多通道声子晶体滤波器的理论研究

推导出一维掺杂声子晶体的转移矩阵,研究了多通道声子晶体滤波器的设计问题.得出:通过调节杂质的厚度能够实现对滤波通道数目的选择和对滤波频率的调谐.通过改变声子晶体材料的声阻抗能够实现对滤波通道的频率半高宽的调节.设计出滤波通道的频率可调范围达600Hz、滤波通道的频率半高宽的可调范围在3Hz-14Hz之间的三通道声子晶体滤波器.     

任意截面预应力混凝土细长柱的非线性分析

提出了轴力和双向弯曲作用下任意截面混凝土和预应力混凝土细长柱的非线性有限元计算模型。分析时既考虑了由单元变形和轴力二次矩引起的几何非线性效应,也考虑了由材料非线性应力应变关系和截面刚度矩阵引起的材料非线性效应。推导了非线性全过程分析的标准有限元公式,得到的单元刚度矩阵可分割成三个子矩阵,分别反映了材料非线性、材料非线性和单元大位移的耦合、轴力二次矩等三种不同的非线性作用效应。计算分析结果和试验结果吻合较好。     

压电周期结构振动主动控制研究

针对周期嵌有压电材料的杆结构中的波动传播特性和振动主动控制问题进行了研究.采用传递矩阵方法,推导了结构中相邻单胞间的传递矩阵.根据矩阵特征值理论,分析了结构中的频带特性,并给出了计算实例.分析表明,对于不同的材料性质,结构中的频带特性会产生很大差异.因此,通过调谐压电材料的阻抗,可以扩大结构的频率禁带范围,加强结构对外界扰动的过滤能力,从而达到了对结构进行振动主动控制的目的.     

基于多模态展开的黏弹性材料复纵波波速反演方法

黏弹性材料广泛应用于水下航行器的降噪、减振或消声,精确获取其动力学参数的需求随着数值仿真技术发展而迅速提升.针对参数获取的声管测量方式,提出了一种使用复反射系数对黏弹性材料复纵波波速快速反演的方法.通过引入多模态展开方法,将复纵波波数超越方程的复平面搜根问题转化为展开系数系统矩阵特征值分解问题,推导出了三种典型背衬情况...     

压电层合板的B样条小波有限元半解析法

利用小波有限元法的优越性可方便地求解压电材料与复合材料混合层合板的某些静力学问题。根据层合结构的特点,将区间B样条尺度函数作为插值函数离散结构的平面域,应用压电材料修正后的H-R(Hellinger-Reissner)变分原理推导了压电材料的Hamilton正则方程的区间B样条小波(BSWI)元列式。该BSWI元的主要特点之一是厚度方向是解析解形式的。针对具体问题的求解,为了保证各层之间力学量和电学量的连续性,进一步应用了状态转移矩阵技术。数值算例表明所提出的区间B样条小波单元是成功的。采用推导压电材料BSWI元的方法可建立磁电弹性材料类似的BSWI元。     

压电/压磁双材料板中弹性波的传播特性

研究由横观各向同性压电和压磁层构成的双材料板中弹性波的传播特性。板的表面是机械自由的,而承受4种形式的电磁边界条件,压电层和压磁层之间是完好连接的。首先采用部分波分析法推导了压电和压磁耦合方程的一般解,然后利用边界和界面条件得到了行列式形式的频散方程。基于推导的频散方程,通过计算CoFe2O4压磁层与BaTiO3、PZT-5A、PZT-2和PZT-4四种压电层构成的双材料板中弹性波的传播速度,揭示了电磁边界条件、压电层和压磁层的厚度比及压电材料性能对频散特性的影响。     

应用传递矩阵测量中间薄层材料声特性

将薄层材料看作三层复合材料的中间层,通过实测得到材料的总传递矩阵和前后两层材料的传递矩阵,中间层材料的传递矩阵可由前材料传递矩阵的逆矩阵、组合材料整体传递矩阵和后材料传递矩阵的逆矩阵相乘得到,由传递矩阵可计算得到中间层材料的声学特性。以基毡和海绵材料为例,通过实验研究并验证中间层材料声特性计算方法的准确性。该方法为薄层材料法向吸收系数和隔声量的测量提供了新的手段。     

用几何平均模型计算多晶材料的X射线弹性常数

推导出几何平均模型并使用这个模型计算了 Ｃｕ和ＴｉＮ 的弹性矩阵和 Ｘ射线弹性常数,计算的结果处于 Ｖｏｉｇｔ和 Ｒｅｕｓｓ模型所定义的多晶材料弹性常数的有效区间内．与 Ｈｉｌｌ、Ｋｒｏｎｅｒ模型的计算结果的最大相对误差小于 ４％,ＴｉＮ［４２２］方向杨氏模量的计算值为 ４２４．３ＧＰａ,与其实验值４１１±４５Ｇｐａ基本一致     

谐振型吸波材料的理论分析与实验研究

本文提出一种以EPS空心球为基体材料的谐振型吸波材料.由电磁波理论,推导出包覆碳粉的EPS空心球的谐振频率和谐振波长,并对这种吸波材料的吸波性能进行了实验研究.经测试,碳粉最佳体积含量为4%,EPS空心球最优粒度为2mm.在测试频段内,低频(2.4～3.85GHz)吸收达到40dB,高频(8～12.5GHz)在45dB以上.最后对这种谐振型吸收材料的阻燃性进行了测试,达到美国UL94V-1级标准.     

