Backscattering Of Electromagnetic Waves Research Articles

Infrared stealth and the flexible metasurface of radar backscattering suppression

Based on the principle of electromagnetic wave cancellation, this paper proposes a coded metasurface which can suppress both radar backscattering and infrared radiation. Two high duty ratio superstructures with two different structures are designed and coded units are worked out on the basis of this. The experimental results indicate that the metasurface can effectively suppress the backscattering of electromagnetic waves in the 8.6–16.3 GHz band, and the average emissivity at infrared atmospheric window is 0.43. At the same time, it has good heat insulation performance, which can effectively suppress infrared radiation. In addition, the metasurface has light mass and flexibility. Therefore, the metasurface has a good prospect for application in the multispectral stealth field.

The antenna system with signal polarization separation

The results of the study of the electrical characteristics of the waveguide-coaxial structure of the polarization separator (orthoplexer) loaded by the waveguide irradiator under the influence of harmonic radiation in the frequency band and pulse signal are presented. The antenna system is designed to study partially-non-reciprocal backscattering of electromagnetic waves.

Computation and Experiment on Linearly and Circularly Polarized Electromagnetic Wave Backscattering by Corner Reflectors in an Anechoic Chamber

Electromagnetic wave backscattering by corner reflectors in an anechoic chamber is studied using our developed computational tool. The tool applies the Finite-Difference Time-Domain (FDTD) method to simulate the propagation of the wave’s electric and magnetic fields. Experimental measurement in an anechoic chamber is also carried out as a comparison. The two results show agreement, including the finding that the backscatter intensity variation amongst the four circularly polarized modes is significantly smaller than the variation amongst the four linearly polarization modes.

Fractal algorithm for surface roughness parameters retrieval using multiband/polarization AIRSAR data

Surface roughness is an important characteristic in analyzing synthetic aperture radar images and three-dimensional (3-D) surfaces that influence the backscattering of electromagnetic waves. We propose an algorithm based on a fractal method for retrieving parameters of a surface. To estimate surface roughness parameters, 10,000 different 3-D surfaces with different rms-height and correlation length are simulated. 3-D simulation of surfaces is carried out based on fractal Brownian motion. The results show that the fractal method represents a good relationship between roughness parameters and fractal dimension. It can be seen that, in some cases, surfaces with different roughness have the same fractal dimension. Roughness index (RI) can be used as a complement to fractal dimension. We present empirical relationships among fractal dimension, roughness parameters, and RI. The method is implemented on L and C bands with HH and HV polarizations of AIRSAR data at different dates. The comparison between field measurement and estimated roughness showed that the accuracy of soil surface roughness estimation for band L with HH polarizations is better than bands L and C with polarizations HV and HH, respectively. The results of this method also are compared with the roughness estimates using the integral equation model (IEM). The analysis of outputs shows that the roughness estimation using the fractal and IEM is very similar in the low moisture at L band in HH polarization. The root mean square error of roughness for data at L band in HH polarization on July 1, 2002, is 0.54 and 0.53 cm for fractal and IEM, respectively.

Backscattering of electromagnetic waves by non-spherical raindrops in double-frequency radar

ABSTRACTThe article is devoted to solving the actual scientific task of restoration of precipitation microstructural characteristics by double-frequency remote sensing with a glance of rain particles nonsphericity. At that, the calculations of radar cross section of raindrops were performed by approximated methods on the basis of spherical drops of equivalent volume and dipole scattering. Results obtained are compared with the calculations of the rigorous method of moments. It was shown that errors of approximate calculations of backscattering characteristics are smaller for the same vertical polarization of frequency channels of double-frequency radar. In addition, the behaviour of the differential backscattering cross section is studied.

Attenuation of Bragg backscattering of electromagnetic waves from density fluctuations near the region of polarization degeneracy in magnetoactive plasma

Specific features of Bragg backscattering under conditions of strong polarization degeneracy near the cutoff surface in an anisotropic medium are studied analytically and numerically. It is shown that the linear interaction of normal waves can substantially affect wave scattering by suppressing the amplification of Bragg backscattering near the cutoff region in the case of weak coupling between normal waves.

Measuring of the reflection coefficients close to 1 with the help of a quasi-optical reflectometer, based on hollow metal-dielectric waveguides

This paper considers the measurement technique features of large reflection coefficients at millimeter wavelengths and structure and design parameters of the measuring bench, containing a quasi-optical reflectometer, built on the basis of hollow rectangular metal-dielectric waveguides. Measurement results of the reflection coefficients of planar samples with reflection coefficient close to 1 (metallized films, fine-period metal grids) are presented. The results may be of interest in the development of foldable antennas and devices for controlling the backscattering of electromagnetic waves from the objects of complicated geometrical form.

