System and method for low loss wireless power transmission
Systems and methods for low loss wireless power transmission are described herein. In one aspect, a transmission coil for transmitting wireless power comprises a first and second spiral coil. Each spiral coil comprises a plurality of turns. A center of the first spiral coil to an outermost turn of the first spiral coil defines a first cross section, and a center of the second spiral coil to an outermost turn of the second spiral coil defines a second cross section. Portions of the first spiral coil along the first cross section and the second spiral coil along the second cross section have a mutual inductance with respect to a receive coil greater than 65% of a maximum mutual inductance along the first and second cross sections. The second spiral coil is counter-wound relative to the first spiral coil.
1. A transmission coil for transmitting wireless power to a receive coil, the transmission coil comprising:
a first spiral coil comprising a plurality of turns, a center of the first spiral coil to an outermost turn of the first spiral coil defining a first cross section; and
a second spiral coil comprising a plurality of turns, a center of the second spiral coil to an outermost turn of the second spiral coil defining a second cross section, portions of the first spiral coil along the first cross section and the second spiral coil along the second cross section having a mutual inductance with respect to the receive coil greater than 65% of a maximum mutual inductance along the first and second cross sections, the second spiral coil counter-wound relative to the first spiral coil.
2. The transmission coil of claim 1 , wherein the second spiral coil is located above or below the first spiral coil.
3. The transmission coil of claim 1 , wherein the second spiral coil is interwoven with the first spiral coil.
4. The transmission coil of claim 1 , wherein a total length of the second spiral coil is a same length as a total length of the first spiral coil, and the second spiral coil is substantially shaped as a reflection of the first spiral coil.
5. The transmission coil of claim 1 , wherein the receive coil comprises a first receive coil and a second receive coil.
6. The transmission coil of claim 1 , wherein the second spiral coil is located substantially on a common plane with the first spiral coil and has a common center with first spiral coil,
the first and second cross sections are located substantially on the common plane, and
a turn distance from the common center to a center of a particular turn along the first or second cross section of the first or second spiral coil is a function of a distance from the common center to the outermost turn of the first or second spiral coil, a first value corresponding to spacings between turns of the first or second spiral coil, a sum of a total number of turns of the first and second spiral coils, and a first number corresponding to the particular turn.
7. The transmission coil of claim 1 , wherein the first and second spiral coil are electrically coupled to a driver circuit and configured to wirelessly transmit power at a level sufficient to charge or power a receiver device.
8. The transmission coil of claim 1 , wherein input signals for first and second spiral coil are configured to be within a frequency range of 6.5 Megahertz to 7 Megahertz.
9. The transmission coil of claim 1 , wherein each turn of the first and second spiral coil is configured to have a turn radius greater than a minimum turn radius of 5 millimeters.
10. A method for transmitting wireless power to a receive coil, the method comprising:
driving with electrical current a first spiral coil comprising a plurality of turns, a center of the first spiral coil to an outermost turn of the first spiral coil defining a first cross section; and
driving with electrical current a second spiral coil comprising a plurality of turns, a center of the second spiral coil to an outermost turn of the second spiral coil defining a second cross section, portions of the first spiral coil along the first cross section and the second spiral coil along the second cross section having a mutual inductance with respect to the receive coil greater than 65% of a maximum mutual inductance along the first and second cross sections, the second spiral coil counter-wound relative to the first spiral coil.
11. The method of claim 10 , wherein the second spiral coil is located above or below the first spiral coil.
12. The method of claim 10 , wherein the second spiral coil is interwoven with the first spiral coil.
13. The method of claim 10 , wherein a total length of the second spiral coil is a same length as a total length of the first spiral coil, and the second spiral coil is substantially shaped as a reflection of the first spiral coil.
14. The method of claim 10 , wherein the receive coil comprises a first receive coil and a second receive coil.
15. The method of claim 10 , wherein the second spiral coil is located substantially on a common plane with the first spiral coil and has a common center with first spiral coil,
the first and second cross sections are located substantially on the common plane, and
a turn distance from the common center to a center of a particular turn along the first or second cross section of the first or second spiral coil is a function of a distance from the common center to the outermost turn of the first or second spiral coil, a first value corresponding to spacings between turns of the first or second spiral coil, a sum of a total number of turns of the first and second spiral coils, and a first number corresponding to the particular turn.
16. The method of claim 10 , wherein the first and second spiral coil are electrically coupled to a driver circuit and configured to wirelessly transmit power at a level sufficient to charge or power a receiver device.
17. The method of claim 10 , wherein input signals for first and second spiral coil are configured to be within a frequency range of 6.5 Megahertz to 7 Megahertz.
18. The method of claim 10 , wherein each turn of the first and second spiral coil is configured to have a turn radius greater than a minimum turn radius of 5 millimeters.