External charger for an implantable medical device for determining position using phase angle or a plurality of parameters as determined from at least one sense coil
A charging system for an Implantable Medical Device (IMD) is disclosed having a charging coil and one or more sense coils preferably housed in a charging coil assembly coupled to an electronics module by a cable. The charging coil is preferably a wire winding, while the sense coils are preferably formed in one or more traces of a circuit board. One or more voltages induced on the one or more sense coils can be used to determine a phase angle between the voltage and a driving signal for the charging coil. The determined phase angle can then be used to determine the position of the charging coil relative to the IMD. Additionally, more than one parameter (phase angle, magnitude, resonant frequency) may be determined using the voltage may be used to determine position, including the radial offset and depth of the charging coil relative to the IMD.
1. An external charger for wirelessly providing energy to an implantable medical device (IMD), comprising:
a charging coil configured when energized by a drive signal to produce a magnetic field to wirelessly provide energy to the IMD;
a sense coil, wherein the sense coil is configured to be induced by the magnetic field with an induced signal affected by a position of the charging coil with respect to the IMD; and
control circuitry configured to
determine a phase angle between the induced signal and the drive signal, and
determine using the phase angle the position of the charging coil with respect to the IMD.
2. The external charger of claim 1 , wherein the sense coil is concentric with the charging coil.
3. The external charger of claim 1 , wherein the control circuitry is configured to produce the drive signal.
4. The external charger of claim 1 , further comprising an electronics module and a charging coil assembly coupled to the electronics module by a cable,
wherein the charging coil and the sense coil are within the charging coil assembly, and
wherein the control circuitry is within the electronics module.
5. The external charger of claim 1 , further comprising a circuit board, wherein the sense coil is formed in one or more traces in the circuit board.
6. The external charger of claim 5 , wherein the charging coil comprises a wire winding placed on a side of the circuit board.
7. The external charger of claim 5 , wherein the charging coil comprises a wire winding, and wherein the circuit board is placed within the wire winding of the charging coil.
8. The external charger of claim 1 ,
wherein the control circuitry is configured to determine from the phase angle whether the charging coil is aligned with or is centered with respect to the IMD,
wherein centered comprises a condition in which the coupling between the charging coil and the IMD is higher than a first coupling value, and
wherein aligned comprises a condition in which the coupling between the charging coil and the IMD is higher than a second coupling value lower than the first coupling value.
9. The external charger of claim 8 ,
wherein the control circuitry further includes a threshold, and
wherein the control circuitry is configured to determine whether the charging coil is aligned with or is centered with respect to the IMD by comparing the phase angle to the threshold.
10. The external charger of claim 1 ,
wherein the control circuitry is configured to determine from the phase angle whether the charging coil is aligned with respect to the IMD, and whether the charging coil is centered with respect to the IMD,
wherein centered comprises a condition in which the coupling between the charging coil and the IMD is higher than a first coupling value, and
wherein aligned comprises a condition in which the coupling between the charging coil and the IMD is higher than a second coupling value lower than the first coupling value.
11. The external charger of claim 10 ,
wherein the control circuitry further includes a first threshold and a second threshold, and
wherein the control circuitry is configured to determine whether the charging coil is centered by comparing the phase angle to the first threshold, and whether the charging coil is aligned by comparing the phase angle to the second threshold.
12. The external charger of claim 1 , wherein the induced signal comprises a voltage.
13. The external charger of claim 1 , further comprising a user interface configured to indicate to a user the determined position of the charging coil with respect to the IMD.
14. The external charger of claim 1 , wherein the charging coil comprises a first radius, and the sense coil comprises a second radius smaller than the first radius.
15. The external charger of claim 1 , wherein the sense coil comprises a circle.
16. The external charger of claim 1 , wherein the sense coil comprises two circles of different radii.
17. The external charger of claim 16 , wherein the two circles are connected such that such that a current flowing through the two circles will flow in different directions in the two circles.