镁基材料储氢器的传质与传热研究

运用由壳层-缩核模型推导出的镁基储氢材料吸氢过程的动力学方程,分析了储氢材料在吸氢过程中的传质与传热规律,并对小型储氢器传质与传热过程进行了计算,其计算结果与试验数据可以较好地吻合,特别是对镁基储氢材料在吸氢过程所形成的‘引燃'过程进行了准确的描述,为储氢器设计提供了必要的理论基础.     

左手材料薄板波导中的传导模

推导了左手材料薄板波导中传导模的色散方程,分析了波导中存在传导模与波导材料和包敷材料参数取值范围之间的关系.数值算例证实了这些关系.     

包含左手介质的4层平板波导的转移矩阵和模式本征方程

研究了一个芯子层由左手介质构成、其他3层由普通介质构成的4层平板光波导系统。从波动方程出发,根据电磁场的边界条件,得到了TE波的转移矩阵和模式本征方程,并用图解法对这种左手介质4层平板波导中TE波的场分布分别进行了数值模拟。     

传递矩阵-驻波管法研究材料隔声性能

从材料内部声场变化以及材料外部声场变化2个方面研究了材料的隔声性能.首先利用传递矩阵法详细分析了层合复合材料的隔声特型,理论推导了垂直入射平面波声压透射系数和隔声量随密度、声速、厚度以及频率变化的关系式.从实际测试的角度介绍了对材料进行隔声量测试的四通道传声器驻波管法原理,并对其使用的数学计算公式进行了推导.在理论与实际的基础上,分别对一定厚度的钢板和复合材料进行了理论仿真计算和实验测试,结果表明二者基本吻合.     

Extended Sneddon and Muki solutions for multilayered elastic materials

This paper extends the Sneddon and Muki solutions to solve elastostatic problems in multilayered elastic materials. Using Hankel transforms, Sneddon and Muki developed general solutions of elastostatic problems in elastic materials occupying either halfspace or one layer regions. Based on the Sneddon and Muki solutions and a transfer matrix method, solutions are presented for elastostatic problems in multilayered elastic materials subject to both external and internal loading. A special technique is adopted to eliminate the ill-conditioned matrices associated with the conventional transfer matrix method for multilayered materials. The extended Sneddon and Muki solutions can be easily calculated using a personal computer. Numerical examples given in the paper show that the extended Sneddon and Muki solution generates results with high accuracy and efficiency. The extended Sneddon and Muki solution has wider applications to engineering science.     

Transverse localization in disordered lattices containing left-handed metamaterials

A numerical study is reported of the propagation of an initially localized wave in a one-dimensional disordered lattice composed of left-handed metamaterials. We first consider the structure made of right-handed and left-handed materials arranged periodically. By allowing disorder in the refractive index of the right-handed materials, the injected wave becomes localized as propagating through the disordered lattice. Then, we consider another photonic lattice comprising only left-handed metamaterials. It is found that the inclusion of disorder in the negative refractive index of the constituents of the system leads to transverse Anderson localization. We also investigate the dispersion effect of metamaterials on the localization behavior. It is demonstrated that inclusion of a dispersive metamaterial in the disordered photonic lattices causes the quality of transverse localization to enhance with increasing wavelength.     

Rigorous electromagnetic analysis of volumetrically complex media using the slice absorption method

There is tremendous demand for numerical methods to perform rigorous analysis of devices that are both large scale and complex throughout their volume. This can arise when devices must be considered with realistic geometry or when they contain artificial materials such as photonic crystals, left-handed materials, nanoparticles, or other metamaterials. The slice absorption method (SAM) was developed to address this need. The method is fully numerical and able to break large problems down into small pieces, or slices, using matrix division or Gaussian elimination instead of eigensystem computations and scattering matrix manipulations. In these regards, the SAM is an attractive alternative to popular techniques like the finite-difference time domain method, rigorous coupled-wave analysis, and the transfer matrix method. To demonstrate the utility of the SAM and benchmark its accuracy, reflection was simulated for a photonic crystal fabricated in SU-8 by multiphoton direct laser writing. Realistic geometry was incorporated into the model by simulating the microfabrication process, which yielded simulation results that matched experimental measurements remarkably well.     

Frequency selective characteristics of gratings with arbitrary profiles composed of left-handed materials

The frequency selective surface (FSS) of gratings with arbitrary profiles composed of left-handed materials is systematically analysed by a method that combines the staircase approximation and the multimode network theory with the rigorous mode matching procedure. The effects of different periodic groove profiles, such as rectangle, ellipse and trapezoid on the reflection characteristics of the FSS are carefully studied and compared with each other. The variations of the frequency selective characteristics with dielectric loss and the comparisons between left-handed and right-handed gratings are also presented with the physical explanations of the related phenomena.     

Numerical study of two-dimensional metamaterial composites: the existence of a stop band

Two-dimensional metamaterial photonic crystals composed of dispersive left-handed materials and a right-handed medium were investigated. The existence of a stop band was studied by finite-difference time-domain calculations incorporated into an auxiliary differential equation (FDTD-ADE) method. The existence of a stop band was studied in the case of Drude-type dispersion responses for the dielectric permittivity and magnetic permeability of the metamaterial. A distinct stop band appears when the dispersive left-handed metamaterials are embedded in a positive-refractive-index medium and spatially isolated from each other. In contrast, the stop band is absent when the metamaterials span the entire photonic crystal.     

左手材料的研究进展

左手材料是一种介电常数ε和磁导率μ同时为负值的电磁材料.介绍了左手材料的基本原理,阐述了微波段、红外和可见光波段左手材料的实现方式,展望了左手材料的应用前景.