3-D B-field Modelling Method of Magnetic Viscosity Effect in Time-Domain Electromagnetic Surveys

A direct three-dimensional (3-D) modeling of B-field in TDEM is proposed in the paper. We first introduce the forward modeling method of static magnetic field for the calculation of initial value of B-field. Then, we achieve the iterative calculation of B-field of magnetic media during the transient electromagnetic (TEM) stage by substituting the Cole–Cole susceptibility model into the B-field diffusion equation of double-curl induced magnetization intensity. The validity of this method is verified using several analytical solutions. A 3-D multi-magnetic anomaly model is established, and the characteristics of B-field responses are observed in three dimensions. This method can realize the 3-D modeling of the B-field of the MV effect in TDEM, which is helpful to accurately understand the characteristics of the B-field attenuation curves and can provide a basis for the direct inversion interpretation of B-field data.