层状双周期结构声子晶体带隙特性研究

设计了一种层状五组元双周期结构声子晶体,并将其等效为一维声子晶体,采用传递矩阵法推导出了该结构的能带结构;在该带隙范围内弹性波或声波的传播能够得到有效抑制,实现对噪声的控制。同时,分析了取消内部周期以后第一带隙的变化以及改变硅橡胶层厚度对第一带隙的影响。结果表明,该结构与简单二元结构相比,在降低带隙频率的同时有效减轻了结构质量,且"内部周期"主要影响带隙宽度;当增加硅橡胶层的厚度时,带隙频率进一步降低。     

一维功能梯度材料声子晶体弹性波带隙研究

应用平面波展开法研究了由功能梯度材料周期复合而成的一维声子晶体中存在的弹性波带隙特征,并得到第一阶带隙归一化起始频率、截止频率和宽度随功能梯度材料表面材料常数、指数因子和组分比变化的关系图。并对功能梯度材料声子晶体与常规材料声子晶体帯隙特征进行了比较,结果表明,功能梯度材料声子晶体较常规材料声子晶体在相同范围内能够出现更多阶带隙结构。这些结果为功能梯度材料声子晶体在工程实际中的广泛应用提供了理论依据和指导。     

散射体特征对隔声超材料性能的影响

为研究应用于轨道车辆降噪的声学超材料，在分析两种晶体结构的基础上，从密度角度出发研究散射体特征对声学超材料性能的影响。建立三维三组元金刚石声子晶体模型，通过控制变量法在控制基体材料和包裹层材料参数一致的情况下，针对散射体密度进行梯度递增，以此求解并绘制不同散射体密度条件下三维三组元金刚石声子晶体能带结构图。结果表明：三维三组元金刚石声子晶体的带隙作用频率在6 725.77 Hz～11 632.62 Hz之间，基本与高速列车噪声覆盖范围重合；带隙随着散射体密度的增加，带隙起始频率和带隙终止频率均从高频开始降低，二者降低幅度有所区别。带隙宽度会随散射体密度的增加而增加，拟合带隙随散射体密度变化的曲线后发现，三维三组元金刚石声子晶体的带隙宽度随密度的变化曲线更倾向于3 阶函数。该结构的扩展结构可应用于轨道车辆地板层、高速铁路 沿线声屏障等有降噪需求的部位。     

低频减振一维声子晶体

以开发小周期尺寸低频率带隙声子晶体为目标,首先给出了固定周期尺寸下带隙起始频率最低对应的材料比计算方法,又验证了等效密度及等效弹性模量在声子晶体带隙计算中的正确性。据此开发了周期尺寸为0.04m,带隙范围为200Hz～1200Hz的声子晶体,并对计算结果进行了实验验证。     

周期声学黑洞结构弯曲波带隙与振动特性

作为一种被动型波操控结构,声学黑洞能对弯曲波起到较好聚集作用,再结合阻尼层能更好抑制结构振动波的传播。从声子晶体角度通过周期性排列构造一种声学黑洞结构与基体结合的一维声子晶体结构,选取合适的晶胞,采用有限元法对周期排列的声学黑洞结构弯曲波带隙特性进行研究,对比分析8周期声子晶体梁与等长度的恒定截面梁及周期楔形梁的振动位移传递函数,讨论黑洞区域材料变化对带隙的影响。结果表明:该声学黑洞结构具有较好弯曲波带隙,在对应带隙及附近频带区间振动位移响应出现较大衰减,表明其抑制振动效果明显;在黑洞区域选择合适的材料可以使带隙向低频移动,同时使得带隙区间增多。     

金属/丁腈橡胶杆状结构声子晶体振动带隙研究

采用平面波方法计算了金属 /丁腈橡胶一维杆状结构声子晶体振动带隙 ,讨论了晶格尺寸、材料组分比、金属密度对声子晶体振动带隙的影响。采用有限元方法计算了材料阻尼特性对振动带隙的影响 ,计算表明 :丁腈橡胶阻尼特性不影响振动带隙的起始频率。金属 /丁腈橡胶杆状结构声子晶体的振动实验验证了文中的主要结论     

