Electromagnetic interference shielding in an implantable medical device
EMI shields for use in implantable medical devices that include inner and outer metal layers separated by a dielectric layer. When assembled as medical devices, the outer metal layer of an illustrative EMI shield is placed into electrical contact with a conductive inner surface of an associated canister for an implantable medical device.
1. An implantable medical device (IMD) comprising:
circuitry including a microcontroller, logic, components and memory;
a housing for containing the circuitry, the housing including an inner surface; and
an electromagnetic interference (EMI) shield for protecting the circuitry; wherein:
the EMI shield is disposed around the circuitry and inside the housing such that gaps exist between the EMI shield and the housing as well as areas of contact between the EMI shield and the housing; and
the EMI shield comprises anti-Corona means for preventing the gaps from becoming sources for nonlinear electrical conduction between the EMI shield and the housing; wherein the anti-Corona means includes conductive material on an area of the EMI shield that contacts the inner surface of the housing.
2. The IMD of claim 1 wherein:
the EMI shield comprises a dielectric layer having an outer side directed toward the housing and an inner side directed toward the circuitry; and
the anti-Corona means comprises conductive material on the outer side of the dielectric layer.
3. The IMD of claim 2 wherein the EMI shield further comprises an inner conductive layer disposed on the inner side of the dielectric layer.
4. The IMD of claim 3 wherein:
the inner conductive layer has an inner side directed toward the circuitry and an outer side in contact with the dielectric layer; and
the EMI shield further comprises an interior dielectric disposed on the inner side of the inner conductive layer.
5. The IMD of claim 4 wherein:
the circuitry has a reference ground; and
the inner conductive layer is electrically coupled to the reference ground.
6. A method of treating a patient comprising:
implanting, in the patient, an implantable medical device (IMD) comprising circuitry including a microcontroller, logic, components and memory, a housing for containing the circuitry, the housing having an inner surface, and an electromagnetic interference (EMI) shield for protecting the circuitry, wherein the EMI shield is disposed around the circuitry and inside the housing such that gaps exist between areas of contact between the EMI shield and the inner surface of the housing and the EMI shield comprises anti-Corona means for preventing the gaps from becoming sources for nonlinear electrical conduction between the EMI shield and the housing, wherein the anti-Corona means comprises conductive material on the EMI shield to contact the inner surface of the housing; and
the IMD delivering an electrical stimulus therapy to the patient, the therapy having an amplitude of more than 50 V.
7. The method of claim 6 wherein, in the IMD, the EMI shield comprises a dielectric layer having an outer side directed toward the housing and an inner side directed toward the circuitry; and the anti-Corona means comprises the conductive material disposed on the outer side of the dielectric layer, such that the anti-Corona means prevents nonlinear electrical conduction between the EMI shield and the housing when the electrical stimulus therapy is delivered.
8. The method of claim 7 wherein, in the IMD, the EMI shield further comprises an inner conductive layer disposed on the inner side of the dielectric layer.
9. The method of claim 8 wherein, in the IMD:
the inner conductive layer has an inside directed toward the circuitry and an outside in contact with the dielectric layer; and
the EMI shield further comprises an interior dielectric disposed on the inner conductive layer.
10. The method of claim 9 wherein, in the IMD:
the circuitry has a reference ground; and
the inner conductive layer is electrically coupled to the reference ground.