External charger for an implantable medical device having alignment and centering capabilities
A charging system for an Implantable Medical Device (IMD) is disclosed having a charging coil and one or more sense coils. The charging coil and one or more sense coils are 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 one or more sense coils are concentric with the charging coil and 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 whether the charging coil is (i) centered, (ii) not centered but not misaligned, or (iii) misaligned, with respect to the IMD being charged, which three conditions sequentially comprise lower coupling between the charging coil and the IMD. A charging algorithm is also disclosed that control charging dependent on these conditions.
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 as a coupled system;
at least one sense coil, wherein each at least one sense coil is concentric with the charging coil and consists of one or more turns at a constant radius, wherein each at least one 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 from at least one parameter determinable using each induced signal a plurality of conditions indicative of the position of the charging coil with respect to the IMD.
2. The external charger of claim 1 , further comprising a user interface configured to indicate each of the determined conditions to a user.
3. The external charger of claim 1 , wherein the at least one parameter comprises a magnitude of at least one induced signal.
4. The external charger of claim 1 , wherein the at least one parameter comprises a phase angle between at least one induced signal and the drive signal.
5. The external charger of claim 1 , wherein the at least one parameter comprises a resonant frequency of the coupled system.
6. The external charger of claim 1 , wherein the conditions comprise whether the charging coil is (i) centered, (ii) not centered but not misaligned, and (iii) misaligned, with respect to the IMD.
7. The external charger of claim 6 ,
wherein centered comprises a condition in which the coupling between the charging coil and the IMD is higher than a first coupling value,
wherein misaligned comprises a condition in which the coupling between the charging coil and the IMD is lower than or equal to a second coupling value lower than the first coupling value, and
wherein not centered but not misaligned comprise a condition in which the coupling between the charging coil and the IMD is greater than the second coupling value but less than or equal to the first coupling value.
8. 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 at least one sense coil are within the charging coil assembly, and
wherein the control circuitry is within the electronics module.
9. The external charger of claim 1 , further comprising a circuit board, wherein the at least one sense coil is formed in one or more traces in the circuit board.
10. The external charger of claim 9 , wherein the charging coil comprises a wire winding placed on a side of the circuit board.
11. The external charger of claim 9 , wherein the charging coil comprises a wire winding, and wherein the circuit board is placed within the wire winding of the charging coil.
12. The external charger of claim 1 , wherein the at least one sense coil comprises only one sense coil.
13. The external charger of claim 12 ,
wherein the control circuitry further includes a first threshold and a second threshold, and
wherein the control circuitry is configured to determine the plurality of conditions by comparing one of the at least one parameters to either or both of the first threshold and the second threshold.
14. The external charger of claim 1 ,
wherein the at least one sense coil comprises a first sense coil of one or more turns at a constant first radius and a second sense coil of one or more turns at a second constant radius larger than the first radius,
wherein the first sense coil is induced with a first induced signal, and
wherein the second sense coil is induced with a second induced signal.
15. The external charger of claim 14 , wherein the control circuitry is configured to determine
from at least one first parameter determinable using the first induced signal whether the charging coil is centered,
from at least one second parameter determinable using the second induced signal whether the charging coil is misaligned, and
from the at least one first parameter and the at least one second parameter whether the charging coil is not centered but not misaligned.