Abstract
This paper presents a rotating focused field eddy-current (EC) sensing technique, which leverages the advantages of magnetic field focusing and rotating magnetic field, for arbitrary orientation defects detection. The sensor consists of four identical excitation coils orthogonally arranged in an upside-down pyramid configuration and a giant magneto-resistive (GMR) detection element. The four coils are connected to form two figure-8-shaped focusing sub-probes, which are fed by two identical harmonic currents with 90 degrees phase difference. A finite element model-based study of arbitrary orientation defects detection was performed to understand the probe operational characteristics and optimize its design parameters. Probe prototyping and experimental validation were also carried out on a carbon steel plate specimen with four prefabricated surface-breaking defects. In-situ spot inspection with the probe rotating above the defect and a manual line-scan inspection were both conducted. Results showed that the probe has the capability of detecting defects with any orientations while maintaining the same sensitivity and the defect depth can be quantitatively evaluated by using the signal amplitude. Compared with the existing rotating field probes, the presented probe does not require additional excitation adjustment or data fusion. Meanwhile, due to its focusing effect, it can generate a strong rotating magnetic field at the defect location with a weak background noise, thus yielding superior signal-to-noise ratio.
Highlights
Eddy current testing (ECT) has been widely applied in the detection of surface and subsurface defects in conductive materials
As the ECT probe’s capability and accuracy for defect detection correlate with the noise level of eddy current signals, one main objective in the ECT probe design is to achieve an output with high signal-to-noise ratio (SNR) [8,9,10]
3D finite element analysis (FEA) is performed by using ANSYS Workbench software to study the effectiveness of the presented probe for detecting arbitrary orientation defects
Summary
Eddy current testing (ECT) has been widely applied in the detection of surface and subsurface defects in conductive materials. As the ECT probe’s capability and accuracy for defect detection correlate with the noise level of eddy current signals, one main objective in the ECT probe design is to achieve an output with high signal-to-noise ratio (SNR) [8,9,10] This can be achieved by improving the probe coil configurations and excitation modes, examples of which have been extensively reported in previous studies [2,10,11,12,13]. They have the same underlying physics for the sensing mechanism but the latter is superior to the former because it avoids the inevitable noise caused by mechanically rotating and is suitable for a C-scan or even a line scan This method employs two orthogonally placed coils driven by two current excitations with 90 degrees phase difference to result in a uniform and rotating eddy current (EC) field in the specimen. The experimental signal had superior SNR and its amplitude can be used to evaluate the depth of arbitrarily oriented defect, demonstrating the effectiveness of the proposed probe
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