Method of detecting presence of implanted power transfer coil

1. A method implemented by a medical implant system having an internal coil implanted within a body of a patient, the internal coil capable of receiving power from an external coil outside the body, the external coil in communication with external processing circuitry configured to perform steps of the method, the method comprising:

detecting a presence of the internal coil based upon a coil detection duty cycle;

determining acceleration of an external component of the medical implant system based upon an output from an accelerometer; and

responsive to acceleration being detected, adjusting the coil detection duty cycle based upon the output from the accelerometer.

2. The method of claim 1 , wherein detecting the presence of the internal coil comprises monitoring a change in a resonance frequency associated with the external coil and the internal coil.

3. The method of claim 2 , wherein when a distance between an expected location of the internal coil and a location of the external coil decreases, the resonance frequency increases.

4. The method of claim 2 , wherein when a distance between an expected location of the internal coil and a location of the external coil increases, the resonance frequency decreases.

5. The method of claim 4 , further comprising:

responsive to the resonance frequency indicating the presence of the internal coil, monitoring a rate at which the resonance frequency rises to a steady state value; and

determining a connectivity of the internal coil based upon the rate at which the resonance frequency rises to the steady state value.

6. The method of claim 5 , further comprising: responsive to the resonance frequency increasing to the steady state value at a rate that falls below a rate threshold, determining that the internal coil is connected to an internal load.

7. The method of claim 1 , further comprising detecting a presence of a metal object based upon whether the external coil is drawing increased power for a given drive current and based upon reception of power regulation packets from the internal coil.

8. The method of claim 7 , wherein detecting the presence of the metal object comprises: responsive to no reception of the power regulation packets within a time interval, determining that the metal object is present.

9. The method of claim 7 , further comprising: responsive to no reception of the power regulation packets within a time interval, determining that there is a fault in one or more internal components of the medical implant system.

10. The method of claim 1 , wherein adjusting the coil detection duty cycle based upon the output from the accelerometer comprises:

increasing the coil detection duty cycle in response to the output from the accelerometer being high; and

decreasing the coil detection duty cycle in response to the output from the accelerometer being low.

11. A medical implant system comprising:

an external coil outside a body of a patient, wherein an internal coil implanted within the body of the patient is configured to receive power from the external coil;

an accelerometer configured to detect acceleration of the external coil;

processing circuitry configured to:

communicate with the external coil;

detect a presence of the internal coil based upon a coil detection duty cycle;

determine acceleration of the external coil based upon an output from the accelerometer; and

responsive to acceleration being detected, adjust the coil detection duty cycle based upon the output from the accelerometer.

12. The medical implant system of claim 11 , wherein the external processing circuitry is configured to adjust the coil detection duty cycle based upon the output from the accelerometer by:

increasing the coil detection duty cycle in response to the output from the accelerometer being greater than zero; and

decreasing the coil detection duty cycle in response to the output from the accelerometer being zero.

13. The medical implant system of claim 11 , wherein the processing circuitry is configured to detect the presence of the internal coil by monitoring a change in a resonance frequency associated with the external coil and the internal coil.

14. The medical implant system of claim 13 , wherein when a distance between an expected location of the internal coil and a location of the external coil decreases, the resonance frequency increases.

15. The medical implant system of claim 13 , wherein when a distance between an expected location of the internal coil and a location of the external coil increases, the resonance frequency decreases.

16. The medical implant system of claim 15 , wherein the external processing circuitry is further configured to:

responsive to the resonance frequency indicating the presence of the internal coil, monitor a rate at which the resonance frequency rises to a steady state value;

determine a connectivity of the internal coil based upon the rate at which the resonance frequency rises to the steady state value.

17. The medical implant system of claim 16 , wherein the external processing circuitry is further configured to: responsive to the resonance frequency increasing to the steady state value at a rate that falls below a rate threshold, determine that the internal coil is connected to an internal load.

18. The medical implant system of claim 11 , wherein the external processing circuitry is further configured to: detect a presence of a metal object based upon whether the external coil is drawing increased power for a given drive current and reception of power regulation packets from the internal coil.

19. The medical implant system of claim 18 , wherein the external processing circuitry is configured to detect the presence of the metal object by: responsive to no reception of the power regulation packets within a time interval, determine that the metal object is present.

20. The medical implant system of claim 18 , wherein the external processing circuitry is further configured to: responsive to no reception of the power regulation packets within a time interval, determine that there is a fault in one or more internal components of the medical implant system.

21. The medical implant system of claim 11 , further comprising the internal coil.

22. The medical implant system of claim 11 , wherein the external processing circuitry is configured to adjust the coil detection duty cycle based upon the output from the accelerometer by:

increasing the coil detection duty cycle in response to the output from the accelerometer being greater than a threshold; and

decreasing the coil detection duty cycle in response to the output from the accelerometer being less than the threshold.