High resolution in non-destructive testing: A review

Since the beginning of applications non-destructive testing/evaluation (NDT/NDE) techniques, efforts have been made consistently to improve their detection sensitivity and resolution. In present paper, factors governing lateral resolution in three major NDT viz., ultrasonic testing (UT), x-ray radiographic (XRT), eddy current (ECT) are presented. Furthermore, a review recent advances these techniques reach theoretically achievable limit or even surpassing same using alternate approaches is also discussed. For example, UT limited half wavelength by Rayleigh limit; however, subwavelength resolutions achieved through near field methods capturing evanescent field. On other hand, XRT primarily source/focal spot size, which many orders magnitude larger than wavelength. Over years, reduction focal from macro-focus micro-focus now nano-focus has led improvement few nanometers, course, combination with suitable magnification required due detectors pixel size (a μm 10 s μm). Similarly, innovations electromagnetic/magnetic sensors significantly improved ECT. Atomic force microscopy, metamaterials, artificial neural network-based employed for obtaining high-resolution NDE images. At end, authors' perspective toward possible directions