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.     

Shear Surface Acoustic Waves in Twinned Piezoelectric Crystals of the $$\bar {6}$$m2 Symmetry Class

Crystallography Reports - Shear surface acoustic waves, whose existence is due to the difference in the signs of piezoelectric modulus tensors of adjoining halves of crystal, are studied on flat...     

Acoustic Waves and Supramolecular Structures in Liquid Crystals

Crystallography Reports - The achievements in the study of the supramolecular structures arising in liquid crystals (LCs) under acoustic waves, which was started by the work of Professor А.P....     

声表面波用压电晶体的新进展

报道了我们在Li2B4O7、Sr3Ga2Ge4O14、LiNbO3、LiTaO3等声表面波用压电晶体材料方面的最新研究进展.采用改进型坩埚下降法成功生长了直径3～4英寸的Li2B4O7晶体,并实现了批量生产.作为硅酸镓镧系列新型压电晶体之一,Sr3Ga2Ge4O14晶体具有最大的压电系数.报道了直径2英寸Sr3Ga2Ge4O14晶体的生长结果,测试了该晶体的压电性能.在CO2(90;)、H2(10;)混合气氛中,分别在700℃和450℃下对LN和LT晶片进行化学还原处理,成功制备了3英寸LN和LT低静电黑片,不仅减少了器件制作工序,而且使成品率提高了5～8百分点.此外,在密封坩埚中生长了低静电LiNbO3晶体,观察到一些新的现象.     

制作压电器件氧化锌单晶的评述

氧化锌材料制作压电器件已经有很长的研究历史,自从Robert F.Service在1997年报道氧化锌可以在短波长范围实现蓝光输出后,氧化锌单晶在质量和体积方面取得了很大的研究进展。通过对比分析20世纪60年代以来氧化锌单晶压电特性的研究结果,指出迄今为止制作压电器件的氧化锌单晶仍然需要继续优化。     

Sr3NbGa3Si2O14和Sr3TaGa3Si2O14压电晶体的声表面波特性研究

本文编程计算了Sr3NbGa3Si2O14(SNGS)和Sr3TaGa3Si2P14(STGS)压电晶体的X,Y和Z切型的声表面波速度、机电耦合系数及能流角,与现有实验结果符合的很好.计算结果指出SNGS的(90°,90°,167.5°)、(0°,90°,0°)和(0°,0°,90°),STGS的(90°,90°,170°)和(0°,90°,0°)切型具有机电耦合系数大、能流角为零等优点,制作声表面器件可以优先考虑这些切型.     

Twist Grain Boundary Phases in the Binary Mixtures of Smectic and Cholesteryl Compounds

Abstract

The binary mixture of Terephthal-bis-p-n-hexadecylaniline (TB16A) and cholesteryl nonanoate (CN) exhibits I - N* - TGB _A - TGB _c*- Sm A - Sm I - Sm F - Sm G - K phases in the concentration region between 95 to 98% of TB16A at higher temperature range. The 90% of TB16A exhibits I - N* - TGB _A - TGB _c - Sm A - Sm I - Sm F - K phases. The mixtures of concentration between 50 to 80% of TB16A exhibits I - Sm A - Sm I - K phases. The frustrated blue phase is also observed in the mixtures of lower concentration of TB16A in CN at higher temperature. Optical, DSC and X-ray studies were carried out for the identification of the different phases. The phase diagram of the Chen-Lubensky model in this context is discussed.     

晶体中负离子配位多面体结晶方位、形变与晶体压电、铁电性

本文研究了压电、铁电晶体中负离子配位多面体的结晶方位与形变,提出了压电晶体中同一种负离子配位多面体的结晶方位是一致的.在铁电晶体中,负离子配位多面体发生形变,伴随着晶体发生顺电-铁电相变,并从这一基本过程出发,对铁电体相变的形成机理进行了讨论.     

Periodic Director Patterns in Twist and Splay Frederiks Transitions in Tobacco Mosaic Virus Liouid Crystals

When a magnetic field is applied in the plane and perpendicular to the unperturbed director of a uniform planar-aligned liquid crystal, a twist Frederiks transition occurs. For fields greater than a critical value, periodic bend-modulated twist distortions are dynamically favored over the uniform twist distortion. This is because the periodic flow pattern associated with the bend twist distortion lowers the effective viscosity more than it raises the elastic restoring torque. Under crossed polarizers the sample has a striped texture with the stripes perpendicular to the initial director. The wavelength of the stripe texture is field dependent.

When the magnetic field is applied perpendicular to the uniform planar sample, a similar striped distortion occurs above a critical field value, dominated by splay rather than twist. The most striking difference from the twist transition is that there is a thickness-dependent angle between the stripes and the original director whereas in thinner samples, the stripes tend to be more parallel to the original director. The initial development of the structure appears as a lattice of diffuse spots on a diamond-shaped grid, a precursor that is not seen in the twist instability, which nucleates as stripes at the boundaries of the cell. The splay Frederiks transition also exhibits a field-dependent wavelength distortion.     

