Anisotropic electromagnetic response modelling of carbon fiber reinforced polymer cable for electromagnetic tomography

Electromagnetic tomography provides a promising non-destructive evaluation approach for carbon fiber reinforced polymer (CFRP) cables, but their anisotropic electrical properties make the electromagnetic response and defect detection mechanism difficult to interpret. This study investigates the anisotropic electromagnetic response of CFRP cables under non-planar coil excitation, focusing on eddy current diffusion, magnetic field attenuation, and effective penetration depth. An equivalent analytical model is established by incorporating an orthotropic conductivity tensor into the electromagnetic formulation to estimate the magnetic field distribution and penetration behaviour. Finite element models are developed and validated to analyse field propagation, eddy current diffusion, and response differences between eddy current testing and electromagnetic tomography. The analytical predictions show reasonable agreement with the numerical simulations, supporting the validity of the analytical model. Electrical anisotropy governs eddy current redistribution, whereas the skin effect dominates magnetic field penetration and attenuation. Compared with conventional eddy current testing, the multi-coil electromagnetic tomography configuration improves the effective penetration depth. Conductivity perturbations caused by defects are more clearly reflected in the real part of the induced voltage, which provides useful information for defect reconstruction. Furthermore, the relationship between effective penetration depth and coil resistance provides guidance for selecting the detection frequency in electromagnetic tomography inspection.