Frequency-dependent reflection of elastic wave from thin bed in porous media

The reflection of elastic wave from thin bed in porous media is important for oil and gas reservoir seismic exploration.The equations for calculating frequency-dependent reflection amplitude versus incident angle(FDAVA) from thin bed in porous media are obtained based on porous media theory. Some conclusions are obtained from numerical analysis, specifically, slow compression wave may be ignored when considering boundary conditions in most situations; the dispersion of reflection from thin bed is much higher than that from thick layer and is periodic in frequency domain, which is affected by the thickness of thin bed, velocity, and incident angle; the reflection amplitude envelope in frequency domain decays exponentially, which is affected by the thickness of thin bed, attenuation, and incident angle; the reflection amplitude increases with thickness of thin bed increasing, and then it decreases when the thickness reaches to a quarter of wavelength.     

Omnidirectional reflectance gaps and resonant tunneling effect in a one-dimensional photonic crystal consisting of two metamaterials

We investigate the properties of electromagnetic wave propagating in a one-dimensional photonic crystal (PC) consisting of two metamaterials with different dispersive model. The reflection gaps of metamaterials multilayer system are independent of the incident angle. Not only TE wave but also TM wave, the omnidirectional reflection gaps exhibit the same behavior with different incident angle for metamaterials as double negative material. We also observed that the frequency regimes of zero-transmission bands are different for TE and TM wave with the same incident angle, when one of metamaterials is the permittivity negative (ε < 0) and the other is the double negative. Correspondingly, we show that the result can be act as an efficient polarization splitter. At last, we discuss the resonant tunneling effect. If the total reflection condition is satisfied, the resonant tunneling effect is enhanced as the incident angle increases, even though the propagation wave is evanescent wave in the single layer medium.     

高斯光束在单轴挛晶界面上的反射与折射

给出了高斯光束入射到挛晶结构的电磁场分布,解出了反射系数和透射系数。根据晶体的色散关系解出了入射角、反射角和折射角关于晶体参量及波矢的方程,并根据角度方程给出了在一定参量下反射角和折射角关于入射角变化的关系图,以图示的方法显示了光束在界面处的异常性质。根据角度关系和反射、透射系数分析了异常光束在界面处能够出现二性折射、负反射、全透射和全反射等光束的奇特性质;分析了出现这些奇特性质对晶体参量和入射角所要求的条件。根据时间平均的能流密度公式,用数值模拟的方法给出了二性折射、全透射和全反射在特定参量下的高斯光束在挛晶内的能流密度分布图及当发生全反射时不同宽度光束在界面处关于入射角的古斯-亨兴(Goos-Hanchen)位移。     

Model and experimental analysis of oblique incident ultrasound in a tissue layer using doublet mechanics theory

The fundamental framework of doublet mechanics (DM) is used to analyze high-frequency ultrasound wave propagation in materials with discrete microstructure. Ultrasonic reflection coefficients were measured from a thin layer of tissue embedded between two glass substrates at oblique incidence. Theoretical calculations for the reflection coefficients of a multi-layered system at oblique angles are performed using both DM theory and the classical continuum mechanics theory (CCM). For example, at the frequency of 10 MHz at incident angle 8° in sample with 30 μm thickness, the discrepancy in the magnitude of the reflection coefficient between experimental results and theoretical prediction is 15.8% for DM but 79.0% for CCM; similar results at other frequencies and incident angle in the samples with 30 and 60 μm thickness have also been obtained, which demonstrates that the DM theory can better describe the wave propagation in tissue. The influence of the incident angles and tissue thickness are also discussed in this paper.     

海面冰层对声波的反射和散射特性

北极海面冰层复杂多变,其对声波的反射和散射严重影响冰下水声信道的传输特性,建立海面冰层的声波反射和散射模型对冰下水声通信研究具有重要意义.假设海面冰层为多层固体弹性介质且冰-水界面粗糙,满足微扰边界条件,导出声波从海水介质入射到海面冰层时相干反射系数满足的线性方程组.对相干反射系数随声波频率、掠射角、冰层厚度的变化进行数值分析.进一步引入根据散射声场功率谱密度计算散射系数的方法,改变掠射角,对冰层厚度、散射掠角对散射系数的影响进行研究.     

