微穿孔板吸声体参数灵敏度分析

轻质耐高温的微穿孔板吸声体的吸声性能主要受腔深、孔径、板厚、穿孔率四个参数的制约,通过等比例减小和增大这些参数来观察微穿孔板吸声体吸声性能的改变。引入吸声系数变化率的概念,以吸声系数变化率作为衡量标准,判断参数的改变对结构吸声性能的影响。整体而言,影响吸声性能的敏感度从高到低的微穿孔板吸声体参数顺序为：腔深、孔径、穿孔率、板厚。研究结果可为工程人员利用微穿孔板吸声体降噪时设计吸声体尺寸提供一定的指导。     

声致振动对3层微穿孔板吸声体吸声性能影响

为了研究声致振动对3层微穿孔板吸声体的吸声性能的影响,基于微穿孔板吸声理论与声电等效电路原理,对考虑声致振动时,3层微穿孔板吸声体的吸声性能进行了计算。研究发现,考虑声致振动时,3层微穿孔板吸声体的低频吸声性能有所降低,高频吸声性能变化不大。且随着微穿孔板的质量密度的增加,考虑声致振动时的3层微穿孔板吸声体的吸声性能曲线逐渐接近未考虑声致振动的情况。当其它参数保持不变时,随着穿孔板穿孔直径和间距的增加两共振峰逐渐向低频方向移动;随着穿孔率的增加,两共振峰逐渐向高频方向移动。因此,声致振动对3层微穿孔板吸声体的吸声性能有一定的影响,其影响程度与微穿孔板的质量密度和结构参数相关。     

复合微穿孔板吸声结构声学性能预测

本文旨在将微穿孔板吸音结构与多孔材料复合，得到中低频吸音性能较好的复合层声学结构。以微穿孔板多边形穿孔截面、穿孔率、空腔厚度和多孔材料类型为变量，设计复合层声学结构，给出复合层声学结构吸声系数的理论计算方法和声学有限元仿真预测模型。利用3D打印技术制备精度较高的微穿孔板实验样本，利用阻抗管法对复合层声学结构的吸声系数进行实验室测量。对比预测结果和实验数据，发现两者具备很好的一致性。研究表明：复合层声学结构具有很好的中低频吸声系数，通过调整微穿孔板穿孔截面形状和穿孔率可以对中低频段（50-1600Hz）噪音进行有效控制。     

微穿孔板吸声体中的板振动

板振动对微穿孔板吸声体的声学特性存在一定的影响。文章对此影响关系从理论方面进行初步分析,并通过不同材料、不同孔径、不同穿孔率样品在低频、中频驻波管中的大量实验,分析板振动对微穿孔板吸声体吸声性能影响关系的规律性,从而得到对微穿也板的实际应用具有指导性的结论。     

多孔材料和微穿孔板复合吸声结构研究

主要研究如何利用多孔材料拓宽微穿孔板的吸声频带,微穿孔板用来吸收低频噪声,同时加入吸声材料来提高中高频的吸声。给出复合结构吸声系数的计算方法,并在阻抗管内进行实验验证,测量结果和计算结果取得很好的一致性。研究结果表明,多孔吸声材料置于微穿孔板之前,并且二者之间有一定的空气层时,可以显著改善微穿孔板的吸声性能。     

复合微穿孔板吸声结构吸声特性分析及优化

针对传统微穿孔板吸声结构（Micro-Perforated Panel Absorber,MPPA）吸声带宽较窄的问题,基于微穿孔板串并联耦合机制,提出了三种不同结构形式的复合MPPA结构。首先,依据声电类比法推导出了复合MPPA法向入射吸声系数的解析计算模型;然后,通过初步设计结构尺寸参数,探究了该类吸声结构的宽带吸声特性;针对500～3 600 Hz的目标吸声频段,采用多种群遗传算法对复合MPPA以及传统简单MPPA、串联MPPA、并联MPPA分别进行优化,对比分析了其最优吸声带宽;最后,利用有限元法对优化后吸声性能最佳的复合MPPA进行了吸声系数仿真测试以及对应的阻抗管实验测试。测试结果表明,所提出的复合MPPA的宽带吸声性能优于传统简单MPPA、串联MPPA和并联MPPA的吸声性能;在500～3 600 Hz频段内,优化后吸声性能最佳的复合MPPA能够实现优异的宽带吸声,平均吸声系数高达0.92。该类吸声结构为宽带噪声控制提供了一定的参考。     

