In this study, absorption of high frequency radio waves in the ionospheric plasma have been investigated. The wave equation was obtained in terms of ionospheric parameters. The numerical values of the absorption have been calculated for 4 MHz, 4.5 MHz and 5 MHz waves. The necessary parameters for calculation have been obtained using an International Reference Ionosphere (IRI) Model. The altitudinal, diurnal, seasonal and the variations of absorption with frequency have been examined. The calculations show that the highest absorption occurs in the D-region. The absorption is higher in summer than in other seasons and is maximum at daylight. In addition, absorption decreases with the increase of frequency.

A high-power electromagnetic (EM) wave can decay into an ion acoustic wave and a scattered EM wave in a plasma through a process called Stimulated Brillouin Scattering (SBS). A one-dimensional fully electromagnetic Finite-Difference Time-Domain (FDTD) method is used in a magnetized plasma with an increasing density ramp to simulate the propagation of a linearly polarized high-frequency (HF) radio wave traveling through the plasma along magnetic field lines. The study shows that the plasma splits the linearly polarized EM wave into two separate counter-rotating circularly polarized waves: the X-mode and the O-mode waves. The specific cutoff points for each of these circularly polarized waves are illustrated, with the X-mode reflecting at lower frequencies compared to the O-mode. As the radio wave approaches the cutoff frequency, it decays into a scattered high-frequency EM wave and a low-frequency wave. By analyzing the frequency spectrum of the scattered wave and the excited electrostatic low-frequency wave, the electrostatic wave is identified as an ion-acoustic (IA) mode, thus confirming the process as SBS. The growth rate of the excited longitudinal electrostatic wave is studied by calculating the excited longitudinal wave energy. The evolution of energy transfer and conversion from the HF wave to IA wave, as well as electron and ion kinetic energy, is investigated. The results indicate that electron and ion density perturbations experience similar fluctuations.

Nano-porous silicon were simply prepared from p-type single crystalline silicon wafer by electrochemical etching technique via exerting constant current density in two different HF-Ethanol and HF-Ethanol-H2O solutions. The mesoporous silicon layers were characterized by field emission scanning electron microscopy and scanning electron microscopy. The results demonstrate that the width of nano-pores changes from 7 nm to 60 nm by varying current density from 10 mA/Cm2 to 40 mA/Cm2, respectively and the depth of nano-pores also alters by applying different values of etching duration. It is concluded that varying current density leads to different width of pores while varying etching duration results in various depth of pores. Such etch tuning process is applicable for fabricating different nano-sized porous silicon for many modern electronic devices.