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Investigation on novel embedded piezoelectric ultrasonic transducers for corrosion monitoring of reinforced concrete

The corrosion monitoring of reinforced concrete is important for the structural safety. A kind of embedded annular piezoelectric ultrasonic transducers suitable for corrosion monitoring of the reinforced concrete were proposed and fabricated, and the electrical impedance spectra and ultrasonic pitch-catch characteristic of the transducers in the steel rebar were discussed. The results show that after the annular piezoceramic disk was encapsulated, the resonance of the piezoelectric ceramic under effects of electric excitation was restricted due to the damping effect of the packaging layer. Comparing with the annular piezoelectric ceramic disk, the wall thickness extensional resonance frequency of the annular ultrasonic transduces decreases, however, the corresponding frequency bandwidth increases. The ultrasonic pitch-catch experimental results indicate that the annular full-electrode transducer has the largest wave duration time and the minimum head wave amplitude than others, but the annular serial transducer has the largest head wave amplitude and peak to peak value. When the excitation frequency of the signal is in the range of 100–160 kHz, the annular serial transducer has the best ability to receive the ultrasonic wave. A good distinguishability of the longitudinal and flexural wave can be obtained in the reception waveform when the distance between the emission and reception transducers is larger than 600 mm in a long round steel rebar.