基于二维声子晶体多通道线缺陷结构的定向声激发

提出一种基于声子晶体线缺陷波导的多通道结构来实现声波定向激发.一束入射声波在该结构中传播时被分割成多束分支,这些分支声束到达输出端时具有相等的相位,进而在输出端产生具有高度准直形态的辐射场分布.该辐射场分布的半高宽具有反比于结构中通道数的特点.数值模拟结果与实验结果同时验证了这种结构的声定向效应.相对于大多数已有的声波定向方案,这种结构具有简单从而易于制备的优点.     

基于二维声子晶体多通道线缺陷结构的定向声激发（英文）

提出一种基于声子晶体线缺陷波导的多通道结构来实现声波定向激发。一束入射声波在该结构中传播时被分割成多束分支,这些分支声束到达输出端时具有相等的相位,进而在输出端产生具有高度准直形态的辐射场分布。该辐射场分布的半高宽具有反比于结构中通道数的特点。数值模拟结果与实验结果同时验证了这种结构的声定向效应。相对于大多数已有的声波定向方案,这种结构具有简单从而易于制备的优点。     

固-固结构声子晶体中弹性波的禁带及其转型

引入四维波矢的概念,推导出弹性波斜入射固-固结构声子晶体的转移矩阵以及透射系数公式.利用这些公式计算了纵波和横波斜入射固-固结构声子晶体时纵波和横波的透射系数.结果表明:当纵波斜入射时,在透射波中纵波会出现禁带,并且也出现了纵波向横波的转型,随着入射角的增大转型越明显.当横波斜入射时也会出现类似于纵波斜入射时的现象.这些公式成功地解决了弹性波斜入射固-固结构声子晶体的传输问题和转型问题.     

两类一维流固声子晶体全向透射特性比较研究

研究了声纵波全向入射到两类一维流固声子晶体(第Ⅰ类满足固体横波传播速度cst大于流体纵波传播速度c1以及第Ⅱ类cst＜cl)的透射特性.推导了其传递矩阵,并应用有限元方法进行验证,二者显示结果一致性.研究表明两类声子晶体呈现的不同声透射特征:第Ⅰ类声子晶体中,高频声波在斜入射角大于第二全反射临界角条件下发生全反射现象,而低频声波却呈现全反射贯穿效应;第Ⅱ类声子晶体中,在整个频段范围内均会出现周期性的透射导带.两类声子晶体均出现了低频声裂隙现象,第Ⅱ类声子晶体低频声裂隙角范围明显大于第Ⅰ类.     

基于微机械加工工艺的声子晶体器件

声子晶体是一种周期复合人工超材料.声子晶体具有独有的声学特性-声学禁带,使其在声波控制和传输领域具有极强的应用潜力.利用微机械加工工艺制备的硅基声子晶体器件,可在微机电系统中实现高频弹性波的定向传输和控制,以及对弹性波能量的局域放大.设计了两种基于MEMS工艺的器件,分别用于实现功分器和谐振器的功能.内容覆盖了硅基声子晶体器件的背景、原理、设计、制造和表征等方面.     

基于声子晶体环形腔的可调声波分插滤波器

设计了两个声子晶体线缺陷波导,通过环形谐振腔耦合,构造出声波分插滤波器,可以上传、下载高品质的声波导模.文中采用有限元方法分析声波在平台中的传播,结果表明,采用方柱体为散射体,谐振腔内腔平滑,可以增强谐振腔局域性;适当旋转耦合方柱体,可以增大透射率,当转角30°时透射率最大;利用环形腔体的旋转可以实现对谐振频率的精细调节.这些研究对声波器件的集成设计具有潜在应用.     

一维固-液型随机失谐声子晶体中波的传播

本文研究了声波在一维固-液型随机失谐声子晶体中的传播,引进局部化因子的概念研究了结构的带隙特性和局部化特征.给出了局部化因子的计算表达式并用传递矩阵法进行了计算,考查了平面波以任意角度入射的情形.结果表明:失谐度对高频区的频带结构有较大的影响,固-液型声子晶体与固-固型声子晶体的频带结构有很大差别.     

