A novel broadband terahertz filter for photonic crystal

Abstract

The influence of the change of the radius of point defect cylinders, scattering dielectric cylinders, dielectric cylinders on both sides of line waveguide on S parameter is studied. According to the resonant coupling principle between micro-cavity and waveguide, a novel broadband terahertz filter is designed. The novel filter is formed by introducing scattering dielectric cylinders into the resonant microcavity, and the point defect cylinders are composed of HgTe material and adjusting the radius of dielectric cylinders on both sides of line waveguide. Results show that the 3 dB bandwidth reaches 74.2 GHz, the return loss is less than ?12.02 dB, the maximum insertion loss in-band reaches 0.35 dB and its drop efficiency is up to 96.79%. The novel terahertz filter has flat passband, sharp rejections at out-bands and its central frequency is 0.338THz. The good performances show that it can meet the requirements of high speed and broadband in terahertz atmosphere communication I window.     

Light scattering simulation by oblate disc spheres using the null field method with discrete sources located in the complex plane

The T-matrix method, which is also known as the null field method (NFM) or extended boundary condition method (EBCM), has established itself as a well known and highly regarded method for calculating light scattering by non-spherical particles. Its biggest advantage is the possibility to obtain all information about the scattering characteristics of the particle and to store it into one matrix. This enables one to do additional investigations with low efforts. Unfortunately the standard NFM fails to converge for particles with extremely non-spherical particle shapes, like long cylinders or coin-like flat cylinders. In this paper we investigate light scattering by finite particles in the form of an oblate disc sphere, which can be described as flat cylinders with a rounded edge. We use an advanced form of the T-matrix method—the null field method with discrete sources (NFM-DS). By presenting light scattering results we would like to demonstrate the potential this advanced NFM-DS offers. It allows one to calculate particle shapes with aspect ratios (relation between radius and thickness of the particle) up to 100:1 and size parameters (relation between radius and wavelength) up to 30.     

Radiative heat transfer of ultra‐fine powder insulation in nonplanar geometry

Abstract

The purpose of this work is to study the radiation heat transfer through some typical ultra‐fine powder insulations. The spectral extinction coefficients for these powders have been measured via infrared transmission measurements. The experimental results are compared with both the dependent and independent scattering and absorption theoretical calculations. The radiative transport process is modeled by the diffusion approximation method. Based on the experimental data, the radiant thermal conductivity between two concentric cylinders and spheres was calculated. The results show that the radiant thermal conductivity between two concentric spheres is about 50 percent higher than that between two cylinders.     

Reconstruction of Scattering Potentials from Incomplete Data

Abstract

In many situations encountered in physics and in other fields, one can frequently experimentally determine some but not all the Fourier components of a scattering potential. In this paper we present an integral equation which makes it possible to reconstruct any square-integrable function f(r) of finite support from the knowledge of its Fourier transform j (K) over any finite three-dimensional domain of K space. We illustrate the use of this integral equation by application to potential scattering at fixed energy and we show how it can be used to reconstruct details of the scattering potential beyond the usual resolution limit from measurements of the scattered field in the far zone of the scatterer.     

Pressure distribution in an assembly of wooden cylinders with various aspect ratios under uniaxial confined compression

Understanding how forces propagate in granular assemblages is important for equipment design and process control in many technologies. Yet, it remains poorly understood. In this study, a cuboidal assembly comprising cylinders of various lengths (aspect ratios AR ranging from 0.9 to 3.6) were subjected to uniaxial confined compression tests. Samples were vertically compressed until the top platen exerted a pressure of 50 kPa on the uppermost particles. This maximum pressure corresponds to the hydrostatic pressure of an approximately 15 m high column of chopped wood that may be encountered in real storage structures. The nonlinear loading curves were obtained depended on the aspect ratios of the cylinders. The modulus of elasticity, calculated from the linear elastic part of the stress–strain curve, monotonically decreased from 10.2 to 8.6 MPa as the aspect ratio increased from 1.2 to 3.6. The elastic modulus and volume fraction exhibited similar trends as functions of the aspect ratio. The horizontal-to-vertical pressure ratio was calculated as the horizontal pressure exerted on the wider walls to the vertical pressure exerted on the top lid during loading–unloading cycles. For ARs up to 3.6, the pressure ratio was approximately 0.31; for the longest cylinders (AR = 3.6), it decreased to approximately 0.27, probably because the assumption of the representative chamber volume was invalidated at this AR.     

