Antennas and their coupling characteristics for wireless power transfer via magnetic coupling

1. An apparatus configured to receive wireless power from a transmitter, the apparatus comprising:

an inductor having an inductance value;

a capacitor electrically connected to the inductor and having a capacitance value; and

an optimizing circuit configured to:

optimize transfer efficiency of power received wirelessly from the transmitter, provided that an amount of the power received wirelessly and provided to a load is greater than or equal to a received power threshold, or

optimize the amount of the power received wirelessly from the transmitter, provided that the power transfer efficiency is greater than or equal to an efficiency threshold.

2. The apparatus of claim 1 , wherein the optimizing circuit is configured to optimize power transfer efficiency or optimize the amount of power received based at least in part on maintaining a first resonant frequency of the transmitter substantially equal to a second resonant frequency of a receive circuit comprising the inductor and capacitor.

3. The apparatus of claim 1 , wherein the optimizing circuit is configured to optimize power transfer efficiency or optimize the amount of power received based at least in part on whether the transmitter is weakly coupled to the receive circuit as compared to when the transmitter is strongly coupled to the receive circuit.

4. The apparatus of claim 1 , wherein the optimizing circuit is configured to maintain a resistance of the inductor substantially equal to a series resistance.

5. The apparatus of claim 1 , wherein the optimizing circuit comprises at least one of a first component configured to vary the inductance value of the inductor, a second component configured to vary the capacitance value of the capacitor, a variable resistor, or an FPGA.

6. A method for wirelessly receiving power from a transmitter, the, the method comprising:

optimizing transfer efficiency of power received wirelessly from the transmitter, provided that an amount of the power received wirelessly and provided to a load is greater than or equal to a received power threshold; or

optimizing the amount of the power received wirelessly from the transmitter, provided that the power transfer efficiency is greater or equal to an efficiency threshold.

7. The method of claim 6 , wherein optimizing power transfer efficiency and optimizing the amount of the received power comprises optimizing based on at least one of maintaining a first resonant frequency of the transmitter substantially equal to a second resonant frequency of a receive circuit comprising an inductor and capacitor or based on whether the transmitter is weakly coupled to the receive circuit as compared to when the transmitter is strongly coupled to the receive circuit.

8. An apparatus configured to receive wireless power from a transmitter, the apparatus comprising:

means for optimizing transfer efficiency of power received wirelessly from a transmitter, provided that an amount of the power received wirelessly and provided to a load is greater than or equal to a received power threshold; or

means for optimizing the amount of the power received wirelessly, provided that the power transfer efficiency is greater or equal to an efficiency threshold.

9. The apparatus of claim 8 , wherein the means for optimizing power transfer efficiency and optimizing the amount of the received power comprises means for optimizing based on at least one of maintaining a first resonant frequency of the transmitter substantially equal to a second resonant frequency of a receive circuit comprising an inductor and capacitor or based on whether the transmitter is weakly coupled to the receive circuit as compared to when the transmitter is strongly coupled to the receive circuit.

10. An apparatus configured to transmit wireless power to a receiver, the apparatus comprising:

an inductor having an inductance value;

a capacitor electrically connected to the inductor and having a capacitance value; and

an optimizing circuit configured to:

optimize transfer efficiency of power transmitted wirelessly to the receiver, provided that an amount of power received wirelessly and provided to a load of the receiver is greater than or equal to a received power threshold; or

optimize the amount of the power received wirelessly, provided that the power transfer efficiency is greater than or equal to an efficiency threshold.

11. The apparatus of claim 10 , wherein the optimizing circuit comprises at least one of a first component configured to vary the inductance value of the inductor, a second component configured to vary the capacitance value of the capacitor, a variable resistor, or an FPGA.

