Measurement of permeability for ferrous metallic plates using a novel lift-off compensation technique on phase signature

Lift-off of sensor affects the prediction of electromagnetic properties for both ferrous and non-ferrous steel plates. In this paper, we developed a strategy to address this issue for ferrous plates. With increased lift-off, the phase of the measured impedance for steel plates reduces. Meanwhile, the magnitude of the impedance signal decreases. Based on these facts, a phase compensation algorithm is developed which corrects the phase change due to lift-off considering the magnitude of the impedance signal. Further, a new magnetic permeability prediction technique is presented, which has been validated by analytical and measured results. With this new technique, the error in permeability prediction is less than 2% within the range of lift-offs tested

Analysis of electrical resonance distortion for inductive sensing applications

Resonating inductive sensors are increasingly popular for numerous measurement techniques, not least in non-destructive testing (NDT), due to the increased sensitivity obtained at frequencies approaching electrical resonance. The highly unstable nature of resonance limits the practical application of such methods while no comprehensive understanding exists of the resonance distorting behaviour in relation to typical measurements and environmental factors. In this paper, a study into the frequency spectrum behaviour of electrical resonance is carried out exploring the effect of key factors. These factors, known to distort the electrical resonance of inductive sensors, include proximity to (or lift-off from) a material surface, and the presence of discontinuities in the material surface. Critical features of resonance are used as metrics to evaluate the behaviour of resonance with lift-off and defects. Experimental results are compared to results from a 2D finite element analysis (FEA) model that geometrically mimics the inductive sensor used in the experiments, and to results predicted by an equivalent circuit transformer model. The findings conclusively define the physical phenomenon behind measurement techniques such as near electrical resonance signal enhancement (NERSE), and show that lift-off and defect resonance distortions are unique, measurable and can be equated to exclusive variations in the induced variables in the equivalence circuit model. The resulting understanding found from this investigation is critical to the future development and understanding of a complete model of electrical resonance behaviour, integral for the design of novel sensors, techniques and inversion models

Second Conference on NDE for Aerospace Requirements

Nondestructive evaluation and inspection procedures must constantly improve rapidly in order to keep pace with corresponding advances being made in aerospace material and systems. In response to this need, the 1989 Conference was organized to provide a forum for discussion between the materials scientists, systems designers, and NDE engineers who produce current and future aerospace systems. It is anticipated that problems in current systems can be resolved more quickly and that new materials and structures can be designed and manufactured in such a way as to be more easily inspected and to perform reliably over the life cycle of the system