“…At the same time, non-destructive testing techniques, such as acoustic emission technology [ 19 , 20 ], ultrasonic testing technology [ 21 ], fiber optics [ 22 ] and X-ray, have been proposed for civil structures [ 23 , 24 , 25 , 26 , 27 , 28 ]. In recent years, piezoceramic materials have been successfully applied to structural damage monitoring or stress monitoring [ 29 , 30 , 31 , 32 , 33 , 34 ], including the smart aggregate enabled active sensing method [ 35 , 36 , 37 , 38 , 39 ], the piezoelectric impedance method [ 40 , 41 , 42 , 43 , 44 ] and the other methods [ 45 , 46 , 47 , 48 , 49 ]. Du et al [ 50 ] investigated the pipeline corrosion pit detection using the time reversal technique with a piezoceramic transducer as a time reversal mirror.…”