Numerical analysis of the "ferris wheel" mice exposure system using an efficient cylindrical FDTD scheme

The objective of this study is to develop a numerical tool for characterizing the "ferris wheel" exposure system employed in a long-term study of RF exposure on mice. The "ferris wheel" is a radial cavity loaded with forty mice around its perimeter. In order to exploit the angular periodicity of the radial exposure system, we developed a Finite Difference in Time Domain (FDTD) code based on a cylindrical grid to analyze a single angular sector of the 40-mouse "ferris wheel". The singularity of the Maxwell equations in the cylindrical FDTD scheme was appropriately removed, and other suitable expedients were implemented to reduce simulation time and memory requirements. In order to estimate RF leakage, the actual openings in the radial cavity, needed to insert the mice, were considered as well. The FDTD scheme incorporates the perfectly matched layer (PML) unsplit formulation (anisotropic medium), as absorbing boundary condition. The code was validated with measurements, showing good agreement. A criterion for assessing the uniformity of the exposure is presented, together with results at 900 MHz and 1.8 GHz.