Accurate thickness measurement of multilayer composites using terahertz time-domain spectroscopy and an improved whale optimisation algorithm - Zhu, Di; Zhang, Yuqi; Cheng, Jiaqiang; Gong, Xiaoyuan; Qu, Qiuhong; Bai, Hua; Sun, Xiaodong; Zhang, Yizhu (Nondestructive testing and evaluation, 2025)