振荡介质中平面波的反射

在复金慈堡-朗道方程描述的振荡介质中研究了平面波的反射.从理论上给出了产生反射的条件,导出了反射波和入射波这两个区域的分界线与两种介质分界线的夹角.发现两类反射,一类为回折射产生的反射,对于这类反射,理论上给出了反射角;另一类为纯反射,它与折射无关.理论分析与数值模拟结果均表明：只有当入射角大于临界入射角才会发生反射,而且反射角等于临界入射角;对于纯反射,反射角随波频率增大而增大. 关键词： 复金慈堡-朗道方程 平面波 反射     

Reflection of Lamb waves obliquely incident on the free edge of a plate

The reflection of obliquely incident symmetric and anti-symmetric Lamb wave modes at the edge of a plate is studied. Both in-plane and Shear-Horizontal (SH) reflected wave modes are spawned by an obliquely incident in-plane Lamb wave mode. Energy reflection coefficients are calculated for the reflected wave modes as a function of frequency and angle of incidence. This is done by using the method of orthogonal mode decomposition and by enforcing traction free conditions at the plate edge using the method of collocation. A PZT sensor network, affixed to an Aluminum plate, is used to experimentally verify the predictions of the analysis. Experimental results provide support for the analytically determined results.     

Application of the wavenumber jump condition to the normal and oblique interaction of a plane acoustic wave and a plane shock

A kinematic approach is considered whereby the wavenumber jump conditions in conjunction with the appropriate dispersion relations is applied to the investigation of the normal and oblique interaction of a plane acoustic wave with a plane shock wave. For the normal interaction of an acoustic wave with a stationary plane shock a logarithmic shift in the wave spectra is obtained. For the normal interaction with a moving shock front it is shown that for shock Mach numbers above a critical value, the frequency of the transmitted wave becomes negative. This results in the fact that the crests of the transmitted signal arrive at a fixed observer in a reverse order to their generation. Finally, the oblique interaction of an acoustic wave with a stationary shock is considered. The “Snell's Law” for the transmitted wave is derived and two special angles of incidence are identified. The first is a no-refraction angle: i.e., the transmitted wave angle is the same as the incident wave angle. The second is a critical angle such that for incident angles greater than this critical angle there is no transmitted wave. A necessary and sufficient condition for the existence of a transmitted wave is derived in terms of the speed of sound and Mach number of the fluid and the frequency and tangential wavenumber component of the incident wave.The dynamics aspects of the interaction concerning the determination of the frequency independent transmission coefficients and shock displacements are determined for the simple case of the normal interaction with a moving shock as an illustration.     

Simulation and analysis of interaction between oblique incidence electromagnetic wave and plasma slab

Numerical simulation of interaction between plasma slab and electromagnetic wave which has different incident frequency and incident angle is discussed in this paper. Some parameters contain reflection coefficient, transmission coefficient, reflectance, transmittance and phase are calculated by transfer matrix method. The relation of these parameters with incident frequency and incident angle is analyzed. The results show that the incident angle has low influence on the parameters when the angle varies from 0° to 30° and from 70° to 90°, but it has high influence on the parameters when it changes from 30° to 70°. These rules have certain directive significance to the research of interaction between oblique incidence electromagnetic wave and plasma slab and to the design of plasma layer.     

