Communicating with an implanted wireless sensor

• US 7,439,723 B2
• Filed: 05/14/2007
• Issued: 10/21/2008
• 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
• Primary Examiner(s): Dole; Timothy J.
• Application Number:
  US11/748,053
• Publication Number:
  US 20070210786A1
• Time in Patent Office: 526 Days
• Field of Search: 324/76.53, 324/601
• US Class Current: 324/76.53
• 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: 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
• CPC Class Codes: H04L 2027/0028 at passband only
• CPC Class Codes: H04L 2027/0055 single phase
• CPC Class Codes: H04L 2027/0067 Phase error detectors

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 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 an 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 generating the energizing signal and varying a frame width of the energizing signal,

wherein the frequency of the energizing signal is determined to be the resonant frequency of the wireless sensor when the second PLL is locked.

2. The system of claim 1, wherein the calibration IF section compares continuous wave signals to determine the phase difference between the energizing signal and the calibration signal.

3. The system of claim 1, wherein the measurement IF section compares continuous wave signals to determine the phase difference between the energizing signal and the sensor signal.

4. The system of claim 1, wherein the calibration IF section creates a continuous wave IF calibration signal using a narrow bandpass filter.

5. The system of claim 1, wherein the measurement IF section creates a continuous wave IF sensor signal using a narrow bandpass filter.

6. The system of claim 1, further comprising:

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

7. The system of claim 1, further comprising:

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