A full finite difference time domain methodology is developed for electromagnetic wave propagation in a plasma. The finite difference grid is consistent with central difference approximation of the curl, divergence and gradient operators that appear in the joint equations of Euler and Maxwell, and the coupling effects between the fluid velocity and the electric field. To accomplish the time advancement, the central difference approximation is invoked for the time derivatives and leapfrog concepts are employed. The resulting difference equations converge to the exact equations, provided that the developed stability requirement is satisfied. Finally, numerical results are provided and compared with the inverse fast Fourier transform results of closed‐form, frequency domain solutions for the half space problem; the agreement between solutions is shown to be excellent.
Nanoparticle synthesis (~10-50 nm) of HCl-doped polyaniline elucidates the impact of limiting solvent (water) and oxidizing agent (ammonium peroxydisulfate) on morphology (XRD and TEM), chemical structure (FTIR), conductivity (two-point DC) and electromagnetic shielding effectiveness (SE) in microwave frequencies (i.e., X-band S-parameter measurements). Detailed comparison of these properties with respect to three distinct polymerization environments indicate that a solvent-free or limited solvent polymerization accomplished through a wet grinding solid-phase reaction produces superior conductivity (27 S/cm) with intermediate crystallinity (66%) for the highest EM shielding-an order of magnitude improvement over conventional polymerization with respect to EM power transmission reduction for all loadings per shielding area (0.04 to 0.17 g/cm(2)). By contrast, the classic oxidation of aniline in a well-dispersed aqueous reaction phase with an abundance of available oxidant in free solution yielded low conductivity (3.3 S/cm), crystallinity (54%), and SE, whereas similar solvent-rich reactions with limiting oxidizer produced similar conductivity (2.9 S/cm) and significantly lower SE with the highest crystallinity (72%). This work is the first to demonstrate that limiting solvent and oxidizer enhances electromagnetic interactions for shielding microwaves in polyaniline nanopowders. This appears connected to having the highest overall extent of oxidation achieved in the wet solid-phase reaction.
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