8.10.2 Full-Wave Numerical Methods
Full-wave numerical methods solve Maxwell’s equations over a representation of the source, surrounding materials, and region of interest. They can determine electric and magnetic fields, currents, power flow, and, when a suitable human or phantom model is included, internal electric fields, specific absorption rate, and absorbed power density.
These methods are particularly useful for reactive and radiating near fields, nonuniform fields, large or complex antenna systems, close-body sources, conductive structures, and assessments against basic restrictions. The choice of method depends on the electrical size and geometry of the problem, material properties, frequency range, required output quantity, available input data, and computational resources.
8.10.3 Finite-Difference Time-Domain Method
The finite-difference time-domain (FDTD) method divides the modeled region into a three-dimensional grid and advances the electric and magnetic fields through small time steps. It is well suited to broadband problems and to interactions involving complex, inhomogeneous volumes, including anatomical human models.
FDTD is widely used to determine specific absorption rate and other dosimetric quantities for hand-held, body-worn, vehicle-mounted, and other nearby transmitters. The cell size must resolve the wavelength, source geometry, tissue boundaries, and regions in which local maxima are sought. The time step, absorbing boundaries, material properties, source representation, and prescribed spatial and temporal averaging can all affect the result.
Grid refinement and convergence checks are therefore essential. The simulation should demonstrate that further reasonable refinement does not materially change the assessed quantity and should use the averaging procedure specified by the applicable exposure or assessment standard.