Research Projects

Eddy Current Testing (ECT) is a process of detecting defects in industrial infrastructure such as pipelines, made of electrically conducting materials (Cu, Al, etc.,) including magnetic materials (eg. Stainless Steel). The technique uses an ac magnetic field, which induces eddy currents and magnetization currents (in magnetic materials) in a material being examined. The magnetic field produced by these currents is measured by scanning the surface of the specimen. This data essentially contains information about various defects in the material. An inhomogeneity in the scanned field data points to the presence of a defect in the test specimen. Pulsed field ECT (PECT), and the Transient Eddy Current Oscillations (TECO) technique are time/frequency domain variants of ECT. Commonly, ECT probes are designed to measure one of the components of the magnetic field. Taking into account the magnetic boundary conditions, we argued that the dominant field component is normal to the sample surface in strongly magnetic materials and parallel to the sample surface in non-magnetic specimens. Our strategy in this proposal is to measure the smaller component (other than the dominant component) so that the defects can be observed with high contrast. We, therefore, proposed to design a probe to measure the three field components to enable testing of a range of materials from purely conducting to strongly magnetic materials. One of the objectives of the ECT is to detect defects buried under the surface of the specimens. An excitation field of frequency ω can penetrate and probe material to a depth equal to the skin depth δ=√(2/μσω), where μ and σ are the magnetic permeability and the electrical conductivity of the material. Our contention in this proposal is that this strategy fails in materials, which are even moderately ferromagnetic due to the onset of significant non-linearities at low applied fields. We have presented as a proof of concept, our preliminary experiments, where the onset of non-linearity can be identified using the TECO technique. In the non-linear regime, we propose that the hysteretic response of the material can be measured by the third harmonic signal. Despite being smaller than the fundamental harmonic, the third harmonic signals contain much less noise. We believe that the third harmonic technique could be a much more sensitive tool to identify the defects.