Passive Wireless Antenna Sensor for Strain, Temperature, Crack and Fatigue Measurement

• US 20110040498A1
• Filed: 02/15/2009
• Published: 02/17/2011
• Est. Priority Date: 02/15/2008
• Status: Active Grant

• Current Assignee: Board of Regents of the University of Texas System (University of Texas System)
• Original Assignee: Board of Regents of the University of Texas System (University of Texas System)
• Inventors: Huang, Haiying, Carter, Ronald L., Chiao, Jung-Chih, Tata, Uday Shankar
• Granted Patent: US 8,868,355 B2
• Time in Patent Office: Days
• US Class Current: 702/34
• CPC Class Codes: G01B 15/06 for measuring the deformation in a solid
• CPC Class Codes: G01B 7/16 for measuring the deformation in a solid, e.g. by resistance strain gauge
• CPC Class Codes: H01Q 1/2225 used in active tags, i.e. provided with its own power source or in passive tags, i.e. deriving power from RF signal
• CPC Class Codes: H01Q 21/065 Patch antenna array

Abstract

An apparatus and method is provided for monitoring a condition of a structure using a passive wireless antenna sensor having a known resonant frequency when mounted on the structure. A series of radio frequency signals are transmitted with sweeping frequencies around the known resonant frequency to the passive wireless antenna sensor. The passive wireless antenna sensor includes a dielectric substrate disposed between an antenna pattern and a ground plane such that a change in the condition of the structure will cause a change in one or more characteristics of the passive wireless sensor. A signal is received from the passive wireless antenna sensor and a resonant frequency of the passive wireless antenna sensor is determined based on the received signal. The determined resonant frequency is then compared to the known resonant frequency, whereby a change in the resonant frequency indicates a change in the condition of the structure.

Claims

1. A method of monitoring a condition of a structure using a passive wireless antenna sensor having a known resonant frequency when mounted on the structure, comprising the steps of:

transmitting a series of radio frequency (RF) signals with sweeping frequencies around the known resonant frequency to the passive wireless antenna sensor, wherein the passive wireless antenna sensor comprises a dielectric substrate disposed between an antenna pattern and a ground plane such that a change in the condition of the structure will cause a change in one or more characteristics of the passive wireless antenna sensor;

receiving a signal from the passive wireless antenna sensor;

determining a resonant frequency of the passive wireless antenna sensor based on the received signal; and

using a digital signal processor, determining the condition of the structure by comparing the determined resonant frequency of the passive wireless antenna sensor to the known resonant frequency of the passive wireless antenna sensor, whereby a change in the resonant frequency of the passive wireless antenna sensor indicates a change in the condition of the structure.

2. The method as recited in claim 1, wherein the step of determining the resonant frequency of the passive wireless antenna sensor based on the received signal comprises the steps of:

converting the received signal to a time-domain signal using an Inverse Fast Fourier Transformation;

normalizing the time-domain signal;

creating a spectrogram for the normalized time-domain signal using a Short Time Fast Fourier Transformation;

determining a time at which a scattering term for the passive wireless antenna sensor occurs using the spectrogram;

time gating the normalized time-domain signal using a Hanning window and the determined time at which the scattering term occurred; and

determining the resonant frequency of the passive wireless sensor from the time gated Hanning windowed signal using a Fast Fourier Transformation.

3. The method of claim 1, further comprising the steps of:

mounting the passive wireless antenna sensor on the structure;

saving the determined resonant frequency in data storage device;

saving the change in the resonant frequency in the data storage device;

retrieving the known resonant frequency from the data storage device; and

notifying a user of the change in the condition of the structure.

4. The method of claim 1, wherein the known resonant frequency comprises:

an original resonant frequency of the passive wireless antenna sensor when the passive wireless antenna sensor was mounted on the structure;

or

one or more previously determined resonant frequencies of the passive wireless antenna sensor.

5. The method of claim 1, wherein:

the one or more characteristics of the passive wireless antenna sensor comprise;

(a) a dimension of the passive wireless antenna sensor, (b) a dielectric property of the passive wireless antenna sensor, (c) a surface roughness of the antenna pattern, or (d) a crack in the ground plane;

the received signal comprises a direct signal or a backscattered signal;

the change in the resonant frequency comprises a frequency shift, a return loss, or a combination thereof; and

the change in the condition of the structure comprises a strain on the structure, a temperature change of the structure, a detected crack in the structure, a change in a known crack in the structure, a fatigue of the structure, or a combination thereof.

6. The method of claim 1, wherein the ground plane comprises a metallic or semi-metallic surface of the structure on which the passive wireless antenna sensor is mounted.

7. The method of claim 1, wherein:

the passive wireless antenna sensor comprises a loop antenna, a patch antenna or a microstrip antenna;

the transmitting and receiving steps are performed by an antenna reader connected to a RF source and a frequency detector; and

the structure comprises a metallic material, a non-metallic material, a composite material, a concrete or a living tissue.

8. The method of claim 7, wherein:

the antenna reader comprises a horn antenna, a patch antenna, a loop antenna or a lens antenna;

the antenna reader further comprises a transceiver connected to a circulator, or a transmitter and a receiver;

the RF source comprises a sweeping frequency synthesizer, as scanning RF source, a broadband RF source, or a vector spectrum analyzer;

or

the frequency detector comprises;

(a) a bandpass filter connected to a low noise amplifier connected to a RF power detector, (b) a bandpass filter connected to a low noise amplifier connected to a mixer connected to a low-pass filter connected to an amplifier connected to a frequency demodulator, (c) a low noise amplifier connected to a RF power detector;

or (d) a vector network analyzer.

