Electromagnetic wave interactions in a time varying medium: Appropriate and different models for a building-up and collapsing magnetoplasma medium.

摘要

The interaction of an electromagnetic wave with a time varying medium is governed by the property of conservation of the wavenumber. This property can be utilized to demonstrate a number of interesting phenomena and potential devices such as a frequency transformer. The time variation in the relative permittivity of the medium is easily produced in a magnetoplasma medium by altering the ionization level. The change of the ionization level can be produced by the dynamic control of the source of ionization. The switching-on action of the source produces a build-up plasma, whereas a switching-off action produces a decaying plasma. Simple mathematical models for the two cases, however, are different. In the case of building-up plasma, the model has to ensure the continuity of the current density. In the case of decaying plasma, the average drift velocity of the surviving electrons has to be continuous. Using these two appropriate models, the effect of the time variation of the plasma frequency as well as the background magnetic field of the magnetoplasma medium is studied. The Finite Difference Time Domain (FDTD) method implemented in MATLABRTM was used extensively to investigate a variety of interesting propagation properties in an unbounded plasma medium, in plasma slabs and within a one-dimensional cavity.