Low frequency transcutaneous energy transfer to implanted medical device
An implantable medical device system advantageously utilizes low frequency (e.g., about 1-100 kHz) transcutaneous energy transfer (TET) for supplying power from an external control module to an implantable medical device, avoiding power dissipation through eddy currents in a metallic case of an implant and/or in human tissue, thereby enabling smaller implants using a metallic case such as titanium and/or allowing TET signals of greater strength thereby allowing placement more deeply within a patient without excessive power transfer inefficiencies.
1. A transcutaneous energy transfer (TET) system for communicating energy from the exterior of a patient to an internal implant, comprising:
a) an external primary power supply;
b) an external primary resonant circuit energized by the primary power supply and including an annular primary coil in electrical communication with capacitance to form a resonant tank circuit having peak resonance at or below 100 kHz, the annular primary coil further comprising:
i) at least one wire wrapped repeatedly about a primary center axis of the primary transmitter coil into a toroid having an annular cross section, wherein the toroid encircles the primary center axis to form an annular ring shape,
ii) a primary circular gap about the primary center axis, the primary circular gap defined by and encircled by the annular ring shape of the primary transmitter coil, and
iii) an elongate ferrite core extending through the gap of the annular ring shape and the center point, the elongate ferrite core being oriented substantially perpendicular to the annular ring shape and extending in a straight line above and below the center point to define a longitudinal axis, the elongate ferrite core only having a first end above the annular ring shape and a second end below the annular ring shape with a uniform core diameter extending therebetween from end to end, wherein the uniform core diameter is smaller than an inner diameter of the circular gap,
c) an internal electrical load comprising a device implantable within the patient; and
d) an internal secondary resonant circuit implantable within the patient and including an annular secondary coil in electrical communication with the annular primary coil to form a resonant tank circuit having peak resonance at or below 100 kHz and to receive TET power from the annular primary coil for powering the internal electrical load, the annular secondary coil further comprising:
i) at least one wire wrapped about a secondary center axis of the annular secondary coil into a toroid having an annular cross section, wherein the annular secondary coil encircles the secondary center axis of the annular secondary coil to define a second annular ring shape with an exterior secondary diameter, and
ii) a secondary circular gap between the secondary center axis and the annular secondary coil;
wherein when the annular secondary coil is implanted within the patient with the exterior secondary diameter substantially parallel to and spaced internally away from the skin, the annular primary coil and the elongate ferrite core are oriented above the skin of the patient with the longitudinal axis of the elongate ferrite core oriented substantially coaxially with the primary center axis of the annular primary coil and with the secondary center axis of the implanted annular secondary coil, and with the annular primary coil and the annular secondary coil substantially perpendicularly aligned with the longitudinal axis, and
the annular primary coil is energized to communicate directly with the implanted annular secondary annular coil via an elliptical toroidal electromagnetic energy field, wherein the elongate ferrite core elongates the elliptical toroidal electromagnetic energy field above and below the annular primary coil and along the longitudinal axis to transfer energy directly to the annular secondary coil and the energy transfer is optimized by the elongation of the toroidal electromagnetic energy field to maximize the power transmission and to maximize implant depth for operative transfer of energy from the external annular primary coil to the annular secondary coil when the annular secondary coil is implanted in a patient.
2. The TET system of claim 1 , wherein the internal secondary resonant circuit further comprises a pair of annular secondary coils physically and electrical in parallel.
3. The TET system of claim 1 , wherein the wire of the annular primary coil comprises multi-turn insulated Litz wire.
4. The TET system of claim 1 , wherein the capacitance comprises a chip-on-glass dielectric capacitor.
5. The TET system of claim 1 , wherein the wire of the annular secondary coil comprises Litz wire.
6. The TET system of claim 1 , further comprising rectification filtering between the secondary resonant circuit and the electrical load.