Efficient near-field wireless energy transfer using adiabatic system variations

• US 8,362,651 B2
• Filed: 10/01/2009
• Issued: 01/29/2013
• Est. Priority Date: 10/01/2008
• Status: Active Grant

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Hamam, Rafif E., Karalis, Aristeidis, Joannopoulos, John D., Soljacic, Marin
• Primary Examiner(s): Fureman, Jared
• Assistant Examiner(s): PEREZ BORROTO, ALFONSO
• Application Number:
  US12/571,949
• Publication Number:
  US 20100148589A1
• Time in Patent Office: 1,216 Days
• Field of Search: 307/104, 307/149, 307/151
• US Class Current: 307/104
• CPC Class Codes: H02J 50/12 of the resonant type
• CPC Class Codes: H04B 5/79 for data transfer in combination with power transfer

Abstract

Disclosed is a method for transferring energy wirelessly including transferring energy wirelessly from a first resonator structure to an intermediate resonator structure, wherein the coupling rate between the first resonator structure and the intermediate resonator structure is κ_1B, transferring energy wirelessly from the intermediate resonator structure to a second resonator structure, wherein the coupling rate between the intermediate resonator structure and the second resonator structure is κ_B2, and during the wireless energy transfers, adjusting at least one of the coupling rates κ_1B and κ_B2 to reduce energy accumulation in the intermediate resonator structure and improve wireless energy transfer from the first resonator structure to the second resonator structure through the intermediate resonator structure.

Claims

1. A method for transferring energy wirelessly, the method comprising:

transferring energy wirelessly from a first resonator structure to an intermediate resonator structure, wherein the coupling rate between the first resonator structure and the intermediate resonator structure is κ

_1B;

transferring energy wirelessly from the intermediate resonator structure to a second resonator structure, wherein the coupling rate between the intermediate resonator structure and the second resonator structure is κ

_B2; and

during the wireless energy transfers, adjusting at least one of the coupling rates κ

_1B and κ

_B2 to reduce energy accumulation in the intermediate resonator structure and improve wireless energy transfer from the first resonator structure to the second resonator structure through the intermediate resonator structure,

wherein the adjustment of the at least one of the coupling rates defines a first mode of operation,

wherein the reduction in the energy accumulation in the intermediate resonator structure is relative to energy accumulation in the intermediate resonator structure for a second mode of operation of wireless energy transfer among the three resonator structures having a coupling rate κ

′

_1B for wireless energy transfer from the first resonator structure to the intermediate resonator structure and a coupling rate κ

′

_B2 for wireless energy transfer from the intermediate resonator structure to the second resonator structure with κ

′

_1B and κ

′

_B2 each being substantially constant during the second mode of wireless energy transfer, and

wherein the adjustment of the coupling rates κ

_1B and κ

_2B in the first mode of operation satisfies

κ

_1B, κ

_B2<

√

{square root over ((κ

′

_1B²+κ

′

_B2²)/2)}.

2. The method of claim 1, wherein the adjustment of at least one of the coupling rates κ

_1B and κ

_B2 minimizes energy accumulation in the intermediate resonator structure and causes wireless energy transfer from the first resonator structure to the second resonator structure.

3. The method of claims 1, wherein the adjustment of at least one of the coupling rates κ

_1B and κ

_B2 maintains energy distribution in the field of the three-resonator system in an eigenstate having substantially no energy in the intermediate resonator structure.

4. The method of claim 3, wherein the adjustment of at least one of the coupling rates κ

_1B and κ

_B2 further causes the eigenstate to evolve substantially adiabatically from an initial state with substantially all energy in the resonator structures in the first resonator structure to a final state with substantially all of the energy in the resonator structures in the second resonator structure.

5. The method of claim 1, wherein the adjustment of at least one of the coupling rates κ

_1B and κ

_B2 comprises adjustments of both coupling rates κ

_1B and κ

_B2 during wireless energy transfer.

