International Journal of Aerospace and Lightweight Structures

doi: 10.3850/S2010428615100096

Near Electrical Resonaance Signal Enhancement (NERSE) For Sub-Millimeter Detection In Aerospace Superalloys

Robert Hughes^1,2,3 and Steve Dixon^{1,2 1}Department of Physics, University of Warwick, Coventry, CV4 7AL. ²School of Engineering, University of Warwick, Coventry, CV4 7AL. ³NDE Lab, Rolls-Royce plc., Bristol, BS34 7QE.

ABSTRACT

The principles for developing a near electrical resonance signal enhancement (NERSE) technique for industrial applications for sub-millimeter defect detection on typical aerospace superalloys, Waspaloy and Titanium 6-4, were investigated. An absolute eddy-current (EC) probe was operated at frequencies close to its electrical resonance in two different modes, sweep and single frequency. A swept measurement provided a large amount of information on the properties of a given EDM notch but is a comparatively slow. Each individual frequency within the sweep suffers from high incoherent noise due to a lack of averaging. With the aim of installing a NERSE approach in an eddy-current array (ECA) technique, an averaged single NERSE frequency (3.6MHz) excitation was investigated. This approach further increased the signal enhancing effects of the NERSE phenomenon to 12-14 times the signal to noise ratio (SNR) of an equivalent measurement at 1MHz. This investigation paves the way for NERSE ECA techniques to improve the inherent limitations of ECA measurements of sub-millimeter defects.

Keywords: Eddy-Current, Resonance, NERSE, Electromagnetic, Coupling, NDT, Defect, detection.

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