Explicit finite-difference 3D transient electromagnetic modeling with a whole-space volume current source

The explicit finite difference 3D transient electromagnetic modeling method is typically constrained by stringent spatial and temporal step size requirements, leading to low computational efficiency. Previous studies reveal that using the electromagnetic field excited by magnetic dipoles in a homogeneous whole-space model as the initial field can relax these constraints and significantly improve computational efficiency. To extend this approach to wire source simulation, we propose a 3D modeling method using a whole-space volume current source initial field: the wire source is represented equivalently as a whole-space volume current source in Maxwell’s equations. The initial field is calculated iteratively based on a homogeneous whole-space model, followed by iterative computation of the secondary field based on the true model. Simulation results of a homogeneous half-space model with a wire source, a homogeneous whole-space model with a loop source, a homogeneous half-space model with a loop source, and a half-space model with a conductive brick demonstrate that: (1) Relative errors between this method and analytical solutions or digital filter solutions are below 4%, indicating high accuracy. (2) The method allows a grid step size ratio of up to 2 between adjacent grids, effectively reducing the number of model grids and iterations, thereby achieving high computational efficiency. (3) The method can simulate wire sources, loop sources, half-space, and whole-space models, showing good adaptability. Examples of aerial, mountainous terrain, and tunnel exploration further validate its broad applicability. The related open-source software WFTEM3D2.0 has been released on GitHub and Gitee.