NON-CONTACT RF STRAIN SENSOR

• US 20070186677A1
• Filed: 02/14/2007
• Published: 08/16/2007
• Est. Priority Date: 02/14/2006
• Status: Abandoned Application

• Current Assignee: New Jersey Institute of Technology, U.S. Government
• Original Assignee: U.S. Government
• Inventors: Federici, John, Lim, Hee, Zunino, James
• Application Number:
  US11/674,835
• Publication Number:
  US 20070186677A1
• Time in Patent Office: Days
• US Class Current: 73/849
• CPC Class Codes: G01L 1/148 using semiconductive material, e.g. silicon
• CPC Class Codes: G01M 5/0041 by determining deflection or stress
• CPC Class Codes: G01M 5/0091 by using electromagnetic excitation or detection
• CPC Class Codes: G01N 2203/0629 using thin films, paintings

Abstract

A passive, non-contact radio frequency (RF) strain sensor changes resonant frequency as it is deformed. The sensor'"'"'s resonant frequency can be determined by monitoring the signals transmitted and/or reflected therefrom upon illumination of the sensor by a known RF signal source. The sensor can be implemented using thin film techniques on a flexible thin substrate that can be attached to the surface of a structural member of interest.

Claims

1. A method of monitoring a deflection of a structural member comprising:

transmitting a first radio frequency (RF) signal toward a closed circuit comprising an inductance and a capacitance coupled in series, at least one of the inductance and capacitance varying as a function of the deflection of the structural member;

receiving a second RF signal from the closed circuit;

determining a resonant frequency of the closed circuit based on the second RF signal; and

comparing the resonant frequency to a reference resonant frequency to provide an indication of the deflection of the structural member.

2. The method of claim 1, comprising:

determining the reference resonant frequency of the closed circuit when the closed circuit is in a reference stressed state.

3. The method of claim 1, comprising:

determining an amplitude of the second RF signal; and

comparing the amplitude of the second RF to a reference amplitude to provide a further indication of the deflection of the structural member.

4. A method of monitoring a corrosion condition of a structural member comprising the method of claim 1, wherein the deflection of the structural member is indicative of the corrosion condition of the structural member.

5. The method of claim 4, wherein the structural member is embedded in a vehicle.

6. A strain sensor comprising:

a flexible substrate; and

a circuit fabricated on the substrate, the circuit comprising an inductive element and a capacitive element coupled in series, at least one of an inductance and a capacitance of the circuit varying as a function of the deflection of the substrate.

7. The strain sensor of claim 6, wherein the inductive element includes a first plurality of conductive segments coupled in a spiral pattern and the capacitive element comprises a second plurality of conductive segments arranged in parallel to a third plurality of conductive segments.

8. The strain sensor of claim 6, wherein a first terminal of the first plurality of conductive segments is coupled to the second plurality of conductive segments and a second terminal of the first plurality of conductive segments is coupled to the third plurality of conductive segments.

9. The strain sensor of claim 6, wherein the second terminal of the first plurality of conductive segments is coupled to the third plurality of conductive segments via a wire.

10. The strain sensor of claim 7, wherein the first, second and third plurality of conductive segments include piezoresistive elements.

11. A system for monitoring a corrosion condition of a structural member comprising the strain sensor of claim 6, wherein the deflection of the structural member is indicative of the corrosion condition of the structural member.

12. The system of claim 11, wherein the structural member is embedded in a vehicle.

13. A strain monitoring system comprising a plurality of strain sensors in accordance with claim 6, wherein each strain sensor is individually readable.

14. The system of claim 13, wherein a first of the plurality of strain sensors has a first resonant frequency and a second of the plurality of strain sensors has a second resonant frequency.

15. The system of claim 14, comprising a reader device which determines the resonant frequencies of the first and second strain sensors.