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Continuous wave terahertz (CW THz) imaging, is a variant of terahertz imaging that has been gaining scientific
and technological relevance in multiple areas. In this paper the fundamental phenomena of CW THz were
studied and a mathematical model was developed that successfully describes the Fabry–Perot interference for
such a system, opening the possibility for measurement of thicknesses and surface curvatures. The capabilities
of the system were tested using different types of defects, such as voids, water infiltrations and thin metallic
wires. The interactions between different materials, features and the radiation beam were numerically studied
using finite element method and the results agreed with the experiments. By comparing the results with other
Non-Destructive Testing methods, it was found that CW THz imaging is particularly interesting to image water
infiltrations and composite materials that incorporate conductive wires.

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This paper presents the development and the results of a customized eddy current (EC) non-destructive testing (NDT) system for highly demanding online inspection conditions. Several planar eddy current array probes were designed, numerically simulated and experimentally compared for the inspection of low conductivity unidirectional carbon fibre reinforced polymer (CFRP) ropes. The inspections were performed using a dedicated scanner device at 4 m/s with 3 mm probe lift-off where defects under 1 mm were detected with an excellent SNR. Different defect morphologies and sizes, such as broken fibres and lateral cuts, were successful detected and compared to conventional probes.

Online monitoring of carbon fiber reinforced plastic (CFRP) ropes requires non-destructive testing (NDT) methods capable of detecting multiple damage types at high inspection speeds. Three NDT methods are evaluated on artificial and realistic imperfections in order to assess their suitability for online monitoring of CFRP ropes. To support testing, the microstructure and electrical conductivity of a carbon fiber rope is characterized. The compared methods are thermography via thermoelastic stress analysis, ultrasonic testing with commercial phased array transducers, and eddy current testing, supported by tailor-made probes. While thermoelastic stress analysis and ultrasonics proved to be accurate methods for detecting damage size and the shape of defects, they were found to be unsuitable for high-speed inspection of a CFRP rope. Instead, contactless inspection using eddy currents is a promising solution for real-time online monitoring of CFRP ropes at high inspection speeds.

Online monitoring of carbon fibre reinforced polymer (CFRP) components requires a Non-Destructive Testing (NDT) method capable of contactless sensing of damage, while enabling high inspection speeds needed for monitoring large components. Eddy current testing (ECT) of CFRP components has great potential for two reasons. First, ECT probes are capable of operating without contact, although minimizing the lift-off is preferred. Second, impedance analysers with high sample rates make high-speed inspection possible. This research assesses the damage detection capabilities of eddy current probes on CFRP samples with artificial and realistic damage. To support the aptitude of the ECT method for these needs, the CFRP material is characterized and numerical simulations are performed in order to develop optimized and tailored ECT probes for the detection of defects with different morphologies, namely fibre breakage and delaminations, and to take into consideration the highly anisotropic electrical bulk resistivity of the CFRP material. Different ECT probes were designed, produced and experimentally validated. The experiments were performed at a high inspection speed (4 m/s) and the high sensitivity of the probes was demonstrated.

The use of non-destructive evaluation (NDE) techniques for assessing microstructural changes in processed materials is of particular importance as it can be used to assess, qualitatively, the integrity of any material/structure. Among the several NDE techniques available, electrical conductivity measurements using eddy currents attract great attention owing to its simplicity and reliability. In this work, the electrical conductivity profiles of friction stir processed Ti6Al4V, Cu, Pb, S355 steel and gas tungsten arc welded AISI 304 stainless steel were determined through eddy currents and four-point probe. In parallel, hardness measurements were also performed. The profiles matched well with the optical macrographs of the materials: while entering in the processed region a variation in both profiles was always observed. One particular advantage of electrical conductivity profiles over hardness was evident: it provides a better resolution of the microstructural alterations in the processed materials. Moreover, when thermomechanical processing induces microstructural changes that modify the magnetic properties of a material, eddy currents testing can be used to qualitatively determine the phase fraction in a given region of the material. A qualitative relation between electrical conductivity measurements and hardness is observed.

Novel eddy current probes were developed to detect sub-millimetre defects with any orientation on the inner surface of pipes. Five different probes were designed, produced and experimentally validated. These probes include arrays of planar trapezoidal coils in a flexible substrate used alone or together with different winded drive coils. Numerical simulations with Finite Element Method were used to predict the probe response to defects with any orientation. Experimental results in austenitic steel jackets used in ITER revealed that the new probes have an improved reliability compared to conventional toroidal bobbin probes, allowing a higher sensitivity to circumferential defects.

This paper describes improvements to the Nondestructive Testing (NDT) technique recently proposed, based on the use of bacterial cell suspensions to identify micro- and nano-surface defects. New bacterial strains were used with magnetic fields to improve bacteria mobility. Different materials and defect morphologies were tested, including nanoindentation defects, micro-powder injection moulding components and micro-laser welding. Nanoindentations with 0.6 µm depth and 5.3 µm side length were successfully detected. Bacterial cells allow identifying different topographic attributes of the surfaces, such as roughness. Cracks of about 0.5 µm wide and 10 µm depth in a reference test block Type 1 were successfully detected.

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