High Frequency Electromagnetic Analysis using Hybrid MOM/FEM Method

MoM, an integral equation technique, is well-suited for modeling complex coil structures while in contrast, FEM is very well suited for modeling inhomogeneous dielectric bodies. The tetrahedral elements used in the volume discretisation for the FEM allow for accurate geometrical representation of volumes with curved surfaces, and the formulation furthermore allows for the variation in the material properties from tetrahedral element to tetrahedral element. Thus when these two methods are coupled together, the result is an extremely capable full-wave electromagnetic modeling technique. The hybrid MoM/FEM method that is used in this work is available using commercial software FEKO (www.feko.co.za). To investigate the capability of the hybrid MoM/FEM method and verify its accuracy in calculating the EMFs in biological samples, it is compared with FDTD [3] (in-house software) solution and hybrid DGF/MOM solution. Two simulation examples are demonstrated in this work. Firstly, a square surface coil with dimension of 120×120mm placed 40mm away from a heterogeneous 4 layer concentric spherical phantom that approximately represent a human head [6] and secondly, a shielded 16 rung high-pass birdcage coil also loaded with the spherical phantom is modeled. The operating frequency for both examples is set at 300MHz (7T) and the dielectric properties and the size of the spherical phantom used in the three different modeling techniques is the same. (a) (b) (c)