Slotted beam piezoelectric composite

• US 7,692,365 B2
• Filed: 11/24/2006
• Issued: 04/06/2010
• Est. Priority Date: 11/23/2005
• Status: Active Grant

• Current Assignee: Hottinger Bruel & Kjaer Incorporated
• Original Assignee: MicroStrain, Inc. (Spectris PLC)
• Inventors: Arms, Steven W., Churchill, David L.
• Primary Examiner(s): SAN MARTIN, JAYDI A
• Application Number:
  US11/604,117
• Publication Number:
  US 20070114890A1
• Time in Patent Office: 1,229 Days
• Field of Search: 310330-332, 310/339
• 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 first spring and a piezoelectric structure, 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, and wherein said piezoelectric structure includes a piezoelectric element bonded to said elevated portions.

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

3. An energy harvesting device as recited in claim 1, 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.

4. An energy harvesting device as recited in claim 3, wherein said piezoelectric element extends across each of said recessed portions and is bonded to each of said elevated portions.

5. An energy harvesting device as recited in claim 4, wherein said first spring has a lower stiffness than said piezoelectric element.

6. An energy harvesting device as recited in claim 3, wherein said first spring includes a long axis, wherein said recessed portions are arranged perpendicular to said long axis.

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

8. An energy harvesting device as recited in claim 7, wherein said plurality of piezoelectric elements are stacked.

9. An energy harvesting device as recited in claim 7, further comprising a plurality of rectifier bridges, wherein each said plurality of piezoelectric elements is connected to a different one of said rectifier bridges.

10. An energy harvesting device as recited in claim 1, 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.

11. An energy harvesting device as recited in claim 10, 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.

12. An energy harvesting device as recited in claim 11, 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.

13. 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.

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

15. An energy harvesting device as recited in claim 1, wherein said piezoelectric structure includes a second piezoelectric element located in said recessed portion.

16. An energy harvesting device as recited in claim 15, wherein said second piezoelectric element includes a bulk piezoelectric material.

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

18. An energy harvesting device as recited in claim 16, 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.

19. An energy harvesting device as recited in claim 15, 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 first spring.

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

22. An energy harvesting device as recited in claim 21, wherein said metal includes a superelestic nickel titanium material.

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

24. An energy harvesting device as recited in claim 23, wherein said mass is movable on said first spring.

25. An energy harvesting device as recited in claim 23, 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.

26. An energy harvesting device as recited in claim 23, wherein said composite structure has a natural frequency of vibration, wherein said composite structure further includes a second element coupled to said first spring, wherein varying a parameter of said second element varies said natural frequency of vibration.

27. An energy harvesting device as recited in claim 26, wherein said second element includes a spring.

28. An energy harvesting device as recited in claim 26, wherein said second element includes a magnet.