新型多重谐振结构声子晶体隔声特性

提出了一种新型多重谐振结构声子晶体,该声子晶体结构属于局域共振结构,在300~2 500 Hz频率内有2个较宽的完全带隙和1个方向带隙。在带隙频率范围内对应有隔声峰,改变内、外层散射体材料能在不同频率范围内获得隔声峰。为拓宽隔声峰的频率范围,通过将不同散射体材料组成不同单元结构复合,在不同频率范围内发挥出较好的隔声效果。通过有限元法分析了影响结构复合隔声效果的关键因素。研究表明,采用结构复合能有效改善隔声效果,复合方式以结构间设置一层空气作为缓冲介质为最佳。     

二维声子晶体能带特性研究

介绍声子晶体的概念及其种类,基于平面波展开法,设计了以环氧树脂为基底,铝为散射体材料的二维XY模式声子晶体,模拟得到了能带范围为5．838KHz至8．981KHz,比较了铝、铝2和铝3的能带结构,得到随着铝密度和杨氏模量的增加,剪切模量的减少,能带宽度增加。同时还比较了随着散射体半径的增加,计算得到能带宽度也增加了。结论为二维XY模式声子晶体器件的制作提供理论参考。     

多带隙声子晶体低频带隙特性研究

利用有限元法计算了一种多带隙声子晶体的特征频率,传递损失和位移矢量,理论推导了反共振产生条件。研究结果表明,这种声子晶体在低频范围内具有多条平直带隙,带隙的耦合影响因素少,具有比一般局域共振声子晶体和Bragg 散射声子晶体更宽的带隙。此外,利用原点反共振模型分析计算了这种多带隙声子晶体的材料和结构参数对带隙的影响。研究表明,在低于2 500 Hz时,多带隙声子晶体的带隙占90%以上,为低频多带隙声子晶体的研究作了探索。     

矩形晶格结构对二维压电声子晶体带隙的影响

通过计算二维压电声子晶体透射系数,研究了矩形晶格结构对声子晶体带隙的影响。为得到声子晶体的透射系数,构建叉指换能器(IDT)中间放置声子晶体的器件模型,IDT作为激发和接收端,声子晶体作为传输通道。通过有限元软件计算出模型的电学参数,分别结合IDT的混合矩阵(P矩阵)和声子晶体的散射矩阵,推导和计算出声表面波的透射系数,并找出带隙范围。该文在128°-YX铌酸锂基片上制作IDT和矩形晶格以圆孔为散射体的声子晶体。通过调整矩形晶格中y方向上晶格常数,理论和实验上均得到了2个方向上的带隙变化。结果表明,随着y方向上晶格常数的增大,x方向上的带隙逐渐分为两段,y方向上的带隙逐渐缩小,使y方向上的带隙夹在x方向两段带隙间。实验结果与计算结果较吻合。     

二维三组元液体系统声子晶体带结构研究

基于平面波展开法,研究了水-四氯化碳/水银和四氯化碳-水/水银两种体系的二维三组元结构的声波带隙,结果表明,在相同填充率下,圆柱形插入体比正方柱形插入体更易得到较高频率范围内的完全带隙;无论插入体的形状为方柱或圆柱,第一带隙相对宽度的变化都是稳定的,但对第二带隙相对宽度的影响较大;圆柱形插入体的第一完全带隙的相对宽度变窄的速率比正方形插入体的快。该文提出通过散射体横切面积的几何形状来控制带隙频率。这对设计液体系统的声子晶体有实际意义。     

一维铝-环氧树脂声子晶体的介观压声效应

用传递矩阵法研究了由铝和环氧树脂两种材料构成了二组元一维声子晶体在应力作用下的透射谱特性。通过分析透射谱线的变化发现,在压变量的影响下,声波带隙能可控的出现和消失及平移,特别是会随着压变量的变化而出现带隙的反转,由通带变为禁带。为与体材料中的声弹性效应区别,参照介观压阻和介观压光效应的提法,称这种效应为介观压声效应。研究了在压变量存在下该结构透射谱线与声子晶体周期数的关系。结果表明,单轴应力对声子晶体带隙有明显的影响。这些特性可为新型声学器件的设计提供理论参考。     

