Communicating with an implanted wireless sensor

• US 8,237,451 B2
• Filed: 04/01/2011
• Issued: 08/07/2012
• 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: Joy, James, Kroh, Jason, Ellis, Michael, Allen, Mark, Pyle, Wilton
• Primary Examiner(s): Dole, Timothy J
• Application Number:
  US13/078,091
• Publication Number:
  US 20110181297A1
• Time in Patent Office: 494 Days
• Field of Search: 324/633, 324/601, 324/76.53
• US Class Current: 324/633
• 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:

providing a calibration cycle, wherein the calibration cycle includes;

generating an energizing signal, by a base unit;

receiving a calibration signal, by the base unit via a coupling loop; and

comparing the energizing signal and the calibration signal to determine a phase difference; and

providing a measurement cycle, wherein the measurement cycle includes;

energizing the wireless sensor, by the base unit;

receiving a sensor signal from the wireless sensor, by the base unit via the coupling loop;

determining a characteristic of the sensor signal; and

using the characteristic to determine the resonant frequency of the wireless sensor.

2. The method of claim 1, wherein the characteristic is amplitude and wherein using the characteristic to determine the resonant frequency of the wireless sensor comprises determining that a frequency of the sensor signal at a maximum amplitude of the sensor signal corresponds to the resonant frequency of the sensor.

3. The method of claim 1, wherein the characteristic is sensor group delay and wherein using the characteristic to determine the resonant frequency of the wireless sensor comprises determining that a frequency of the sensor signal at a maximum sensor group delay of the sensor signal corresponds to the resonant frequency of the sensor.

4. The method of claim 1, wherein the calibration signal corresponds to an energizing leakage signal.

5. The method of claim 1, further comprising:

adjusting a phase of the energizing signal; and

providing additional calibration cycles until the phase difference between the energizing signal and the calibration signal corresponds to a predetermined value.

6. The method of claim 1, further comprising:

adjusting a frequency of the energizing signal; and

providing another measurement cycle.

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

a transmitter in a base unit operable to transmit an energizing signal during a calibration cycle and during a measurement cycle;

a receiver in the base unit operable to receive a calibration signal during the calibration cycle and a sensor signal from the wireless sensor during the measurement cycle via a coupling loop,

a plurality of signal processing components; and

at least one processor;

wherein the signal processing components and the at least one processor are operable to;

compare the energizing signal and the calibration signal to determine a phase difference during the calibration cycle,

determine a characteristic of the sensor signal during the measurement cycle, and

use the characteristic of the sensor signal to determine the resonant frequency of the wireless sensor.

8. The system of claim 7, wherein the characteristic is amplitude and the signal processing components and the at least one processor are operable to determine a maximum amplitude of the sensor signal and use a frequency of the sensor signal at the maximum amplitude of the sensor signal to determine the resonant frequency of the sensor.

9. The system of claim 7, wherein the characteristic is sensor group delay and the signal processing components and the at least one processor are operable to determine a maximum sensor group delay and use a frequency of the sensor signal at the maximum sensor group delay to determine the resonant frequency of the sensor.

10. The system of claim 7, wherein the signal processing components include a first phase lock loop (PLL) and the first PLL is operable to adjust a phase of the energizing signal.

11. The system of claim 10, wherein the signal processing components include a second phase lock loop (PLL) and the second PLL is operable to adjust a frequency of the energizing signal.

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

energizing, by a base unit, the wireless sensor using an energizing signal, wherein a phase difference between the energizing signal and an energizing leakage signal received by a coupling loop is a predetermined value;

receiving a sensor signal from the wireless sensor by the base unit via the coupling loop;

determining a characteristic of the sensor signal; and

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

13. The method of claim 12, wherein energizing the wireless sensor using an energizing signal, comprises:

generating the energizing signal by the base unit;

receiving the energizing leakage signal by the base unit;

comparing the energizing signal and the energizing leakage signal to determine the phase difference; and

adjusting the phase of the energizing signal until the phase difference is the predetermined value.

14. The method of claim 12, wherein the characteristic is amplitude and wherein using the characteristic to determine the resonant frequency of the wireless sensor comprises determining that a frequency of the sensor signal at a maximum amplitude of the sensor signal corresponds to the resonant frequency of the sensor.

15. The method of claim 12, wherein the characteristic is sensor group delay and wherein using the characteristic to determine the resonant frequency of the wireless sensor comprises determining that a frequency of the sensor signal at a maximum sensor group delay of the sensor signal corresponds to the resonant frequency of the sensor.

16. The method of claim 12, further comprising:

adjusting a frequency of the energizing signal until a phase difference between the energizing signal and the sensor signal corresponds to a predetermined value.