Terahertz Time-Domain Spectroscopy for Multilayer Thickness Characterization: A Whale Optimization Algorithm-Enhanced Inversion Methodology

Terahertz time-domain spectroscopy (THz-TDS) technology has received wide attention and rapid development in recent decades, and has been applied as an effective detection tool in various technical fields. Aiming at the problems of low algorithmic efficiency and easy to fall into local optimisation of THz-TDS technology in the thickness inversion of multilayered layered materials, a high-precision layer thickness measurement method based on the improved Whale Optimization Algorithm (WOA) is proposed. The efficiency of model parameter inversion is optimised by establishing a joint time-frequency domain objective function and combining a dynamic weight adjustment strategy with a physical constraint mechanism. The experimental results show that the absolute error of single-layer thickness measurement is ≤3.8 μm (relative error ≤6.5%), which is a significant improvement in accuracy over the traditional algorithm. This method provides an efficient solution for real-time non-destructive testing of composite coatings.