十字型结构声子晶体带隙及等效模型研究

该文设计了一种新型十字型声子晶体结构,并采用有限元法对其进行了研究;分析了此结构若干共振频率下的振动模态,分别建立了带隙起始频率与截止频率处振动模态的简化模型,探究了结构与材料参数对带隙的影响,验证了简化模型的合理性;最后计算了结构的反射系数与透射系数。结果表明,该结构带隙产生机理属局域共振型,能够在中低频段内产生一个完全带隙。通过对金属芯体密度、基体密度、包覆层的宽度及弹性模量等因素的调节,可以实现对带隙上、下界频率的调节,结构的反射系数与透射系数随入射波频率的变化也与带隙图相应证,当带隙图显示出现带隙时,结构的透射系数也随之下降。     

二维光子晶体1.55μm带隙中心的优化设计

利用平面波展开法对正方晶格二维光子晶体带隙随结构参数的变化进行了研究,计算结果表明,能带频率随着归一化半径r/a的增大有减小的趋势,带隙宽度是先增大后减小.带隙宽度随介电常数比ε的变大而增加,能带频率有减小的趋势.当格子常数a=0.594μm,r/a=0.16,ε=13时得到能带中心波长为1.55μm,最大能带归一化频率宽度为0.15.     

一维声子晶体在防止低频噪声中的应用

应用集中质量法研究了集中质量数n、晶格常数a、组分比t、弹性模量E及密度ρ等因素对一维声子晶体带隙的影响.结果表明,带隙起始频率及带宽随a增加而减小,随t增加而快速增大(当t>1);带隙起始频率随两种材料E差值与ρ差值增加而减小,而带隙截止频率却不变;带隙精度则随n增加而增大.据此设计出一种能屏蔽约59～557 Hz范围内低频噪声的复合结构声子晶体.     

磁导率对光子晶体带隙特性的影响

利用时域有限差分(FDTD)法,计算了磁介质材料光子晶体(PC)的能带结构.结果表明,磁性散射也能形成光子禁带.增大PC构筑单元的磁导率,不仅能够增大带隙宽度,而且能够增加带隙个数和带隙深度.PC中引入磁性材料,增加了能带工程的调节自由度,为阻抗匹配设计提供了更多的可调参数,能更有效地吸收调频电磁干扰,对器件性能的改善具有广泛的应用价值.对其作用机理进行了探讨.     

Acoustooptic interactions in AlGaAs-GaAs planar multilayerwaveguide structures

The acoustooptic interaction of guided optical waves and surface acoustic waves (SAW's) is studied in multilayered structures of dimensions of the order of those seen in multiple-quantum-well (MQW) structures. The guided mode profiles and SAW-induced electric field and strain profiles are used to calculate the diffraction efficiency, using an expression derived from coupled mode theory. Diffraction efficiency is plotted as a function of SAW frequency, and the effects of acoustic power, acoustic aperture, and material structure are considered. For a specific structure, the diffraction efficiency is seen to increase with increasing aluminum content for low concentrations and the opposite is seen for higher concentrations. This is explained in terms of the opposing effects of guided optical mode parameters and material properties. Possibilities for optimization of the diffraction efficiency through tailoring of the refractive index profile of the material structure are suggested     

The loss mechanism in a composite acoustic microwave resonator based on a sapphire single crystal

Acoustic loss in a composite longitudinal-wave resonator structure operating in the microwave band are studied. The resonator structure contains a rather thick sapphire plate coated with a piezoelectric film with electrodes. It is shown that, in a wide frequency band, attenuation is determined by interaction with acoustic phonons. The role of diffraction loss is discussed. Scattering of acoustic waves by asperities of reflecting surfaces is considered, and the contribution of scattered acoustic waves to the total loss is estimated.     

SiO2/W反射叠层的分布电容对体波谐振器的影响

该文使用SiO₂和金属材料钨（W）构造布喇格反射叠层,将其应用于由横向电场激励体声波谐振器（XBAR）,并分析了金属层对谐振器性能的影响。所设计的谐振器以128°YX-切铌酸锂为压电层,Al为电极,SiO₂和W为周期层叠结构,单晶硅作为衬底的固态装配型谐振器（SMR）,利用叉指电极换能器（IDT）激发出A1模式。首先计算声阻抗层厚度对SiO₂/W叠层传输系数的影响,得到中心频率为3.7 GHz的布喇格阻带。横波（主模）在经过叠层时被反射,纵波（杂模）则部分地泄露到衬底。由于钨具有电导性,致使IDT与钨之间形成并联分布电容,改变了原有的电场分布,导致谐振器的耦合系数下降。通过实验测试谐振器的实际性能,获得耦合系数为12%。虽然W具有高声阻抗,但分布电容的影响恶化了电气参数。     

