Spatial Variation Of Permittivity Research Articles

Design and analysis of gradient index metamaterial-based cloak with wide bandwidth and physically realizable material parameters

A cloak based on gradient index metamaterial (GIM) is proposed. Here, the GIM is used, for conversion of propagating waves into surface waves and vice versa, to get the cloaking effect. The cloak is made of metamaterial consisting of four supercells with each supercell possessing the linear spatial variation of permittivity and permeability. The spatial variation of material parameters in supercells allows the conversion of propagating waves into surface waves and vice versa, hence results in reduction of electromagnetic signature of the object. To facilitate the practical implementation of the cloak, continuous spatial variation of permittivity and/or permeability, in each supercell, is discretized into seven segments and it is shown that there is not much deviation in cloaking performance of discretized cloak as compared to its continuous counterpart. The crucial advantage, of the proposed cloaks, is that the material parameters are isotropic and in physically realizable range. Furthermore, the proposed cloaks have been shown to possess bandwidth of the order of 190% which is a significantly improved performance compared to the recently published literature.

Monovalent Ions and Water Dipoles in Contact with Dipolar Zwitterionic Lipid Headgroups-Theory and MD Simulations

The lipid bilayer is a basic building block of biological membranes and can be pictured as a barrier separating two compartments filled with electrolyte solution. Artificial planar lipid bilayers are therefore commonly used as model systems to study the physical and electrical properties of the cell membranes in contact with electrolyte solution. Among them the glycerol-based polar phospholipids which have dipolar, but electrically neutral head groups, are most frequently used in formation of artificial lipid bilayers. In this work the electrical properties of the lipid layer composed of zwitterionic lipids with non-zero dipole moments are studied theoretically. In the model, the zwitterionic lipid bilayer is assumed to be in contact with aqueous solution of monovalent salt ions. The orientational ordering of water, resulting in spatial variation of permittivity, is explicitly taken into account. It is shown that due to saturation effect in orientational ordering of water dipoles the relative permittivity in the zwitterionic headgroup region is decreased, while the corresponding electric potential becomes strongly negative. Some of the predictions of the presented mean-field theoretical consideration are critically evaluated using the results of molecular dynamics (MD) simulation.

An analytical model for conduction and valence band edge profiles of bandgap graded and displaced heterojunctions

An analytical model for conduction and valence band edge profiles applicable for a wide variety of p–n heterojunction devices is presented by analytically solving the Poisson equation, taking the displacement of p–n junction relative to material junction as well as spatial variation of permittivity into account. The model is applicable for abrupt and compositionally (linearly and parabolically) graded systems. Unlike other analytical models, the present model considers the variation of the built-in potential depending on the positions of the depletion edges in the graded region. A displacement of the p–n junction into the wide bandgap semiconductor is shown to cause strong barriers in the conduction band and the width and height of the barrier increase with the amount of displacement. Displacement into narrow bandgap semiconductors is found to cause dips in the conduction band, the depths of which increase with the amount of displacement. The developed analytical expressions are particularly suitable for circuit simulation purposes as well as for the design of heterojunction devices like heterojunction bipolar transistors (HBT).