Piezoelectric Composite Beam with Automatically Adjustable Natural Frequency

• US 20100141096A1
• Filed: 02/18/2010
• Published: 06/10/2010
• Est. Priority Date: 11/23/2005
• Status: Active Grant

• Current Assignee: Lord Corporation (Parker-Hannifin Corporation)
• Original Assignee: MicroStrain, Inc. (Spectris PLC)
• Inventors: Arms, Steven W., Churchill, David L.
• Granted Patent: US 7,898,157 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

An energy harvesting system includes a composite structure that has a first spring, a piezoelectric structure, and a proof mass. The piezoelectric structure and the proof mass are mounted on the first spring. The composite structure has a natural frequency of vibration. The natural frequency of vibration of the composite structure is automatically adjustable.

Claims

1. An energy harvesting system, comprising a composite structure including a first spring, a piezoelectric structure, and a proof mass, wherein said piezoelectric structure and said proof mass are mounted on said first spring, wherein said composite structure has a composite structure natural frequency of vibration, wherein said composite structure natural frequency is automatically adjustable.

2. An energy harvesting system as recited in claim 1, further comprising a substrate, wherein said composite structure is mounted on said substrate, wherein said substrate has a substrate vibration frequency, wherein said composite structure natural frequency is automatically adjustable to tune said composite structure to have a composite structure natural frequency about equal to said substrate vibration frequency.

3. An energy harvesting system as recited in claim 2, wherein position of said proof mass on said first spring is automatically adjustable to provide said composite structure with a composite structure natural frequency that is about equal to said substrate vibration frequency.

4. An energy harvesting system as recited in claim 2, further comprising a controller, wherein a feedback signal from said piezoelectric element is used by said controller to automatically adjust said natural frequency of said composite structure.

5. An energy harvesting system as recited in claim 4, wherein said controller automatically adjusts said natural vibration frequency to about equal said substrate vibration frequency.

6. An energy harvesting system as recited in claim 4, wherein said controller automatically adjusts position of said mass on said first spring to provide said composite structure with a natural frequency about equal to said substrate vibration frequency.

7. An energy harvesting system as recited in claim 1, further comprising a second element coupled to said first spring, wherein varying a parameter of said second element varies said composite structure natural frequency.

8. An energy harvesting system as recited in claim 7, wherein said second element includes a second spring.

9. An energy harvesting system as recited in claim 7, wherein said second element includes a magnet.

10. An energy harvesting system as recited in claim 1, wherein said first spring includes a taper.

11. An energy harvesting system as recited in claim 1, wherein said first spring has a first spring surface having elevated portions separated by a recessed portion, wherein said piezoelectric structure substantially crosses said recessed portion.

12. An energy harvesting system as recited in claim 11, wherein said piezoelectric structure includes a piezoelectric element bonded to said elevated portions.

13. An energy harvesting system as recited in claim 12, wherein said first spring surface has a plurality of said recessed portions, wherein an elevated portion is located on both sides of each said recessed portion.

14. An energy harvesting system as recited in claim 13, wherein said piezoelectric element extends across each of said recessed portions and is bonded to each of said elevated portions.

15. An energy harvesting system as recited in claim 14, wherein said first spring includes a taper.

16. An energy harvesting system as recited in claim 14, wherein said first spring has a lower stiffness than said piezoelectric element.

17. An energy harvesting system as recited in claim 13, wherein said first spring includes a long axis, wherein said recessed portions are arranged perpendicular to said long axis.

18. An energy harvesting system as recited in claim 11, wherein a low stiffness material is located within said recessed portion, wherein said piezoelectric element is bonded to said low stiffness material.

19. An energy harvesting system as recited in claim 11, wherein said first spring has a damping characteristic about equal to that of a first spring without said recessed portion.

20. An energy harvesting system as recited in claim 11, wherein said piezoelectric structure includes a second piezoelectric element located in said recessed portion.

21. An energy harvesting system as recited in claim 20, wherein said second piezoelectric element includes a bulk piezoelectric material.

