Novel application of wavelet synchrosqueezed transform (WSST) in laser-vibrometer measurements for condition assessment of cementitious materials

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Early damage detection is of interest in the non-destructive testing of civil infrastructure. Traditional wave velocity-based methods are not sufficient as they use only one data point of information, neglecting the frequency content of ultrasonic signals. This paper demonstrates the advantages of applying the wavelet synchrosqueezed transform (WSST) to include the wave attenuation approach for condition assessment of cementitious materials.The application of the WSST is presented in three steps. First, synthetic models are studied to demonstrate the capabilities and limitations of the WSST technique, focusing on the ultrasonic frequency range. Next, the WSST is used to extract the main vibration modes to characterize ultrasonic transducers using a state-of-the-art laser vibrometer. Finally, a new WSST-based attenuation analysis technique is used for the evaluation of localized damage in a cemented sand specimen.Our results show that the WSST technique can be used to detect damage using ultrasonic measurements as long as the main frequency components are well separated. The characterization of ultrasonic transducers using WSST gives a better understanding of the frequency content of transmitted signals, which are generated not only by the resonance of piezoelectric crystal but also by the resonance of the surface-wearing plate of the transducer itself. The application sections of the paper show that the proposed approach can be successfully used for early damage detection in the case of localized damage. The WSST-based technique can improve the sensitivity of attenuation analysis in the detection of localized damage up-to 36%.