NONDESTRUCTIVE TESTING AND MATERIAL CHARACTERIZATION BY TERAHERTZ PULSED IMAGING AND TIME-DOMAIN SPECTROSCOPY
MetadataShow full item record
Terahertz (THz) imaging and time-domain spectroscopy are employed for nondestructive evaluation (NDE) and material characterization for scientific studies and applications. For the thickness and uniformity measurement of optically thin layers on steel, three signal-processing techniques, namely, frequency-wavelet domain deconvolution (FWDD), sparse deconvolution (SD), and autoregressive spectral extrapolation (AR), are employed to beat the axial resolution limit to enable thickness measurements of optically thin layers. The success of resolving mill-scale films on steel with thickness down to ∼ 5 µm, and identifying individual layers in multilayer paint coatings, validates the applicability of THz technology to the steel industry. In addition, THz techniques are also utilized for stratigraphic characterization of materials with complex layer structure. A dispersion model is incorporated into deconvolution algorithms for enhancing the performance of processing time-domain THz pulses during propagation in materials. The stratigraphy of a complex sample incorporating both optically thick and thin layers is reconstructed successfully after deconvolution, even in the absence of prior structural information of the material investigated. We also use THz techniques for material characterization using. As a noncontact, nonionizing, and nondestructive approach, THz technology can not only investigate THz birefringence and surface homogeneity of nanoporous Al2O3 films grown through a two-step electrochemical anodization process, quality control of commercial injection-molded thermoplastic components, but also characterize the optical and dielectric properties of off-the-shelf thermoplastics over a broad frequency range for high-frequency microelectronics packaging. These findings demonstrate the promising laboratory- and field-based applications of THz science and technology.