Communicating with an Implanted Wireless Sensor

• US 20060196277A1
• Filed: 03/06/2006
• Published: 09/07/2006
• 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: Ellis, Michael, Miller, Donald J., Allen, Mark G., Kroh, Jason
• Granted Patent: US 7,498,799 B2
• Time in Patent Office: Days
• US Class Current: 73/861.12
• 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 resonant frequency of 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; and

using the frequency of the energizing signal to determine the resonant frequency of 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 phase slope 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. A method for determining a resonant frequency of a wireless sensor, comprising:

adjusting a frequency of an energizing signal by;

receiving a sensor signal from the wireless sensor during a measurement cycle;

processing the sensor signal during a period within the measurement cycle to create a continuous wave IF sensor signal;

determining a phase difference between the IF sensor signal and the energizing signal;

based on the phase difference adjusting the frequency of the energizing signal to reduce the phase difference; and

determining the frequency of the energizing signal when the phase difference corresponds to a predetermined value; and

using the frequency of the energizing signal when the phase difference corresponds to the predetermined value to determine the resonant frequency of the sensor.

6. The method of claim 5, further comprising:

adjusting a phase of the energizing signal by;

generating the energizing signal;

receiving a calibration signal during a calibration cycle;

processing the calibration signal during a first period within the calibration cycle to create a continuous wave IF calibration signal;

determining a first phase difference between the IF calibration signal and a reference signal; and

based on the first phase difference adjusting the phase of the energizing signal to reduce the first phase difference.

7. The method of claim 6, wherein generating the energizing signal comprises adjusting a frame width of the energizing signal between a first cycle and a second cycle.

8. The method of claim 6, wherein processing the calibration signal during a first period within the calibration cycle comprises allowing the calibration signal to propagate into a calibration section during the first period.

9. The method of claim 6, further comprising preventing the calibration signal from propagating into a measurement section during the calibration cycle.

10. The method of claim 6, wherein adjusting the phase of the energizing signal comprises using a first phase locked loop (PLL) and adjusting the frequency of the energizing signal comprises using a second PLL.

11. The method of claim 6, wherein adjusting a phase of an energizing signal is repeated until the first phase difference between the IF calibration signal and the reference signal corresponds to a first predetermined value.

12. The method of claim 5, wherein processing the sensor signal during a period within the measurement cycle comprises allowing the sensor signal to propagate into a measurement section during the period.

13. The method of claim 5, further comprising:

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

14. The method of claim 5, wherein adjusting a frequency of the energizing signal is repeated until the phase difference corresponds to the predetermined value.

15. The method of claim 5, wherein processing the sensor signal during a period within the measurement cycle comprises processing the sensor signal to determine a center frequency of the sensor signal.

16. A system for determining a resonant frequency of a wireless sensor, comprising:

a receive section for receiving a calibration signal and a sensor signal;

a calibration path including;

a calibration IF section for determining a phase difference between the energizing signal and the calibration signal; and

a first phase lock loop (PLL) for adjusting a phase of the energizing signal based on the phase difference between the energizing signal and the calibration signal;

a measurement path including;

a measurement IF section for determining a phase difference between the energizing signal and the sensor signal; and

a second PLL for adjusting a frequency of the energizing signal based on the phase difference between the energizing signal and the sensor signal; and

an energizing signal generator for varying a frame width of the energizing signal.

17. The system of claim 16, wherein the measurement IF section compares continuous wave signals to determine the phase difference between the energizing signal and the calibration signal.

18. The system of claim 16, wherein the calibration IF section compares continuous wave signals to determine the phase difference between the energizing signal and the sensor signal.

19. The system of claim 16, wherein the calibration IF section creates a continuous wave IF calibration signal using a narrow bandpass filter.

20. The system of claim 16, wherein the measurement IF section creates a continuous wave IF sensor signal using a narrow bandpass filter.

21. The system of claim 16, further comprising:

a control for controlling propagation of the sensor signal into the measurement section.

22. The system of claim 16, further comprising:

a control for controlling propagation of the calibration signal into the calibration section.

23. A system for determining a resonant frequency of a wireless sensor, comprising:

means for generating an energizing signal;

means for receiving a calibration signal and a sensor signal;

means for determining a first relationship between the energizing signal and the calibration signal using a continuous wave IF calibration signal;

means for determining a second relationship between the sensor signal and the calibration signal using a continuous wave IF sensor signal; and

means for determining the resonant frequency of the wireless sensor based on the first relationship and the second relationship.

24. The system of claim 23, wherein the means for generating an energizing signal includes means for adjusting a frame width of the energizing signal between a first cycle and a second cycle.

25. The system of claim 23, wherein the means for generating an energizing signal includes means for adjusting a phase of the energizing signal based on the first relationship.

26. The system of claim 23, wherein the means for generating an energizing signal includes means for adjusting a frequency of the energizing signal based on the second relationship.

27. The system of claim 23, further comprising:

means for controlling the calibration signal into the means for determining a first relationship between the energizing signal and the calibration signal.

28. The system of claim 23, further comprising:

means for controlling the sensor signal into the means for determining a second relationship between the sensor signal and the calibration signal.

29. The system of claim 23, wherein the means for determining a first relationship between the energizing signal and the calibration signal creates the continuous wave IF calibration signal using a narrow bandpass filter.

30. The system of claim 23, wherein the means for determining a second relationship between the sensor signal and the calibration signal creates the continuous wave IF sensor signal using a narrow bandpass filter.