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Two-Dimensional Finite Element Analysis
Published in Özlem Özgün, Mustafa Kuzuoğlu, ®-based Finite Element Programming in Electromagnetic Modeling, 2018
All real surfaces in nature are rough, and amount of roughness relative to wavelength is the dominant factor for understanding the behavior of electromagnetic waves scattered by rough surfaces. Roughness of a surface is dependent on several parameters, such as frequency, material parameters and angle of incidence. Scattered field values are dominated by mechanisms such as reflection, diffraction and multiple scattering. Accurate modeling of scattering from rough surfaces has attracted much interest in many areas, such as low-altitude target detection and tracking, imaging and remote sensing, radar surveillance, etc. If the surface is perfectly smooth, only specular reflection takes place, and the characteristics of reflection can be described by the well-known Fresnel coefficients. However, when the surface is rough, scattered power diffuses in all directions. The rougher the surface, the more the scattered power diffuses (see Fig. 5.60). Among all scattering directions, forward direction (specular direction) and backward direction (opposite to the direction of transmitted wave) have special importance in radar applications. For example, fading might occur in received signals, or target elevation might be erroneously estimated due to multipath effects. In addition, modeling of backscatter from rough sea surfaces (i.e., sea clutter) is important for radars operating in surveillance mode to detect, track and classify targets over sea surface, because radars must be able to distinguish between returns from targets and those from rough sea surface.
Nondestructive Testing
Published in Dale Ensminger, Leonard J. Bond, Ultrasonics, 2011
Dale Ensminger, Leonard J. Bond
Surface roughness affects the resolution and sensitivity of an ultrasonic nondestructive test in much the same manner as grain conditions. Scattering from rough surfaces can significantly reduce signals and, in some cases, make inspection at a particular frequency impossible if the wavelength is similar to the dimensions of the asperities. Some fundamental aspects of wave–material interaction were discussed in Chapter 2. However, the analysis considered only plane-surface interactions. Scattering from many real surfaces is more complex and depends on the depth and characteristic dimensions of roughness expressed as a function of the incident wavelength: random rough surfaces is considered extensively by Ogilvy [24]. The interaction of ultrasound with internal structures, such as grains, is treated and discussed by Goebbels [25,26] and Papadakis [27,28], and a more comprehensive review of scattering theory, for both canonical problems and a range of classes of targets, is provided in an article by Pao, which cites many references [29].
A spectral domain integral equation technique for rough surface scattering problems
Published in Waves in Random and Complex Media, 2021
The analysis of electromagnetic wave scattering from rough surfaces has been widely studied due to its number of applications in the areas of remote sensing, geophysics, material and surface science, optics, under water communication applications, etc. [1–5]. To derive the scattering fields from rough surface, two well-known theoretical methods of small perturbation approximation (SPM) [6] and Kirchhoff method (KM) [7] have been applied regarding their limitations in their domain of validity. Specifically, SPM is valid when the surface variations are much smaller than the incident wavelength and the slopes of the rough surface are relatively small, whereas KM applies tangent plane approximation to calculate the surface fields which is valid if the radius of curvature of the surface is larger than the wavelength. Other than analytical methods, method of moment (MoM) [8] is a frequently resorted powerful numerical approach, which is based on the transformation of integral equation into a linear system. Basically, the total field or its normal derivative on the rough surface is calculated by the linearized integral equations to obtain the scattered field [9–11]. In the majority of the MoM-based solutions, tapered wave [12,13] excitation has been considered in order to avoid artificial edge effects.