Implanted antenna and radio communications link

• US 20050154428A1
• Filed: 12/30/2004
• Published: 07/14/2005
• Est. Priority Date: 12/30/2003
• Status: Active Grant

• Current Assignee: Cochlear Limited
• Original Assignee: Cochlear Limited
• Inventors: Bruinsma, Ian
• Granted Patent: US 7,392,091 B2
• Time in Patent Office: Days
• US Class Current: 607/60
• CPC Class Codes: A61N 1/40 Applying electric fields by inductive or capacitive coupling microwave apparatus A61N5/00; Applying radio-frequency signals
• CPC Class Codes: H01Q 1/27 Adaptation for use in or on movable bodies H01Q1/08, H01Q1/12, H01Q1/18 take precedence

Abstract

A medical implant comprising a housing and an antenna member carried by the housing. The antenna member is configured to be capacitively coupled to body tissue in which the housing is implanted. This forms, together with the impedance of the body tissue, part of a resonant circuit. A reference electrode carried by the housing as a return for the antenna member also forms a further part of the resonant circuit. Transceiver circuitry is also provided and is operable as at least one of a source and a load for the antenna member and forms yet a further part of the series resonant circuit

Claims

1. A medical implant comprising:

a housing;

an antenna member carried by the housing, the antenna member being configured to be capacitively coupled to body tissue in which the housing is implanted to form, together with the impedance of the body tissue, part of a resonant circuit;

a reference electrode carried by the housing as a return for the antenna member, the reference electrode forming a further part of the resonant circuit; and

transceiver circuitry operable as at least one of a source and a load for the antenna member and forming yet a further part of the resonant circuit.

2. A medical implant according to claim 1, wherein the resonant circuit is a series resonant circuit.

3. A medical implant according to claim 2, wherein the series resonant circuit is completed by an impedance matching network arranged between the antenna member and the transceiver circuitry.

4. A medical implant according to claim 3, wherein the impedance matching network comprises at least an inductor.

5. A medical implant according to claim 4, wherein the impedance matching network comprises a passive inductor and capacitor network.

6. A medical implant according to claim 5, wherein the impedance matching network is used to transform a total load impedance of the body tissue and the antenna member capacitance to a value optimised for maximum power transfer between the transceiver circuitry and the body tissue.

7. A medical implant according to claim 6, wherein the impedance matching network is further used to optimise one or more of the resonant circuit voltages, currents and impedances and to perform signal coupling/decoupling functions.

8. A medical implant according to claim 7, wherein the impedance matching network is electrically adjustable to compensate for varied implant conditions.

9. A medical implant according to claim 1, wherein the antenna member is arranged within the housing.

10. A medical implant according to claim 9, wherein the housing is a radio opaque housing and allows capacitive coupling between the antenna member and the body tissue.

11. A medical implant according to claim 10, wherein the housing is sufficiently thin to create a capacitance between the antenna member and the body tissue.

12. A medical implant according to claim 11, wherein the housing is further arranged to have a high dielectric co-efficient to increase the capacitance between the antenna member and the body tissue.

13. A medical implant according to claim 1, wherein the antenna member is arranged externally on the housing and is in direct contact with the body tissue.

14. A medical implant according to claim 13, wherein the impedance matching network contains a low frequency block to isolate the presence of any low frequency stimulation currents.

15. A medical implant according to claim 1, wherein the reference electrode is arranged externally of the housing and is in direct contact with the body tissue.

16. A medical implant according to claim 1, wherein the reference electrode is arranged within the housing and is capacitively isolated from the body tissue.

17. A medical implant according to claim 15, wherein the reference electrode and the antenna member are capacitively coupled to each other.

18. A medical implant according claim 1, wherein the transceiver circuitry comprises a radio frequency circuit.

19. A medical implant according to claim 18, wherein the radio frequency circuit allows communication in an MICS frequency band.

20. A medical implant according to claim 18, wherein the transceiver circuitry contains a combination of a transmitter, a receiver, a demodulator, a detector and related signal processing circuitry.

21. A medical implant according to claim 1, wherein the implant is a stimulation device and the housing contains a stimulation drive circuit module.