Enhanced backscattering of electromagnetic waves from randomly rough gratings on negative magnetic metamaterials

We investigate the scattering formalism of the Green's theorem including a discontinuity in the magnetic permeability μ (isotropic and homogeneous). For this purpose we make use of the continuity or saltus conditions for the EM field across the interface between media having different ɛ and μ. Numerical analysis has been made for linearly polarized light and randomly rough media with negative μ on the phenomenon of backscattering enhancement. We obtain enhanced backscattering peaks for both polarizations ( s and p) in the case of rough surfaces with large correlation length. On the other hand, in the case of subwavelength roughness, enhanced backscattering is also observed, but mediated by s-polarized surface-plasmon polaritons (negative μ) similar to that mediated by p-polarized surface-plasmon polaritons for conventional metallic media (negative ɛ).

Comment on “Stimulated Raman scattering of laser from periodically spaced nanoparticles” [Phys. Plasmas 16, 093106 (2009)

Parashar [Phys. Plasmas 16, 093106 (2009)] studied the Raman backscattering of electromagnetic waves from nanoparticle lattice. We have demonstrated that the uncoupled dispersion curves have incorrect cutoff frequencies and the electromagnetic dispersion curves do not have correct asymptotic behavior at large frequencies. It has been shown that Parashar obtained an incorrect diagram of the growth rate for which the pump wave frequency goes below the cutoff frequency of the electromagnetic wave. Correct diagrams for the Raman backscattering as well as forward scattering are presented. It has been shown that backscattering has a larger maximum growth rate. We also found no instability if scattered radiation belongs to the lower branch of the dispersion curves.

Low-Frequency Limit of Unified Models for Backscattering From Oceanlike Surfaces

In the context of electromagnetic-wave backscattering from oceanlike surfaces, by using the first two orders of unified models, like the small slope approximation and the local curvature approximation, we recently proposed an original technique to reduce the number of numerical integrations to two for easier numerical implementation. In this letter, this technique is simplified in the low-frequency limit, allowing us to bring a correction to the first-order small perturbation method.

Backscattering of electromagnetic waves by the vertex area of a thin conducting screen

The backscattering of the electromagnetic waves by the vertex area of a thin metal screen is investigated. A special case when the magnetic field of the incident wave is perpendicular to the diagonal of the vertex area is considered. The dependence of the vertex-scattered signal on the grazing angle is experimentally found. At a certain angle, an extremum in the radar scattering is discovered. At the extremum, good agreement between the results predicted by the asymptotic theory and the experimental results is observed.

Numerical implementation of local unified models for backscattering from random rough sea surfaces

In the context of electromagnetic wave backscattering from ocean-like surfaces, by using the lowest order of the SSA (SSA-1) model, Bourlier et al. proposed an original technique to reduce the number of numerical integrations to two for easier numerical implementation. To be consistent with microwave measurements, closed-form expressions of the Fourier coefficients with respect to the wind direction of the backscattering normalized radar cross-section (NRCS) are obtained. For Gaussian statistics, previous work is extended in this paper to kernels of unified models expanded up to second order, like full SSA and full LCA. Thus, with the help of Bessel functions and by analytical integrations over the azimuthal angles, the second-order backscattering (BNRCS) is expressed in terms of two-fold integrations and another independent integration instead of four-fold integrations, if no analytical integration is made. This approach allows us to obtain fast results (less than one second). Numerical results are then presented for different microwave frequencies and wind speeds.

The mechanism of backscattering of electromagnetic waves by a pine forest in the meter wave band

A synthetic-aperture multifrequency polarimetric radar complex is used for experiments on studying the features of reflection of electromagnetic waves from pine forests. It is found that the intensity of the reflected power is proportional to the biometric characteristics of the forests. The hydrology and spatial fluctuations of the dielectric characteristics of the upper layer of the forest soil are studied at different depths. It is shown that spatial fluctuations of the soil’s dielectric characteristics can be used to explain the features of reflection from the forest. Reflection from a forest in the meter wave band at horizontal (HH) and vertical (VV) polarizations is simulated. It is found that mechanisms of reflection from the forest may be different for the HH and VV polarizations. Experimental data confirming the presence of specific effects in the radar images obtained in the meter wave band at the HH and VV polarizations are presented.

