[2A1] Resonant eddy current testing: principles, applications and limitations

R Hughes
University of Bristol, UK 

Eddy-current testing (ECT) techniques traditionally avoid electrical resonance, due to its perceived instability and oversensitivity to environmental changes. This ensures that measurements are stable and are only affected by changes in the mutual electromagnetic interactions between the coil and the material under test. However, resonating inductive sensors have become increasingly popular for a range of measurement techniques, not least in nondestructive testing, where, due to their increased sensitivity at frequencies around electrical resonance, improvements in defect detectability can be gained. These approaches have become more common in dealing with low, and anisotropic, conductivity materials such as aerospace superalloys and carbon fibre composites, where increased sensitivity to small variations in the materials is desired. However, a detailed understanding of how resonance behaves due to changes in environment is still lacking, thereby limiting the implementation of resonant-based measurements to niche applications. In this paper, the principles behind resonance sensing are summarised and research towards characterising, understanding and modelling the behaviour of resonant ECT sensors is presented, with reference to applications in defect detection and carbon fibre composite characterisation. Finally, the potential opportunities and limitations of these techniques are discussed.