Microwave reflection properties of planar anisotropy FesoNi50 powder/paraffin composites

The reflection properties of planar anisotropy Fe50Ni50 powder/paraffin composites have been studied in the microwave frequency range.The permeability of Fe50Ni50 powder/paraffin composites is greatly enhanced by introducing the planar anisotropy,and can be further enhanced by using a rotational orientation method.The complex permeability can be considered as the superposition of two types of magnetic resonance.The resonance peak at high frequency is attributed to the natural resonance,while the peak at low frequency is attributed to the domain-wall resonance.The simulated results of the microwave reflectivity show that the matching thickness,peak frequency,permeability,and permittivity are closely related to the quarter wavelength matching condition.The Fe50Ni50 powder/paraffin composites can be attractive candidates for thinner microwave absorbers in the L-band(1-2 GHz).     

表面损伤衍射双向反射分布函数模型建立及分析

建立了包括划痕和坑点在内的表面损伤的衍射双向反射分布函数(BRDF)模型,并分析了模型在各领域中的应用.通过使用非傍轴标量衍射理论,提出了采用相干窗口函数滤波的方法得到非相干光条件下的表面损伤衍射BRDF模型,得到了表面划痕和坑点的散射特性.该方法在表面损伤检测、表面损伤杂光分析以及图像渲染技术等领域都有重要的应用价值...     

The coefficients of reflection and refraction on interface of the crystals in the Savart polariscope

According to the boundary conditions of the electromagnetic field, the coefficients of reflection and refraction on the interface of crystal in the Savart polariscope are obtained for ordinary ray (o-ray) and extraordinary ray (e-ray).The coefficients of reflection and refraction are different from an isotropic medium and have more complicated forms than isotropic medium.     

一致性绕射理论求解球面反射点的快速方法

射线寻迹是应用一致性几何绕射理论分析电大尺寸目标电磁辐射和散射特性的关键,它的精度和速度对场值求解结果影响很大。根据反射定律,推导得出了球面反射点的参量必须满足的一元四次方程,通过求解方程得到球面反射点。给出了应用此方法得到的部分球面反射点,并给出了球柱模型附近半波振子天线的远场方向图。一致性绕射理论结果与FEKO仿真结果吻合较好。     

Measurement of ultrasonic scattering attenuation in austenitic stainless steel welds: Realistic input data for NDT numerical modeling

Multipass welds made of 316L stainless steel are specific welds of the primary circuit of pressurized water reactors in nuclear power plants. Because of their strong heterogeneous and anisotropic nature due to grain growth during solidification, ultrasonic waves may be greatly deviated, split and attenuated. Thus, ultrasonic assessment of the structural integrity of such welds is quite complicated. Numerical codes exist that simulate ultrasonic propagation through such structures, but they require precise and realistic input data, as attenuation coefficients. This paper presents rigorous measurements of attenuation in austenitic weld as a function of grain orientation. In fact attenuation is here mainly caused by grain scattering. Measurements are based on the decomposition of experimental beams into plane-wave angular spectra and on the modeling of the ultrasonic propagation through the material. For this, the transmission coefficients are calculated for any incident plane wave on an anisotropic plate. Two different hypotheses on the welded material are tested: first it is considered as monoclinic, and then as triclinic. Results are analyzed, and validated through comparison to theoretical predictions of related literature. They underline the great importance of well-describing the anisotropic structure of austenitic welds for UT modeling issues.     

一维多孔硅光子晶体反射特性及制作的理论研究

在一维光子晶体光学传输特性理论的基础上,运用传输矩阵法推导了一维多孔硅光子晶体的反射特性,并对其反射特性与结构参数的关系进行了分析。给出了采用脉冲电化学阳极腐蚀法制备一维多孔硅光子晶体的制作模型。利用计算机数值模拟的方法给出了各种一维多孔硅光子晶体的典型反射谱。为多孔硅光子晶体的实际应用奠定了理论基础。     

The double reflection on the interface of uniaxial crystals in the Savart polariscope

The reflection in the Savart polariscope is different from the isotropic medium. The double reflection of rays in the Savart polariscope is analyzed and discussed on the basis of the Snell law. The double reflection formulae of the extraordinary ray and the ordinary ray are given. These results may provide a theoretical and practical guide for studying, developing and engineering polarization interference imaging spectrometers. Supported by the National Natural Science Foundation of China (Grant Nos. 40375010 and 60278019), the Science and Technology Plan Foundation of Shaanxi Province (Grant No. 2005K04-G18), and the Special Research Project of Shaanxi Provincial Educational Department (Grant No. 07JK261)     

剩余反射在激光主动探测中的适用条件分析

阐述用激光主动探测的原理及实验技术.以红外光学系统为例,运用矩阵光学追迹法对光学系统中各镜片的回波强度、分布及影响因素作定性、定量分析,并用实验加以验证.研究结果表明,回波强度受探测距离、扫描激光光束的入射角等因素影响非常大.例如,在主动扫描装置与被探测观瞄仪器相距约1000m、扫描光束的入射角从Orad增大到0.18rad时,光学系统的前两块透镜表面所产生回波能量与发射脉冲能量之比由理想条件下的28.4％下降到0％.     

反位缺陷对碳化硅纳米管电子结构和光学性质影响研究

采用基于密度泛函理论的第一性原理计算对含有反位缺陷（5,5）单壁碳化硅纳米管的电子结构和光学性质进行了研究.纳米管进行结构优化的结果显示,C_Si缺陷在纳米管表面形成了凹陷,Si_C缺陷形成了凸起;反位缺陷在纳米管的导带底附近形成了缺陷能级,使纳米管表现出n型导电的特点,由价带顶到缺陷能级的跃迁,在垂直和平行于纳米管管轴方向上形成了新的介电峰.     