6. The method of claim 1, wherein the resonator structures each have a quality factor larger than 10.

7. The method of claim 1, wherein resonant energy in each of the resonator structures comprises electromagnetic fields.

8. The method of claim 7, wherein the maximum value of the coupling rate κ

_1B and the maximum value of the coupling rate κ

_B2 for inductive coupling between the intermediate resonator structure and each of the first and second resonator structures are each larger than twice the loss rate Γ

for each of the first and second resonators.

9. The method of claim 8, wherein the maximum value of the coupling rate κ

_1B and the maximum value of the coupling rate κ

_B2 for inductive coupling between the intermediate resonator structure and each of the first and second resonator structures are each larger than four (4) times the loss rate Γ

for each of the first and second resonators.

10. The method of claim 7, wherein each resonator structure has a resonant frequency between 50 KHz and 500 MHz.

11. The method of claim 1, wherein the maximum value of the coupling rate κ

_1B and the maximum value of the coupling rate κ

_B2 are each at least five (5) times greater than the coupling rate between the first resonator structure and the second resonator structure.

12. The method of claim 1, wherein the intermediate resonator structure has a rate of radiative energy loss that is at least twenty (20) times greater than that for either the first resonator structure or the second resonator structure.

13. The method of claim 1, wherein the first and second resonator structures are substantially identical.

14. The method of claim 1, wherein the adjustment of at least one of the coupling rates κ

_1B and κ

_B2 causes peak energy accumulation in the intermediate resonator structure to be less than five percent (5%) of the peak total energy in the three resonator structures.

15. The method of claim 1, wherein adjusting at least one of the coupling rates κ

_1B and κ

_B2 comprises adjusting a relative position and/or orientation between one or more pairs of the resonator structures.

16. The method of claim 1, wherein adjusting at least one of the coupling rates κ

_1B and κ

_B2 comprises adjusting a resonator property of one or more of the resonator structures.

17. The method of claim 16, wherein the resonator property comprises mutual inductance.

18. The method of claim 1, wherein at least one of the resonator structures comprises a capacitively loaded loop or coil of at least one of a conducting wire, a conducting Litz wire, and a conducting ribbon.

19. The method of claim 1, wherein at least one of the resonator structures comprises an inductively loaded rod of at least one of a conducting wire, a conducting Litz wire, and a conducting ribbon.

20. The method of claim 4, wherein the adjustment of at least one of the coupling rates κ

_1B and κ

_B2 causes peak energy accumulation in the intermediate resonator structure during the wireless energy transfers to be less than ten percent (10%) of the peak total energy in the three resonator structures.

21. The method of claim 1, wherein the wireless energy transfers are non-radiative energy transfers mediated by a coupling of a resonant field evanescent tail of the first resonator structure and a resonant field evanescent tail of the intermediate resonator structure and a coupling of the resonant field evanescent tail of the intermediate resonator structure and a resonant field evanescent tail of the second resonator structure.

22. The method of claim 1, wherein the first and second resonator structures each have a quality factor greater than 50.

23. The method of claim 1, wherein the first and second resonator structures each have a quality factor greater than 100.

24. The method of claim 1, wherein the first mode of operation has a greater efficiency of energy transferred from the first resonator to the second resonator compared to that for the second mode of operation.

25. The method of claim 24, wherein the first and second resonator structures are substantially identical and each one has a loss rate Γ

_A, the intermediate resonator structure has a loss rate Γ

_B, and wherein Γ

_B/Γ

_A is greater than 50.

26. The method of claim 1, wherein a ratio of energy lost to radiation and total energy wirelessly transferred between the first and second resonator structures in the first mode of operation is less than that for the second mode of operation.

27. The method of claim 26, wherein the first and second resonator structures are substantially identical and each one has a loss rate Γ

_A and a loss rate only due to radiation Γ

_A,rad, the intermediate resonator structure has a loss rate Γ

_B and a loss rate only due to radiation Γ

_B,rad and wherein Γ

_B,rad/Γ

_B>

Γ

_A,rad/Γ

_A.

28. The method of claim 1, wherein in the first mode of operation the intermediate resonator structure interacts less with extraneous objects than it does in the second mode of operation.