Ferrite core telemetry coil for implantable medical device
An implantable medical device such as a cardiac pacemaker with a telemetry coil located in the device header rather than the conductive housing. The telemetry coil has a core made of magnetically permeable material such as ferrite in order to increase the efficiency of the coil and lessen space requirements.
1. An implantable medical device, comprising:
a metal housing for containing electronic circuitry;
a non-conductive header for receiving external lead wires that are electrically connected to the electronic circuitry within the housing;
telemetry circuitry for communicating with an external programmer;
a telemetry coil assembly located in the header and connected to the telemetry circuitry, wherein the coil assembly includes coil windings wrapped around a core made of ferrite, and wherein the core is encapsulated so as to be biocompatible; and,
wherein the coil assembly is encapsulated with polyurethane and includes a bobbin having biocompatible end caps for supporting the assembly within a molding vessel.
2. The device of claim 1 wherein the core is encapsulated with polyurethane.
3. The device of claim 1 wherein the core is coated with paralyne and then encapsulated in polyurethane.
4. The device of claim 1 wherein the coil assembly is encapsulated in glass and then encapsulated in polyurethane.
5. The device of claim 4 wherein the polyurethane is tecothane.
6. The device of claim 1 wherein the telemetry coil windings are constructed of wire with a silver core and a stainless steel sheath.
7. The device of claim 1 wherein the telemetry coil windings are constructed of wire with a tantulum core and a stainless steel sheath.
8. A method for constructing an implantable medical device, comprising:
disposing telemetry circuitry in a metal housing;
assembling a telemetry coil by wrapping coil windings around a ferrite core;
encapsulating the core in a manner that renders the core biocompatible;
encapsulating the coil assembly with polyurethane;
wrapping the coil windings around a bobbin having biocompatible end caps for supporting the assembly within a molding vessel; and,
disposing the telemetry coil in a non-conductive header and electrically connecting the telemetry coil to the telemetry circuitry within the metal housing.
9. The method of claim 8 further comprising encapsulating the core with polyurethane.
10. The method of claim 8 further comprising coating the core with paralyne and then encapsulating the core in polyurethane.
11. The method of claim 8 further comprising encapsulating the coil assembly in glass and then in polyurethane.
12. The method of claim 11 wherein the polyurethane is tecothane.
13. The method of claim 8 wherein the telemetry coil windings are constructed of wire with a silver core and a stainless steel sheath.
14. The method of claim 8 wherein the telemetry coil windings are constructed of wire with a tantulum core and a stainless steel sheath.