The effect of surface cleanness of thin defects on the reflection of ultrasound

In a previous paper, the authors described experiments in which simulated defects of thickness 20–200 nm were detected ultrasonically. The defects were produced by creating thin gaps between the surfaces of optical flats. A relation between reflectivity and cleanness of the surfaces was noted.This paper describes new experiments and some theoretical considerations which further explore the relation between cleanness and reflectivity. It is concluded that the surface properties of the thin defects tested affect the reflectivity. In particular, it appears that the surface energy of the defect attracts additional material, which provides a mechanism for transmission of sound across the defect.     

CCD扫描法检测模具表面缺陷的研究

介绍了用由面阵 CCD组成的单列阵扫描法测量大型显像管玻壳模具的表面裂纹和砂眼等缺陷。同时还介绍了用软件对图像进行拼接的方法 ,以及采用分维数理论对灰度值进行分割等数据处理技术 ,并获得了较好的实验结果。由实验结果表明 ,该方法的分辨率达到了 0 .0 5 mm。     

Theoretical consideration of an X‐ray Bragg‐reflection lens using the eikonal approximation

On the basis of the eikonal approximation, X‐ray Bragg‐case focusing by a perfect crystal with parabolic‐shaped entrance surface is considered theoretically. Expressions for focal distances, intensity gain and distribution around the focus spot as well as for the focus spot sizes are obtained. The condition of point focusing is presented. The experiment can be performed using X‐ray synchrotron radiation sources (particularly free‐electron lasers).     

Static and dynamic detection of axial surface defects on metallic wires by conical triple laser reflection

The quality of the surface of metallic wires is relevant for different applications. The reflection of a laser beam on the surface of a metallic cylindrical wire provides an efficient way to inspect the quality of its surface. Our interest is focused in the detection of axially oriented defects, which are the most relevant for the wire drawing process. We present a simple interference-geometrical model to describe the light pattern reflected from a wire with defects. This model adequately accounts for the observed results from an industrial prototype developed for the purpose. It incorporates three-laser beams incident on the wire at equidistant locations in its perimeter, which produce three reflection cones with a CCD. This configuration permits to explore the whole perimeter of the wire. Several results are presented, both in static operation and in production line, in agreement with qualitative and quantitative predictions.     

光的反射、折射和全反射演示器

利用自制教具演示了光的反射、折射和全反射现象 ,克服了传统实验仪器的不足 .本文介绍了教具的制作和使用方法     

漫反射各向异性散射介质内的温度热流场

本文采用射线踪迹结合节点分析法和谱带模型,研究了漫反射不透明边界下吸收、发射、各向异性散射介质内的热辐射传递过程。考虑介质辐射能的入射和散射方向,导出漫反射、不透明边界、各向异性散射介质的辐射传递系数。在辐射平衡的情况下,考察了表面发射率和散射反照率对介质内辐射热流和温度场的影响。研究表明,介质不透明边界处存在温度跃迁现象,而且,内界面发射率越大,相应界面温度跃迁越小。     

Reduced back reflection design for an etched diffraction grating based planar demultiplexer

A design for a planar etched diffraction grating (EDG) demultiplexer is presented to reduce the back reflection. By reducing the diffracted field at the input waveguide, the present design makes the best effort to reduce the optical return loss. A design example is given to verify the performance. The spectral response at the input waveguide is simulated and the results show that at the wavelengths that cause back reflection, the reduced back reflection design only receives –47.7 dB of the input power, whereas the design without reduced back reflection receives –3.7 dB of the input power.     

Using ultrasonic wave reflection to measure solution properties

Ultrasonic wave reflection coefficients of aqueous solutions were measured using high-impact polystyrene as a buffer material to provide enhanced sensitivity over metal or ceramic buffer materials. The wave reflection values showed linear reduction when the concentration of chemical species in solution was increased, but a distinct relation between concentration and reflection coefficient was obtained for each solute species tested. However, more unified relationships were observed between reflection coefficient and other solution parameters – solution density, acoustic impedance, and P-wave velocity – that were consistent for all solution species. Based on this behavior an expression to compute solution density solely from reflection coefficient is derived, which can be applied to estimate solution density in solutions of unknown solute species and concentration when other measurements, such as wave velocity, are not possible.     

光在单轴晶体内表面上的反射

基于电磁波边界条件,从几何光学的角度,对单轴日 体内表面上光的反射规律进行了分析和讨论,给出了寻常光和非常光波法线和光线反射的公式,同时指出了上述结果与由费马原理导出的结果是一致的。     

An approximate treatment of reflection coefficient in the phased beam tracing method for the simulation of enclosed sound fields at medium frequencies

The phased beam tracing method (PBTM) was suggested as a medium-frequency simulation technique for the calculation of impulse response, although main assumptions of geometric acoustics still hold. The phased method needs the reflection coefficient for characterizing the acoustic property of a surface and the complex wave number for describing the propagation characteristics. In this study, two types of approximate real reflection coefficients derived from the measured absorption coefficient were tested for a practical applicability. As a test example, pressure impulse responses and energy impulse responses computed from the PBTM were compared with those from the measurement and the ordinary beam tracing method. The PBTM employing the approximate reflection coefficients greatly increased the accuracy of the prediction compared to the ordinary beam tracing method, in particular at the medium-frequency range in octave bands above the Schroeder cutoff frequency. A comparison was made between angle-dependent and angle-independent reflection coefficients in the calculation of acoustic measures. Although the angle-dependent reflection coefficient yielded best matched results with measured data, but the simple angle-independent reflection coefficient can be also used with a reasonably good precision.