二维声子晶体多点缺陷局域模的分离特性

以二维铝圆柱/空气正方格子声子晶体为研究对象,利用平面波展开法结合超原胞的方法研究了点缺陷局域模的分离特性及模场分布特性.结果表明,多点缺陷引入将使局域声子因散射波之间的干涉而产生局域模的分离,且分离程度与多点缺陷所形成腔的几何形状、封闭程度以及边缘的构造有关;带隙中局域模的模场分布与它在带隙中的位置有关.点缺陷局域模的分离特性在声方向滤波器、窄带声波导方面将有很大的应用价值.     

一维固-液声子晶体表面消逝波传播模式

为了研究一维固-液声子晶体,应用Bloch定理和边界条件解析推导出一维固-液声子晶体的表面消逝波传播模式存在条件的方程.在一定条件下,一维固-液声子晶体存在表面模式.对表面模式,声波位移场集中在半无限一维固-液声子晶体的表面,在背景材料和声子晶体内部声波衰减.在所有层中,一维固-液声子晶体的表面模式均具有消逝波性质的位移场.随后的数值研究证明了分析结果.     

基于普通介质无缺陷一维光子晶体高Q值多通道滤波器

设计用常规介质构成的无缺陷的一维光子晶体,用特征矩阵法研究光波在其中的传输特性.在消逝波和传输波相互耦合的传播模式条件下,对特定的入射角度,有多个分离的高Q值频道可以让光波传播.因此可以将该结构用作多通道高Q值频率滤波器.通道位置和数目可以通过入射角度和结构的周期数目进行调节.     

隔声超构材料的研究进展

声学超构材料的概念起源于局域共振型声子晶体。作为一种新型复合人工结构材料,声学超构材料具备许多优异的特性,如相对于传统隔声材料可以灵活、精准地操控声波,采用小型化、轻质化的结构解决宽频带、低频隔声等问题。本文综述了声学超构材料在隔声方面的最新研究进展,从带隙理论和表征参数出发论述了声学超构材料隔声机理,重点介绍了相关代表性工作,包括Helmholtz式隔声超构材料、薄膜薄板式隔声超构材料、折叠卷曲空间式隔声超构材料以及组合式隔声超构材料的设计理念和方法,最后对这一新兴领域的应用进行了展望。     

Compression of Acoustic Beams at Conversion Reflection in Hexagonal Crystals

It is shown how the entire energy of an acoustic beam incident on a boundary of a hexagonal crystal can be directed into a narrow reflected beam propagating at a small angle to the surface. This process is accompanied by mode conversion: the incident and reflected beams belong to different acoustic branches. The conversion near the total internal reflection is implemented by matching the orientations of the sagittal plane and surface and thereby eliminating the loss for parasitic wave reflection. The found conversion conditions and resonant reflection parameters are expressed in terms of the moduli of elasticity of crystal.     

非均匀局域共振型声子晶体隔声特性研究

建立局域共振声子晶体单元结构模型,通过有限元方法研究了阵列排布、填充率排列及散射体厚度排列对非均匀声子晶体隔声特性的影响,以期使各类非均匀声子晶体结构在不同频段发挥隔声效果及减少隔声频段内的局部衰减.结果表明,散射体靠近入射方向的阵列排布具有较大的隔声量;填充率由中间列向两端递增的形式下局部衰减情况较少;散射体厚度由中间列向两边减小的排布适合中高频隔声,由中间列向两边增大的排布适合低频隔声;分别由铝振子、钢振子、铅振子构成的声子晶体在低频段具有相似的隔声特性,中高频处的隔声频段随着振子密度的增加向低频段移动.此结果为非均匀声子晶体获得良好降噪效果提供了理论支持.     

Light Scattering and Contrast in Thermally Addressed Liquid Crystal Displays

The effects of structural order on the light scattering characteristics of liquid crystal display cells containing smetic p-n-octyl-p′-cyanobiphenyl have been investigated. The scattering characteristics of different structures in the cell due to surface treatments are qualitatively analyzed for their effects on the contrast ratio when used in the thermally addressed liquid crystal display (TALC). Of the four structures investigated, i.e., homeotropic, fan-like, uniaxial rods and spherulites, the spherulitic structure has been found to exhibit the scattering profile best suited for high contrast because of the near-zero scattering near the incident beam. Based on the light scattering theory for spherulites, optimization of structural parameters such as size and order of spherulites, and device design such as collecting angle of projection lens for maximum display contrast has been predicted. Methods to improve contrast have also been discussed.     

