“…Ultrasonic stress waves, either passive acoustic emission signals or active guided waves, propagating in a structure can be employed to interpret the structural status, especially to detect small structural damage, such as debonding, lamination, crack, corrosion, etc. Over the past few decades, the corresponding methods and techniques have also been proven effective and promising in a variety of metal, composite, concrete and other materials and structures [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 ]. Ultrasonic stress waves, generated by either transducers or a rapid release of energy within a stressed material, are often at a fairly high frequency, from several tens of kHz to approximately several MHz.…”