Accurate thickness measurement method for thin layer in thick materials using terahertz technology

Aiming to address the challenge of insufficient resolution in detecting thin-layer thickness within thick materials using terahertz time-domain spectroscopy (TDS) technology, we propose two innovative time-domain fitting methods: the experimental reference signal-based method (TDF-ER), which provides a more accurate measurement, and the simulated reference signal-based method (TDF-SR), which is used when it is difficult to obtain an experimental reference signal. Through simulation analysis, it is demonstrated that the TDF-ER method enables precise measurement of surface coatings on metal substrates with a minimum detectable thickness of 4 μm and a thickness measurement deviation below 10%. Compared to the existing thickness identification methods, our method has better resolution ability for thin layer thickness measurements in thick materials. Experimental validation further demonstrates that the TDF-SR method successfully identifies layer thicknesses of 260 μm and 610 μm in 20 and 40 mm-thick polymer bonded explosive (PBX) samples, respectively. Furthermore, the TDF-ER method showcases excellent capability in accurately identifying these layer thicknesses in 50 mm-thick PBX samples. Both simulation and experimental results indicate that the proposed TDF-ER and TDF-SR methods significantly enhance the resolution of thin-layer thickness measurements within thick materials, offering practical solutions for applications involving layered material characterization.