On the Validity of Soft-particle Approximations for the Scattering of Light by Infinitely Long Homogeneous Cylinders

Abstract

The relationship between the Hart-Montroll approximation and various other soft particle approximations has been examined for the scattering of light by infinitely long homogeneous cylinders. Numerical comparisons of this approximation with exact results and other approximations have been presented. It is noted that this approximation can be used to obtain the diameter of the particles to within 1% in the domain 1·05  m  1·15 and 5  x  20·0, m and x being the relative refractive index and the size parameter of the particle respectively.     

A Rigorous Theory for Problems of Scattering: The Delta Boundary Operator Method

Abstract

A rigorous approach for solving a large class of scattering problems is presented and implemented for the classical problem of scattering by a perfectly conducting circular cylinder. This method is characterized by the preliminary calculations of a ψ distribution, deduced from a new kind of boundary value problem. This ψ distribution allows us to express the surface current density in the form of the integral of a known function, valid for any kind of incident wave. Numerical comparisons with the classical method are performed. A numerical study of ψ allows us to deal with cylinders having diameters larger than 100 wavelengths on a HP 1000 F minicomputer.     

Single scattering of light by circular cylinders

We consider two topics pertaining to light scattering by circular cylinders. (A) Scattering properties of cylinders with increasing aspect ratio are studied. It is shown that the solution for finite cylinders does not converge to the solution for infinitely long cylinders if the aspect ratio increases. This is due to differences in the treatment of diffraction for finite and infinite cylinders. (B) Finite cylinders have sharp edges, so their scattering properties differ from those of spheroids having the same aspect ratio. To illustrate these differences we present scattering matrix elements of cylinders and spheroids for a large set of aspect ratios. To handle the large amount of data, the scattering matrix elements as functions of aspect ratio and scattering angle are presented in so-called three-dimensional figures.     

Validity of the cylindrical localized approximation for arbitrary shaped beams in generalized Lorenz-Mie theory for circular cylinders

Abstract

A so-called cylindrical localized approximation, allowing one to speed up the evaluation of beam shape distributions in generalized Lorenz-Mie theory for circular infinitely long cylinders, has been previously introduced and, in the case of Gaussian beams, rigorously justified. In this paper, we examine and demonstrate the validity of this approximation for arbitrary shaped beams.     

Local cross-sections and energy efficiencies in the multiple electromagnetic/optical scattering by two perfect electrically-conducting cylindrical particles

Exact mathematical expressions for the intrinsic electromagnetic (EM) cross–sections (i.e. extinction, scattering and absorption) for a pair of perfectly conducting circular cylinders in a homogeneous non–absorptive medium are derived. The multipole expansion method in cylindrical coordinates and the translational addition theorem, applicable to any range of frequencies or particle sizes are used. An effective EM field, incident on the probed cylinder is defined first, which includes the initial and re-scattered field from the second cylinder. It is used jointly with the scattered field to derive the mathematical expressions for the intrinsic/local cross–sections. Numerical computations for the intrinsic extinction (or scattering) energy efficiencies per unit-length for a pair of conducting circular cylinders with different radii in a homogeneous medium are considered. The results computed a priori can be useful in the full characterization of a multiple scattering system of many particles, in conjunction with experimental data for the extrinsic cross–sections.     

