Research on Ultrasonic Damage Imaging Based on Total Focus Method

Ultrasonic phased array Total Focus Method (TFM) is used to process the signal with the data obtained by the Full Matrix Capture(FMC) mode, which has the advantages of high imaging accuracy and high signal-to-noise ratio(SNR). However, the frequency dispersion of the Lamb wave largelyaffected the imaging accuracy of the TFM. Therefore, the wavelet analysis time domain filtering in multi-band method was proposed to decompose an ultrasonic wide frequency band signal into several narrow band ones for suppressing dispersion effect, furthermore, the damage signal is extracted without reference signal and thus the damage is imaged in frequency domain, which improves the imaging accuracy. In this paper also analyzes the whole process of ultrasonic excitation, the interaction between the incident wavefield and damage as well as the sensor receiving signal, and establishes a quantitative imaging method of inverse scattering model with the reflectivity of the damaged surface as the index,further improve the imaging accuracy. Moreover, a numerical model and an experimental platform for prefabricated artificial damage of metal aluminum plate were established to compare the imaging effects of TFM in frequency domain and TFM with inverse scattering model in frequency domain. The results show that new algorithm is more accurate in locating damage and has stronger characterization ability.