ABSTRACT
We saw in the previous chapter that one of the strengths of FDTD is that results for a wide frequency band can be obtained by applying Fourier transform techniques to transient FDTD results. The level of development of FDTD currently places a limitation on this in that the constitutive parameters must be specified as constants, i.e., μ, ε, and σ must be described by a single number. While this is true for free space, good conductors, and ideal dielectrics, it is only approximately true for most real materials. For some materials over a narrow band of frequencies the approximation is excellent, while for other materials over a wider band of frequencies it is not. For some materials, such as plasmas and ferrites, the permittivity may be zero or negative, so that the FDTD equations we have presented thus far cannot be used at all at certain frequencies as some of the terms become singular.