Simulation of multiple scattering in lidar measurements using pure rotational raman scattering (PRRS)

Abstract

Pure rotational Raman scattering signals from atmospheric gases such as nitrogen and oxygen can be used to deduce the temperature of the atmosphere. Previously, this method has been successfully implemented as a remote temperature sensing lidar system. In this paper, theoretical studies of the method have been carried out using Monte Carlo simulations for different temperature profiles from radio sonde data. The geometry of the lidar as well as the aerosol profiles of the atmosphere can be specifically defined in this method. It is important to understand whether or not multiple scattering will have a significant effect on the accuracy of temperature retrieval from the measured lidar returns. From the exact pure rotational Raman scattering matrix, we have computed the lidar returns of individual Raman lines. We have given the ratios of multiple to single scattering return signals for atmospheres without clouds, with water clouds and with cirrus clouds. The results indicate that the effect of multiple scattering does not give errors to the temperature inversion for typical atmospheric conditions.     

Scattering of light by polydisperse, randomly oriented, finite circular cylinders

We use the T-matrix method, as described by Mishchenko [Appl. Opt. 32, 4652 (1993)], to compute rigorously light scattering by finite circular cylinders in random orientation. First we discuss numerical aspects of T -matrix computations specific for finite cylinders and present results of benchmark computations for a simple cylinder model. Then we report results of extensive computations for polydisperse, randomly oriented cylinders with a refractive index of 1.53 + 0.008i, diameter-to-length ratios of 1/2, 1/1.4, 1, 1.4, and 2, and effective size parameters ranging from 0 to 25. These computations parallel our recent study of light scattering by polydisperse, randomly oriented spheroids and are used to compare scattering properties of the two classes of simple convex particles. Despite the significant difference in shape between the two particle types (entirely smooth surface for spheroids and sharp rectangular edges for cylinders), the comparison shows rather small differences in the integral photometric characteristics (total optical cross sections, single-scattering albedo, and asymmetry parameter of the phase function) and the phase function. The general patterns of the other elements of the scattering matrix for cylinders and aspect-ratio-equivalent spheroids are also qualitatively similar, although noticeable quantitative differences can be found in some particular cases. In general, cylinders demonstrate much less shape dependence of the elements of the scattering matrix than do spheroids. Our computations show that, like spheroids and bispheres, cylinders with surface-equivalent radii smaller than a wavelength can strongly depolarize backscattered light, thus suggesting that backscattering depolarization for nonspherical particles cannot be universally explained by using only geometric-optics considerations.     

Suppression of Multiple Scattering by Photon Cross-correlation Techniques

Abstract

With growing scientific interest in concentrated colloidal systems, multiple scattering becomes a major obstacle in many light-scattering experiments. Stimulated by work of Phillies and Drewel, three different dual-beam dual-detector dynamic light scattering experiments are discussed, which all achieve the isolation of singly scattered light by photon cross-correlation. All three experiments allow for a large variation of the scattering angle—an important requirement for studies of interacting systems.     

Scattering Matrices for Slightly Non-spherical Particles

Abstract

In this paper the theory of light scattering by slightly non-spherical particles is developed and the forms of the amplitude and Stokes scattering matrices are derived. Forward-scatter and backscatter and the information they give about the shape of the particle are discussed as special cases.     

Analytic study of radiative heat transfer in ultra‐fine powder insulations with dependent scattering and absorption

Abstract

In this work, the radiative heat transfer of the ultra‐fine powder insulation Aerosil 380, with dependent scattering and absorption, is investigated theoretically. The radiative transport process is modeled by the two‐flux model and the diffusion approximate method to solve the government equations of transfer. The radiative properties of Aerosil 380 have been determined by the Rayleigh scattering theory because of the small values of particle size parameter. The results show that the dependent effect of scattering will reduce the scattering efficiency; however, the absorption efficiency will be increased due to the dependent absorption. The overall thermal radiation resistance is increased by the dependent effect. A comparison of radiative thermal conductivity has been calculated by the two models. The comparison reveals that the difference is small at a mean temperature of 300°K, but that the difference goes up to about 30 percent at a mean temperature of 400°K.     

