Communications in Physics

Comparison of optical features in nitrobenzene-core PCF with hexagonal and square lattices in the claddings

2024-12-03T12:04:37+07:00

This paper proposes two novel photonic crystal fibers (PCFs) with a nitrobenzene core, designed using hexagonal and square lattice structures. The characteristics of the PCFs were numerically analyzed in detail and compared to selecting the proposed optimal structure for supercontinuum generation. This study investigates the influence of core diameter (D_C) on the characteristics of PCF. The fiber’s nonlinear properties are significantly enhanced by varying the core diameter. The hexagonal PCF structures provide flatter dispersion curves and are closer to zero dispersion than the square lattice, which is beneficial for supercontinuum generation. In contrast, the square PCF structures show higher nonlinear coefficients and lower attenuation than the corresponding hexagonal structures. Based on the simulation results, six optimized structures with all-normal and anomalous dispersion were selected to study the characteristics at the pump wavelength. Results indicate that the proposed PCFs exhibit near-zero flat dispersion, low attenuation and high nonlinearity. The selected optimal structures show potential for efficient supercontinuum generation, enabling broad and highly coherent spectra.

Implementation of atmospheric proton spectrum in GEANT4 simulations for space applications

2024-11-27T10:04:29+07:00

A major part of cosmic rays consists of the primary protons, and this portion plays a crucial role in the space applications such as shielding of spacecrafts. In this study, the proton flux values measured at the top of the atmosphere through the BESS-TeV spectrometer in 2004 are introduced into the GEANT4 simulations by using a probability grid that generates the corresponding discrete kinetic energies with a certain discrete probability. The introduced scheme is tested over a set of the shielding materials such as aluminum, polypropylene, Kevlar, polyethylene, and water by computing the total absorbed dose, which is the measure of the cumulative energy deposited in the investigated target volumes by protons per unit mass in Gy. It is shown that the present recipe provides the opportunity to use the discrete energy values together with the experimental flux values, thereby demonstrating a beneficial capability in the GEANT4 simulations for diverse space applications.

Expanding the absorption bandwidth with two-layer graphene metamaterials in gigahertz frequency range

2024-10-07T19:06:30+07:00

This work investigates the design and performance of a bilayer graphene metamaterial absorber operating in the GHz region. We initially analyzed a single-layer metamaterial absorber composed of a conductive ink graphene structure on a FR-4 dielectric substrate backed by a continuous copper sheet. Subsequently, a second graphene-FR4 layer of identical dimensions was added to create a bilayer structure. While the number of absorption peaks increased, they remained isolated, failing to achieve the desired broadband effect. To overcome this limitation, we explored graphene layers with varying surface resistances. Our findings demonstrate that the bilayer graphene metamaterial absorber achieves an absorption exceeding 90% with a remarkable bandwidth of 9.1 GHz, spanning frequencies from 6.21 GHz to 15.31 GHz. This significant bandwidth expansion is attributed to the synergistic interactions and contributions between the graphene and metal layers within the structure. To gain a deeper understanding of the underlying absorption mechanism, we investigated the surface current distribution, the impact of conductivity, and the individual contributions of each layer. Additionally, we examined the influences of both incident angle and polarization angle on the absorption performance of the proposed bilayer MA. These comprehensive analyses provide valuable insights into the mechanisms responsible for the enhanced absorption observed in multilayer metamaterial structures. Our work holds relevance and might be useful to develop electromagnetic wave shielding technologies and devices operating in the GHz frequency range.