Antennas for implantable medical devices

1. An apparatus, comprising:

an implantable medical device comprising:

a housing including an implantable telemetry circuit configured to wirelessly transfer information electromagnetically;

a dielectric compartment mechanically coupled to the housing, wherein the dielectric compartment includes first and second substantially parallel face portions, and a third face portion extending between the first and second face portions;

an antenna assembly configured to be mechanically attached to the dielectric compartment and electrically coupled to the implantable telemetry circuit, the antenna assembly including a spiral conductor comprising a planar spiral pattern folded into first, second, and third spiral conductor portions that extend adjacent the first, second, and third face portions, respectively, of the dielectric compartment,

wherein the first, second, and third spiral conductor portions define an interior region, wherein at least a portion of the third spiral conductor portion extends inwardly into the interior region, and wherein the at least a portion of the third spiral conductor portion that extends inwardly into the interior region includes a surface defining a curvature that has a bend radius.

2. The apparatus of claim 1 , wherein the at least a portion of the third spiral conductor portion that extends inwardly into the interior region is located substantially halfway between the first and second substantially parallel face portions of the dielectric compartment.

3. The apparatus of claim 1 , wherein the spiral pattern comprises concentric turns.

4. The apparatus of claim 3 , wherein the spiral conductor includes at least five turns.

5. The apparatus of claim 1 , further comprising an implantable lead, the implantable lead including an electrode configured for location at a tissue site, and coupled to electronic circuitry within the housing to provide one or more of electrostimulation of tissue or sensing of activity, at the site of the electrode, wherein the dielectric compartment comprises a header configured to provide an electrical and mechanical connection to the implantable lead.

6. The apparatus of claim 1 , wherein the spiral conductor includes a cross section having a lateral width that is greater than a sidewall height of the cross section.

7. The apparatus of claim 6 , wherein a sidewall of one of the first, second, or third spiral conductor portions is oriented so that the sidewall provides a sidewall face that is substantially parallel to one of the first, second, or third face portions of the dielectric compartment.

8. The apparatus of claim 6 , wherein a separation between adjacent turns of the spiral conductor is decreased to provide a specified input impedance range within a specified range of operating frequencies.

9. The apparatus of claim 6 , wherein a total surface area of the spiral conductor is increased to provide a specified input impedance range within a specified range of operating frequencies.

10. A method comprising:

providing an implantable medical device comprising:

a housing including an implantable telemetry circuit configured to wirelessly transfer information electromagnetically;

a dielectric compartment mechanically coupled to the housing, where the dielectric compartment includes first and second substantially parallel face portions, and a third face portion extending between the first and second face portions;

an antenna assembly configured to be mechanically attached to the dielectric compartment and electrically coupled to the implantable telemetry circuit, the antenna assembly including a spiral conductor comprising a planar spiral pattern folded into first, second, and third spiral conductor portions that extend adjacent the first, second, and third face portions, respectively, of the dielectric compartment, wherein the first, second, and third spiral conductor portions define an interior region, wherein at least a portion of the third spiral conductor portion extends inwardly into the interior region, and wherein the at least a portion of the third spiral conductor portion that extends inwardly into the interior region includes a surface defining a curvature that has a bend radius; and

wirelessly transferring information electromagnetically using the implantable antenna assembly.

11. The method of claim 10 , wherein the at least a portion of the third spiral conductor portion that extends inwardly into the interior region is located substantially halfway between the first and second substantially parallel face portions of the dielectric compartment.

12. The method of claim 10 , wherein the spiral pattern comprises concentric turns.

13. The apparatus of claim 12 , wherein the spiral conductor includes at least five turns.

14. The method of claim 10 , further comprising an implantable lead including an electrode configured for location at a tissue site, and coupled to electronic circuitry within the housing to provide one or more of electrostimulation of tissue, or sensing of activity, at the site of the electrode, and wherein the dielectric compartment comprises a header configured to provide an electrical and mechanical connection to the implantable lead.

15. The method of claim 10 , wherein the spiral conductor includes a cross section having a lateral width that is greater than a sidewall height of the cross section.

16. The method of claim 15 , comprising:

orienting a sidewall of one of the first, second, or third spiral conductor portions so that the sidewall provides a sidewall face that is substantially parallel to one of the first, second, or third face portions of the dielectric compartment.

17. The method of claim 10 , further comprising:

providing the spiral conductor with the spiral pattern that includes concentric turns; and

folding the spiral pattern so that a portion of the spiral pattern is located adjacent the third face portion of the dielectric compartment.