长度调制的声子晶体梁弯曲振动带隙特性分析

提出一种长度可调制的双周期声子晶体梁结构,研究弯曲波的带隙特性。在无限周期条件下采用传递矩阵法计算准周期声子晶体梁弯曲振动中的弹性波能带结构,并与简单二组元声子晶体梁结构的能带进行对比,然后进一步分析调制参数对带隙的调节机制,结果表明准周期声子晶体梁结构较简单二元声子晶体梁能够产生更大带宽、更多频段的带隙。在有限周期条件下采用有限元法计算准周期声子晶体梁的振动传递特性,证明理论计算的正确性。所提出的准周期声子晶体梁结构可在使用较少材料的基础上大幅度拓宽带隙并具有更强的带隙调控力,为梁类工程结构的减振提供更多选择,并可为新型滤波器、隔振平台的设计提供新思路。     

二维复合结构声子晶体的振动特性与实验研究

声子晶体可以获得低频带隙,抑制特定频率振动的传播。建立二维复合结构声子晶体的有限元模型,分析其传输特性,以得到各组元参数对带隙的起止频率及带宽的影响。分析声子晶体的各种材料参数、结构参数、周期数、排列方式等对带隙的影响。利用铝板、硅胶、钢片材料制作复合结构声子晶体样件,进行传输特性实验,得到的频率响应曲线与有限元仿真结果吻合很好。进而为声子晶体在中低频减振中的具体应用提供依据。     

平面周期管系对轴向波与弯曲波的隔离特性

管路的振动小仅造成噪声污染,而且造成机器设备的损坏.将声子晶体布拉格带隙原理引入到管壁的结构设计中,将管壁设计成沿轴向交替排列的周期复合结构,采用传递矩阵法,计算此周期弯管中轴向波及弯曲波的传输特性,同时用MSC有限元软件验证了传递矩阵法计算的正确性.研究表明平面周期管路存在弯曲振动、轴向振动带隙特性,在带隙频率范围内,对相应的振动波传播具有很强的衰减作用.进一步,研究材料阻尼比对管路振动特性的影响.     

一维声子晶体振动特性与仿真

研究了一维细长杆声子晶体振动特性。利用平面波展开法，计算一维无限周期结构声子晶体的带隙结构，发现每一带隙的宽度与材料的组份比有关。对于有限结构的一维声子晶体，利用MSC／NASTRAN进行防真，仿真结果与实验吻合较好。并通过仿真不同直径的声子晶体研究了横波对带隙的影响。     

The band gap of 1D viscoelastic phononic crystal

The band gap of one dimensional (1D) phononic crystal with viscoelastic host material is studied in this paper. The standard solid model is used to simulate the viscoelastic behavior of the host material and the fillers embedded in the host material are still assumed elastic material. The band gap problem in 1D phononic crystal leads to an eigenvalue problem by using the plane wave expansion method and the Bloch–Floquet wave theory in a periodic structure. An iterative algorithm is designed to obtain the band gap structure due to the dependence of elastic constants on frequency for the viscoelastic host material. A numerical example is given for steel/epoxy phononic crystal. The band gap of 1D phononic crystal is evaluated for different viscoelastic constants, namely, relaxation time, initial and final state elastic modulus. It is found that the viscoelastic constants of host material affect not only the location but also the width of band gaps.     

