Preventing False Locks in a System that Communicates With an Implanted Wireless Sensor

• US 20070100215A1
• Filed: 09/06/2006
• Published: 05/03/2007
• Est. Priority Date: 09/06/2005
• Status: Active Grant

• Current Assignee: St. Jude Medical Luxembourg Holdings Ii S.A.R.L.
• Original Assignee: CardioMEMS Incorporated
• Inventors: Powers, Richard, Ellis, Michael, Miller, Donald, Kroh, Jason
• Granted Patent: US 7,492,144 B2
• Time in Patent Office: Days
• US Class Current: 600/300
• CPC Class Codes: A61B 2560/0223 of calibration, e.g. protocols for calibrating sensors
• CPC Class Codes: A61B 5/0031 Implanted circuitry
• CPC Class Codes: A61B 5/02014 Determining aneurysm
• CPC Class Codes: A61B 5/0215 by means inserted into the body catheters A61M25/00
• 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: A61B 5/726 using Wavelet transforms
• CPC Class Codes: G01D 21/00 Measuring or testing not otherwise provided for

Abstract

The present invention determines the resonant frequency of a wireless 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. The system receives the ring down response of the sensor and determines the resonant frequency of the sensor, which is used to calculate a physical parameter. The system uses a pair of phase locked loops to adjust the phase and the frequency of the energizing signal. The system identifies false locks by detecting an unwanted beat frequency in the coupled signal, as well as determining whether the coupled signal exhibits pulsatile characteristics that correspond to a periodic physiological characteristic, such as blood pressure.

Claims

1. A method for identifying a false lock, comprising:

generating an energizing signal with a first phase and a first frequency;

receiving a calibration signal;

determining a first phase difference between the calibration signal and the energizing signal;

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

energizing a wireless sensor with an energizing signal having the first frequency;

receiving a sensor signal;

determining whether the sensor signal includes a predetermined beat frequency; and

if the sensor signal includes the predetermined beat frequency, then determining that the first frequency of the energizing signal corresponds to a false lock.

2. The method of claim 1, wherein determining whether the sensor signal includes a predetermined beat frequency comprises:

sampling the sensor signal using multiple sampling points;

determining an average of the multiple sampling points; and

based on the average, determining whether the sensor signal includes the predetermined beat frequency.

3. The method of claim 2, wherein determining whether the sensor signal includes the predetermined beat frequency, comprises:

if the average is zero or greater, then determining that the sensor signal includes the predetermined beat frequency;

otherwise, determining that the sensor signal does not include the predetermined beat frequency.

4. The method of claim 2, wherein the multiple sampling points comprise three sampling points and wherein a second sampling point is approximately 2.2 microseconds after the start of the energizing signal that energizes the sensor, a first sampling point is approximately 800 ns prior to the second sampling point and a third sampling point is approximately 800 ns after the second sampling point.

5. The method of claim 2, wherein the multiple sampling points occur within a single measurement cycle.

6. The method of claim 2, wherein the multiple sampling points occur in consecutive measurement cycles.

7. The method of claim 1, wherein the predetermined beat frequency corresponds to a multiple of approximately 500 kHz above or below a resonant frequency of the sensor.

8. The method of claim 1, wherein the beat frequency is based on a pulse width of the energizing signal and characteristics of the sensor.

9. The method of claim 1, further comprising:

if the sensor signal includes the predetermined beat frequency, then providing an output to a user indicating a false lock.

10. A method for identifying a false lock, comprising:

energizing a wireless sensor with an energizing signal having a first frequency;

receiving a sensor signal;

sampling the sensor signal using multiple sampling points;

determining whether the sensor signal includes a predetermined beat frequency; and

if the sensor signal includes the predetermined beat frequency, then determining that the first frequency of the energizing signal corresponds to a false lock.

11. The method of claim 10, wherein the predetermined beat frequency corresponds to a multiple of approximately 500 kHz above or below a resonant frequency of the sensor.

12. The method of claim 10, wherein determining whether the sensor signal includes a predetermined beat frequency comprises:

determining an average of the multiple sampling points;

if the average is zero or greater, then determining that the sensor signal includes the predetermined beat frequency; and

if the average is less than zero, then determining that the sensor signal does not include the predetermined beat frequency.

13. The method of claim 10, further comprising:

if the sensor signal includes the predetermined beat frequency, then providing an output to a user indicating a false lock.

14. The method of claim 10, wherein the multiple sampling points occur within a single cycle.

15. The method of claim 10, wherein the multiple sampling points occur in consecutive cycles.

16. A method for identifying a false lock, comprising:

energizing a wireless sensor with an energizing signal having a first frequency;

receiving a sensor signal;

determining energy within the sensor signal for each of a plurality of predetermined frequency ranges;

comparing the energy in the predetermined frequency ranges to determine whether the sensor signal includes pulsatile characteristics based on a periodic physiological characteristic; and

if the sensor signal does not include pulsatile characteristics based on periodic physiological characteristic, then determining that the first frequency of the energizing signal corresponds to a false lock.

17. The method of claim 16, wherein the multiple predetermined frequency ranges include a lower frequency range and a higher frequency range and wherein comparing the energy in the predetermined frequency ranges comprises:

determining whether a maximum value within the lower frequency range is two times a maximum value within the higher frequency range.

18. The method of claim 17, wherein the lower frequency range includes 0.5-2 Hz and the higher frequency range includes 2-4.5 Hz.

19. The method of claim 17, wherein the lower frequency range is approximately 0.5-13 Hz and the higher frequency range is approximately 14-26 Hz.

20. The method of claim 16, wherein if the sensor signal does not include pulsatile characteristics based on periodic physiological characteristic, then providing an output to a user indicating a false lock.

21. The method of claim 16, wherein the periodic physiological characteristic corresponds to a fluidic pressure within the body.

22. The method of claim 21, wherein the fluidic pressure within the body is blood pressure.

23. A system for identifying a false lock, comprising:

an energizing signal generator for generating an energizing signal;

a receiver for receiving a sensor signal from a wireless sensor;

a time to frequency domain transform module for transforming a signal corresponding to a change of frequency of the energizing signal;

a comparison module for comparing energy in a lower frequency range with energy in a higher frequency range over a predetermined time period to determine whether the signal includes pulsatile characteristics based on a periodic physiological characteristic; and

an output module for identifying a false lock when the comparison module determines that the signal does not include pulsatile characteristics based on the periodic physiological characteristic.

24. The system of claim 23, wherein the time to frequency domain transform module implements a Fourier transform.

25. The system of claim 23, wherein the time to frequency domain transform module comprises bandpass filters.

26. The system of claim 23, wherein the output module provides an output to a user indicating a false lock when the comparison module determines that the signal does not include pulsatile characteristics based on the periodic physiological characteristic.

27. The system of claim 23, wherein the output module prevents the system from locking when the comparison module determines that the signal does not include pulsatile characteristics based on the periodic physiological characteristic.

28. The system of claim 23, wherein the output module prevents the first frequency from being used to determine a physical characteristic using a resonant frequency of the sensor when the comparison module determines that the signal does not include pulsatile characteristics based on the periodic physiological characteristic.

29. The system of claim 23, wherein the lower frequency range is approximately 0.5-13 Hz, the higher frequency range is approximately 14-26 Hz.

30. The system of claim 23, wherein the lower frequency range is approximately 0.5-2 Hz and the higher frequency range is approximately 2-4.5 Hz.

31. The method of claim 23, wherein the periodic physiological characteristic corresponds to a fluidic pressure within the body.

32. The method of claim 31, wherein the fluidic pressure within the body is blood pressure.