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本文提出了一种计算数值绕射系数有有效方法,并将之用于提取表面具有分形结构金属劈的绕射系统,利用时域有限差分法提供的散射场,根据几何绕射理论建立含有绕射系数未知量的方程组,通过联立方程组的求解,得到散射体边缘的数值绕射系数。具体计算例子表明,该算法是有效的。 相似文献
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本文介绍了一种计算目标绕射系数的通用数值方法--根据时域有限差分(FDTD)方法提供的散射场,通过联立方程组求解绕射系数,所述方法对二维TM、TE波均适用,有无涂层情况下金属条板绕射系数的计算例子表明该方法是可行的。 相似文献
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涂覆型大尺寸有限长圆柱散射特性的混合解法 总被引:2,自引:0,他引:2
本文首先从理论上导出了能计算斜入射绕射场的阻抗劈并矢绕射系数,然后利用该绕射系数结合物理光学法对涂覆型大尺寸有限长圆柱的散射特性进行了分析和计算。在绕射区计及了一阶和二阶绕射贡献,在镜反射方向附近作了驻相法近似,由此得到的数值结果与实验结果吻合较好。 相似文献
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由散射数据计算数值绕射系数 总被引:1,自引:1,他引:0
本文研究数值一致性绕射系数的提取方法。在建立散射模型并确认其散射中心后,用FDTD方法计算散射场,并通过电流加窗方法或联立方程组方法以提取所关心散射中心的一致性绕射系数。金属板边缘的例子验证了这一途径的可行性。最后,用这种方法获得了涂层金属板的一致性统射系数,其结果与阻抗劈的UTD结果一致。 相似文献
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本文针对散射问题中时域近场一远场转换问题,探讨了两种新的算法.其一是采用Stratton-Chu散射场的积分表示式,由表面感应流直接求时域散射远场.其二是采用拉氏变换和卷积的方法,导出求解3-D和2-D时域散射远场形式上统一的公式.文中以规则形体为计算实例,验证了算法的可行性. 相似文献
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A numerical technique is presented for analysing diffraction gratings of arbitrary groove shape. The method is based on the application of finite element technique. It is suggested that this technique, thus far reserved mostly for the problems of bounded extent, may be used to advantage for analysing this problem. To this end, the infinite space is divided into two regions, one finite and the other infinite in extent. A series solution is employed in the infinite region, and in the finite one a functional is used. The two solutions are then matched on the common boundary of the two regions. The resulting equation for the field is finally solved by application of the finite element technique. The numerical results obtained for echelette gratings are favourably compared with a number of similar results reported in the literature. 相似文献
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We consider an axisymmetric obstacle illuminated by a plane wave propagating along the axis of symmetry. The surface fields in the shadow zone are given, far from the axis, by the geometrical theory of diffraction formulas. The point on the axis is a creeping wave focus and the gtd formulas predict an infinite result at this point. We compute, by using an asymptotic expansion method, a solution for the fields in the vicinity of the focus. This solution merges with gtd results far from the focus and remains bounded at the focus. Comparison with method of moment results on prolate and oblate spheroids show a good agreement. 相似文献
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本文采用CFD数值模拟方法和试验数据相结合的方式对半球型动压气浮轴承径向偏心3%和轴向偏心3%的流场进行分析.对轴承同一偏心率下有、无螺旋槽的轴径向刚度、轴径向承载力、姿态角、功率等特性进行了比较.结果表明,半球型动压气浮轴承的数值仿真结果与试验数据吻合较好.刻有螺旋槽的轴承,压力沿螺旋槽逐渐上升,在螺旋槽顶达到峰值,跨过螺旋槽后压力逐渐降低.由于圆周均布了多个螺旋槽,螺旋槽的导流作用使得高压区均匀的分布在轴承圆周面上.没有螺旋槽的轴承在径向偏心时存在一个对称分布的高压区和低压区,二者夹角近似180度,但在轴向偏心时却无法形成动压效应,轴承支撑力几乎为0.相比无螺旋槽的轴承,有螺旋槽压力分布更均匀,能提供轴、径向支撑力,且姿态角和功率更小,更有助于电机稳定的高速旋转. 相似文献
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The fast Fourier transform (FFT) is used in conjunction with analytical techniques to obtain an approximate expression for the Sommerfeld integral associated with a vertical electric dipole above a half-space. The resulting expression, which is an analytic function of the source and observation locations, can be used in lieu of a numerical integration of the Sommerfeld integral. It can be used in either the near zone or the far zone, and it can even be applied for observation angles close to grazing. The accuracy of the expansion directly depends on the number of terms used in the FFT. Results obtained using the expansion are compared with those obtained both from a direct numerical integration of the Sommerfeld integral and the reflection coefficient method 相似文献
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针对金属微纳结构在表面增强拉曼光谱领域的应用,研究了金属基底亚波长单槽结构产生的电磁场增强。采用全矢量方法严格计算了平面波照明下金属槽外部区域电磁场的分布情况。建立了法布里-珀罗(F-P)半解析模型,该模型能够精确预言全矢量方法的计算结果,能够节省设计最优槽深的计算量。基于该模型分析了金属槽外部区域电场增强的物理机制,结果表明达到相长叠加共振状态的金属槽内基模在槽外空间中激励的透射电场是金属槽外空间中电场增强的主要来源。研究了槽外空间电场增强的范围,结果表明对于不同的槽宽和入射波长,在垂直距离槽口0.1倍波长的范围内电场增强较为明显,在该范围之外,电场增强因子迅速衰减到1的数量级。 相似文献
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Makoto Ohki Haruo Sakurai Shogo Kozaki 《Journal of Infrared, Millimeter and Terahertz Waves》1997,18(10):2031-2045
This paper is described for T-matrix analysis of the electromagnetic wave diffraction from a Fourier grating that the boundary value problem is treated by applying the extended boundary condition. The rigorous form of the expression of matrix elements is presented in the term of Bessel functions of the first kind. The error of power conservation versus the truncated number has been examined for mode number. Diffraction efficiencies versus groove depth and wavelength for a second or third harmonic wave of Fourier grating have been discussed. Numerical results are in good agreement with those obtained from other method and experimental values. Reasonable numerical results are presented for a groove depth per period of the Fourier grating less than 0.25. 相似文献
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为了获得36MnVS4连杆裂解槽最优的切割质量,采用正交实验法对裂解槽进行了激光切割理论分析和实验验证,通过激光共聚焦显微镜测量裂解槽的深度、宽度、张角及曲率半径等几何尺寸,同时采用扫描电镜观测裂解槽底部微观形貌及热影响区的厚度,采用极差分析法得到了峰值功率、脉冲宽度、切割速率和脉冲频率对裂解槽几何尺寸的影响,并获得了最优实验参量组合。结果表明,裂解槽热影响区厚度皆小于100μm且裂解槽底部存在微裂纹及气孔,各参量组合对裂解槽宽度、张角及曲率半径的影响较小,对裂解槽深度的影响较大;脉冲宽度和峰值功率对槽深的影响较大,脉冲频率和切割速率对槽深的影响较小;优化后切割速率为1.0m/min,峰值功率为700W,脉冲频率为1000Hz,脉冲宽度为50μs。这一结果对实际生产具有重要意义。 相似文献