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Smart Structures and Systems
  Volume 16, Number 4, October 2015, pages 683-699

Design, analyses, and evaluation of a spiral TDR sensor with high spatial resolution
Quan Gao, Guangxi Wu and Xiong Yu

    Time Domain Reflectometry (TDR) has been extensively applied for various laboratory and field studies. Numerous different TDR probes are currently available for measuring soil moisture content and detecting interfaces (i.e., due to landslides or structural failure). This paper describes the development of an innovative spiral-shaped TDR probe that features much higher sensitivity and resolution in detecting interfaces than existing ones. Finite element method (FEM) simulations were conducted to assist the optimization of sensor design. The influence of factors such as wire interval spacing and wire diameter on the sensitivity of the spiral TDR probe were analyzed. A spiral TDR probe was fabricated based on the results of computer-assisted design. A laboratory experimental program was implemented to evaluate its performance. The results show that the spiral TDR sensor featured excellent performance in accurately detecting thin water level variations with high resolution, to the thickness as small as 0.06 cm. Compared with conventional straight TDR probe, the spiral TDR probe has 8 times the resolution in detecting the water level changes. It also achieved 3 times the sensitivity of straight TDR probe.
Key Words
    time domain reflectometry; TDR; spiral TDR probe; sensor; interface detection; computer-aid design
Quan Gao and Xiong Yu: Department of Civil Engineering, Case Western Reserve University, Cleveland, OH, USA
Guangxi Wu: Department of Electrical Engineering and Computer Science, Case Western Reserve University, Cleveland, OH, USA

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