System and method for low loss wireless power transmission

Abstract

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.

What is claimed is: 
     
       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.