封闭式背腔微穿孔板吸声结构

为提高微穿孔板吸声体的吸声性能,提出一种宽频带封闭式背腔微穿孔板吸声结构.使用薄膜封闭背腔中的特定气体,改变背腔声抗,配合参数合理的微穿孔板,能够提升低频吸声性能并有效拓宽吸声频带.基于声电类比法推导该吸声体的吸声系数计算方法,通过有限元仿真以及阻抗管实验对理论计算结果进行验证,最后探究背腔气体、微穿孔板振动和薄膜厚度...     

变截面背腔结构的微穿孔板吸声器的设计与研究

如何实现微穿孔板吸声结构的宽频吸声是近年来的研究热点之一。针对微穿孔板吸声结构的宽频吸声问题,本文设计了一种不规则背腔结构,并将其应用到单层和双层微穿孔板的吸声器上,对其吸声性能进行了研究。利用声电类比模型获得吸声器各部分的阻抗关系,然后通过理论计算得到吸声结构的阻抗和吸声系数。理论、仿真和实验结果表明：在不增加结构厚度的情况下,通过内层变截面隔板对背腔进行不等体积分割,可拓宽微穿孔板吸声带宽,且结构相对简单。该研究为微穿孔板吸声器的宽带低频吸声及其应用提供了新的设计思路。     

蜂窝微穿孔吸声体的宽频吸声性能优化设计

针对蜂窝微穿孔吸声体结构,利用粒子群优化(Particle Swarm Optimization,PSO)算法优化吸声体结构的吸声性能.以三蜂窝芯的蜂窝微穿孔吸声体结构中微穿孔板的孔径、穿孔率和背腔深度为优化设计变量,以吸声体的吸声系数和吸声频带为优化目标,得到吸声体宽频范围吸声时的优化结构参数.将三参数优化、两参数优...     

折叠背腔微穿孔结构的宽频吸声特性研究

为拓宽吸声带宽,提高低频吸声效果,提出新型折叠背腔微穿孔板吸声结构。建立单个折叠背腔微穿孔吸声单元的理论模型,通过传递矩阵法求解其吸声系数,通过有限元仿真验证理论计算结果。在此基础上,分析由不同背腔深度单元组成的折叠背腔微穿孔板吸声结构的垂直入射吸声特性。随着组合单元数目的增加,吸声带宽得到进一步拓展。结果表明,整体厚度仅为30.3 mm的10 单元组合折叠背腔微穿孔板吸声结构在450 Hz～1 600 Hz内的吸声系数大于0.6,在1 200 Hz～1 550 Hz范围内的吸声系数大于0.8。     

A biocompatible chitosan composite containing phosphotungstic acid modified single-walled carbon nanotubes

Surface modification of carbon nanotubes is crucial for the dispersion and interfacial adhesion of carbon nanotubes in polymer composites. Here we present a novel method to construct single-walled carbon nanotube/chitosan composites using phosphotungstic acid as an anchor reagent to modify single-walled carbon nanotubes. The most direct benefit from this method is that this modification is mild but effective: the induced defects on single-walled carbon nanotubes are negligible based on Raman and transmission electron microscopy observations; and homogeneous dispersion of single-walled carbon nanotubes in chitosan matrices and strong binding between single-walled carbon nanotubes and chitosan are achieved. Moreover, according to the results of tetrazolium-based colorimetric assays in vitro, we demonstrate that the produced phosphotungstic-acid-modified single-walled carbon nanotube/chitosan composites have good biocompatibility. Thus, our study provides a feasible route to fabricate biocompatible composites containing single-walled carbon nanotubes for potential application in bone tissue engineering.     