周期附加质量充液管路减振特性研究

以充液管路振动控制为目标研究周期附加质量的新型声子晶体管路振动传播特性。利用传递矩阵法建立周期附加质量充液管路带隙理论模型,深入分析影响带隙特性关键因素,包括附加质量尺寸、安装位置及材料阻尼。数值计算表明,声子晶体管路存在低频振动带隙可有效抑制振动传播,且设计方法简单、操作方便、减振效果明显,以期为充液管路减振设计提供新思路。     

Study on vibration characteristics in periodic plate structures using the spectral element method

Periodic structures have great scientific potential because of their superior structural dynamic properties. The aim of this study is to analyze the dynamic behavior of periodic plate structures using the spectral element method (SEM). The spectral equations of the plate elements with two parallel sides that are simply supported are established. Then, the spectral dynamic stiffness matrix of the whole periodic plate structure is assembled. The frequency responses are obtained by the calculation of the spectral equations to illustrate the characteristics of the band gaps. From the results, it is seen that the SEM can be effectively applied to study the vibration properties of the periodic structures. Compared with the results calculated by the finite element method, it can be observed that more accurate results in high-frequency ranges can be achieved by the SEM. These results indicate that the band gap characteristics depend on both the material properties and unit cell numbers. Furthermore, the effects of the structure damping and type on the frequency responses are investigated.     

声子晶体中弹性波带隙与散射

声子带隙产生条件是声子晶体研究的一个重要问题,首先对钢圆柱体嵌入空气基质组成的声子晶体散射截面进行计算,然后用平面波方法计算了弹性波带结构。结果表明声子带隙将出现在两个完全分离的共振态之间。因此,声子晶体产生完全带隙的条件是弹性波在基质材料中的传播被禁止并远离共振。     

Control over the spectral position of the band gap of opal photonic crystals

We demonstrate that the width and spectral position of the band gap of opal photonic crystals can be controlled by varying the concentration of solution in the opal pores. An experimental technique is proposed which enables identification of both the first and second photonic band gaps in the reflection spectrum of opal. The ability to observe the second band gap allows a dispersion relation to be derived for the refractive index of the infiltrated substance. The calculations are performed using a model for a one-dimensional periodic layered medium with two refractive indices. We obtain an ω(k) dispersion relation and the reflection spectra of a photonic crystal in the [111] direction at different solution concentrations.     

Theoretical modelling of one dimensional photonic crystal based optical demultiplexer

An optical demultiplexer through one-dimensional Si–SiO₂ photonic crystal structure in the presence of air cavity with a single crystal PMN-0.38PT material is presented. The transmittance of this structure is obtained using the transfer matrix method. The transmittance of this structure shows a sharp passband in the band gap region. It is observed that by introducing PMN-0.38PT layer in both sides of the air cavity, the existing band gap region of Si–SiO₂ structure is slightly increased. Here, PMN-0.38PT material is working as a tunable element for passband. By applying some external potential on PMN-0.38PT crystal, the thickness of cavity layer can be tuned and the passband can be placed at any desired wavelength in the band gap region. Since the photonic band gap region contains a range of wavelengths which are not allowed to pass through the structure can be considered as a multiplex signal for the proposed demultiplexer. Therefore, any optical signal that lies in the band gap region of the structure can be separated into its components as a pass band. Hence, the proposed structure will work as an optical demultiplexer.     

The effect of excess titanium and crystal symmetry on electronic properties of Pb(Zr1−xTix)O3 compounds

In this paper the structural and electronic properties including band structure, energy gap and density of states have been studied for different phases of Pb(Zr_1−xTi_x)O₃ compounds with a wide range of Ti/Zr ratio (i.e. from x = 0 to x = 1). The calculations were performed in the framework of density functional theory (DFT), using the full potential-linearized augmented plane wave (FP-LAPW) method with the generalized gradient approximation (GGA). In general, our results show that for all cases (x = 0, 0.33, 0.5, 0.66 and 1) by increasing the amount of Ti atoms the band gap decreases, because of the strong hybridization between Ti-3d and O-2p orbital. But, in other hand, decreasing the crystal symmetry results in widening the band gap. For the monoclinic phase (x = 0.5) the effect of excess Ti on the band gap is less than the effect of crystal symmetry, so there is an increase in the band gap.