• Journal of electromagnetic engineering and science
• /
• 제10권2호
• /
• pp.61-66
• /
• 2010

This paper is concerned with an analysis of the back scattering of electromagnetic waves from a target moving along random rough surfaces such as the desert, and sea. First, the discrete ray tracing method(DRTM) is introduced, and then, this method is applied to the back scattering problem in order to investigate the effect of the back scattering from random rough surfaces on the electric field intensities. Finally, numerical examples of various height deviations of the Gaussian type of rough surfaces are shown. It is numerically demonstrated that the back scattering is dominated by the diffractions related to the reflections from the random rough surfaces.

• 전기학회논문지
• /
• 제59권6호
• /
• pp.1114-1119
• /
• 2010

This paper is concerned with an numerical analysis of electromagnetic wave propagation from randomly rough surfaces as a desert, sea surface and so on. We propose discrete ray tracing method (DRTM) for analysis of characteristics of wave propagation along one dimensional (1D) and two dimensional (2D) random rough surfaces. The point of the present method is to discretize not only rough surface but also ray tracing. This technique helps saving computer memories and does simplifying ray searching algorithm resulting in saving computation time. Numerical calculations are carried out for 1D and 2D random rough surfaces and electric field distributions are shown to check the effectiveness of the proposed DRTM.

• 대한원격탐사학회:학술대회논문집
• /
• 대한원격탐사학회 2005년도 Proceedings of ISRS 2005
• /
• pp.725-728
• /
• 2005

The scattering problem of the randomly rough surface is examined by the method of moments(MoM), small perturbation method (SPM), integral equation method (IEM) and the semi-empirical polarimetic model. To apply the numerical technique of the MoM to microwave scattering from a rough surface, at first, many independent randomly rough surfaces with a rms height and a correlation length are generated with Gaussian random deviate. Then, an efficient Monte Carlo simulation technique is applied to estimate the scattering coefficients of the surfaces.

• 한국전자통신학회논문지
• /
• 제5권3호
• /
• pp.233-238
• /
• 2010

본 논문에서는 무선 망 설계에 필요한 전자파 전파 특성 예측을 위한 방법 중 하나인 광선 추적법을 이용하여 2차원 불규칙 조면에서의 전파 특성 조사하기 위한 이산 광선 추적법을 제안 하였다. 이 방법은 불규칙 조면과 광선 추적에도 이산화 방법을 적용한다. 제안한 방법은 불규칙 조면 생성에 컴퓨터 메모리를 절약할 수 있으며, 광선 추적에 소요되는 계산 시간을 단축 할 수가 있다. 2차원 불규칙 조면에 대해 이산 광선 추적법을 적용하여 전계 분포에 대한 수치 계산을 행하였으며, 이산 광선 추적법의 유효성에 대해서도 조사하였다.

• 대한수학회지
• /
• 제58권1호
• /
• pp.69-90
• /
• 2021

In this paper, we prove weighted norm inequalities for rough singular integrals along surfaces with radial kernels h and sphere kernels Ω by assuming h ∈ △γ(ℝ+) and Ω ∈ ����β(Sn-1) for some γ > 1 and β > 1. Here Ω ∈ ����β(Sn-1) denotes the variant of Grafakos-Stefanov type size conditions on the unit sphere. Our results essentially improve and extend the previous weighted results for the rough singular integrals and the corresponding maximal truncated operators.

• Journal of electromagnetic engineering and science
• /
• 제18권2호
• /
• pp.136-140
• /
• 2018

We propose an improved semi-empirical scattering model for X-band radar backscattering from rough sea surfaces. This new model has a wider validity range of wind speeds than does the existing semi-empirical sea spectrum (SESS) model. First, we retrieved the small-roughness parameters from the sea surfaces, which were numerically generated using the Pierson-Moskowitz spectrum and measurement datasets for various wind speeds. Then, we computed the backscattering coefficients of the small-roughness surfaces for various wind speeds using the integral equation method model. Finally, the large-roughness characteristics were taken into account by integrating the small-roughness backscattering coefficients multiplying them with the surface slope probability density function for all possible surface slopes. The new model includes a wind speed range below 3.46 m/s, which was not covered by the existing SESS model. The accuracy of the new model was verified with two measurement datasets for various wind speeds from 0.5 m/s to 14 m/s.