Barrelling of aluminium solid cylinders during cold upset forging with constraint at one end

Abstract

Experiments were carried out to generate data on the cold upset forging of solid cylinders of annealed aluminium using different lubricants, with a die at one end providing a constraint. The die had created back extrusion of metal through its hole and developed two barrels in the unrestrained portion of the cylindrical specimens. The curvatures of the barrels, top and bottom, developed in the unrestrained portion were found to conform one to one to calculated values using experimental data. The calculations were made on the assumption that the curvatures of the barrels followed circular arc geometry. It was further found that the measured radius of curvature of both barrels exhibited a straightline relationship with the new geometrical shape factor, irrespective of the aspect ratios of the cylinders. Further empirical relations were found to exist between the measured radius of curvature of both barrels and other variables, namely hydrostatic stress and stress ratio parameter.     

Silver Halide (Sensitized) Gelatin in Agfa-Gevaert Plates: The Optimized Procedure

Abstract

Silver halide sensitized gelatin (SHSG) is one of the most promising techniques for the fabrication of transmission holographic optical elements, achieving relatively high sensitivity of photographic material with the low scattering and high light stability of dichromated gelatin. In this paper we present the optimized procedure in Agfa-Gevaert plates. Diffraction gratings with a diffraction efficiency up to 80% and a noise level of less than 1% are obtained with a sensitivity 10³ times better than dichromated gelatin.     

Scattering matrix of infrared radiation by ice finite circular cylinders

Scattering matrix characteristics of polydisperse, randomly oriented, small ice crystals modeled by finite circular cylinders with various ratios of the length to diameter (L/D) ratio are calculated by use of the exact T-matrix approach, with emphasis on the thermal infrared spectral region that extends from the atmospheric short-wave IR window to the far-IR wavelengths to as large as 30 microm. The observed ice crystal size distribution and the well-known power-law distribution are considered. The results of the extensive calculations show that the characteristics of scattering matrix elements of small ice circular cylinders depend strongly on wavelengths and refractive indices, particle size distributions, and the L/D ratios. The applicability of the power-law distribution and particle shapes for light scattering calculations for small ice crystals is discussed. The effects of the effective variance of size distribution on light scattering characteristics are addressed. It seems from the behavior of scattering matrix elements of small ice crystals that the combination of 25 and 3.979 microm has some advantages and potential applications for remote sensing of cirrus and other ice clouds.     

Mixed convection of non-Newtonian nanofluid in an H-shaped cavity with cooler and heater cylinders filled by a porous material: Two phase approach

In the present problem, two-phase mixed convection of a non-Newtonian nanofluid in a porous H-shaped cavity is studied. Inside the enclosure there are four rotating cylinders, using the Boussinesq approximation, mixed convection is created. Nanofluid includes H₂O + 0.5% CMC and copper oxide nanoparticles. The mixture model was used to model physical phenomena. Different aspect ratios were used in order to achieve the best heat transfer rate. The Darcy and Richardson numbers ranges are 10⁻⁴ ≤ Da ≤ 10⁻² and 1 ≤ Ri ≤ 100 respectively. Also, the aspect ratio and dimensionless angular velocities of cylinders ranges are 1.4 ≤ AR ≤ 1.6 and −10 ≤ Ω ≤ 10 respectively. Streamlines and isotherm-lines contours have been obtained for the variation of Darcy and Richardson numbers, aspect ratio and angular velocity. The heat transfer rates have been obtained for various aspect ratios, Darcy and Richardson numbers, and the direction of the cylinder's rotation, and are compared with each other. The results show that the direction of cylinders rotation influences the strength and extent of the generation vortices. Also, the use of porous material in high permeability can be a good alternative to lowering the angular velocity of the cylinders and ultimately reducing the need for less energy.