3-D B-Field Modeling Method of Magnetic Viscosity Effect in Time-Domain Electromagnetic Surveys

With the development of the superconductive quantum interference device-transient electromagnetic (SQUID-TEM) system, stable B-field data with a higher signal-to-noise ratio and a longer time range can be obtained, which provides the possibility for high-precision and large-depth observation. However, due to the magnetic field properties of the magnetic viscosity (MV) effect and remanent magnetization intensity, using the traditional time-domain electromagnetic (TDEM) forward modeling method for simulation and analysis of B-field will introduce errors and cannot accurately depict the diffusion and attenuation characteristics of B-field. Therefore, a direct 3-D modeling of B-field in TDEM is proposed in the article. 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 double-curl B-field diffusion equation of magnetization intensity. The validity of this method is verified using several analytical solutions. 3-D multimagnetic anomaly models are 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.