Method and system for passive wireless strain gauge

• US 20090188324A1
• Filed: 10/24/2008
• Published: 07/30/2009
• 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: Gregory, Otto, Conkle, John, Birnbaum, Thomas, Shaw, Jeffrey C.
• Granted Patent: US 7,849,752 B2
• Time in Patent Office: Days
• 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;

(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.

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 shifting comprises the steps of

(i) passing selected frequencies from the wideband signal;

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

5. The method of claim 4 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.

6. The method of claim 5 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 the isolated harmonic.

7. The method of claim 6 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.

8. 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;

9. The system of claim 8 wherein the passive strain gauge is a thin film construction type gauge.

10. The system of claim 8 wherein the passive strain gauge is approximately massless with respect to the mass of the rotating object to which it is affixed.

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

12. A method of detecting the amount of strain in a rotating object where a strain gauge has bee 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.

13. The method of claim 12 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.

14. The method of claim 12 wherein the transmitted wireless wideband signal is in the range of about 2 GHz to about 6 GHz.

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

16. The method of claim 12 wherein the step of creating at least one harmonic uses a diode frequency doubler.

17. The method of claim 12 wherein the step of isolating uses a Savitzky-Golay filter.

18. The method of claim 13 wherein the step of estimating includes using at least one of Yule Walker equations, minimum mean square error and forward linear prediction.