12. An apparatus for receiving power via a wireless field and for delivering power to a load, the apparatus comprising:

a first antenna circuit coupled to the load and comprising an antenna, the first antenna circuit being configured to receive power via the wireless field for powering the load, the received power corresponding to a time-varying voltage signal from a second antenna circuit, the load being characterized by a reactance X and the first antenna circuit being characterized by an inductance L and a capacitance C, at least one of the inductance L and capacitance C configured to maintain the reactance X to be substantially equal to a first value that is inversely proportional to the capacitance C minus a second value that is directly proportional to the inductance L; and

a controller coupled to the first antenna circuit and configured to adjust at least one parameter of the first antenna circuit.

13. The apparatus of claim 12 , wherein the first antenna circuit comprises a variable inductor and a variable capacitor, wherein the controller is configured to adjust the inductance L by adjusting the variable inductor, and wherein the controller is configured to adjust the capacitance C by adjusting the variable capacitor.

14. The apparatus of claim 12 , wherein the controller comprises an FPGA.

15. The apparatus of claim 12 , wherein the first antenna circuit comprises a first inductive coil.

16. The apparatus of claim 12 , wherein the received power is coupled from a near-field of the second antenna circuit.

17. The apparatus of claim 12 , wherein the first antenna circuit is configured to oscillate at a frequency substantially equal to a resonant frequency of the first antenna circuit in response to the wireless field produced by the second antenna circuit.

18. A method of receiving power via a wireless field and for delivering power to a load, the apparatus comprising:

wirelessly receiving power at a first antenna circuit for powering the load, the received power corresponding to a time-varying voltage signal from a second antenna circuit, the load being characterized by a reactance X and the first antenna circuit being characterized by an inductance L and a capacitance C, at least one of the inductance L and capacitance C configured to maintain the reactance X to be substantially equal to a first value that is inversely proportional to the capacitance C minus a second value that is directly proportional to the inductance L; and

adjusting at least one parameter of the first antenna circuit.

19. The method of claim 18 , wherein the first antenna circuit comprises a variable inductor and a variable capacitor, wherein adjusting the at least one parameter comprises adjusting the variable inductor, and wherein adjusting the at least one parameter comprises adjusting the variable capacitor.

20. The method of claim 18 , wherein wirelessly receiving power comprising coupling power from a near-field of the second antenna circuit.

21. The method of claim 18 , wherein the first antenna circuit is configured to oscillate at a frequency sustainably equal to a resonant frequency of the first antenna circuit in response to the wireless field produced by the second antenna circuit.

22. An apparatus for receiving power via a wireless field and for delivering power to a load, the apparatus comprising:

means for wirelessly receiving power for powering the load, the received power corresponding to a time-varying voltage signal from a second antenna circuit, the load being characterized by a reactance X and the means for wirelessly receiving power being characterized by an inductance L and a capacitance C, at least one of the inductance L and capacitance C configured to maintain the reactance X to be substantially equal to a first value that is inversely proportional to the capacitance C minus a second value that is directly proportional to the inductance L; and

means for adjusting at least one parameter of the means for wirelessly receiving power.

23. The apparatus of claim 22 , wherein the means for wirelessly receiving power comprises a first antenna circuit comprising a variable inductor and a variable capacitor, wherein the means for adjusting comprises means for adjusting the variable inductor, and wherein the means for adjusting comprises means for adjusting the variable capacitor.

24. The apparatus of claim 22 , wherein the means for adjusting comprises a controller.

25. The apparatus of claim 22 , wherein the received power is coupled from a near-field of the second antenna circuit.

26. The apparatus of claim 22 , wherein the means for wirelessly receiving power is configured to oscillate at a frequency substantially equal to a resonant frequency of the means for wirelessly receiving power in response to the wireless field produced by the second antenna circuit.

27. An apparatus for delivering power to a load via a wireless field, the apparatus comprising:

a power source configured to output a time-varying voltage signal at a voltage level and characterized by a reactance X; and

a first antenna circuit configured to receive the voltage signal from the power source and to output power to a second antenna circuit to power the load via the wireless field, the first antenna circuit characterized by an inductance L and a capacitance C, at least one of the inductance L and capacitance C configured to maintain the reactance X to be substantially equal to a first value that is inversely proportional to the capacitance C minus a second value that is directly proportional to the inductance L.