22. A medical implant according to claim 21, wherein the stimulation drive circuit module communicates with the transceiver circuitry via a data link.

23. A medical implant according to claim 22, wherein the data link is a digital radio data and control link.

24. A medical implant according to claim 22, wherein the stimulation drive circuit module performs one or more of the tasks of, generating the signals for stimulation, and monitoring the condition of an internal battery of the implant.

25. A medical implant according to claim 24, wherein the stimulation drive circuit module is microprocessor controlled.

26. A medical implant according claim 1, wherein the antenna member is arranged to capacitively couple RF current into the body tissue.

27. A medical implant according to claim 26, wherein the antenna member has a surface area large enough to effect capacitive coupling between the antenna member and the body tissue.

28. A medical implant comprising:

a housing;

control circuitry contained within the housing;

a plurality of electrodes each of which is connected via a lead to the control circuitry; and

a frequency-dependent isolating module interposed between at least one of the electrode leads and the control circuitry to permit the at least one electrode and its lead to function as an antenna for transmission of signals between the control circuitry and an external unit arranged externally of a patient'"'"'s body.

29. A medical implant according to claim 28, wherein each lead is fed through the housing of the implant through a hermetically sealed feedthrough element.

30. A medical implant according to claim 28, wherein the control circuitry includes transceiver circuitry which feeds data, at a radio frequency, to the external unit.

31. A medical implant according to claim 28, wherein the control circuitry includes transceiver circuitry which receives radio signals from the external unit.

32. A medical implant according to claim 30, wherein the transceiver circuitry includes an impedance matching network for the electrode and lead functioning as the antenna.

33. A medical implant according to claim 32, wherein the control circuitry further includes a stimulation circuit module which contains the electronics for generating stimulation signals for application to the patient'"'"'s body via the electrodes.

34. A medical implant according to claim 33, wherein the stimulation circuit module is microprocessor controlled and includes a battery for operation of the implant.

35. A medical implant according to claim 28, wherein the frequency-dependent isolating module comprises, a radio frequency choke which passes a lower frequency stimulation signal and blocks the higher, radio frequency signals, to enable the electrode to operate as a stimulation electrode.

36. A medical implant according to claim 35, wherein the isolating module further includes a radio frequency coupling element which blocks the low frequency stimulation signal and couples the radio frequency signal to ground.

37. A medical implant according to claim 36, wherein additional electrodes and their associated leads are used as ground references for the antenna in addition to being used as electrodes for stimulation purposes.

38. A medical implant according to claim 37, wherein the additional electrodes are coupled to the control circuitry via isolating modules.

39. A medical implant according to claim 28, wherein the implant further includes a return electrode plate mounted on the housing.

40. A medical implant according to claim 39, wherein the electrode plate is mounted externally on the housing to be in direct contact with body tissue in which the implant is implanted.

41. A medical implant according to claim 39, wherein the electrode plate is mounted within the housing to be isolated from direct contact with the body tissue but which still allows capacitive coupling to the body tissue.

42. A medical implant according to claim 28, wherein the electrode used as the antenna is radio frequency isolated from the body tissue by providing a choke in-line with said electrode at an appropriate length.

43. A medical implant according to claim 42, wherein the electrode used as the antenna is capacitively coupled to the body tissue so that the body tissue is used as an extension of the antenna.

44. A method of transmitting a signal between a medical implant and an external unit arranged externally of a patient'"'"'s body, the method including the steps of:

feeding signals to an antenna member of the implant, the antenna member being capacitively coupled to body tissue in which the implant is arranged; and

using the capacitively coupled body tissue as an extension of the antenna to transmit the signals between the implant and the external unit.

45. A method of transmitting a signal between a medical implant and an external unit arranged externally of a patient'"'"'s body, the implant including a plurality of electrodes each of which is connected by an electrode lead to control circuitry in a housing of the implant, the method including the steps of:

generating signals to be transmitted to or from the implant;

electrically coupling at least one of the electrodes and its associated lead to the control circuitry of the implant; and

using the at leat one electrode and its associated lead as an antenna to effect transmission of signals between the implant and the external unit.

46-47. -47. (canceled)