高容错光纤声波传感器的数学模型与特性研究

光纤传感器具有抗电磁干扰、无源、耐腐蚀等优 良特性,适用于易燃易爆、强电磁干扰、水下等恶 劣环境。本文提出了一种基于反射式强度调制原理,以实现声波对光强的调制为目的光纤声 波传感器。设 计了一种新型传感结构,该结构通过光纤准直器收发光信号、采用逆反射材料设计了振动膜 片,基于准直 器的聚焦原理和膜片的逆反射原理有效扩大光束接收角、增强光强接收能力以实现传感器的 高容错测量, 提高传感器的稳定性。研究并建立了传感器的光强调制数学模型,制作传感器并测试了其性 能,实验结果 表明,该新型传感器能够有效探测声波信号,对频率为1000 Hz左右的声波具有良好的响应。该传感器具有 工作距离长、结构容错能力强、还原声音能力强等优势,可应用于国防安全监听等领域。     

Enhanced backscattering: the universal wave phenomenon

Backscattering enhancement is discussed as a universal wave phenomenon inherent to waves of whatever physical nature: electromagnetic, acoustic, spin, etc. This phenomenon arises due to multichannel wave propagation from a source to a scatterer and back and may be observed in the vicinity of the source because of mutual coherence of waves passing in opposite directions along identical (coherent) channels. Backscattering enhancement may be revealed when the wave field is scattered: by a system of chaotically distributed scatterers or by a system of inhomogeneities; by a body embedded in a turbulent medium; by a single body placed near an interface or within a waveguide (randomness of body position is assumed); by a body of complex form or a system of several scatterers randomly oriented in space; by a rough surface; and by many other physical systems. Possible practical applications of these effects are analyzed     

The long-wave theory of N pairwise alternate homogeneous and heterogeneous layers difraction

Basic physics of theory is comparison of electrodynamic properties of heterogeneous media of nonuniform layer with chaotic or regular distribution of scatterers with small wave size and uniform anisotropic media with efficient values of components of dielectric permittivity and magnetic permeability tensors. Scattering coefficients of perpendicular and parallel polarization waves of bounded sequence are obtained by using circuit theory and matrix functions methods. We consider thick periodic grates of magnetodielectric bars with equal and orthogonal symmetry lines orientation and different geometrical and material parameters as two periodic nonuniform layers. We proved direct analytic formulas, which describe width and position of quasitransparency (quasicutoff) zones of band-pass and resonant wave passage and its dynamics on parametric relations of reflection factors. It is discovered effects that prove an opportunity of investigated structure usage in multifunctional electromagnetic field directors.     

A metamaterial based on a 2D two-element lattice of cylinders with right- and left-handed surface conductivity

A new method is proposed for calculating the effective constitutive parameters of small-period 2D lattices. A two-element lattice of resonance chiral cylindrical scatterers with the opposite signs of chirality is investigated. It is found that such a structure exhibits the properties of the Veselago medium in a narrow frequency band.     

Photonic band gap of 2D complex lattice photonic crystal

It is of great significance to present a photonic crystal lattice structure with a wide photonic bandgap. A two-dimension complex lattice photonic crystal is proposed. The photonic crystal is composed of complex lattices with triangular structure, and each single cell is surrounded by six scatterers in an hexagon. The photonic band gaps are calculated based on the plane wave expansion (PWE) method. The results indicate that the photonic crystal has tunable large TM polarization band gap, and a gap-midgap ra...     

用叉指换能器制作高频声体波换能器的理论研究

从理论上介绍一种利用叉指换能器制作高频声体波换能器的方法，具有结构和工艺简单，声波模式纯度较高，换能损耗较小和容易消除各种反射波影响的特点。     

Recognition of isotropic plane target from RCS diagram

The use of electromagnetic waves for the recognition of a structure represented by point scatterers is a fundamental problem. Much research is done on this subject, and the study of aircraft observed in the yaw plane gives interesting results. But to apply these methods it is necessary to use many sophisticated acquisition systems. In the letter, we give a new method which can be applied for plane structures composed of isotropic scatterers. This method is quite interesting because it uses power measurements only and necessitates only a classical tracking radar.