Systems and Methods of Detecting a Change in Object Presence in a Magnetic Field

• US 20120256620A1
• Filed: 04/11/2011
• Published: 10/11/2012
• Est. Priority Date: 04/11/2011
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Oettinger, Eric Gregory
• Granted Patent: US 9,912,201 B2
• Time in Patent Office: Days
• US Class Current: 324/239
• CPC Class Codes: G01R 33/0041 using feed-back or modulation techniques
• CPC Class Codes: G01R 33/028 Electrodynamic magnetometers
• CPC Class Codes: H01F 38/14 Inductive couplings for wireless supply or distribution of electric power using inductive coupling H02J50/10
• CPC Class Codes: H02J 50/10 using inductive coupling
• CPC Class Codes: H02J 50/12 of the resonant type
• CPC Class Codes: H02J 50/90 involving detection or optimisation of position, e.g. alignment
• CPC Class Codes: H02J 7/0049 Detection of fully charged condition
• CPC Class Codes: H04B 5/26 using coils
• CPC Class Codes: H04B 5/79 for data transfer in combination with power transfer

Abstract

The systems and methods of detecting a change in object presence in a magnetic field disclosed herein inject a low amplitude signal near the resonant frequency into the coil until the system comes to equilibrium. At this point the feedback is measured. The feedback signal can be measured as at least one of several signals, for example, but not limited to the voltage on the resonant capacitor, the current in the coil, and the voltage between the resonant capacitor and the coil. A change in the steady state response indicates a change in device presence.

Claims

1. A system comprising:

a primary coil driven by an injected signal at a substantially constant frequency to create a magnetic field and configured to receive a response during a driving phase of the injected signal; and

a controller configured to monitor a response to the injected signal and to determine a change in a presence of an object in the magnetic field emitted from the primary coil, the determination based on the monitored response.

2. The system of claim 1, wherein an analog signal is transmitted from the primary coil at substantially a resonant frequency.

3. The system of claim 2, wherein the feedback is a response to the analog signal.

4. The system of claim 1, wherein the feedback is sampled substantially synchronously to the analog signal in at least two points and the at least two points have at least one of a substantially 180 degree phase difference and a substantially 90 degree phase difference.

5. The system of claim 4, wherein the sampling is performed after the feedback has reached a steady state condition.

6. The system of claim 2, wherein a change in object presence is detected when a change in the feedback is detected.

7. The system of claim 1, wherein the feedback is detected as at least one of:

voltage on a resonant capacitor, current in the primary coil, and voltage node between the resonant capacitor and the primary coil.

8. The system of claim 1, wherein the primary coil is driven by at least one of a full bridge resonant circuit and a half bridge resonant circuit.

9. A method of determining change in object presence in a magnetic field comprising:

driving a primary coil with an injected signal at a substantially constant frequency to create a magnetic field;

receiving a response during a driving phase of the injected signal;

monitoring the response; and

determining a change in object presence in the magnetic field emitted from the primary coil based on the monitored response.

10. The method of claim 9, further comprising transmitting an analog signal from the primary coil at substantially a resonant frequency.

11. The method of claim 10, wherein the feedback is in response to the transmitting of the analog signal.

12. The method of claim 9, further comprising sampling the feedback substantially synchronously to the analog signal in at least two points with a phase difference of at least one of substantially 180 degrees and substantially 90 degrees.

13. The method of claim 12, wherein the sampling is performed after the feedback has reached a steady state condition.

14. The method of claim 10, further comprising determining object presence when a change in the feedback is detected.

15. The method of claim 9, wherein the feedback is detected on at least one of:

voltage on a resonant capacitor, current in the primary coil, and voltage node between the resonant capacitor and the primary coil.

16. A wireless charging system comprising:

a charger comprising;

a power control circuit;

a primary coil driven by an injected signal from the power control circuit at a substantially constant frequency to create a magnetic field and configured to receive a response during a driving phase of the injected signal; and

a controller configured to monitor a response to the injected signal and to determine a change in presence of an object in the magnetic field emitted from the primary coil, the determination based on the monitored response.

17. The wireless charging system of claim 16, wherein an analog signal is transmitted from the primary coil at substantially a resonant frequency.

18. The wireless charging system of claim 17, wherein the feedback is a response to the analog signal.

19. The wireless charging system of claim 16, wherein the feedback is sampled substantially synchronously with the analog signal in at least two points and the at least two points have at least one of a substantially 180 degree phase difference and a substantially 90 degree phase difference.

20. The wireless charging system of claim 19, wherein the sampling is performed after the feedback has reached a steady state condition.