Terahertz time domain spectroscopy and imaging application for analysis of sandwich panel with embedded fibre Bragg grating sensors and piezoelectric transducers

Abstract Sandwich structures are commonly used in many objects, e.g. deck components in bridge deck panel. Safety requirements result in development of structural health monitoring (SHM) systems that are implemented into sandwich structures. Such systems based on different types of sensors that can be embedded into the structure. The paper presents THz time domain spectroscopy and imaging application for internal structure analyses of a sandwich panel with glass fibre reinforced polymer skin and polyurethane foam fulfilment. In the adhesive bond between skin and fulfilment, an array of fibre Bragg grating (FBG) sensors and piezoelectric (PZT) transducers was embedded. The analyses were focused on detection and localisation of embedded sensors and transducers and their influence on THz wave propagation. The analysis contains differences in THz wave parameters, like refractive index and absorption coefficient and image analyses. Methods that allow to detect and localise of transducers and fibre optics with FBG sensors as well as damage (debonding between GFRP skin and foam fulfilment in sandwich structure) were proposed.