Sharif Digital Repository

HF radar systems are widely used for the measurement of ocean surface currents and wave parameters. Theoretical analysis of high frequency radio wave backscattering from the sea has been derived in the past. Also, the relationship between Bragg frequencies and surface currents is determined and has been proved by HF radars. It is known that when surface currents are present, the Bragg frequencies move to new frequencies. Their movement is proportional to the surface current in the direction toward radar. In addition, it is observed that sea surface current changes the second order part of the spectrum of radar reflection from the sea surface. In this paper, a theoretical analysis of... 

Electromagnetic scattering from thin resistive strips is formulated using an integral equation approach. The formulation is then specialized to strips of constant curvature and arbitrary size allowing the employment of the method of moments to solve the scattering problem  

Electromagnetic scattering from thin resistive strips is formulated using an integral equation approach. Analytical expressions for the electric current density over wide and narrow strips are derived based on the physical optics and quasistatic approximation of the pertinent integral equations, respectively. The solutions are used to find closed form expressions for the echo width of the strip  

Scattering of a Gaussian beam by a spherical dielectric object is studied using the vectorial Gaussian beam tracing method. Expansion to a few Gaussian beams with the smaller waists has been used to extend the method to a more generalized one. This method can be applied to a large variety of different shape objects and incident beam profiles. Numerical results of this computationally fast method show a good agreement with the results represented in the literature. © 2004 IEEE  

In this paper, we investigate the impact of the electromagnetic scattering caused by other objects in nonfree space on the time-averaged force exerted upon a Rayleigh particle, which is conventionally referred to as the backaction effect. We show that backaction modifies the gradient force, radiation pressure, and spin curl force exerted upon Rayleigh particles, and gives rise to an additional force term which stems from the gradient of the backaction field in nonfree space. As a numerical example, we look into the trapping of a dielectric nanoparticle at the center of curvature of a spherical mirror, and study how it is affected by the backaction effect. We show that backaction can enhance... 

There are various cases in physics and engineering sciences (especially communications) where one requires the envelope probability density function (pdf) of the sum of several random sinusoidal signals. According to the correspondence between a random sinusoidal signal and a random vector, the sum of random vectors can be considered as an abstract mathematical model for the above sum. Now it is desired to obtain the pdf of the length of the resulting vector. Considering the common and reasonable assumption of uniform distributions for the angles of vectors, many researchers have obtained the pdf of the length of the resulting vector only for special cases. However in this paper, the pdf is... 

Recently, a group of novel devices based on conducting interfaces is proposed. These conducting interfaces can be implemented by using the inversion layer of MOS structures, trapped charges or depletion layer charges. It has been shown that these structures can support surface electromagnetic waves. In this paper, the coupling of surface electromagnetic waves supported by conducting interfaces is analyzed and an analytical formula is driven by using the coupled mode theory. It is shown that one can program the coupling length of this structure by applying a transverse voltage and obtain a new type of optical modulator. The results obtained by coupled mode theory are verified by solving... 

In this paper, we propose a frequency-independent method for calculation of scattered electromagnetic (EM) fields by the human body in millimeter-wave (MMW) band. The surface of the body is accurately modeled by non-uniform rational B-spline (NURBS) surfaces and is illuminated by a plane wave. The scattered EM fields are formulated by physical optics (PO) approximation. This approximation yields PO surface highly oscillatory integrals that are solved by numerical steepest descent path (NSDP) method, frequency-independently. This paper provides an efficient and accurate method for considering human body in indoor propagation, surveillance and medical imaging, and detection of human body by... 

In this study a 3D robust, systematic, semi-analytical method to characterize electromagnetic scattering from periodic arrays of discrete scatterers is presented. The proposed method is based on the multiple-scattering T-matrix in connection with the Ewald method. The formulation is systematic, quite general, easily traceable, and fast. Its high speed of analysis makes it well suited to design optimizations. The formulation is well developed for obliquely incident plane waves, and can be extended to Gaussian beams by means of suitable plane wave decomposition. For validating the proposed method, an example of a scattering problem is solved, and the resulting scattering spectrum, and the... 

An efficient method for scattering analysis from slightly rough surfaces is introduced. This method can be used in ray tracing algorithm where the computational efficiency is important due to the complexity and size of problems. In this method, the Kirchhoff approach is used for a periodic extension of the finite surface, which is approximated by strong harmonics of its Fourier series. Typical asphalt surfaces are analyzed by this method in millimeter-wave band and validated with the method of moments. The dominant scattering angles and ray widths of the scattered field can be easily used in ray tracing algorithm. The computation time and accuracy of results show that this method can be used... 

The integral equation technique, in combination with the method of moments, is widely used for treating the electromagnetic scattering from periodic rough surfaces. This method, however, requires the computation of a kernel (a periodic Green's function) that consists of a slowly converging infinite series of conventional Green's functions. To accelerate the convergence of this series, different methods have been proposed in literature. In this paper, we use a complex image (CI) technique to find a closed-form expression for the periodic Green's function, which is then used to analyze the electromagnetic scattering from arbitrary periodic rough surfaces. The resulting CI Green's function... 

Eelectromagnetic analysis of periodic structures is important in the electromagnetic theory. Among them, the electromagnetic wave scattering analysis from rough surfaces is of importance due to both theoretical and practical points of view. For slow variation periodic surfaces the solution can be obtained under the Rayleigh hypothesis in terms of Floquet modes [1]. Integral equation approaches in combination with the method of Moments are among the most frequently used in the solution of scattering problems related to periodic surface due to their flexibility in modeling different geometries [2-3]. Due to slowly convergence of infinite series periodic Green's function, these methods need... 

In this paper, we study the degrees of freedom (DoF) region and sum DoF of the time-selective K-user interference channel in the presence of intelligent reflecting surfaces (IRSs). We consider both active and passive IRSs. While both types of IRS can attenuate the amplitude and change the phase of a reflected electromagnetic wave, active IRSs are also capable of amplifying the wave. We derive inner and outer bounds for the DoF region and lower and upper bounds for the sum DoF of the K-user interference channel in the presence of an active IRS and prove that the maximum value of K for the sum DoF can be achieved if the number of IRS elements exceeds a certain finite value. The analysis...