Suppression of Electromagnetic Edge Effect in Planar Electromagnetic Tomography

Electromagnetic tomography (EMT) is a non-destructive testing method based on boundary measurement value projection to reconstruct the distribution of electrical parameters. Planar EMT can meet the requirements of metal plane defect monitoring, but there is an electromagnetic edge effect at the edge of the metal plane. Magnetic field distortion and magnetic leakage cause the coil excitation-detection performance to change, destroying the consistency of the coil array and reducing the image reconstruction quality. To solve this problem, the characteristics of the shielding layer, which guides the magnetic field, are utilised to suppress the electromagnetic edge effect. First, the equivalent magnetic circuit model of planar EMT is introduced, and the relationship between the boundary measurement value, sensitivity matrix, and shielding layer is derived. Then, by combining simulation and experiment, the effects of ferrite and aluminum shielding layers on the edge effect, and the effects of shielding layers of different thicknesses and positions on planar EMT, are compared. The results demonstrate that aluminum, as a shielding layer, can effectively suppress the edge effect and improve image reconstruction accuracy.