RFID Tag and Transponder Detection in Wireless Energy Transfer Systems

• US 20170098149A1
• Filed: 10/06/2016
• Published: 04/06/2017
• Est. Priority Date: 10/06/2015
• Status: Active Grant

• Current Assignee: WiTricity Corporation
• Original Assignee: WiTricity Corporation
• Inventors: Katz, Noam, Kesler, Morris P., Alinger, Dustin J., Twelker, Karl, Atasoy, Oguz, Vora, Shrenik
• Granted Patent: US 10,248,899 B2
• Time in Patent Office: Days
• CPC Class Codes: G06K 19/0726 the arrangement including a circuit for tuning the resonance frequency of an antenna on the record carrier
• CPC Class Codes: H02J 50/12 of the resonant type
• CPC Class Codes: H02J 50/60 responsive to the presence of foreign objects, e.g. detection of living beings
• CPC Class Codes: H02J 50/80 involving the exchange of data, concerning supply or distribution of electric power, between transmitting devices and receiving devices
• CPC Class Codes: H04B 5/79 for data transfer in combination with power transfer

Abstract

The disclosure features wireless power transmitters configured to detect a radio frequency identification (RFID) tag, the transmitters including a transmitter resonator, a transmitter impedance matching network coupled to the transmitter resonator, an amplifier coupled to the transmitter impedance matching network, a detection subsystem connected to the transmitter resonator, and a controller coupled to the amplifier and to the detection subsystem and configured so that during operation of the transmitter, the controller is configured to control the transmitter resonator, the amplifier, and the impedance matching network to cycle the transmitter between a power transmission mode and a RFID tag detection mode.

Claims

1. A wireless power transmitter configured to detect a radio frequency identification (RFID) tag, the transmitter comprising:

a transmitter resonator;

a transmitter impedance matching network coupled to the transmitter resonator;

an amplifier coupled to the transmitter impedance matching network;

a detection subsystem connected to the transmitter resonator; and

a controller coupled to the amplifier and to the detection subsystem and configured so that during operation of the transmitter, the controller is configured to control the transmitter resonator, the amplifier, and the impedance matching network to cycle the transmitter between a power transmission mode and a RFID tag detection mode,

wherein in the power transmission mode;

the RFID tag detection mode is interrupted; and

the transmitter resonator generates a power magnetic field at a frequency f_power to transfer power to a wireless power receiver;

wherein in the RFID tag detection mode;

the power transmission mode is interrupted;

the transmitter resonator generates at least one detection magnetic field at a frequency between f₁ and f₂ to excite a RFID tag;

the detection subsystem measures a reflected impedance of the transmitter resonator at each frequency; and

the controller determines whether a RFID tag is present in proximity to the transmitter based on the reflected impedance of the transmitter resonator; and

wherein f₁ and f₂ are greater than f_power.

2. The transmitter of claim 1, wherein the detection subsystem measures a real part of the reflected impedance of the transmitter resonator, and wherein the controller determines whether a RFID tag is present in proximity to the transmitter based on the real part of the reflected impedance of the transmitter resonator.

3. The transmitter of claim 1, wherein the detection subsystem measures an imaginary part of the reflected impedance of the transmitter resonator, and wherein the controller determines whether a RFID tag is present in proximity to the transmitter based on the imaginary part of the reflected impedance of the transmitter resonator.

4. The transmitter of claim 1, wherein f₁ and f₂ are each between 8 MHz and 22 MHz.

5. The transmitter of claim 1, wherein the amplifier provides one or more driving currents corresponding to the frequency of the at least one detection magnetic field to generate the at least one detection magnetic field.

6. The transmitter of claim 5, wherein the transmitter resonator comprises a resonator coil, the transmitter further comprising:

a first capacitor C₁ connected in series with the resonator coil; and

one or more capacitors each connected to C₁ through a different associated switch,

wherein the controller is configured to activate the transmitter resonator to generate each detection magnetic field by;

activating the amplifier to provide a driving current corresponding to a frequency of the detection magnetic field to the transmitter resonator; and

closing one of the associated switches to connect one of the capacitors to C₁ through a continuous circuit pathway.

7. The transmitter of claim 5, wherein the transmitter comprises a tunable capacitor connected to the controller, and wherein the controller is configured to activate the transmitter resonator to generate each detection magnetic field by:

activating the amplifier to provide a driving current corresponding to a frequency of the detection magnetic field to the transmitter resonator; and

adjusting a capacitance value of the tunable capacitor based on the frequency of the detection magnetic field.

