An expanding-grid algorithm for the finite-difference time-domain method [EM deposition in human body]

Recognizing that EM deposition in the human body at higher frequencies is primarily superficial (in the eyes, the frontal lobe of the brain, gonadal area, etc.), the authors have modified the finite-difference-time-domain (FD-TD) algorithm to use a logarithmically expanding grid rather than a uniform grid. The expanding-grid algorithm allows cell-to-cell expansion factors that can differ along the three axes. Expansion factors α of the order of 1.03 to 10.8 have been found to give internal fields that are in excellent agreement with those obtained analytically for 2-D homogeneous and layered lossy cylinders and for 3-D homogeneous spheres. In air outside the body, the increasing cell sizes are obviously acceptable and are still a small fraction of the free-space wavelength (<λ₀/10). In the interior of the body, the increasing cell sizes are also acceptable because there is little or no energy deposition in these regions, particularly at high frequencies