Microwave Backscattering Model for a Bare Soil Field

In the remote sensing area theoretical models of microwave scattering properties from a bare soil field are needed to interpret the measured data and to generate simulated data for developing retrieval algorithms when the measured data is scarce or does not exist at all. A model for electromagnetic wave backscattering from a bare soil field is developed in this paper. The model developed is based on the integral equation model. The ground-based measurement system measures brightness temperatures and backscattering coefficients at frequencies between 1 and 2 GHz. For evaluating the model availability, comparisons of model prediction with the measured data are shown. The unknown quantity in the model is the surface correlation length. The surface correlation length is chosen to fit the measured data. The parameters of soil moisture content, surface root mean square height, and surface correlation length will affect the scattering strength from bare soil. Further, the soil composition of sand, loam, and clay will also influence the scattering coefficient from the bare soil surface. It is seen that satisfactory agreement is obtained between the model prediction and measured data. The difference between the model prediction and measured data is less than a dB.

Bistatic Scattering and Backscattering of Electromagnetic Waves by Conducting and Coated Dielectric Spheroids: A New Analysis Using Mathematica Package

Bistatic Scattering and Backscattering of Electromagnetic Waves by Conducting and Coated Dielectric Spheroids: A New Analysis Using Mathematica Package

Bistatic Scattering and Backscattering of Electromagnetic Waves By Conducting and Coated Dielectric Spheroids: a New Analysis Using Mathematica Package - Abstract

Solutions to electromagnetic scattering at any angle of incidence by a perfectly conducting spheroid and a homogeneous dielectric spheroid coated with a dielectric layer are obtained by solving Maxwell's equations together with boundary conditions. The method used is that of expanding electric and magnetic fields in the spheroidal coordinates in terms of the spheroidal vector wave functions and matching their respective boundary conditions at spheroidal interfaces. In this formulation, the column vector of the series expansion coefficients of the scattered field is obtained from that of the incident field by means of a matrix transformation, which is in turn obtained from a system of equations derived from boundary conditions. The matrix depends only on the scatterer's properties; hence the scattered field at a different direction of incidence is obtained without repeatedly solving a new set of simultaneous equations. Different from the previous work, the present work developed an accurate and efficient Mathematica source code for more accurate solution to the problem. Normalized bistatic and backscattering cross sections are obtained for conducting (for verification purpose), homogeneous dielectric (for verification purpose), and coated dielectric prolate (for some new results) spheroids, with real and complex permittivities. Numerically exact results for the coated dielectric prolate spheroids are newly obtained and are not found in existing literature.

Ocean wave imaging mechanism by imaging radar

Analytical representations of the high frequency spectra of ocean wave and its variation due to the variation of ocean surface current are derived from the wave-number spectrum balance equation. The ocean surface imaging formulation of real aperture radar (RAR) is given using electromagnetic wave backscattering theory of ocean surface and the modulations of ocean surface winds, currents and their variations to RAR are described. A general representation of the phase modulation induced by the ocean surface motion is derived according to standard synthetic aperture radar (SAR) imaging theory. The detectability of ocean current and sea bottom topography by imaging radar is discussed. The results constitute the theoretical basis for detecting ocean wave fields, ocean surface winds, ocean surface current fields, sea bottom topography, internal wave and so on.

Electromagnetic wave backscattering from a cloud of alpha-emitting radioactive elements in air

A track model is proposed for the electromagnetic wave scattering from a cloud of radioactive elements in air. Relationships are derived for estimating the radar cross section of the cloud of alpha-emitting radioactive elements as a function of the cloud activity and the wavelength of the electromagnetic wave. The activity of a cloud detected by a standard radar is estimated.

Nonresonant mechanism of scattering of electromagnetic waves by sea surface: Scattering by steep sharpened waves

We develop an asymptotic theory of nonresonant backscattering of electromagnetic waves in the X-band by the ocean surface. Small-height (5÷20 cm) breaking surface waves with sharpened edges are assumed to be the main cause of nonresonant scattering. Using the methods of physical optics and geometrical theory of diffraction, we calculate the contribution of breaking sharpened waves to the scattering cross section for two orthogonal polarizations of electromagnetic scattering. It is shown that the main contribution to the backscattering is from the mirror reflection from the leading edge of such a wave, and the sharpness of the wave edge leads to the fact that the backscattering cross section of horizontally polarized radiation can exceed that of the vertically polarized radiation.

Backscattering of electromagnetic waves by large-scale inhomogeneities in a periodically inhomogeneous medium

It is shown that backscattering of electromagnetic waves is possible in a periodically inhomogeneous medium by random inhomogeneities whose scale is greater than the wavelength. A small scattered field emerges in the case of appearance of the Bragg cavity when the periodic layer is a matching system for the incident wave. Scattering is effective even for inhomogeneities whose scale is much greater than the Fresnel radius of the inhomogeneous layer. The correlation radius of the scattered field can also be that large.