Bidirectional reflectance distribution function modeling of one-dimensional rough surface in the microwave band

In this study, the bidirectional reflectance distribution function(BRDF) of a one-dimensional conducting rough surface and a dielectric rough surface are calculated with different frequencies and roughness values in the microwave band by using the method of moments, and the relationship between the bistatic scattering coefficient and the BRDF of a rough surface is expressed. From the theory of the parameters of the rough surface BRDF, the parameters of the BRDF are obtained using a genetic algorithm. The BRDF of a rough surface is calculated using the obtained parameter values. Further, the fitting values and theoretical calculations of the BRDF are compared, and the optimization results are in agreement with the theoretical calculation results. Finally, a reference for BRDF modeling of a Gaussian rough surface in the microwave band is provided by the proposed method.     

Bidirectional reflectance one-dimensional rough distribution function modeling of surface in the microwave band

In this study, the bidirectional reflectance distribution function （BRDF） of a one-dimensional conducting rough surface and a dielectric rough surface are calculated with different frequencies and roughness values in the microwave band by using the method of moments, and the relationship between the bistatic scattering coefficient and the BRDF of a rough surface is expressed. From the theory of the parameters of the rough surface BRDF, the parameters of the BRDF are obtained using a genetic algorithm. The BRDF of a rough surface is calculated using the obtained parameter values. Further, the fitting values and theoretical calculations of the BRDF are compared, and the optimization results are in agreement with the theoretical calculation results. Finally, a reference for BRDF modeling of a Gaussian rough surface in the microwave band is provided by the proposed method.     

Drying of particulate media coatings

Experimental curves of particulate media drying rates show a rapid loss of solvent, which is suggested to be related to thermocapillary fluid convection, and a slower final drying stage related to diffusion. Adsorbed resin plays a major role in preventing void formation.     

Double-layer particulate magnetic recording media

Double-layer media employ two layers with different magnetic characteristics, with the objective of optimizing performance and/or reducing the overall cost. The idea has recently been applied to longitudinally oriented thin top layers of Ba-ferrite (BF) or metal particle (MP) coated over thicker Co-iron oxide (CoFe) or non-magnetic (NM) underlayers resulting in significantly improved recording performance for high recording density video, digital audio and data applications.     

Optical constants of particulate minerals from reflectance measurements: The case of calcite

In this work we describe a new method for the derivation of the optical constants of a particulate sample by means of the Hapke theory, starting from directional-hemispherical reflectance measurements. This approach has been applied to calcite fine grains, whose spectra have been obtained in our laboratory in the spectral range .     

Bi-directional reflectance study on particulate layers: Effects of pore liquid absorption coefficient

We have made bi-directional reflectance distribution function (BRDF) measurements on particulate layers wetted by absorbing liquids. The measurement results indicate that the BRDF tends to become more Lambertian as the interstitial pore liquid becomes more absorbing. The directional hemispherical reflectance, or albedo, of such a layer decreases nonlinearly with a wetting liquid's absorption coefficient. This behavior may be fit by two empirical relationships which independently treat the reflectance from the front surface and reflectance from the bulk material.     

Soft X-ray fluorescence from particulate media: Numerical simulations

We introduce a Monte Carlo ray tracing code for soft X-ray fluorescence in particulate media. We use the code to investigate the observation geometry dependent effects on absolute fluorescence line intensities and relative line ratios due to the medium porosity, incident spectrum, and particle size distribution. In particular, we assess the differences between the results given by the simulations and by the analytical fundamental parameters equation of X-ray fluorescence.     

Ray-tracing simulation of ionization-free filamentation

A new ray-tracing scheme is proposed to simulate the non-linear propagation of ultra-short pulses. The results are in good agreement with experimental data and numerical solving of the non-linear Schrödinger equation in both the self-focusing and the filamentation regions. In particular, they indicate a major contribution of the photon bath in the self-guided propagation of ultra-short pulses. The model suggests that a pure-Kerr self-guiding mode can allow filamentation without ionization. PACS 42.65.Jx; 42.15.Dp     

Inverse solution of ear-canal area function from reflectance

A number of acoustical applications require the transformation of acoustical quantities, such as impedance and pressure that are measured at the entrance of the ear canal, to quantities at the eardrum. This transformation often requires knowledge of the shape of the ear canal. Previous attempts to measure ear-canal area functions were either invasive, non-reproducible, or could only measure the area function up to a point mid-way along the canal. A method to determine the area function of the ear canal from measurements of acoustic impedance at the entrance of the ear canal is described. The method is based on a solution to the inverse problem in which measurements of impedance are used to calculate reflectance, which is then used to determine the area function of the canal. The mean ear-canal area function determined using this method is similar to mean ear-canal area functions measured by other researchers using different techniques. The advantage of the proposed method over previous methods is that it is non- invasive, fast, and reproducible.     

