Ken, Sun

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    Design and characterization of passive wireless strain sensor
    (2006) Ken, Sun; Jia, Yi; College of Engineering; Serrano, David; Just Agosto, Frederick A.; Toledo Quiñones, Manuel; Department of Mechanical Engineering; Ierkic, Henrick M.
    In order to predict and avoid disasters due to the structure failure, reliable strain information is necessary to be monitored in real time. Existing strain sensing technologies offer outstanding performance in terms of the resolution and time response. However, these technologies require either physical connection of signal communication, battery power supply or expensive equipment for acquiring strain information. These limitations make existing strain sensing technologies unsuitable for structures such as aircraft and vehicle. A novel passive wireless strain sensor has been developed in this research to overcome the limitations of existing strain sensing technologies. The sensor employs a planar inductor which is series connected to an interdigital capacitor to eliminate the wire connection for power supply and data transmission. The sensor is activated by electromagnetic wave and the resonant frequency of the sensor is interrogated remotely with a single loop antenna by monitoring the frequency response of the voltage across it. The sensor was modeled and the strain effect on resonant frequency of the sensor was investigated. The prototype sensor and the rudiment of a hand-held reader circuit were designed and fabricated. By carrying out an efficient and systematic multi-objective optimization method, the sensor geometric size can be minimized, and strain sensitivity, quality factor and reading distance can be maximized. Experiments for measuring the dielectric permittivity of piezoelectric polymer based on micro-strip transmission line theory were carried out in order to study its strain dependent dielectric permittivity and possibility of strain sensing enhancement. A very friendly graphic interface for real-time data display was programmed in MATLAB. The results of sensor calibration on a cantilever beam with III position-independent surface strain showed a great linearity and sensitivity. The innovative wireless strain sensing technology presented has demonstrated a great potential to extend its applications in structural health monitoring, damage detection, condition-based maintenance, failure prevention and non-destructive evaluation.