Eddy current testing is widely used to inspect safety-critical components, where it is important to find surface-breaking defects and fatigue cracks at their earliest stage of growth. This requires finding sub-millimetre length defects, which usually means the electromagnetic skin depth of the eddy current must be &lt;1 mm. To achieve skin depths of &lt;1 mm on low conductivity metals such as Ti and TiAl, the frequency of the excitation current needs to be greater than several MHz. Eddy current sensor frequencies of up to 40 MHz, providing good signal to noise ratios have been achieved by situating circuitry directly behind the coils. However, even when locating the electronics close to the coils, increasing frequency will always lead to an increase in electrical noise as stray capacitances become more significant. As an alternative, lower frequency (&lt;1 MHz) parametric approaches have been investigated, where magnitude and phase of the eddy current signal are independently measured.&nbsp;The work described in this presentation is effectively a combination of these two approaches, operating at frequencies above 1 MHz and locating the sensor electronics behind the coils, whilst simultaneously measuring the magnitude and phase of the eddy current signal. We have found that our approach can reliably detect small simulated defects of less than 500 microns in length formed by laser micromachining and that the phase of the signal on the receiving coil may be of particular interest, where it can provide measurements less susceptible to variations caused by changes in lift-off. We present a combination of 2D surface scans and lift-off measurements with simulated defects produced by laser micromachining&nbsp;on Titanium, Titanium Aluminide (Ti-45Al-2Mn-2Nb-1B) and 316L stainless steel to support these findings, along with some finite element modelling.

Improved Eddy Current Testing Sensitivity Using Phase Information

Paper Proceedings: https://asmedigitalcollection.asme.org/qnde/QNDE2021/volume/85529

ASME 2021 48th Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE2021)

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.