Analysis of one-dimensional rough surface scattering based on bidirectional reflectance distribution function model

Through in-depth analysis of the scattering properties of a one-dimensional random rough surface, a method to calculate the spatial bidirectional reflectance distribution function (BRDF) characteristics of a randomly rough surface is proposed. The scattering characteristics of an electrically large rough surface can be substituted by combination of subsection electromagnetic fields. The radar cross-section (RCS), which is transformed from the BRDF, is compared with numerical results from the Method of Moment (MoM). The agreement of the results verifies that this method could calculate the electromagnetic scattering field efficiently and straightforwardly. Moreover, the resulting combined fields from the BRDF of subsections in the rough surface show a good match with the entire scattering field of a whole surface, which indicates that a large electrically rough surface could be feasibly and effectively substituted with the combination of scattering elements using the BRDF method and the statistical method.     

基于神经网络的粗糙表面双向反射分布函数建模

分析粗糙表面双向反射分布函数的测量方法,提出一种使用人工神经网络技术建立目标表面材料双向反射分布函数模型的方法。给出测量样品多个入射角度下的BRDF随散射角变化的曲线,从中选取部分曲线输入到神经网络,使用贝叶斯正则化方法训练网络,最终获取双向反射分布函数和入射角、散射角的映射关系模型。使用网络模型计算参与训练和未参与训练的输入角度的散射分布曲线,与实验测量曲线进行比较,结果表明：建立的模型正确,具有应用价值。     

Scattering of waves from nonlinear media with rough surfaces

Abstract

Reflection and scattering of waves from plane and statistically rough interfaces between nonlinear media are studied theoretically. New hysteresis-type dependences of the reflection and transmission coefficients on the amplitude of the incident wave and on the angle of incidence are predicted. Scattering diagrams for diffusely reflected and transmitted fields are calculated. It is found that when the dielectric constant is a steep function of the incident amplitude, nonlinearity suppresses the Bragg resonant scattering mechanism. Smooth roughness of the boundary is shown to enhance the penetration of evanescent waves into nonlinear media.     

Maximum time-resolved hemispherical reflectance of absorbing and isotropically scattering media

This paper presents a parametric study of the time-resolved hemispherical reflectance of a plane-parallel slab of homogeneous, cold, absorbing, and isotropically scattering medium exposed to a collimated Gaussian pulse. The front surface of the slab is transparent while the back surface is assumed to be cold and black. The 1-D time-dependent radiation transfer equation is solved using the modified method of characteristics. The parameters explored include (1) the optical thickness, (2) the single scattering albedo of the medium, and (3) the incident pulse width. The study pays particular attention to the maximum transient hemispherical reflectance and identifies optically thin and thick regimes. It shows that the maximum reflectance is independent of the optical thickness in the optically thick regime. In the optically thin regime, however, the maximum hemispherical reflectance depends on all three parameters explored. The transition between the optically thick and thin regimes occurs when the optical thickness is approximately equal to the dimensionless pulse width. Finally, correlations relating the maximum of the hemispherical reflectance as a function of the optical thickness, the single scattering albedo of the materials, and the incident pulse width have been developed. These correlations could be used to retrieve radiation characteristics or serve as initial guesses for more complex inversion schemes accounting for anisotropic scattering.     

Reduced-order modeling of time-dependent reflectance profiles from purely scattering media

Due to the widespread existence and importance of foam, inverse techniques for characterizing industrial foams are of interest. An essential element in an inverse method used to characterize a foam layer is a model of the time-dependent reflectance of a laser pulse. Monte Carlo methods may be used to accurately model reflectance, but these methods are computationally expensive. Computationally efficient methods based on the diffusion approximation have been developed, but this approach is not sufficiently accurate in many cases of interest. Therefore, a computationally efficient and robust method is desirable. This paper presents a computationally efficient method for modeling the time-dependent reflectance of a laser pulse from a non-absorbing, scattering plane layer that is based on reduced-order modeling techniques. The accuracy of the proposed method is demonstrated by comparing reflectance profiles for randomly selected foam layer properties with corresponding profiles that were generated from Monte Carlo simulations.     

Sweep rate measurements of coercivity in particulate recording media

The coercivity dependence on the sweep rate is measured for different particulate recording media. The data is fitted to a new theory form which the anisotropy field H_K is calculated using the activation volume of reversal. The values of H_K obtained from the fit are smaller than the values for torque measurements.     

The determination of the fluctuation field in particulate media

We have measured the fluctuation field as a function of applied field using Néel method and a new waiting time experiment which given H_f directly from time dependence measurements. Both methods give similar values for the fluctuation field although the latter technique has the advantage that X_irr need not be determined.     

降低微通道板输入面电极反射率的技术途径

 为了降低透明或半透明光电阴极的光子在微通道板输入面上引起的散射噪声,通过对微通道板输入面蒸镀Ni-Cr电极后对反射率影响的定性分析以及镀膜方式、镀层厚度、电极深入通道内的深度和微通道板的开口面积比等测试分析,在兼顾微通道板对输入电极其他要求的前提下,获得了降低反射率的有效技术途径,即：采用电子束加热的蒸镀方式,用表面电阻大小来间接表征膜层厚度,使其控制在100 Ω左右;电极深入通道内的深度为通道直径的35%;微通道板的开口面积比尽可能大些,可把反射率降低到4%以下,以此降低微光像增强器的光子散射噪声。