Fabrication, characterization and mode locking application of single-walled carbon nanotube/polymer composite saturable absorbers

We present the fabrication of a high optical quality single-walled carbon nanotubes (SWNTs) polyvinyl alcohol (PVA) composite film. The composites demonstrate strong saturable absorption at ～1.5 μm, the spectral range for optical communications. By measuring the nonlinear transmission of a sub-picosecond pump pulse through the film, we were able to deduce a saturation fluence of ～13.9 μJ/cm² and a modulation depth ～16.9% (in absorption) at a high pulse fluence ～200 μJ/cm². Transient saturable absorption is investigated by measuring the transmitted autocorrelation traces at various incident power levels. Observed side-peak suppression indicates a fast recovery time on the scale of ～1 ps for our saturable absorber devices. Furthermore, we use these SWNT-PVA composite saturable absorbers as mode-lockers in an Er³⁺ fiber ring laser and achieve ～560 fs pulse generation with good jitter performance and long term stability. The laser performance is also associated with the parameters of our SWNT based saturable absorber.     

非平面界面的多层高分子复合材料吸声性能

主要研究非平面界面的新型多层高分子复合材料在不同温度和压力下的吸声性能。制备了非平面界面的新型多层高分子复合材料和平面界面的传统多层高分子复合材料, 并在声管中测试其吸声系数。结果表明, 在所研究的频率范围内, 新型多层高分子复合材料吸声系数大于传统的多层高分子复合材料吸声系数; 这种新型多层高分子复合材料吸声系数峰值随温度的升高向低频方向移动, 而随压力变化不大。因此, 合理设计多层高分子复合材料的界面形状可以提高复合材料的吸声性能。      

Evolution of hollow dodecahedron carbon coated FeCo with enhance of electromagnetic properties

FeCo@C with a hollow porous dodecahedron structure was obtained through carbonization of ZIF-67 etched with Fe³⁺. During the pyrolysis process, the organic skeleton of the ZIF-67 was carbonized, forming graphitic carbon and carbon nanotubes. The etching effect of Fe³⁺ with different concentrations on the morphology of ZIF-67 is studied. The MOF-derived porous carbon bimetallic nanocomposites exhibited stronger electromagnetic wave absorption performance than the monometallic ones. Specifically, the optimized sample has a reflection loss of ?70.69 dB at 11.28 GHz, as the thickness is 2.07 mm. The enhanced electromagnetic wave (EMW) absorption performance of the nanocomposites can be attributed to the multiple interfaces and capacitive structure formed by catalytically produced carbon nanotubes. This achievement could be used as a reference for the development of MOF-derived porous carbon nanocomposite EMW absorbers.     

变截面微穿孔板吸声特性研究

传统的微穿孔板要获得较佳的吸声性能,需要较小孔径的微孔（〈0．3mm）;在穿孔率不变的情况下,增加板厚,那么板的吸声性能将下降。为了避免这个问题,提出一种新型的微穿孔板结构——变截面微穿孔板。与传统微穿孔板不同,它的微孔的截面积沿其轴向不是恒定的,而是在轴向的一定位置发生突变,从而板存在孔径差异较大的两部分。在马大猷的理论基础上,分析了变截面微穿孔板的吸声特性,并利用传递函数法,通过阻抗管进行了实验。分析和实验结果显示,变截面微穿孔板的吸声性能主要由孔径较小的部分决定,孔径较大的部分主要是增加了板的厚度,对板的吸声性能贡献较小;因此,通过变截面的方法,在增加板厚的同时也能使板维持在较佳的吸声性能水平。     

用单壁纳米碳管制备葡萄糖生物传感器的研究

以单壁纳米碳管为代表材料,对利用纳米碳管制备葡萄糖生物传感器中纳米碳管的作用和纳米碳管修饰电极的方法、酶的固定化方法及电极种类等因素对传感器性能的影响进行了研究.研究结果表明,纳米碳管的加入能有效地改善传感器的电化学性能,利用二茂铁和单壁纳米碳管共同修饰电极所制得的传感器的性能要好于仅用单壁纳米碳管修饰电极制得的传感器.在酶的固定化方法中,戊二醛交联法要略好于明胶包埋法;而利用铂电极制备出的生物传感器对葡萄糖的响应电流要明显高于利用金电极和玻碳电极制备出的生物传感器.这些结论对于开发纳米碳管在生物传感领域及生命科学相关领域的应用有参考价值.     

