Review of advances in microwave and millimetre-wave NDT&E: principles and applications.

Microwave and millimetre-wave non-destructive testing and evaluation (NDT&E) has a long history dating back to the late 1950s (Bahr 1982 ; Zoughi 2000 ; Feinstein 1967 ; Ash 1973 In ; Auld 1981 , 149-154; Case 2017 ). However, sustained activities in this field date back to the early 1980s (Zoughi 1995 , 71-74; Zoughi 2018 , 1051-1057; Kharkovsky 2007 , 26-38). Owing to various limitations associated with using microwaves and millimetre waves for NDT&E, these techniques did not see much utility in the early days.