Communicating with an implanted wireless sensor

• US 7,679,355 B2
• Filed: 01/07/2009
• Issued: 03/16/2010
• Est. Priority Date: 11/01/2004
• Status: Active Grant

• Current Assignee: St. Jude Medical Luxembourg Holdings Ii S.A.R.L.
• Original Assignee: CardioMEMS Incorporated
• Inventors: Miller, Donald J., Ellis, Michael, Allen, Mark G., Kroh, Jason
• Primary Examiner(s): Dole; Timothy J
• Application Number:
  US12/349,606
• Publication Number:
  US 20090115396A1
• Time in Patent Office: 433 Days
• Field of Search: 324/76.51, 324/76.52, 324/682
• US Class Current: 324/76.51
• CPC Class Codes: A61B 2560/0219 of externally powered implanted units
• CPC Class Codes: A61B 2560/0223 of calibration, e.g. protocols for calibrating sensors
• CPC Class Codes: A61B 5/0002 Remote monitoring of patients using telemetry, e.g. transmission of vital signals via a communication network A61B5/07 takes precedence; transmission systems for measured values G08C; transmission H04B; transmission of digital information H04L; wireless communication networks H04W
• CPC Class Codes: A61B 5/0031 Implanted circuitry
• CPC Class Codes: A61B 5/05 Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves impedance plethysmography A61B5/0295; measuring movement of the entire body or parts thereof A61B5/11; detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof A61B5/24
• CPC Class Codes: A61B 5/076 Permanent implantations telemetry using implanted circuitry A61B5/0031; implanted stimulators for therapy A61N1/3605, A61N1/362, A61N1/372
• CPC Class Codes: G01D 21/00 Measuring or testing not otherwise provided for
• CPC Class Codes: G01F 15/066 involving magnetic transmission devices
• CPC Class Codes: G01R 23/12 by converting frequency into phase shift
• CPC Class Codes: G01R 23/145 by heterodyning or by beat-frequency comparison with the harmonic of an oscillator

Abstract

The present invention determines the resonant frequency of a sensor by adjusting the phase and frequency of an energizing signal until the frequency of the energizing signal matches the resonant frequency of the sensor. The system energizes the sensor with a low duty cycle, gated burst of RF energy having a predetermined frequency or set of frequencies and a predetermined amplitude. The energizing signal is coupled to the sensor via magnetic coupling and induces a current in the sensor which oscillates at the resonant frequency of the sensor. The system receives the ring down response of the sensor via magnetic coupling and determines the resonant frequency of the sensor, which is used to calculate the measured physical parameter. The system uses a pair of phase locked loops to adjust the phase and the frequency of the energizing signal.

Claims

1. A method for determining a physical parameter associated with a wireless sensor, comprising:

generating an energizing signal;

receiving a sensor signal from the wireless sensor;

sampling the sensor signal using at least two sample points;

based on the at least two sample points, adjusting a frequency and a phase of the energizing signal;

using the frequency of the energizing signal to determine the resonant frequency of the wireless sensor; and

using the determined resonant frequency of the wireless sensor to determine a physical parameter associated with the wireless sensor.

2. The method of claim 1, further comprising using the at least two sample points of the sensor signal to determine whether a frequency difference exists.

3. The method of claim 1, further comprising determining a sum of the sample points, wherein adjusting a frequency and a phase of the energizing signal comprises using the sum to adjust the phase of the energizing signal.

4. The method of claim 1, further comprising determining a difference of the sample points, wherein adjusting a frequency and a phase of the energizing signal comprises using the difference to adjust the frequency of the energizing signal.

5. The method of claim 1, wherein the physical parameter is capacitance.

6. A method for determining a resonant frequency of a wireless sensor, comprising:

generating an energizing signal;

receiving a sensor signal from the wireless sensor;

sampling a phase of the sensor signal using at least two sample points;

based on the at least two sample points, adjusting a frequency and a phase of the energizing signal; and

using the frequency of the energizing signal to determine the resonant frequency of the wireless sensor.

7. The method of claim 6, further comprising:

using the determined resonant frequency of the wireless sensor to determine a capacitance associated with the wireless sensor.

8. The method of claim 6, further comprising using the at least two sample points of the sensor signal to determine whether a frequency difference exists.

9. The method of claim 6, further comprising determining a sum of the sample points, wherein adjusting a frequency and a phase of the energizing signal comprises using the sum to adjust the phase of the energizing signal.

10. The method of claim 6, further comprising determining a difference of the sample points, wherein adjusting a frequency and a phase of the energizing signal comprises using the difference to adjust the frequency of the energizing signal.

11. A method for determining a resonant frequency of a wireless sensor, comprising:

generating an energizing signal;

receiving a sensor signal from the wireless sensor;

sampling a phase difference signal using at least two sample points, wherein the phase difference signal corresponds to a phase difference between the energizing signal and the sensor signal;

based on the at least two sample points, adjusting a frequency and a phase of the energizing signal; and

using the frequency of the energizing signal to determine the resonant frequency of the wireless sensor.

12. The method of claim 11, further comprising:

using the determined resonant frequency of the wireless sensor to determine a physical parameter associated with the wireless sensor.

13. The method of claim 12, wherein the physical parameter is capacitance.

14. The method of claim 11, further comprising using the at least two sample points of the sensor signal to determine whether a frequency difference exists.

15. The method of claim 11, further comprising determining a sum of the sample points, wherein adjusting a frequency and a phase of the energizing signal comprises using the sum to adjust the phase of the energizing signal.

16. The method of claim 11, further comprising determining a difference of the sample points, wherein adjusting a frequency and a phase of the energizing signal comprises using the difference to adjust the frequency of the energizing signal.