Electromagnetic interference shielding of carbon nanotube-fluoropolymer elastomer composites with layered structure

Abstract

This paper presents carbon nanotubes-containing polymer composites with layered gradient structure having electromagnetic interference (EMI) shielding properties. Polymer composite films were obtained on metal surface by aerosol deposition of a dispersion of carbon nanotubes in the solution of a copolymer of vinylidene fluoride with hexafluoropropylene (SCF-26) in acetone. Single-wall TUBALL (OCSiAl) carbon nanotubes were used. Three-layer coatings were formed with a concentration of nanotubes decreasing in each subsequent deposited layer. The reflection coefficient of electromagnetic radiation in the range of 20–35?GHz was measured. Gradient samples had significantly better characteristics compared to samples with uniform concentration of carbon nanotubes: the reflection coefficient reached ?6dB at 35?GHz. The outer layer of gradient structure with 0.1?wt % CNT provides a better matching of the wave resistance with free space and a smooth entrance of an electromagnetic wave into the sample. The subsequent layers with an increasing concentration of single-walled carbon nanotubes (0.3 and 0.5%) absorb electromagnetic radiation. Polymer elastomer composite EMI shielding coatings with concentration gradient can be applied by aerosol deposition to the surfaces of any composition and shape. Our results could serve as a design tool in carbon nanotubes - based EMI shielding flexible polymer coatings.     

Raman and electrochemical impedance studies of sol-gel titanium oxide and single walled carbon nanotubes composite films

Titanium oxide grown by a sol-gel route on single-walled carbon nanotubes was studied by Raman and Electrochemical Impedance techniques and compared with mixtures obtained by mechanical grinding. In spite of the superior dispersion of single-walled carbon nanotubes bundles in sol-gel composites, the lost of the small-diameter carbon nanotubes in the oxidizing sol-gel bath was inferred from their Raman spectra and the lower capacitive current of the voltammograms in 0.1 M H2SO4. We proposed proton electrosorption as the main charge storage mechanism for sol-gel composites, favoured by the hydroxylation and n-type conductivity of the oxide, while electrodes based on mixtures were dominated by double-layer charging, developing some pseudocapacitance with potential cycling due to the reversible oxidation of carbon nanotubes. Comparsion with TiO2/Carbon Blacks composites shows the effective role of single-walled carbon nanotubes as templates to control the mesoporous nature of sol-gel composite electrodes.     

A semi-continuum finite element approach to evaluate the Young’s modulus of single-walled carbon nanotube reinforced composites

This paper describes a micromechanical finite element approach for the estimation of the effective Young’s modulus of single-walled carbon nanotube reinforced composites. These composite materials consist of aligned carbon nanotubes that are uniformly distributed within the matrix. Based on micromechanical theory, the Young’s modulus of the nanocomposite is estimated by considering a representative cylindrical volume element. Within the representative volume element, the reinforcement is modeled according to its atomistic microstructure while the matrix is modeled as a continuum medium. Spring-based finite elements are employed to simulate the discrete geometric structure and behavior of each single-walled carbon nanotube. The load transfer conditions between the carbon nanotubes and the matrix are modeled using joint elements of changeable stiffness that connect the two materials, simulating the interfacial region. The proposed model has been tested numerically and yields reasonable results for variable stiffness values of the joint elements. The effect of the interface on the performance of the composite is investigated for various volume fractions. The numerical results are compared with experimental and analytical predictions.