22. An energy harvesting system as recited in claim 21, wherein said bulk piezoelectric material includes a single crystal piezoelectric material.

23. An energy harvesting system as recited in claim 21, wherein said first spring surface has an elevated portion defining a level, wherein a portion of said bulk piezoelectric material is located at said level.

24. An energy harvesting system as recited in claim 20, further comprising a flex circuit having wiring, wherein said piezoelectric structure contacts said wiring within said recessed portion.

25. An energy harvesting system as recited in claim 24, wherein said flex circuit extends along an edge of said first spring.

26. An energy harvesting system as recited in claim 1, wherein said composite structure includes a plurality of said piezoelectric elements.

27. An energy harvesting system as recited in claim 26, wherein one said piezoelectric element is located on a first side of said first spring and a second said piezoelectric element is located on a second side of said first spring.

28. An energy harvesting system as recited in claim 27, wherein two said piezoelectric elements are located on a first side of said first spring and two said piezoelectric elements are located on a second side of said first spring.

29. An energy harvesting system as recited in claim 28, wherein said two piezoelectric elements located on said first side of said first spring are stacked and wherein said two piezoelectric elements located on said second side of said first spring are stacked.

30. An energy harvesting system as recited in claim 26, wherein said plurality of piezoelectric elements are stacked.

31. An energy harvesting system as recited in claim 26, further comprising a plurality of rectifier bridges, wherein each of said plurality of piezoelectric elements is connected to a different one of said rectifier bridges.

32. An energy harvesting system as recited in claim 1, wherein said first spring is fabricated of metal.

33. An energy harvesting system as recited in claim 32, wherein said metal includes a superelestic nickel titanium material.

34. An energy harvesting system, comprising substrate, a composite structure, and a controller, wherein said composite structure includes a first spring, a piezoelectric structure, and a mass, wherein said first spring has a first spring surface having elevated portions separated by a recessed portion, wherein said piezoelectric structure substantially crosses said recessed portion, wherein said mass is mounted on said first spring, wherein said composite structure has a composite structure natural frequency of vibration, wherein said composite structure is mounted on said substrate, wherein said substrate is subject to vibration at a substrate frequency, wherein said substrate frequency is variable, wherein said composite structure natural frequency is adjustable to match said substrate frequency, wherein a feedback signal from said piezoelectric element is used by said controller to automatically adjust said composite structure natural frequency to match said substrate frequency.

35. An energy harvesting system as recited in claim 34, wherein said first spring includes a taper.

36. An energy harvesting system as recited in claim 34, wherein said piezoelectric structure includes a piezoelectric element bonded to said elevated portions.

37. An energy harvesting system as recited in claim 34, wherein said first spring surface has a plurality of said recessed portions, wherein an elevated portion is located on both sides of each said recessed portion.

38. An energy harvesting system as recited in claim 37, wherein said piezoelectric element extends across each of said recessed portions and is bonded to each of said elevated portions.

39. An energy harvesting system as recited in claim 34, wherein said first spring has a lower stiffness than said piezoelectric element.

40. An energy harvesting system as recited in claim 34, wherein said composite structure includes a plurality of said piezoelectric elements.

41. An energy harvesting system as recited in claim 40, wherein said plurality of piezoelectric elements are stacked.

42. An energy harvesting system as recited in claim 40, further comprising a plurality of rectifier bridges, wherein each said plurality of piezoelectric elements is connected to a different one of said rectifier bridges.

43. An energy harvesting system as recited in claim 34, wherein said controller automatically adjusts position of said mass on said first spring to provide said composite structure with a composite structure natural frequency that is about equal to said substrate vibration frequency.

44. An energy harvesting system as recited in claim 34, wherein said composite structure further includes a second element coupled to said first spring, wherein varying a parameter of said second element varies said composite structure natural frequency, wherein said controller automatically adjusts said parameter.

45. An energy harvesting system as recited in claim 44, wherein said second element includes a second spring.

46. An energy harvesting system as recited in claim 44, wherein said second element includes a magnet.