FDFD: A 3D Finite-Difference Frequency-Domain Code for Electromagnetic Induction Tomography

A new 3D code for ElectroMagnetic Induction Tomography (EMIT) with intended applications to environmental imaging problems has been developed. The approach consists of calculating the fields within a volume using an implicit finite-difference frequency-domain (FDFD) formulation. The volume is terminated by an anisotropic perfectly matched layer (PML) region that simulates an infinite domain by absorbing outgoing waves. Extensive validation of this code has been done using analytical and semianalytical results from other codes and some of those results are presented in this paper. The new code is written in Fortran 90 and is designed to be easily parallelized, but this feature has yet to be tested. Finally, an adjoint method, developed for solving the inverse problem for conductivity imaging (for mapping underground plumes), uses this code as its forward field solver.