Absorption Coefficient Of Electromagnetic Wave Research Articles

Synthesis of nanosized spinel ferrites MnFe2O4 on the surface of carbon nanotubes for the creation of polymer composites with enhanced microwave absorption capacity

Currently, the creation of new protective materials able to absorb the electromagnetic (EM) radiation is an important direction strongly linked to the use of high-tech electronics which leads to EM pollution in a wide range of high frequencies. The wide-band absorption and large bandwidth are two important factors affected the absorbing performance of materials. In this research, the development of polymer nanocomposites based on the multi-walled carbon nanotubes (CNTs) as a conductive component modified by manganese ferrite (MnFe2O4) nanoparticles as a magnetic component made it possible to increase the efficiency of absorption of EM waves in the frequency range 1–41 GHz as a result of good impedance matching characteristics in comparison with pure manganese ferrite. Finally, the absorption coefficient of EM waves in the frequency range of 5–20 GHz for MnFe2O4/0.065 vol.%CNT nanocomposites about 2.5–3 times higher than for MnFe2O4. The present work shows, that the introduction of MnFe2O4/CNT composites into the both amorphous (epoxy resin) and crystalline (polychlorotrifluoroethylene) polymer matrices makes it possible to manage microwave absorbing properties as well as a shift of the region of frequencies of maximum peak values of the absorption coefficient and reflection loss. The obtained relations prove that by the change of the amount of the modifying component (MnFe2O4) on the surface of carbon nanotubes, the content of the MnFe2O4/CNT nanocomposite in the polymer matrixes, and the thickness of the polymer composites it is possible to control the absorption coefficient and reflection loss of EM waves in the high frequency range. The MnFe2O4/0.044CNT–PCTFE and MnFe2O4/0.065CNT–epoxy resin composites exhibit higher bandwidth in relation to other reported composites or structures at the same thickness.

Absorption of Electromagnetic Waves in Non-Dispersive Plasma due to Effect of Ponderomotive Force

The absorption coefficient of electromagnetic wave propagating through overdense absorbing plasma is calculated by using Fresnel’s formula. Also, the force acting per unit volume of the electron fluid is calculated along z direction. The Fresnel’s formula is reduced in terms of conductivity and angular frequency so that nature of absorption coefficient with respect to conductivity of plasma and angular frequency of wave is studied, with the assumption that conductivity and angular frequency are two independent terms. By keeping conductivity of plasma constant, it is seen that the absorption coefficient is increased with increase in angular frequency and also absorption coefficient has the lowest value for the highest value of conductivity. At constant angular frequency of incidence, the absorption coefficient is decreased with increase in conductivity and also absorption coefficient has the highest value of angular frequency of incidence. Also the nature of force on the plasma is studied by considering that the conductivity of plasma is very large with compare to angular frequency of incident laser. The expression of absorption coefficient is separated into real and imaginary parts, and then plots are studied with respect to these parts. It is found that in both cases, the force on plasma is existed for short in time and distance, and then damps exponentially. Also, the variation of potential with distance is cleared that the potential is shielded within multiple distance of Debye length.

Absorption of Electromagnetic Waves by Plasma Oscillations in an Infinite Two-Dimensional Electron Gas in a Magnetic Field

New weakly damping magnetoplasmon modes in an unbounded two-dimensional electron system have recently been predicted. It can be expected that, if the frequency of light at a given wave vector is lower than the frequency of magnetoplasma oscillations, these oscillations should be manifested in optical coefficients, e.g., in the absorption coefficient of electromagnetic waves incident on the two-dimensional system. We analyze the reflection, transmission, and absorption coefficients of electromagnetic waves obliquely incident on the two-dimensional electron system whose conductivity has a Drude form taking into account dissipation and a magnetic field normal to the system. It has been found that all these coefficients have no poles near magnetoplasma waves. However, the dependence of the absorption coefficient on the angle of incidence can have a pronounced maximum near predicted magnetoplasmon modes.

Absorption of electromagnetic waves by a moving non-uniform plasma

The absorption coefficient of electromagnetic waves by a moving non-uniform plasma slab is investigated theoretically. Two cases of movement are considered: (1) the plasma slab moves parallel to the interface and (2) the plasma slab moves perpendicular to the interface. In both the cases, the influences of six typical plasma parameters on the absorption coefficient are discussed in detail by analyzing the relativistic model. It has been obtained that the absorption coefficient is strongly affected by the velocity of the moving plasma. Various interesting features concerning the variation of the absorption coefficient are obtained, which are very important for applications in space exploration.

Absorption of electromagnetic waves in a nonmagnetic conductor-ferromagnet structure

The absorption coefficient of electromagnetic waves in the structure that consists of a nonmagnetic conducting layer having the width less than that of the skin layer and a ferromagnetic layer (ferrite) has been studied both analytically and numerically. The frequency dependences of the absorption coefficient of electromagnetic waves have been obtained. It has been shown that, for particular parameters of the structure, the absorption coefficient can be close to unity over a wide frequency range due to the formation of a standing electromagnetic wave in the upper conducting layer.

A mathematic simulation of the process of hydrochloric acid impact on heating of a carbonate-bearing oil bed exposed to a high-frequency electromagnetic field

A model of the process of heating of a carbonate-bearing oil bed under a combined exposure to hydrochloric acid and a high-frequency electromagnetic field is proposed. The space-time temperature distributions are calculated; the contributions from various physical processes depending on the absorption coefficient of electromagnetic waves in the bed are analyzed. It is found that the temperature distribution over the bed thickness can be controlled by injecting hydrochloric acid in a high-frequency electromagnetic field.

Modelling of GPR waves for lossy media obeying a complex power law of frequency for dielectric permittivity

ABSTRACTThe attenuation of ground‐penetrating radar (GPR) energy in the subsurface decreases and shifts the amplitude spectrum of the radar pulse to lower frequencies (absorption) with increasing traveltime and causes also a distortion of wavelet phase (dispersion). The attenuation is often expressed by the quality factor Q. For GPR studies, Q can be estimated from the ratio of the real part to the imaginary part of the dielectric permittivity.We consider a complex power function of frequency for the dielectric permittivity, and show that this dielectric response corresponds to a frequency‐independent‐Q or simply a constant‐Q model. The phase velocity (dispersion relationship) and the absorption coefficient of electromagnetic waves also obey a frequency power law. This approach is easy to use in the frequency domain and the wave propagation can be described by two parameters only, for example Q and the phase velocity at an arbitrary reference frequency. This simplicity makes it practical for any inversion technique. Furthermore, by using the Hilbert transform relating the velocity and the absorption coefficient (which obeys a frequency power law), we find the same dispersion relationship for the phase velocity. Both approaches are valid for a constant value of Q over a restricted frequency‐bandwidth, and are applicable in a material that is assumed to have no instantaneous dielectric response.Many GPR profiles acquired in a dry aeolian environment have shown a strong reflectivity inside dunes. Changes in water content are believed to be the origin of this reflectivity. We model the radar reflections from the bottom of a dry aeolian dune using the 1D wavelet modelling method. We discuss the choice of the reference wavelet in this modelling approach. A trial‐and‐error match of modelled and observed data was performed to estimate the optimum set of parameters characterizing the materials composing the site. Additionally, by combining the complex refractive index method (CRIM) and/or Topp equations for the bulk permittivity (dielectric constant) of moist sandy soils with a frequency power law for the dielectric response, we introduce them into the expression for the reflection coefficient. Using this method, we can estimate the water content and explain its effect on the reflection coefficient and on wavelet modelling.