• 대한기계학회논문집A
• /
• 제26권10호
• /
• pp.2180-2186
• /
• 2002

In a micro-scale contact, capillary force and van der Waals interaction significantly influence the contact between asperities of rough surfaces. Little is, however, known about the variation of these surface forces as a function of chemical property of the surface (wet angle), relative humidity and deformation of asperities in the real area of contact. A better understanding of these surface forces is of great necessity in order to find a solution for reducing friction and adhesion of micro surfaces. The objective of this study is to investigate the surface forces in micro-scale rough surface contact. We proposed an effective method to analyze capillary and van der Waals forces in micro-scale contact. In this method, Winkler spring model was employed to analyze the contact of rough surfaces that were obtained from atomic force microscopy (AFM) height images. Self-mated contact of DLC(diamond like carbon) coatings was analyzed, as an example, by the proposed model. It was shown that the capillary force was significantly influenced by relative humidity and wet angle of the DLC surface. The deformation of asperities to a critical magnitude by external loading led to a considerable increase of both capillary and van der Waals forces.

• Tribology and Lubricants
• /
• 제19권4호
• /
• pp.230-236
• /
• 2003

In applications such as MEMS and NEMS devices, the adhesion force and contact load may be of the same order of magnitude and the static friction coefficient can be very large. Such large coefficient may result in unacceptable and possibly catastrophic adhesion, stiction, friction and wear. To obtain the static friction coefficient of contacting real surfaces without the assumption of an empirical coefficient value, numerical simulations of the contact load, tangential force, and adhesion force are preformed. The surfaces in dry contact are statistically modeled by a collection of spherical asperities with Gaussian height distribution. The asperity micro-contact model utilized in calculation (the ZMC model), considers the transition from elastic deformation to fully plastic flow of the contacting asperity. The force approach of the modified DMT model using the Lennard-Jones attractive potential is applied to characterize the intermolecular forces. The effect of the surface topography on the static friction coefficient is investigated for cases rough, intermediate, smooth, and very smooth, respectively. Results of the static friction coefficient versus the external force are presented for a wide range of plasticity index and surface energy, respectively. Compared with those obtained by the GW and CEB models, the ZMC model is more complete in calculating the static friction coefficient of rough surfaces.

• 한국전자파학회논문지
• /
• 제17권4호
• /
• pp.393-399
• /
• 2006

본 논문에서는 비교적 큰 규모의 불규칙 조면에 의한 산란 특성을 예측하기 위해 ray tracing 기법을 적용하였다. 전자계를 평가하기 위하여, 회절 레이(ray)에 대해서 knife edge 회절에 의한 회절 계수를 사용하였고, 반사 레이에 관해서는 Fresnel의 반사 계수를 사용하였다. 또한 레이 추적 방법에는 수신기에 도달하는 모든 레이의 경로를 정확히 찾아주는 image method를 채용하였으며, 불규칙 조면에 회절계를 고려하였다. 파도 모양의 조면에 의한 산란 특성과 빌딩 모양의 표면에 의한 지연 확산(delay spread) 특성에 대해 수치 계산하였다. 불규칙 조면에 의한 산란 특성을 수치적으로 해석하는데 ray tracing 기법을 적용하여 그 유효성을 입증하였다.

• Tribology and Lubricants
• /
• 제14권1호
• /
• pp.54-63
• /
• 1998

In many practical lubricated contacts such as a rough concentrated contact on the sliding of nominally flat surfaces, the fluid may be of molecular (nanometer) scale owing to the asperity interactions on the surfaces. Under this condition, there is insufficient lubricant on the concentrated contact spot to maintain a realistic continuum. Rheological behavior for this kind of concentrated contact has been studied extensively to know whether the application of viscous fluid model is appropriate. The interaction of two rough surfaces is simplified as perfectly flat-rough surfaces contact under certain conditions by "composite topography" and for a nanometer scale fluid film, three kinds of rheological fluid behavior are analyzed in elastohydrodynamic asperity point contact.t contact.