A comparative study of infrared, terahertz and air-coupled ultrasonic NDT for cultural heritage

Abstract

This work is based on a comparative study of three Non-destructive Testing NDT techniques for the inspection of an old book that was bound in the XIXth century. Infrared thermography (IRT), terahertz time-domain spectroscopy (THz-TDS) and air-coupled ultrasonic C-scan (ACU) were used to retrieve both damages and defects in the book cover. Then, the results were compared and analysed; in addition, specific defects were determined and explained via a comparison. Advanced image processing techniques were applied in order to highlight the shapes of subsurface features.