Underwater FDTD simulation at low frequencies

Modern anti-ship mines can be detonated by the electromagnetic signature of a surface ship [1]. For this reason, it is desirable to have simulation methods to study the propagation of extremely low frequency (ELF) electromagnetic waves under water. The finite-difference time-domain (FDTD) method [2-5] is one of the most widely used methods in electromagnetic simulation. Unfortunately, the discrete Fourier transform method used to quantify the results of the time-domain simulation is not practical at ELF. Furthermore, the Bessel/Legendre expansion method used to verify the FDTD results is also not valid at low frequencies. These two major issues are addressed in this paper. Results comparing the FDTD and an analytic method confirm the accuracy of FDTD at low frequencies.