What is the role of terahertz imaging in security screening and nondestructive testing?

Terahertz imaging exploits the ability of terahertz radiation to penetrate many common materials that are opaque to visible light (clothing, paper, plastic, ceramics, dry wood) while being reflected by metals and absorbed by water. For security screening, terahertz imaging systems produce body images through clothing to detect concealed weapons, explosives, and contraband without exposing subjects to ionizing radiation. For nondestructive testing (NDT), terahertz imaging inspects composite materials, pharmaceutical tablet coatings, paint layers, semiconductor packages, and paper products by measuring reflected or transmitted terahertz pulses that reveal internal layer structure, defects, voids, and delaminations. Time-domain spectroscopy (THz-TDS) provides both spatial and depth information by analyzing the time-of-flight of reflected terahertz pulses, enabling three-dimensional tomographic imaging of layered structures.