8. The transmitter of claim 1, wherein the transmitter resonator comprises a resonator coil and the transmitter comprises a first capacitor C₁ connected in series with the resonator coil, wherein the detection subsystem is configured to measure a first voltage across a combination of the first capacitor and the resonator coil and a second voltage across the first capacitor, and wherein the controller is configured to determine the reflected impedance based on the measured first and second voltages.

9. The transmitter of claim 8, wherein the controller is configured to determine a current through the resonator coil based on the second voltage, and to determine the reflected impedance based on the first voltage and the current through the resonator coil.

10. The transmitter of claim 1, wherein the controller is configured to determine whether a RFID tag is present in proximity to the transmitter by identifying one or more local maximum values in the reflected impedance of the transmitter resonator at frequencies between f₁ and f₂.

11. The transmitter of claim 10, wherein the controller is configured to determine whether a RFID tag is present in proximity to the transmitter by determining frequencies associated with the one or more local maximum values, and comparing the determined frequencies to reference information comprising resonance frequencies associated with RFID tags.

12. The transmitter of claim 10, wherein the controller is configured to determine whether a RFID tag is present in proximity to the transmitter by comparing the determined frequencies to one or more threshold frequency values corresponding to resonance frequency limits for RFID tags.

13. The transmitter of claim 1, wherein the controller is configured to reduce an amplitude of the power magnetic field if a RFID tag is determined to be present in proximity to the transmitter.

14. The transmitter of claim 1, wherein in a single cycle, the transmitter operates for a first time period t₁ in the power transmission mode and for a second time period t₂ in the RFID tag detection mode, and wherein t₂ is 500 microseconds or less.

15. The transmitter of claim 14, wherein t₂ is 300 microseconds or less.

16. The transmitter of claim 14, wherein a total cycle time corresponding to a sum of t₁ and t₂ is between 0.5 seconds and 2 seconds.

17. The transmitter of claim 1, wherein in the RFID tag detection mode, the controller is configured to adjust a bus voltage in the amplifier to maintain a constant current in the transmitter resonator as each detection magnetic field is generated.

18. A method for detecting a radio frequency identification (RFID) tag, the method comprising:

operating a wireless power transmitter in a power transmission mode, wherein the operating comprises using a transmitter resonator of the transmitter to generate a power magnetic field at a frequency f_power to transfer power to a wireless power receiver;

operating the wireless power transmitter in a RFID tag detection mode, wherein the operating comprises;

using the transmitter resonator to generate at least one detection magnetic field at a frequency between f₁ and f₂ to excite a RFID tag;

measuring a reflected impedance of the transmitter resonator at each frequency; and

determining whether a RFID tag is present in proximity to the transmitter based on the measured reflected impedance of the transmitter resonator; and

cycling the wireless power transmitter between the power transmission mode and the RFID tag detection mode,

wherein f₁ and f₂ are greater than f_power.

19. The method of claim 18, further comprising measuring a real part of the reflected impedance of the transmitter resonator, and determining whether a RFID tag is present in proximity to the transmitter based on the real part of the reflected impedance of the transmitter resonator.

20. The method of claim 18, wherein f₁ and f₂ are each between 8 MHz and 22 MHz.

21. The method of claim 18, further comprising activating an amplifier of the wireless power transmitter to provide one or more driving currents corresponding to the frequency of the at least one detection magnetic field to generate the at least one detection magnetic field.

22. The method of claim 21, further comprising, for each detection magnetic field:

activating the amplifier to provide a driving current corresponding to a frequency of the detection magnetic field to the transmitter resonator; and

connecting at least one capacitor with a capacitor C₁ of the wireless power transmitter through a continuous circuit pathway,

wherein C₁ is connected in series with a coil of the transmitter resonator.

23. The method of claim 18, wherein the transmitter resonator comprises a resonator coil and the transmitter comprises a first capacitor C₁ connected in series with the resonator coil, the method further comprising:

measuring a first voltage across a combination of the first capacitor and the resonator coil and a second voltage across the first capacitor; and

determining the reflected impedance based on the measured first and second voltages.

24. The method of claim 18, further comprising determining whether a RFID tag is present in proximity to the transmitter by:

identifying one or more local maximum values in the reflected impedance of the transmitter resonator at frequencies between f₁ and f₂;

determining frequencies associated with the one or more local maximum values; and

comparing the determined frequencies to reference information comprising resonance frequencies associated with RFID tags.