Uniform Field Eddy Current Probe: Experiments and Inversion for Realistic Flaws

Design and Characterization of Uniform Field Eddy Current Probes

“…8 are shown as solid lines; the symbols represent theoretical predictions based on Auld's uniform field theory. The probe was calibrated with a cylindrical recess, as described in more detail in [3]. We found excellent agreement between theory and experiment for the three larger flaws (A-C).…”

“…Measurement methods for flaws are described and illustrated with results on a series of semi-elliptical EDM slots in Ti-6A~-4V. A companion paper describes in detail extensive experiments on both real and simulated surface flaws, the calibration procedures that were used, and inversion results [3].…”

A Self-Calibrating Eddy-Current Instrument

“…The relationship is given by Auld's reciprocity formula: (2) where 6. Z flAW is the flaw-induced change in probe impedance, I is the excitation current, n is a unit vector normal to the surface of integration, and E and H are the incident electric and magnetic fields, where primed quantities refer to the fields in the presence of the fla~ and unprimed quantities refer to fields without a flaw present.…”

“…Third, quantitative flaw sizing can only be accomplished over a limited range with such calibration methodology, and the accuracy of sizing flaws with this method is brought into question by the aforementioned inequality of slots and cracks. Even if laboratory-produced cracks were to be used routinely for calibration (a prohibitively expensive option), quantitative sizing could be compromised by the occurrence of crack closure effects [2].…”

Calibration and Characterization of Eddy Current Probes by Photoinductive Field Mapping

“…Even if laboratory-produced cracks were to be used for routine calibration (a prohibitively expensive option), the accuracy of calibration or quantitative sizing could be compromised by the occurrence of crack c10sure effects. 4 Another approach to the calibration problem is to map the magnetic field of the probe to be calibrated. Previous eddy-current probe field mapping techniques have been based on the use ofHall probes,5 SQUID probes and small pickup cOils,6 and smaH defects ofknown geometry.7 However, these approaches suffer from several drawbacks: poor noise immunity, large sensor size, introduction of significant perturbations to the probe field, or insensitivity to the tangential component of the H field.…”