Improved terahertz nondestructive detection of debonds locating in layered structures based on wavelet transform

Debonds locating is the difficulty of terahertz (THz) nondestructive detection within a multi-layered structure sample, since the air layer of debond part is too thin to detect. To solve this problem, we propose a wavelet transform method to process the THz detection 3D data, and reconstruct the three-dimensional image of the testing sample by wavelet coefficients. Through these we can clearly identify the debond area and accurately locate it. In order to distinguish the small interface peaks and noise, Lipschitz index was used as the basis, which is a reliable tool. Base on this method, we analysis two samples with debond layer respectively on the upper and lower interface of 2 mm-thick insolation felt, the 3D reconstruction images provides excellent agreement with the actual samples.