Communicating with an implanted wireless sensor

• US 7,550,978 B2
• Filed: 12/20/2006
• Issued: 06/23/2009
• 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:
  US11/613,645
• Publication Number:
  US 20070096715A1
• Time in Patent Office: 916 Days
• Field of Search: 324/601, 324/633
• 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;

receiving a calibration signal; 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;

receiving a sensor signal from the wireless sensor;

comparing the sensor signal and a reference signal to determine a second phase difference; and

using the second phase difference to determine the resonant frequency of the wireless sensor.

2. The method of claim 1, wherein the calibration signal is an energizing leakage signal.

3. The method of claim 1, wherein the reference signal is an energizing leakage signal.

4. The method of claim 1, wherein the calibration cycle further comprises:

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

5. The method of claim 1, wherein energizing the wireless sensor comprises using the energizing signal to energize the wireless sensor, further comprising:

adjusting a frequency of the energizing signal to reduce the second phase difference.

6. The method of claim 5, wherein using the second phase difference to determine the frequency of the wireless sensor, comprises:

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

7. The method of claim 5, wherein the measurement cycle is repeated until the second phase difference is a predetermined value.

8. The method of claim 5, wherein the calibration cycle and the measurement cycle are repeated until the second phase difference is a predetermined value.

9. The method of claim 1, wherein energizing the wireless sensor comprises using a second energizing signal to energize the wireless sensor, further comprising:

adjusting a frequency of the second energizing signal to reduce the second phase difference.