Broad spectrum and wide amplitude range vibration energy harvester: bistable piezoelectric transduction, synchronized extraction, self-actuated adaptation

• US 10,224,835 B1
• Filed: 04/11/2016
• Issued: 03/05/2019
• Est. Priority Date: 04/09/2015
• Status: Active Grant

• Current Assignee: Iowa State University Research Foundation Incorporated (Iowa State University)
• Original Assignee: Iowa State University Research Foundation Incorporated (Iowa State University)
• Inventors: Singh, Kanishka Aman, Kumar, Ratnesh, Weber, Robert J.
• Primary Examiner(s): Martin, J. San
• Application Number:
  US15/095,836
• Time in Patent Office: 1,058 Days
• Field of Search: 310339
• CPC Class Codes: H02K 35/02 with moving magnets and stationary coil systems
• CPC Class Codes: H02N 2/181 Circuits; Control arrangements or methods
• CPC Class Codes: H02N 2/186 Vibration harvesters
• CPC Class Codes: H10N 30/306 Cantilevers

Abstract

The invention relates to a bistable piezoelectric cantilever-based vibration energy harvester that increases the energy harvested over a broad frequency of vibrations by introducing bistability to the cantilever through use of two repelling magnets, one mounted on the cantilever and one at a location facing the first. This increases the amplitude and velocity of cantilever vibration, hence harvested power, while nonlinearity makes the system efficient over almost the entire range of frequencies, lower than the natural resonant frequency of the linear version without the magnets. Such improved performance is seen while the cantilever remains in the bistable mode. To broaden the range of vibration amplitudes over which the harvester continues to operate in bistable mode, the harvester includes a mechanical way of tuning the magnetic force, by spring-loading the magnet facing the mounted one, enabling self-adjustment of the distance between the magnets automatically that favors bistable operation over a larger range of excitations, and that too without needing any extra energy.

Claims

1. A piezoelectric cantilever based bistable harvester comprising:

a piezoelectric cantilever;

a first permanent magnet operatively connected to the piezoelectric cantilever;

a second magnet positioned relative to the first permanent magnet such that repulsive magnetic force between the first permanent magnet and the second magnet causes the piezoelectric cantilever to bend away from an axis thereby creating two distinct equilibrium states;

a spring operatively connected to the second permanent magnet to provide for spring loading to mechanically tune the repulsive magnetic force by automatically applying motion to the second permanent magnet during bending of the piezoelectric magnet between the two distinct equilibrium states so that as the first permanent magnet on the piezoelectric cantilever approaches the spring-loaded second permanent magnet, the spring compresses, increasing the distance between the first and second permanent magnets, and conversely, as the piezoelectric cantilever recedes, the spring pushes the first and second permanent magnets closer;

one or more guide members for restricting the motion of the second permanent magnet in a linear domain; and

a synchronized energy extraction circuit operatively connected to the piezoelectric cantilever.

2. The piezoelectric cantilever based bistable harvester of claim 1, wherein the synchronized energy extraction circuit comprises a synchronized charge extraction (SCE) circuit.

3. The piezoelectric cantilever based bistable harvester of claim 1, wherein the synchronized energy extraction circuit comprises a parallel synchronized switch harvesting on inductor (SSHI) circuit.

4. The piezoelectric cantilever based bistable harvester of claim 1, wherein the linear domain is a linear horizontal domain.

5. The piezoelectric cantilever based bistable harvester of claim 1, wherein the one or more guide members comprises a cylindrical sleeve.

6. The piezoelectric cantilever based bistable harvester of claim 1, further comprising an electromechanical coupling operatively associated with the second magnet to further harvest energy from the motion of the second magnet.

7. A method of harvesting energy, the method comprising:

providing a piezoelectric cantilever based bistable harvester comprising (a) a piezoelectric cantilever, (b) a first permanent magnet positioned at a tip of the piezoelectric cantilever, and (c) a second permanent magnet positioned relative to the first permanent magnet such that repulsive magnetic force between the first permanent magnet and the second permanent magnet causes the piezoelectric cantilever to bend away from an axis thereby creating two distinct equilibrium states;

maintaining the piezoelectric cantilever based bistable harvester within a bistable mode by mechanically tuning the repulsive magnetic force by operatively connecting the second permanent magnet to a mechanical mechanism which automatically changes the distance between the first and second permanent magnets during bending of the piezoelectric cantilever between the two distinct equilibrium states by increasing the distance between the first and second permanent magnets as the first permanent magnet on the piezoelectric cantilever approaches the second permanent magnet, and pushing the first and second permanent magnets closer as the piezoelectric cantilever recedes; and

restricting motion of the second permanent magnet in a linear domain by one or more guide members.

8. The method of claim 7, wherein the tuning the repulsive magnetic force is performed by applying motion to the second permanent magnet with the repulsive magnetic force.

9. The method of claim 7, wherein the mechanical mechanism connected to the second permanent magnet comprises a spring operatively connected to the second permanent magnet to provide for spring loading to mechanically tune the magnetic force.

10. The method of claim 7, wherein the linear domain is a linear horizontal domain.

11. The method of claim 7, wherein the one or more guide members comprises a cylindrical sleeve.

12. The method of claim 7, wherein the piezoelectric cantilever based bistable harvester further comprises a synchronized energy extraction circuit.

13. The method of claim 12, wherein the synchronized energy extraction circuit comprises a synchronized charge extraction (SCE) circuit.

14. The method of claim 12, wherein the synchronized energy extraction circuit comprises a parallel synchronized switch harvesting on inductor (SSHI) circuit.

15. The method of claim 12, wherein the synchronized energy extraction circuit comprises a synchronized charge extraction (SCE) circuit and a parallel synchronized switch harvesting on inductor (SSHI) circuit.

16. A piezoelectric cantilever based bistable harvester, comprising:

a piezoelectric cantilever;

a first magnet positioned on the piezoelectric cantilever;

a second magnet positioned relative to the first magnet and operatively connected to a mechanical mechanism that allows the second magnet to move to vary the distance between the first and second magnets;

wherein a repulsive force between the first and second magnets causes the piezoelectric cantilever to bend away from an axis thereby creating two distinct equilibrium states;

wherein the piezoelectric cantilever based bistable harvester is configured to mechanically tune magnetic force so as to promote operation within a bistable mode for energy harvesting by operatively connecting the second magnet to the mechanical mechanism which automatically changes the distance between the first and second magnets during bending of the piezoelectric cantilever between the two distinct equilibrium states by increasing the distance between the first and second magnets as the first magnet on the piezoelectric cantilever approaches the second magnet, and pushing the first and second magnets closer as the piezoelectric cantilever recedes,

wherein the mechanical mechanism connected to the second magnet comprises a spring and a guide member configured to restrict the motion of the second magnet in a substantially linear domain, and

wherein the motion of the second magnet can be electromagnetically coupled for additional energy harvesting.