Piezoelectric energy harvester

• US 7,649,305 B2
• Filed: 03/27/2008
• Issued: 01/19/2010
• Est. Priority Date: 09/26/2006
• Status: Expired due to Fees

• Current Assignee: Hilti Aktiengesellschaft (Hilti Martin Family Trust), Board of Regents of the University of Texas System (University of Texas System)
• Original Assignee: Board of Regents of the University of Texas System (University of Texas System)
• Inventors: Priya, Shashank, Myers, Robert D.
• Primary Examiner(s): Dougherty; Thomas M
• Application Number:
  US12/057,107
• Publication Number:
  US 20080174273A1
• Time in Patent Office: 663 Days
• Field of Search: 310/339
• US Class Current: 310/339
• CPC Class Codes: H02J 7/32 for charging batteries from a charging set comprising a non-electric prime mover rotating at constant speed
• CPC Class Codes: H02N 2/188 adapted for resonant operation
• CPC Class Codes: H10N 30/306 Cantilevers
• CPC Class Codes: Y02B 40/00 Technologies aiming at improving the efficiency of home appliances, e.g. induction cooking or efficient technologies for refrigerators, freezers or dish washers

Abstract

A mechanism for capturing mechanical energy and converting it to electrical energy for use continually charging or providing emergency power to mobile, battery-powered devices comprises a plurality of elongated piezoelectric elements mounted at one or support points to one or more support structures. The plurality of piezoelectric elements are preferably structured and arranged so that at least each three-dimensional coordinate axis has at least one element with a dominant mode of deflection in a plane normal to the axis, in order to permit harvesting energy from forces applied in any direction without regard to the orientation of the energy harvesting mechanism to the source of forces. This results in improved coupling of the transducer with the random movements or vibrations that may not confined to any particular plane or in a plane that is not necessarily aligned with the plane in which a piezoelectric element is designed to bend, thus improving the efficiency of energy capture.

Claims

1. An energy harvesting apparatus comprising at least three elongated piezoelectric elements for generating a voltage when strained, each element having an axis extending along its length;

each element supported for flexing comparatively easily within a predetermined bending plane as compared to other planes in which its axis lays;

a first one of the at least three piezoelectric elements being mounted with its predetermined bending plane facing a first direction, a second one of the at least three piezoelectric elements being mounted with its predetermined bending plane facing in a second direction, and a third one of the at least three piezoelectric elements being mounted with its predetermined bending plane facing a third direction;

the first, second and third directions being non-parallel, wherein the at least three elongated, elements comprise a first array of cantilevered, elongated piezoelectric elements with axes oriented in the first direction, a second array of cantilevered, elongated piezoelectric elements with axes oriented in the second direction, and a third array of cantilevered, elongated piezoelectric elements with axes oriented in the third direction, wherein the at least three elongated elements include a sensitivity to at least two different frequencies.

2. The energy harvesting apparatus of claim 1, wherein the first, second and third directions are mutually orthogonal.

3. The energy harvesting apparatus of claim 1, wherein each of the at least three elongated piezoelectric elements has a length at least 10 times the width and the width is at least 5 times the thickness of the elongated piezoelectric elements.

4. The energy harvesting apparatus of claim 3, wherein the mass of at least one of the at least three elongated piezoelectric elements is not evenly distributed along its length, wherein the mass is concentrated in the free end of the elongated piezoelectric elements to lower the resonance frequency.

5. The energy harvesting apparatus of claim 1, wherein at least one of the at least three piezoelectric elements is supported in a cantilevered fashion, with one end fixed and one end free to move, and wherein relatively more mass of the at least one of the at least three elongated piezoelectric elements is distributed near its free end as compared to other locations along its length.

6. The energy harvesting apparatus of claim 1, further comprising at least three AC to DC conversion circuits;

a first one of the at least three AC to DC conversion circuits coupled with the first of the at least three piezoelectric elements, a second one of the at least three AC to DC conversion circuits coupled with the second of the at least three piezoelectric elements, and a third one of the at least three AC to DC conversion circuits coupled with the third of the at least three piezoelectric elements.

7. The energy harvesting apparatus of claim 1, wherein the at least three elongated, elements include a difference in dimensions, tip loading, and cascaded electrical connection to be sensitive to a different frequency.

8. The energy harvesting apparatus of claim 7, wherein each of the first, second and third arrays include at least two cantilevered, elongated piezoelectric elements arranged side-by-side and include a different length and tip mass to be sensitive to a different frequency to form the broadband response.

9. The energy harvesting apparatus of claim 7, wherein at least one of the first, second and third arrays of cantilevered, elongated piezoelectric elements are formed on a monolithic semiconductor substrate with a layered arrangement.

10. The energy harvesting apparatus of claim 1, wherein each of the at least three elongated piezoelectric elements are formed on a monolithic semiconductor substrate.

11. The energy harvesting apparatus of claim 1, wherein each of the at least three elongated piezoelectric elements are comprised of a piezoelectric bimorph.

12. The energy harvesting apparatus of claim 1, wherein each of the at least three piezoelectric elements has dimensions and distribution of mass causing it to have a resonance frequency of between 10 and 30 hertz.

13. The energy harvesting apparatus of claim 1, wherein each of the at least three elongated piezoelectric elements is supported at one fixed point in a cantilevered fashion, with one end free to move.

14. The energy harvesting apparatus of claim 1, wherein each of the at least three elongated piezoelectric elements is supported by at least two fixed points, with segments of the element between the fixed points free to flex.

18. The energy harvesting apparatus of claim 7, wherein the first, second and third arrays are arranged in a multi-axis cantilever array structure on a silicon substrate with layered arrangement to form a cube.

15. A portable device comprising a circuit and a battery for powering at least the circuit, the device electrically coupled with an energy harvester for charging the battery, the energy harvester comprising at least three elongated piezoelectric elements for generating a voltage when strained, each element having an axis extending along its length;

each element supported for flexing comparatively easily within a predetermined bending plane as compared to other planes in which its axis lays;

a first one of the at least three piezoelectric elements being mounted with its predetermined bending plane facing a first direction, a second one of the at least three piezoelectric elements being mounted with its predetermined bending plane facing in a second direction, and a third one of the at least three piezoelectric elements being mounted with its predetermined bending plane facing a third direction;

the first, second and third directions being non-parallel, wherein the three elongated piezoelectric elements include a sensitivity to at least two different frequencies.

16. The portable device of claim 15 wherein the energy harvester further comprises at least three AC to DC conversion circuits;

a first one of the at least three AC to DC conversion circuits coupled with the first of the at least three piezoelectric elements, a second one of the at least three AC to DC conversion circuits coupled with the second of the at least three piezoelectric elements, and a third one of the at least three AC to DC conversion circuits coupled with the third of the at least three piezoelectric elements.

17. The portable device of claim 15, wherein the device comprises a mobile telephone.