a base spring maximum thickness, wherein said first piezoelectric element has a first piezoelectric element thickness, wherein said base spring maximum thickness is greater than said first piezoelectric element thickness.