Lossy Medium
Again, similar as for absolute permittivity, relative permittivity for lossy materials can be formulated as:
in terms of a "dielectric conductivity" σ (units S/m, siemens per meter), which "sums over all the dissipative effects of the material; it may represent an actual conductivity caused by migrating charge carriers and it may also refer to an energy loss associated with the dispersion of ε' " (, p. 8). Expanding the angular frequency ω = 2πc/λ and the electric constant ε0 = 1/(µ0c2), it reduces to:
where λ is the wavelength, c is the speed of light in vacuum and κ = µ0c/2π ≈ 60.0 S−1 is a newly-introduced constant (units reciprocal of siemens, such that σλκ = εr" remains unitless).
Read more about this topic: Relative Permittivity
Famous quotes containing the word medium:
“I devoutly believe it is the writer who has matured the film medium more than anyone else in Hollywood. Even when he knew nothing about his work, he brought at least knowledge of life and a more grown-up mind, a maturer feeling about the human being.”
—Dudley Nichols (1895–1960)