ENERGY HARVESTING DEVICE

• US 20100148519A1
• Filed: 01/29/2008
• Published: 06/17/2010
• Est. Priority Date: 01/29/2007
• Status: Active Grant

• Current Assignee: Drexel University
• Original Assignee: Drexel University
• Inventors: Shih, Wei-heng, Shih, Wan Y., Yegingil, Hakki
• Granted Patent: US 8,110,964 B2
• Time in Patent Office: Days
• US Class Current: 290/1.R
• CPC Class Codes: H02N 2/188 adapted for resonant operation
• CPC Class Codes: H10N 30/306 Cantilevers
• CPC Class Codes: H10N 30/8548 Lead-based oxides

Abstract

A piezoelectric energy harvesting device (PEHD) comprising a driving element, conducting element, piezoelectric layer and non-piezoelectric layer capable of converting ambient mechanical energy into electrical energy. The piezoelectric layer may be constructed from PMN-PT or PZT having a thickness of about 1-150 ?m. The PEHD may be used to generate about 1 W. The harvested energy may be stored and used to power microelectronic devices and rechargeable battery technologies.

Claims

1. A piezoelectric energy harvesting system comprising a cantilever including a conducting element, at least a first piezoelectric layer and a non-piezoelectric layer, wherein said piezoelectric layer has a thickness of about 1 μ

m-about 150 μ

m, and an electrical connection to a device which stores or uses energy.

2. The system of claim 1, wherein said piezoelectric layer and non-piezoelectric layer have different lengths.

3. The system of claim 1, wherein said piezoelectric layer has a thickness of about 8 μ

m-about 127 μ

m.

4. The system of claim 1, wherein said piezoelectric layer is selected from the group consisting of PZT and PMN-PT.

5. The system of claim 1, wherein said cantilever comprises a second piezoelectric layer and a device for applying an alternating current to said second piezoelectric layer.

6. The system of claim 5, wherein said second piezoelectric layer has a different length from at least one of the first piezoelectric layer or the non-piezoelectric layer.

7. The system of claim 5, wherein said cantilever is capable of operation at a resonance frequency of the first piezoelectric layer.

8. The system of claim 5, wherein said cantilever is capable of operation at two or more resonance frequencies of the first piezoelectric layer.

9. The system of claim 1, wherein a ratio of a thickness of the piezoelectric layer to a thickness of the non-piezoelectric layer is from about 0.04 to about 12.5.

10. The system of claim 1, wherein the piezoelectric layer is made by a method which produces a PMN-PT freestanding film.

11. The system of claim 10, wherein the PMN-PT freestanding film has a piezoelectric coefficient −

d₃₁ of at least about 2000 pm/V at E=about 10 kV/cm.

12. The system of claim 11, wherein the dielectric constant of the PMN-PT freestanding film decreases with increasing electric field.

13. The system of claim 12, wherein the PMN-PT freestanding film has a strain of at least 0.3% measured under an applied electric field of from about 8 kV/cm to about 12 kV/cm.

14. The system of claim 12, wherein the PMN-PT freestanding film is unpoled and has a strain of at least 3% measured at an applied electric field of about 10 kV/cm.

15. The system of claim 1, comprising a plurality of cantilevers to form an array, and wherein each said cantilever is electrically connected to a device for storing or using electrical energy.

16. A method harvesting energy harvesting comprising the steps of:

a. exposing at least one piezoelectric cantilever including a driving element, at least a first piezoelectric layer having a thickness of about 1 μ

m-about 150 μ

m, a conductive element, and a non-piezoelectric layer, to a mechanical or vibrational force, and

b. harvesting electrical energy generated by conversion of said mechanical or vibrational energy into electrical energy.

17. The method of claim 16, further including the step of storing said harvested electrical energy.

18. The method of claim 16, wherein the piezoelectric cantilever further includes a second piezoelectric layer and the method further comprises the step of applying an alternating voltage to said second piezoelectric layer to operate said cantilever at frequency which is about a resonance frequency of said first piezoelectric layer.

19. The method of claim 18, wherein a ratio of a thickness of said first piezoelectric layer to a thickness of said non-piezoelectric layer is from about 0.04 to about 12.5.

20. The method of claim 19, wherein the first piezoelectric layer is made by a method which produces a PMN-PT freestanding film having a piezoelectric coefficient −

d₃₁ of at least about 2000 pm/V at E=about 10 kV/cm.