Reflection and transmission of plane waves at the interface of pyroelectric bi-materials

A simple reflection and transmission theory of plane waves at the interface of pyroelectric media is studied in this paper. In an infinite homogeneous pyroelectric medium, there are four bulk wave modes: quasi-longitudinal (QL), two quasi-transversal (QT) and one temperature (T) waves, whose velocities depend on the frequency and incident angle. Simultaneously, a quasi-surface (QS) wave on each side of the interface of pyroelectric bi-materials will appear in the general reflection and transmission problem. The quasi-surface wave has the same wave vector component with the incident waves along the interface plane. So, the reflection and transmission problem is different with the propagation wave in the infinite homogeneous space, but it is still solvable. In the reflection and transmission problem, there are ten complex continuous conditions on the interface, which are satisfied by the bulk and quasi-surface waves together. Numerical calculations are performed for bi-material PZT-6B/BaTiO₃. Incidences of the quasi-longitudinal and quasi-transversal waves from the side of PZT-6B or BaTiO₃ medium are discussed. The reflection and transmission amplitude coefficients and energy flow ratios varying with the incident angle are examined.     

各向异性光子晶体的全反射隧穿偏振特性

为了研究一维各向异性光子晶体的全反射隧穿偏振特性,利用传输矩阵法计算了TE波和TM波以大于全反射角入射一维各向异性光子晶体时的透射率,在透射波中发现了TE波和TM波的一、二级全反射隧穿带.得出了与一维各向同性光子晶体的全反射隧穿效应的不同点,即TE波和TM波的一、二级全反射隧穿带的频率中心和频率宽度存在着较大的差异,利用这个特性可以将两种偏振光进行频率分离,为设计优质偏振滤波器提供理论依据.     

电介质膜对受抑全内反射结构中古斯-汉欣位移的增强

受抑全反射结构中,反射光束和透射光束的古斯汉欣(Goos-Hanchen)位移同时存在,对称双棱镜结构的受抑全反射古斯汉欣位移通常只有波长量级,在实验中很难测量。计算了在入射角大于棱镜与空气界面的临界角小于棱镜与薄膜界面临界角时,镀有电介质膜的对称双棱镜的受抑全反射过程中入射光束的反射系数和透射系数的复数表达式。利用稳态相位法计算得出透射光束和全反射光束的古斯汉欣位移。结果表明,反射光束和透射光束古斯汉欣位移量相同,与入射角大小、薄膜厚度以及空气层厚度有关。在入射角小于但接近棱镜与薄膜界面的临界角,薄膜厚度和空气层厚度一定时,古斯汉欣位移量共振增强达到波长的数百倍。     

Double and negative reflection of cold atoms in non-Abelian gauge potentials

Atom reflection is studied in the presence of a non-Abelian vector potential proportional to a spin-1/2 operator. The potential is produced by a relatively simple laser configuration for atoms with a tripod level scheme. We show that the atomic motion is described by two different dispersion branches with positive or negative chirality. As a consequence, atom reflection shows unusual features, since an incident wave may split into two reflected ones at a barrier, an ordinary specular reflection, and an additional nonspecular one. Remarkably, the latter wave can exhibit negative reflection and may become evanescent if the angle of incidence exceeds a critical value. These reflection properties are crucial for future designs in non-Abelian atom optics.     

微波光学组合实验中大角度入射时反射波波强极大方向的确定

利用PASCO微波光学组合实验装置,分析了微波大角度反射偏离反射定律的原因,给出了可视为大角度入射时的最小入射角,定量地计算了大角度入射时微波反射波极大时的反射角.     

Study on modulation of near infrared radiation based on plasma photonic crystal

In this paper, a plasma photonic crystal (PPC) for infrared radiation modulation which is composed of indium tin oxide (ITO) and plasma is proposed. The performance of plasma photonic crystal in near infrared radiation modulation is researched by transfer matrix method (TMM). The simulation results show that the near infrared radiation pass band can be adjusted by the changing of plasma frequency of plasma. The reflection to near infrared radiation by plasma photonic crystal increases with plasma frequency and that of absorption decreases. In addition, the modulation performance of the plasma photonic crystal at different incidence wave angles is also studied. The results show that the incident wave angles have little effect on the transmission of plasma photonic crystal in near infrared band. The reflection of the plasma photonic crystal to near infrared radiation decreases with increasing of the incident wave angle, but that of the absorption increases with the incident wave angle. Therefore, the proposed plasma photonic crystal has a potential application in tunable near infrared filter devices.     

