Controlling field distribution of a wireless power transmitter

1. A transmitter for wirelessly transferring power to a receiver device, comprising:

a transmit antenna configured to generate a first magnetic field for wirelessly transferring power to the receiver device, the transmit antenna comprising a first resonant circuit configured to resonate at a first frequency corresponding to an operating frequency;

at least one parasitic antenna comprising a second resonant circuit configured to resonate at a second frequency different than the operating frequency; and

a controller configured to activate the at least one parasitic antenna that is configured to steer the first magnetic field generated by the transmit antenna to a charging region when activated.

2. The transmitter of claim 1 , wherein the at least one parasitic antenna is configured to generate a second magnetic field at the second frequency in response to the first magnetic field generated by the transmit antenna.

3. The transmitter of claim 1 , wherein the controller is configured to activate the at least one parasitic antenna by at least one of selectively close-circuiting or open-circuiting the at least one parasitic antenna.

4. The transmitter of claim 1 , wherein the first resonant circuit comprises a first capacitor having a first capacitance, and wherein the second resonant circuit comprises a second capacitor having a second capacitance having a value less than the first capacitance.

5. The transmitter of claim 1 , wherein the first resonant circuit comprises a first capacitor having a first capacitance, and wherein the second resonant circuit comprises a second capacitor having a second capacitance having a value greater than the first capacitance.

6. The transmitter of claim 1 , wherein the second resonant circuit comprises a plurality of capacitors, and wherein the controller is configured to selectively switch one or more of the capacitors into the parasitic antenna to actively steer the first magnetic field into the charging region or away from the charging region.

7. The transmitter of claim 1 , wherein the parasitic antenna is configured to steer the first magnetic field to increase uniformity of the first magnetic field across a surface of the charging region.

8. The transmitter of claim 1 , wherein the at least one parasitic antenna comprises an array of parasitic antennas positioned in rows or columns.

9. The transmitter of claim 8 , wherein the least one parasitic antenna comprises a multi-dimensional array of parasitic antennas positioned in columns and rows.

10. The transmitter of claim 8 , wherein the transmit antenna is further configured to wirelessly transfer charging power to the receiver device via the first magnetic field.

11. The transmitter of claim 10 , wherein the charging region includes a charging mat.

12. A method of wirelessly transferring power to a receiver device, comprising:

generating a first magnetic field with a transmit antenna comprising a first resonant circuit configured to resonate at a first frequency corresponding to an operating frequency; and

steering the first magnetic field to a charging region in response to activating at least one parasitic antenna comprising a second resonant circuit configured to resonate at a second frequency different than the first frequency.

13. The method of claim 12 , wherein the activating the at least one parasitic antenna comprises at least one of selectively open-circuiting or close-circuiting a loop of the at least one parasitic antenna.

14. The method of claim 12 , wherein the activating the at least one parasitic antenna further comprises switching at least one capacitor into or out of the loop of the at least one parasitic antenna.

15. The method of claim 12 , further comprising generating a second magnetic field at the second frequency in response to the generated first magnetic field.

16. The method of claim 12 , wherein:

the first resonant circuit comprises a first capacitor having a first capacitance, and the second resonant circuit comprises a second capacitor having a second capacitance having a value less than the first capacitance,

the parasitic antenna includes a first loop concentrically positioned within a second loop of the transmit antenna, and

the parasitic antenna is configured to reduce a first field strength outside the first loop and increase a second field strength within the first loop.

17. The method of claim 12 , wherein:

the first resonant circuit comprises a first capacitor having a first capacitance, and the second resonant circuit comprises a second capacitor having a second capacitance having a value greater than the first capacitance,

the parasitic antenna includes a first loop positioned within a second loop of the transmit antenna, and

the parasitic antenna is configured to increase a first field strength outside the first loop and reduce a second field strength within the first loop.

18. A transmitter for wirelessly transferring power to a receiver device, comprising:

means for generating a magnetic field, the generating means comprising a first means for resonating at a first frequency corresponding to an operating frequency; and

means for steering the magnetic field to a desired charging region in response to activating a second means for resonating at a second frequency different than the first frequency.

19. The transmitter of claim 18 , wherein the means for steering the magnetic field comprises at least one parasitic antenna, and wherein the generating means and the at least one parasitic antenna are positioned in a concentric layout relative to each other.

20. The transmitter of claim 18 , wherein the means for steering the magnetic field comprises at least one parasitic antenna, and wherein the generating means and the at least one parasitic antenna are positioned in a charging mat, the receiver device placed thereon to receive the wirelessly transferred power.