Testing tuned circuits

• US 9,571,166 B2
• Filed: 07/19/2012
• Issued: 02/14/2017
• Est. Priority Date: 07/19/2012
• Status: Active Grant

• Current Assignee: Cochlear Limited
• Original Assignee: Cochlear Limited
• Inventors: Metzenthen, Bill
• Primary Examiner(s): Le, Long V
• Assistant Examiner(s): Impink, Bradley
• Application Number:
  US13/553,798
• Publication Number:
  US 20140024919A1
• Time in Patent Office: 1,671 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: A61B 2560/0219 of externally powered implanted units
• CPC Class Codes: A61B 2560/0271 using a remote monitoring unit
• CPC Class Codes: A61B 2562/0223 Magnetic field sensors
• CPC Class Codes: A61B 2562/046 in a matrix array
• CPC Class Codes: A61B 5/0031 Implanted circuitry
• CPC Class Codes: A61B 5/1075 for measuring dimensions by non-invasive methods, e.g. for determining thickness of tissue layer A61B8/0858 takes precedence
• CPC Class Codes: A61N 1/36038 Cochlear stimulation
• CPC Class Codes: A61N 1/37223 Circuits for electromagnetic coupling
• CPC Class Codes: A61N 1/37252 Details of algorithms or data aspects of communication system, e.g. handshaking, transmitting specific data or segmenting data
• CPC Class Codes: H04B 5/24 Inductive coupling
• CPC Class Codes: H04R 25/606 acting directly on the eardrum, the ossicles or the skull, e.g. mastoid, tooth, maxillary or mandibular bone, or mechanically stimulating the cochlea, e.g. at the oval window

Abstract

Methods and systems for determining one or more parameters of a tuned circuit forming part of a wireless energy transmission system in an implanted (or implantable) medical device are described. The method involves energizing the tuned circuit then receiving a signal back from it. This signal is then analyzed to determine a property of the circuit such as its quality factor (Q) or resonant frequency. Also described herein is a method and system for determining the implantation depth of a component of an implanted medical device. The method involves determining the position of a magnetic element which is mounted in a fixed physical relationship with the component of the medical device. The methods can be performed on an implanted medical device without the need to explant the device.

Claims

1. A method of testing an implantable medical device, the implantable medical device including a tuned circuit having a coil for transferring energy between the implantable medical device and another device, the method comprising:

inducing, with a signal generator and a test coil connected to the signal generator, an EMF in the coil of the tuned circuit;

disconnecting the signal generator from the test coil;

selectively connecting the test coil to a digitizer;

detecting, with the test coil and the digitizer, a resonance of the tuned circuit in response to the EMF induced in the coil of the tuned circuit; and

analyzing the detected resonance over a period of time to determine a property of the tuned circuit.

2. The method of claim 1, wherein the inducing the EMF includes:

applying a time varying magnetic field to the coil of the tuned circuit.

3. The method of claim 2, wherein the inducing the EMF includes:

applying the time varying magnetic field for at least an amount of time sufficient for the tuned circuit of the implantable medical device to reach a threshold state, prior to detecting a resonance of the tuned circuit.

4. The method of claim 1, wherein the analyzing includes:

determining a quality factor (Q) of the tuned circuit as the property thereof.

5. The method of claim 1, wherein the analyzing includes:

determining at least one resonant frequency of the tuned circuit as the property thereof.

6. The method of claim 1, wherein the detecting resonance includes:

detecting a time varying magnetic field generated by the tuned circuit.

7. The method of claim 6, wherein the analyzing includes:

generating a time varying voltage signal in response to the time varying magnetic field; and

sampling the time varying voltage signal over a sampling interval to generate instantaneous voltage samples at corresponding times.

8. The method of claim 7, wherein the analyzing the detected resonance includes:

fitting a curve to the sampled instantaneous voltage values over at least the sampling interval.

9. The method of claim 8, wherein:

the curve fitted to the sampled instantaneous voltage values has a decaying sinusoidal form.

10. The method of claim 8, wherein the curve fitted to the sampled instantaneous voltage values is of the general form:

11. The method of claim 10, wherein the curve fitted to the sampled instantaneous voltage values further includes terms to account for at least one of more of the following:

a predictable unwanted component in the generated time varying voltage signal;

an artefact introduced into the instantaneous voltage samples by the sampling process; and

a distortion caused by the presence of a non-linear component in the tuned circuit.

12. The method of claim 1, wherein:

the method is performed prior to implantation of the implantable medical device.

13. The method of claim 1, wherein:

the method is performed on an implantable medical device in vivo.

14. The method of claim 1, wherein the implantable medical device is an implanted auditory prosthesis.

15. A system for testing an implantable medical device, the implantable medical device including a tuned circuit having a coil for transferring energy between the implantable medical device and another device, the system comprising:

a signal generator configured to induce, via a test coil, an EMF in the coil of the tuned circuit;

a digitizer configured to detect, via the test coil, a resonance of the tuned circuit in response to the EMF induced in the coil of the tuned circuit;

a switch circuit configured to alternatively connect the test coil to the signal generator and the digitizer; and

a processing system configured to analyze the detected resonance over a period of time to determine a property of the tuned circuit.

16. A method of testing an implantable medical device, comprising:

selectively connecting, via a switch, a signal generator of a testing system to a dual-function test coil;

inducing, with the signal generator, an EMF in an implantable coil of a tuned circuit;

selectively connecting the dual-function test coil to a digitizer;

detecting, with the digitizer, a resonance of the tuned circuit in response to the EMF induced in the implantable coil; and

analyzing the detected resonance to determine a property of the tuned circuit.

17. The method of claim 16, wherein the inducing the EMF includes:

applying a time varying magnetic field to the implantable coil.

20. The method of claim 16, wherein the detecting resonance comprises:

detecting a time varying magnetic field generated by the tuned circuit.

21. The method of claim 20, wherein the analyzing includes:

generating a time varying voltage signal in response to the time varying magnetic field; and

sampling the time varying voltage signal over a sampling interval to generate instantaneous voltage samples at corresponding times.

22. The method of claim 21, wherein the analyzing includes:

fitting a curve to the sampled instantaneous voltage values over at least the sampling interval.

23. The method of claim 16, further comprising:

monitoring an amplitude of the detected resonance to detect an alignment of the dual-function test coil with the implantable coil.

18. The method of 16, wherein the analyzing comprises:

determining a quality factor (Q) of the tuned circuit.

19. The method of 16, wherein the analyzing comprises:

determining at least one resonant frequency of the tuned circuit.