Communicating with an implanted wireless sensor

• US 7,839,153 B2
• Filed: 05/15/2009
• Issued: 11/23/2010
• 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: Allen, Mark, Ellis, Michael, Pyle, Wilton, Joy, James, Kroh, Jason
• Primary Examiner(s): Dole; Timothy J
• Application Number:
  US12/466,541
• Publication Number:
  US 20090224773A1
• Time in Patent Office: 557 Days
• Field of Search: 324/633, 324/601
• 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 for determining a first relationship between an energizing signal and a calibration signal; and

providing a measurement cycle for receiving a sensor signal, determining a second relationship between the sensor signal and the energizing signal and determining the resonant frequency of the wireless sensor based on the first relationship and the second relationship.

2. The method of claim 1, wherein the first relationship is a phase difference.

3. The method of claim 2, wherein the calibration cycle further comprises:

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

4. The method of claim 1, wherein the first relationship is a phase difference due to a time delay caused by component aging.

5. The method of claim 1, wherein the second relationship is a phase difference.

6. The method of claim 5, wherein the measurement cycle further comprises:

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

7. The method of claim 1, wherein the second relationship is a phase difference due to a time delay caused by component aging.

8. The method of claim 1, wherein a first phase locked loop (PLL) is used to provide the calibration cycle and a second PLL is used to provide the measurement cycle.

9. The method of claim 8, wherein the first PLL is faster than the second PLL.

10. 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;

receiving a calibration signal; and

determining a first relationship between the energizing signal and the calibration signal; and

providing a measurement cycle, wherein the measurement cycle includes;

energizing the wireless sensor;

receiving a sensor signal from the wireless sensor;

determining a second relationship between the sensor signal and the energizing signal; and

using the first relationship and the second relationship to determine the resonant frequency of the wireless sensor.

11. The method of claim 10, wherein the first relationship is a phase difference.

12. The method of claim 11, wherein the calibration cycle further comprises:

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

13. The method of claim 10, wherein the second relationship is a phase difference.

14. The method of claim 13, wherein the measurement cycle comprises:

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

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

a transmitter for transmitting an energizing signal to the wireless sensor;

a receiver for receiving a calibration signal during a calibration cycle and for receiving a sensor signal during a measurement cycle; and

circuitry connected to the transmitter and the receiver for;

determining a first relationship between the energizing signal and the calibration signal; and

determining a second relationship between the sensor signal and the energizing signal; and

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

16. The system of claim 15, wherein the circuitry includes a first phase locked loop (PLL) and a second PLL and wherein the first PLL is used to provide the calibration cycle and the second PLL is used to provide the measurement cycle.

17. The system of claim 16, wherein the first PLL is faster than the second PLL.