| When the medium surrounding a source wave changes in time, interesting transformations happen: changes occur not only in amplitude and polarization, but also in frequency. Such transformations are studied in detail in this thesis.; This research was performed in a one-dimensional cavity that fundamentally consists of two rectangular perfect electric conductor (PEC) plates, separated by a small distance. Initially the cavity medium is free space and has an elliptically polarized standing wave present. The medium in the cavity is then converted to a lossy magnetoplasma with an arbitrary space and time profile. Essentially this amounts to altering the medium in the cavity from a simple to a dynamic, dispersive (frequency dependent), anisotropic (direction dependent) and inhomogeneous (location dependent) medium. The case of longitudinal modes is considered.; It is shown that the elliptically polarized source wave transforms into three circularly polarized waves, as a consequence of the medium change. It is further shown that each of the transformed waves has a unique frequency, amplitude and phase (with respect to the source wave). However, if the strength of the external magnetic field is reduced to zero, the transformed wave consists of just a single upshifted mode and a zero-frequency but space-varying magnetic field, also known as a wiggler magnetic field. The strength and direction of this wiggler magnetic field is shown to be controllable by appropriately selecting the system parameters.; The study in this dissertation has been done by two methods: theory and numerical analysis using the Finite-Difference Time-Domain (FDTD) method. Theoretical expressions for the electric field and magnetic field are obtained for the transformed waves for sudden-switching of the cavity medium. A FDTD model is also derived and applied to compute the field values. The results obtained by the two methods are found to be in agreement, thus each method validates the other. |
