Microwave dual waveguide sensor system for the measurement of gap between concrete and metal surfaces

A microwave dual waveguide sensor system has been proposed and applied for the measurement of gap between concrete and metal surfaces. The system includes two rectangular waveguides embedded in a metal plate and opened in a concrete member to create a dual waveguide sensor arrangement, transceiver that generates, transmits and receives microwave signals using the dual sensor, and a measurement unit that measures reflection and transmission coefficients. The sensor system along with concrete specimen has been modeled and extensive simulations were conducted with CST Microwave Studio. It is shown that the proposed dual sensor system can measure relatively small gaps between concrete and metal surfaces at relatively low frequencies within X-band (8.2 GHz" 12.4 GHz). The sensor has been designed, built and tested with the system and concrete-metal specimens. Measurement and simulation results show that the proposed system can be used for detection and evaluation of the gap in composite concrete-metal structures such as concrete-filled steel tubes.