Читать книгу Introduction To Modern Planar Transmission Lines - Anand K. Verma - Страница 152

The relative permittivity (ε_r) and the permeability (μ_r) are not necessarily uniform throughout the volume of a medium. These parameters could also be position‐dependent. The variation in ε_r and μ_r could be in discrete steps, or they could be continuous functions of the position. Likewise, the conductivity of a medium can also be a function of position. If the parameters ε_r, μ_r, and σ are uniform throughout the medium, the medium is called homogeneous; otherwise, it is a nonhomogeneous medium or an inhomogeneous medium. A multilayer dielectric medium, forming a parallel capacitor, as shown in Fig. (4.3), is a nonhomogeneous medium, where the relative permittivity ε_r(x) is a function of position x in discrete steps. The conductivity of a doped Si substrate is a function of the depth of penetration of the charged carrier, forming a continuously variable nonhomogeneous medium.