MultiCoil Eddy Current Sensor For Nondestructive Testing of Carbon Fiber-Reinforced Structures

Depth-resolved characterization of carbon fiber reinforced polymer (CFRP) laminates remains challenging due to signal superposition from multiple layers in conventional eddy current testing. This letter presents a novel multi-coil sensor architecture that enables simultaneous measurements at different penetration depths. The sensor comprises one transmitter coil and four receiver coils. One concentric coil with the transmitter arranged around the receiver for shallow layer sensitivity, and three additional receivers arranged concentrically around each other but with an offset to the primary pair for enhanced depth discrimination. By exploiting the distinct electromagnetic coupling characteristics of each receiver configuration and combining this spatial diversity with frequency-multiplexed excitation, the sensor provides complementary information about layer-specific fiber orientations and defects. Experimental validation on symmetric multilayer CFRP laminates with deliberately introduced anomalies demonstrates the sensor's capability to distinguish features in individual layers that were previously indistinguishable with single-coil approaches.