The physical concept and the mathematical formalism of the wave permittivity are introduced and analyzed through the Maxwell stress tensor theory. The concept of the wave permittivity may be proved extremely useful in order to characterize propagation parameters, in terms of stored energy associated with delayed wave formation phenomena such as partial standing waves, which in turn give rise to rapid precursors observable in the time domain. Such phenomena has been observed in air, in the radiating zone, or indispersive media such as waveguides. Engineering applications related to the concept of the wave permittivity are outlined.
George C. Giakos, George C. Giakos,
"Engineering and physical concepts of the wave permittivity", Proc. SPIE 2275, Advanced Microwave and Millimeter-Wave Detectors, (14 September 1994); doi: 10.1117/12.186724; https://doi.org/10.1117/12.186724