9. The method of claim 1, wherein the passive wireless antenna sensor comprises an array or network of individually addressable passive wireless antenna sensors and frequency division is used to multiplex the signals to the passive wireless antenna sensors.

10. The method of claim 1, wherein two or more passive wireless antenna sensors are used and each passive wireless antenna sensor has a different known resonant frequency.

11. The method of claim 1, wherein the passive wireless antenna sensor is tunable.

12. The method of claim 1, wherein the passive wireless antenna further comprises:

a crack fabricated in the ground plane; and

a mechanical actuator attached to the ground plane to open or close the fabricated crack.

25. The method of claim 3, wherein notifying a user of the change in the condition of the structure comprises notifying the user only when the change in the resonant frequency exceeds a threshold value.

13. An apparatus for monitoring a condition of a structure, comprising:

a receiver for receiving a signal from a wireless passive wireless antenna sensor mounted on the structure, wherein the passive wireless antenna sensor has a known resonant frequency when mounted on the structure and comprises a dielectric substrate disposed between an antenna pattern and a ground plane such that a change in the condition of the structure will cause a change in one or more characteristics of the passive wireless sensor;

a transmitter that transmits a series of radio frequency (RF) signals with sweeping frequencies around the known resonant frequency to the passive wireless antenna sensor; and

a digital signal processor that, using the received signal from the passive wireless antenna sensor, determines a resonant frequency of the passive wireless antenna sensor based on the received signal, and determines the condition of the structure by comparing the determined resonant frequency of the passive wireless antenna sensor to the known resonant frequency of the passive wireless antenna sensor, whereby a change in the resonant frequency of the passive wireless antenna sensor indicates a change in the condition of the structure.

14. The apparatus as recited in claim 13, wherein the monitoring device determines the resonant frequency of the passive wireless antenna sensor based on the received signal by:

converting the received signal to a time-domain signal using an Inverse Fast Fourier Transformation;

normalizing the time-domain signal;

creating a spectrogram for the normalized time-domain signal using a Short Time Fast Fourier Transformation;

determining a time at which a scattering term for the passive wireless antenna sensor occurs using the spectrogram;

time gating the normalized time-domain signal using a Hanning window and the determined time at which the scattering term occurred; and

determining the resonant frequency of the passive wireless sensor from the time gated Hanning windowed signal using a Fast Fourier Transformation.

15. The apparatus of claim 13, wherein the monitoring device is further configured to save the determined resonant frequency in data storage device, save the change in the resonant frequency in the data storage device, retrieve the known resonant frequency from the data storage device, notify a user of the change in the condition of the structure.

16. The apparatus of claim 13 wherein the known resonant frequency comprises:

an original resonant frequency of the passive wireless antenna sensor when the passive wireless antenna sensor was mounted on the structure;

or

one or more previously determined resonant frequencies of the passive wireless antenna sensor.

17. The apparatus of claim 13, wherein:

the one or more characteristics of the passive wireless antenna sensor comprise;

(a) a dimension of the passive wireless antenna sensor, (b) a dielectric property of the passive wireless antenna sensor, (c) a surface roughness of the antenna pattern, or (d) a crack in the ground plane;

the received signal comprises a direct signal or a backscattered signal;

the change in the resonant frequency comprises a frequency shift, a return loss, or a combination thereof; and

the change in the condition of the structure comprises a strain on the structure, a temperature change of the structure, a detected crack in the structure, a change in a known crack in the structure, a fatigue of the structure, or a combination thereof.

18. The apparatus of claim 13, wherein the ground plane comprises a metallic or semi-metallic surface of the structure on which the passive wireless antenna sensor is mounted.

19. The apparatus of claim 13, wherein:

the passive wireless antenna sensor comprises a loop antenna, a patch antenna or a microstrip antenna;

the transmitting and receiving steps are performed by an antenna reader connected to a RF source and a frequency detector; and

the structure comprises a metallic material, a non-metallic material, a composite material, a concrete or a living tissue.

20. The apparatus of claim 19, wherein:

the antenna reader comprises a horn antenna, a patch antenna, a loop antenna or a lens antenna;

the antenna reader comprises a transceiver connected to a circulator, or a transmitter and a receiver;

the RF source comprises a sweeping frequency synthesizer, as scanning RF source, a broadband RF source, or a vector spectrum analyzer;

or

the frequency detector comprises;

(a) a bandpass filter connected to a low noise amplifier connected to a RF power detector, (b) a bandpass filter connected to a low noise amplifier connected to a mixer connected to a low-pass filter connected to an amplifier connected to a frequency demodulator, (c) a low noise amplifier connected to a RF power detector;

or (d) a vector network analyzer.

21. The apparatus of claim 13, wherein the passive wireless antenna sensor comprises an array or network of individually addressable passive wireless antenna sensors and frequency division is used to multiplex the signals to the passive wireless antenna sensors.

22. The apparatus of claim 13, wherein two or more passive wireless antenna sensors are used and each passive wireless antenna sensor has a different known resonant frequency.

23. The apparatus of claim 13, wherein the passive wireless antenna sensor is tunable.

24. The apparatus of claim 13, wherein the passive wireless antenna further comprises:

a crack fabricated in the ground plane; and

a mechanical actuator attached to the ground plane to open or close the fabricated crack.