Aiming at the problem of rebar corrosion monitoring in reinforced concrete structures

a surface acoustic wave（ SAW） capacitive sensor for monitoring rebar corrosion is proposed. This sensor consists of a SAW delay line and a plate capacitor. The two electrodes of the plate capacitor are arranged around the reinforcement and are connected to the reflection gating of the SAW delay line. Since corrosion of reinforcement causes a change in the impedance between the reflection grating and the plate capacitor

rebar corrosion sensing can be achieved by detecting changes in amplitude and phase of echo signal. Coupling of modes（ COM） theory is used to analyze the performance of the SAW delay line device with a center frequency of 184 MHz and determine structural parameters of the SAW delay line device. SAW delay line device is fabricated using the lift-off process

and a sensor monitoring system is set up. Amplitude and phase changes of echo signal is tested by network analyzer. Compare and analyze test results and simulation results. It illustrates the accuracy of COM theory and validates the feasibility of SAW capacitive sensor. The echo amplitude sensitivity of the sensor is 0. 73 d B/mm with respect to the rebar corrosion thickness

and the nonlinearity error is 0. 35 %. The sensitivity of the echo phase is 6. 24°/mm with respect to the rebar corrosion thickness

and the nonlinearity error is 1. 04%.