Method and system for passive wireless strain gauge

• US 7,849,752 B2
• Filed: 10/24/2008
• Issued: 12/14/2010
• Est. Priority Date: 10/24/2007
• Status: Active Grant

• Current Assignee: Argon St Incorporated (The Boeing Co.)
• Original Assignee: Argon St Incorporated (The Boeing Co.)
• Inventors: Conkle, John, Shaw, Jeffrey C., Gregory, Otto, Birnbaum, Thomas
• Primary Examiner(s): Noori; Max
• Application Number:
  US12/289,306
• Publication Number:
  US 20090188324A1
• Time in Patent Office: 781 Days
• Field of Search: 73760-860
• US Class Current: 73/773
• CPC Class Codes: G01B 7/16 for measuring the deformation in a solid, e.g. by resistance strain gauge
• CPC Class Codes: G01B 7/22 using change in capacitance

Abstract

A system and method of using a passive wireless gauge to detect the physical properties on an object.

Claims

1. A method of detecting the amount of deformation of an object using a strain gauge affixed to the object comprising the steps of:

(a) transmitting a wireless RF signal to the gauge;

(b) receiving the RF signal at the gauge;

(c) shifting the RF frequency as a function of the deformation of the object, comprising;

(i) passing selected frequencies from the wideband signal; and

(ii) creating at least one harmonic of the selected frequencies;

(d) transponding the shifted RF frequency signal to an analyzer; and

(e) in the analyzer, determining a strain in the object as a function of the shift in RF frequency;

wherein the steps are performed without providing power to the gauge; and

wherein the step of transmitting the shifted RF frequency includes transponding the selected frequencies and at least one harmonic as a wireless signal to an analyzer wherein the step of determining a strain comprises the steps of

(i) isolating the at least one harmonic from the transponded signal; and

(ii) estimating the amount of strain as a function of isolated harmonic.

2. The method of claim 1 wherein the object is a rotating turbine blade.

3. The method of claim 1 wherein the step of shifting the RF frequency uses a series RLC circuit and a diode frequency doubler.

4. The method of claim 1 wherein the step of estimating comprises:

(a) estimating the peak value of the harmonic;

(b) determining a shift in capacitance as a function of the estimated peak; and

(c) measuring the strain as a function in the shift in capacitance.

5. A system for determining the strain in a rotating object comprising:

a transceiver for transmitting and receiving a wireless wideband signal;

a signal processor that provides an estimate of strain as a function of a received wireless wideband signal;

a passive strain gauge affixed to a rotating object comprising;

a wideband antenna;

a series RLC circuit;

a diode frequency doubler.

6. The system of claim 5 wherein the passive strain gauge is a thin film construction type gauge.

7. The system of claim 5 wherein the passive strain gauge is approximately massless with respect to the mass of the rotating object to which it is affixed.

8. The system of claim 5 wherein the passive strain gauge changes resonant frequency proportional to the deformity of the rotating object to which it is affixed.

9. A method of detecting the amount of strain in a rotating object where a strain gauge has been affixed to the object comprising the steps of:

(a) transmitting a wireless wideband signal to the gauge;

(b) receiving the broadband signal at the gauge and performing the following steps;

(i) passing selected frequencies from the wideband signal;

(ii) creating at least one harmonic of the selected frequencies;

(iii) transponding the selected frequencies and at least one harmonic as a wireless signal to an analyzer;

(c) receiving the wireless transponded signals at the analyzer and performing the following steps;

(i) isolating the at least one harmonic from the transponded signal; and

(ii) estimating the amount of strain as a function of the isolated harmonic.

10. The method of claim 9 wherein the step of estimating comprises:

(a) estimating the peak value of the harmonic;

(b) determining a shift in capacitance as a function of the estimated peak; and

(c) measuring the strain as a function in the shift in capacitance.

11. The method of claim 9 wherein the transmitted wireless wideband signal is in the range of about 2 GHz to about 6 GHz.

12. The method of claim 9 wherein the step of passing selected frequencies uses an RLC circuit.

13. The method of claim 9 wherein the step of creating at least one harmonic uses a diode frequency doubler.

14. The method of claim 9 wherein the step of isolating uses a Savitzky-Golay filter.

15. The method of claim 10 wherein the step of estimating includes using at least one of Yule Walker equations, minimum mean square error and forward linear prediction.