Selective optical properties of a multilayered periodic gyrotropic structure at an arbitrary angle of incidence of waves

A multilayered periodic gyrotropic structure consisting of an arbitrary number of unit cells is considered. The gyrotropic properties of this multilayered structure are due to the external magnetic field. A matrix is calculated on the basis of the boundary conditions for waves in each layer, which relates a wave incident at an arbitrary angle with the transmitted and reflected waves. The complex amplitude transmittance and reflectance are found for the entire multilayered structure from the calculated matrix elements. The optimal parameters of a structure consisting of layers of potassium dihydrogen phosphate and europium-doped glass are calculated. The dependences of the intensity, ellipticity, and the angle of rotation of the major axis of the polarization ellipse of reflected and transmitted waves on the number of cells, light frequency, and magnetic field at an arbitrary angle of incidence of waves are obtained in graphical form. The structure considered is characterized by selective reflection of electromagnetic waves and can be used as a polarization converter controlled by a magnetic field.     

Ca3NbGa3Si2O14晶体的BAW传播特性

本文计算了沿Ca3NbGa3Si2O14(CNGS)晶体的x、y和z方向传播的声体波(BAW)的声速,绘制了yz、xy和xz面传播的慢速度分布曲线.这些结果对CNGS晶体在压电器件的设计、开发及利用方面具有一定的理论指导意义.     

Light propagation in stratified chiral media. The 4 × 4 matrix method

Propagation of electromagnetic waves in stratified bianisotropic chiral structures is described by the 4 × 4 matrix method. At arbitrary layer parameters, the amplitude and the polarization characteristics (intensity, polarization azimuth, and ellipticity) of reflected and transmitted electromagnetic waves are studied as functions of the angle of the wave incidence onto the structure.     

Investigation of the properties of weakly reflective metamaterials with compensated chirality

The properties of an artificial anisotropic structure formed by microhelices have been numerically simulated by the example of a specially designed sample. The sample contains paired helices with right- and left-handed twisting directions, due to which the metamaterial chirality is compensated for. Helices are characterized by precalculated optimal parameters; as a result, the permittivity and permeability of metamaterial are approximately equal. Therefore, the wave impedance of the structure is close to the impedance of free space in the frequency range near 2 THz and the reflection of normally incident electromagnetic waves is weak. A boundary problem is solved and an analytical expression is obtained for the reflection and transmission coefficients of an electromagnetic wave passing through the structure. The simulated properties of the structure are compared with experimental results.     

Hydrodynamics of layered and cubic quasicrystals

The dissipative processes associated with sound absorption in layered and cubic quasicrystals have been studied within the framework of the hydrodynamic approach. The decagonal, octagonal, and dodecagonal quasicrystals are considered as layered quasicrystals. Proceeding from the general theory, the complex law of dispersion is calculated for various directions of the propagation and polarization of sonic waves in layered and cubic quasicrystals. The effect of the phason modes on the process of sound absorption and the role of symmetry constraints are analyzed. The validity of the macroscopic consideration is discussed in terms of the theory of the generalized color symmetry.     

Combination of a reflectometer and a nonmagnetic waveguide for experiments with polarized neutron microbeams

Neutron waveguides are three-layer thin-film structures which transform part of a collimated (with an angular divergence of 0.01°) and relatively wide (0.1 mm) incident neutron beam into a narrow (0.1 μm wide) and divergent (0.1°) beam at the output. This submicron beam (which cannot be obtained using conventional focusing elements) is promising for studying nanostructures. We propose a combination of a polarized-neutron reflectometer and a nonmagnetic (independent of the neutron spin) waveguide for experiments employing polarized neutron beams with a submicron spatial resolution. This scheme can be applied, for example, for position-sensitive studies of magnetic nanostructures.