Jun Yao

Graduation Semester and Year

2016

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Electrical Engineering

Department

Electrical Engineering

First Advisor

Saibun Tjuatja

Second Advisor

Haiying Huang

Abstract

Microstrip antenna-sensor has received considerable interests in recent years due to its simple configuration, compact size, and multi-modality sensitivity. Due to its simple and conformal planar configuration, antenna-sensor can be easily attached on the structure surface for Structure Health Monitoring (SHM). As a promising sensor, the resonant frequency of the antenna-sensor is sensitive to different structure properties: such as planar stress, temperature, pressure and moisture. As a passive antenna, antenna-sensor’s resonant frequency can be wirelessly interrogated at a middle range distance without using an on-board battery. However, a major challenge of antenna-sensor’s wireless interrogation is to isolate the antenna backscattering from the background structure backscattering to avoid “self-jamming” problem. The goal of this thesis is to develop a high-speed wireless interrogation mechanism for antenna-sensor to realize real- time SHM. Furthermore, since the proposed antenna sensor-node is designed without using any electronics this dynamic remote sensing system can be used in high-temperature harsh environment. In our researches, High-speed wireless interrogation of antenna-sensor for vibratory strain sensing is firstly achieved in room temperature using an amplitude modulator and a Frequency Modulated Continue Wave (FMCW) interrogator. A rectangular patch antenna was bonded on aluminum beam to perform as a stress sensor as well as a wireless transceiver. By switching the load of the antenna-sensor between an open and a matching load using a square wave, the antenna backscattering signal is an amplitude modulated signal whose envelop is a square wave. The resonant frequency of the antenna-sensor can be determined at the frequency which has the largest amplitude in the envelop curve. Since the FMCW can sweep the interrogation frequency at a rate up to 300 Hz, real-time interrogation of antenna-sensor can be easily realized. Far-field static antenna-senor interrogation for high temperature sensing was also developed. In this study, a patch antenna was used as temperature sensing unit and a Reactive Impedance Surface (RIS) based Ultra-wide Band (UWB) antenna was added as a passive wireless transceiver (Tx/Rx) for the antenna-sensor. A mircrostrip delay line was implemented in the sensor node circuitry to connect the Tx/Rx antenna and patch antenna-sensor. Since the new sensor node contains no electronics it can be applied in harsh environment which has a temperature up to 300 °C. Due to the time delay caused by the microstrip delay line in the sensor node, the antenna backscattering can be separated from the background structure backscattering in time domain using time-gating technology. The gated time domain sensing signal was converted into frequency domain using Fast Fourier Transform (FFT). The frequency spectrum of the gated signal indicates the reflection coefficient of the antenna-sensor and the resonant frequency of the antenna-sensor can be determined at the frequency which has the lowest reflection coefficient. Furthermore, dynamic wireless interrogation of antenna-sensor for temperature sensing in harsh environment was realized by using a FMCW radar interrogator and non-electronics sensor node. Since this approach performs the time gating in the frequency domain instead of time domain substantial improvement on the interrogation speed can be achieved without adding any electronics in the sensor node. A down-conversion RF mixer was implemented in the interrogator circuit to demodulate the reflected FMCW interrogation signal and get the backscattering from both structure and sensor. Due to the difference of the beat frequencies of those two signals, the sensor backscattering can be easily separated from the structure backscattering using a digital band pass filter. In this study, a high interrogation speed of 50 Hz was achieved and the accuracy of the FMCW interrogator was validated using a temperature testing. Compact FMCW interrogator was also developed for an antenna-based foot pressure sensing system. The interrogator consists of three parts: a FMCW synthesizer, a RF circulator and a power detector. The power consumption of this interrogator is only 160 mw and the interrogation rate is up to 55 Hz. Static pressure tests were performed to validate the accuracy of the proposed FMCW interrogator and the experimental results were compared with those from network analyzer measurements. The normalized discrepancies of two measurements are within 0.002%.

Keywords

Antenna-sensor, Wireless interrogation, Structural health monitoring, Strain sensing, Temperature sensing, Pressure sensing

Disciplines

Electrical and Computer Engineering | Engineering

Comments

Degree granted by The University of Texas at Arlington

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