CTAS和CNAS晶体的声表面波特性研究

本文计算了Ca3TaAl3Si2O14(CTAS)和Ca3NbAl3SiO14(CNAS)压电晶体的X,Y和Z切型的声表面波速度、机电耦合系数.计算结果表明:CTAS和CNAS机电耦合系数最高可达1.04;,是石英晶体(最大0.3;)三倍多,而CTAS晶体的声表面波速度(最小值约为3070 m/s)比石英(最小值为3200 m/s)小4.0;.给出声表面波特性比较好的切型,为CTAS和CNAS的声表面波应用提供了理论依据.     

确定一维声子晶体缺陷模的解析方法

为了确定一维声子晶体缺陷模位置,本文从周期结构的布洛赫原理出发,通过解析方法推导出一维声子晶体缺陷模式所满足的条件及确定的方法.所得结果与其它数值方法进行比较,两者完全吻合.     

晶体和准晶旋声性质的旋转不变性

依据群论原理对计算张量的群论方法作了改进,采用非对称化基函数取代对称化基函数,以便于编程.用MATLAB编制了用于计算属于SO(2)群各阶张量的软件.借助于该软件得到了具有SO(2)群对称性的旋声张量的形式.指出晶体中属于六角系的6、6 mm和622晶类和准晶中属于五角系的5、52、5 m晶类的旋声性质具有围绕晶体或准晶中唯一高次轴的任意旋转不变性.该结果对于旋声性的应用有重要意义.     

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.     

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.     

Particularities of the Dynamics of Linear Domains in Liquid Crystals under a Binary Acoustic Action

Crystallography Reports - The dynamical properties of a system of linear domains induced by shear oscillations in a planar layer of a nematic liquid crystal under the joint action of shear and...     

Dynamic Aspects of Dislocation Behaviour Near Low-Angle Boundary in Molybdenum Single Crystals

The dislocation behaviour was inventigated in specimens of monocrystals of molybdenium during in — situ stretching in the direction [001] near low — angle twist boundary which was close to be parallel to the direction of the external force. Low-angle boundary is easily penetrable for the fast moving nonscrew dislocations and acts as an effective stopper for screw dislocations which are quite parallel to the forming boundary dislocations. The mixed tipe dislocations emission by the low-angle boundary was noticed. On the stage when plastic deformation is performed mainly by the motion of screw dislocations the “relay-race”-like transmission of the dislocations motion through the boundary was observed.     

3m点群晶体纵向压电性能的研究

本文详细地介绍了通过坐标变换研究晶体压电性能随空间变化的方法.在以前的工作基础上,对LiNbO3、LiTaO3和PZT60/40等3m点群晶体纵向压电系数d33及机电耦合系数k33在空间分布的共同规律进行了归纳总结,发现它们在空间中的分布具有明显的各向异性,并存在着一些特殊方向,沿这些方向,晶体的压电性能有较大幅度的提高.在此基础上,本文还根据不同文献中报道,对另一著名的3m点群晶体β-BaB2O4的压电系数数据进行了比较和分析.     

基于边界元法的三相声子晶体能带结构的计算

发展了计算二维三组元局域共振型声子晶体带隙结构的边界元法,该方法在一个单胞内分别对基体和含有包覆层的嵌入体(三相材料)建立边界积分方程,在基体边界上施加Bloch条件,并考虑不同相之间的界面条件后得到一个线性的特征值方程.该方法的计算结果和对应的二组元体系计算结果进行了比较,结果表明,在三相体系中声波发生局部共振,此时中间包覆层材料的作用类似于一个软弹簧;而且由于包覆层材料的密度很低且声速很小,所以对应的系统共振频率较低,使声带隙出现在较低频段.另外,本文还分析了“包覆层”材料的特性以及边界元法计算三组元声子晶体的特点.     

面向水声换能器的压电单晶复合材料设计研究

压电单晶复合材料具有高压电常数、高机电耦合系数和高水声优值的优点,是制备下一代高性能水声换能器的关键材料。不同类型水声换能器对压电材料的性能要求不同,如何根据器件的具体应用需求,对压电单晶复合材料的结构和性能进行设计具有重要的意义。为了能够准确选取压电单晶复合材料中压电相与聚合物相两相材料特性、体积分数、宽高比等参数,本文提出了一种将解析模型与数值模型相结合的综合设计方法。实验结果证实,该方法可以准确高效地预测1-3型压电单晶复合材料的振动模态及宏观等效性能参数,实现以器件性能为指导的压电单晶复合材料设计。