Eddy Current Non-Destructive Testing Techniques

Eddy current non-destructive testing (ECT) exploits electromagnetic induction to detect subsurface defects in conductive materials without requiring disassembly or contact. An alternating current in a probe coil generates a time‐varying magnetic field that induces circulating currents, or eddy currents, in the test piece. Disruptions caused by cracks, corrosion or material inhomogeneities alter the amplitude and phase of these currents, which are sensed by the same or adjacent coils. Over the past decade, techniques have evolved from single-frequency excitation to multi-frequency, pulsed and swept-frequency methods, improving penetration depth and defect characterisation. Advances in probe design—including array configurations, flexible printed coils and integration with magneto-resistive sensors—have enhanced sensitivity and conformity to complex geometries. Concurrent progress in signal processing, modelling and machine-learning algorithms has enabled quantitative sizing of flaws and real-time imaging. ECT now plays a pivotal role in aerospace, energy, transport and additive-manufacturing industries, supporting safety, reliability and cost-effective maintenance worldwide.

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Recent work has demonstrated the capability of eddy current probes to inspect additively manufactured metals. A study on stainless-steel and titanium parts fabricated by laser powder-bed fusion showed that both absolute and reflection eddy current probes can detect subsurface notches as small as 0.07 mm, with coating layers employed to mitigate surface roughness effects and enhance signal stability. The investigation revealed distinct probe suitability: absolute coils for crack detection and reflection coils for blind-hole characterisation, suggesting integrated approaches for in-process monitoring.

Another development utilises wireless power transfer principles to drive a flexible printed coil array for curved surfaces. Dual‐resonance responses of a single excitation coil and multiple receiving coils were exploited to extract parameters related to defect geometry, lift-off and material properties. Feature fusion via deep-learning enabled three-dimensional reconstruction of a dent on a pipe, highlighting the potential for quantitative mapping on complex structures without wired connections.

Foundational reviews of pulsed eddy current (PEC) techniques have consolidated understanding of transient eddy‐current behaviour and its spectral richness. Analytical and numerical models now guide probe optimisation for wall‐thickness assessment and corrosion monitoring in sectors ranging from aerospace to water utilities. Emerging challenges include the real-time inversion of transient signals and the integration of PEC with robotics for automated scanning of large assets.

Eddy Current Non-Destructive Testing Techniques publication trend

The graph below shows the total number of articles in eddy current non-destructive testing techniques across all publications each year (not limited to Nature Index journals).

Technical terms

Eddy current: Circulating electric currents induced in a conductor by a time-varying magnetic field, used to infer material defects.

Lift-off effect: Variation in signal amplitude caused by changes in distance between probe and surface, affecting sensitivity and calibration.

Pulsed eddy current (PEC): A transient excitation method using current pulses to generate broad spectral components, enhancing penetration and multi-layer inspection.

Flexible printed coil array: A conformable sensor composed of etched excitation and reception coils on a flexible substrate, designed for complex geometries.

Wireless power transfer (WPT): Transfer of excitation energy to the probe coil without physical wires, enabling remote or rotating inspections on challenging surfaces.

References

1. Pulsed Eddy Current Non-destructive Testing and Evaluation: A Review. Chinese Journal of Mechanical Engineering (2017).
2. Giant Magnetoresistance Sensors: A Review on Structures and Non-Destructive Eddy Current Testing Applications. Sensors (2016).
3. Wireless power transfer-based eddy current non-destructive testing using a flexible printed coil array. Philosophical Transactions of the Royal Society A Mathematical Physical and Engineering Sciences (2020).
4. Non-Destructive Testing Using Eddy Current Sensors for Defect Detection in Additively Manufactured Titanium and Stainless-Steel Parts. Sensors (2022).