均匀等离子体光栅的色散特性研究

最近研究表明,两束交叉激光脉冲在等离子体中传播时,可以诱导生成周期等离子体密度调制(或称等离子体布拉格光栅). 分别利用传输矩阵法和耦合模理论,推导了激光斜入射时等离子体光栅的色散关系. 两种方法均表明,均匀等离子体光栅存在着光子带隙结构,并且在带隙附近有强烈的色散. 当激光斜入射时,带隙结构会呈现不同的偏振特性：S偏振光的带隙宽度随着入射角的增大而逐渐变宽,而P偏振光的带隙宽度随着入射角的增大先迅速变窄,在布儒斯特角入射时带隙消失,然后又随着入射角的增大而迅速变宽. 超宽的光子带隙和超高的激光损伤阈值,使得等离子体光栅有望成为一种新型的操纵强激光脉冲的光子器件. 关键词： 等离子体光栅 传输矩阵法 耦合模理论 光子带隙     

Improving attosecond pulse reflection by large angle incidence for a periodic multilayer mirror in the extreme ultraviolet region

The improvement of attosecond pulse reflection by large angle incidence for a periodic multilayer mirror in the extreme ultraviolet region has been discussed. Numerical simulations of both spectral and temporal reflection characteristics of periodic multilayer mirrors under various incident angles have been analyzed and compared. It was found that the periodic multilayer mirror under a larger incidence angle can provide not only higher integrated reflectivity but also a broader reflection band with negligible dispersion, making it possible to obtain better a reflected pulse that has a higher pulse reflection efficiency and shorter pulse duration for attosecond pulse reflection. In addition, by increasing the incident angle, the promotion of attosecond pulse reflection capability has been proven for periodic multilayer mirrors with arbitrary layers.     

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提出碰撞吸收型等离子体的等效折射指数,重新计算了折射角,并与利用常规方法得到的折射角进行了比较。分析了等离子体密度和碰撞频率对折射角的影响。考察了斜入射电磁波在吸收型等离子体中的折射特性,并以一维非均匀碰撞吸收型等离子体为例,对斜入射电磁波的反射特性进行了考察。结果表明,等效折射指数的概念涵盖了入射角度的影响,在考察斜入射时更准确、便捷。     

线偏振光在手征负折射介质中的古斯汉欣位移特性研究

从理论上分析了手征负折射介质中的横向位移特性,给出了线极化波入射条件下发生全反射时的横向位移随入射角的关系曲线。当入射角处于两个本征波的临界角之间时,TE和TM分量对应的横向位移方向相反。而当入射角大于全内反射角时,两个分量都将朝着正方向发生横向位移。通过比较发现手征负折射介质中的古斯汉欣位移特性与常规介质和一般手征介质也有着很大的不同之处。     

Rayleigh wave scattering from a vertical edge of isotropic substrates

The paper numerically studies the harmonic Rayleigh wave scattering at the 90-degree corner of isotropic substrate. The finite element method is used. The main attention is paid to two cases. The first one is the apex of the substrate corner is rounded off. The second one consists in that a layer of foreign material is deposited on the face which scatters the Rayleigh wave. The dependence of the reflection and the transmission coefficients on the Poisson ratio, the angle of incidence, the fillet radius, and the layer thickness are obtained. It is found that if the Rayleigh wave is incident perpendicularly to the substrate border, then the fillet of small radius as compared to the wavelength increases the reflection coefficient and decreases the transmission coefficient by factors 1.3–1.8. At normal incidence, the Poisson ratio does not change qualitatively the dependence of the reflection and transmission coefficients on the fillet radius. But the Poisson ratio can substantially affect the angle dependence of these coefficients if the wave is incident obliquely on the corner rounded off. It is also found out that a layer can modify the conditions of scattering such that the incident wave is totally reflected without transmission and conversion into bulk waves in a wide interval of angle of incidence, although, in principle, the bulk wave generation is allowed within a part of this angle interval.