Time-Frequency Based Thermal Imaging: An Effective Tool for Quantitative Analysis

Recent achievements in TWDAR (thermal wave detection and ranging) technology has made it possible to utilize a range of thermal imaging techniques for analyzing the characteristics of materials used in various industries. Moreover, the distinctive features of nonstationary thermal imaging have piqued attention of researchers in non-destructive evaluation (NDE). For a detailed defect visualization, it is essential to employ a dependable processing technique that accurately extracts the relevant time–frequency components from the chirped thermal response. In this study, a nonstationary thermal wave imaging technique is utilized by using quadratic frequency modulation (QFM) in conjunction with a cutting-edge technique of fractional Fourier transform (FrFT), to assess material quality. An experimentation has been carried out on carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP) samples with defects of different sizes at varying depths, to evaluate their characteristics. Experimental results have validated the efficiency of the proposed FrFT processing approach through rigorous qualitative and quantitative analysis, which has involved measurements of some merit figures, such as signal-to-noise ratio (SNR), full width at half maxima (FWHM), and probability of detection (PoD). From the results, it is evident that the proposed method provides a distinct and precise visualization of defects promising to be a useful technique in identifying and retrieving information of internal defects in materials.