Introduction to RF Radiation Safety / 8 / 8.10 / 8.10.4

8.10.4 Finite-Element Method

The finite-element method (FEM) divides the modeled region into interconnected elements whose size and shape can be adapted to the geometry. Local mesh refinement allows small or irregular features to be represented without applying the finest resolution throughout the entire model.

FEM is useful for antennas, waveguides, resonant structures, medical and industrial equipment, and biological tissues with complex boundaries. It can be formulated in the frequency or time domain. As with FDTD, the mesh, material properties, source excitation, boundary conditions, solver settings, convergence, and uncertainty must be appropriate to the required result.

8.10.5 Method Of Moments

The method of moments (MoM) commonly represents currents or charges on conducting wires and surfaces and calculates the fields they produce. It is particularly useful for antennas, antenna arrays, towers, vehicles, and scattering from conducting structures, and can determine both near-field distributions and far-field radiation patterns.

MoM can be efficient for open radiating structures because only the relevant conductors or surfaces need to be discretized. Problems containing large volumes of complex, inhomogeneous tissue or material may favor a volume-based method or a hybrid approach that couples MoM with another numerical technique.

8.10.6 Ray-Based And Hybrid Methods

At microwave and millimeter-wave frequencies, buildings and other large objects may be many wavelengths in size. Ray-based methods approximate propagation along paths involving direct transmission, reflection, diffraction, and scattering. They can efficiently estimate field distribution over buildings, urban areas, tunnels, transport facilities, and other electrically large environments.

Ray-based methods do not normally replace a full-wave model close to an antenna, within a strongly reactive field, or when internal dosimetric quantities are required. Hybrid assessments can combine a full-wave model of the antenna or nearby body with a ray-based or other large-scale propagation model, provided the interfaces and assumptions are validated.