An improved impedance tube test method based on multi-modal decomposition to determine the sound absorption coefficients at high frequencies

In this study,an improved impedance tube test method is proposed to determine the sound absorption coefficients of materials at high frequencies up to 10 kHz.Specifically,a multi-modal decomposition method is used to measure the sound absorption coefficients above the cut-off frequency of plane waves in the impedance tube.During the measurement process,an array of microphones is placed in the circumferential and axial directions of the tube.Then,the first three acoustic circumferential modes are...     

充水粘弹性管道的频散曲线计算分析*

针对谱方法分析计算充水粘弹性管道的广义特征值问题,根据Chebyshev多项式及微分矩阵、位移和应力连续条件,将波动方程离散为相应的线性方程。利用MATLAB数值编程计算充水弹性和粘弹性管道对应频率下的轴对称纵向导波频散曲线和衰减曲线。分析表明,波传播在粘弹性管道中不仅具有衰减特性,而且由于水和粘弹性壳体交叉耦合作用,在一定频率范围内产生两种截断模态。     

多阶声模态分解的改进阻抗管法测量材料的高频吸声系数

为了测量高频材料吸声系数,采用声模态分解的方法,基于阻抗管构建测试设备,在阻抗管内测量超过平面波截止频率的的高频吸声系数。测量过程中,通过在阻抗管的周向和轴向分别布置传声器阵列,分离管道内前3阶周向声模态以及各阶声模态的轴向传播入射波和反射波,从而得到最高频率达10000 Hz的材料吸声系数,并通过对比常规阻抗管测试方法的测量结果,说明采用声模态分解法对高频材料吸声系数的准确性。     

基于四水听器的充水弹性管声速测量方法*

实验室中水声材料声学参数的测量主要在水声声管中进行。管内平面波声速是正确测量这些参数的基础。该文提出一种基于四水听器结合不同边界的测量充水弹性管中声速的新方法。该方法利用4个固定位置处的水听器,采用最小二乘的方法,使得两组水听器分别得到的声管末端入射波声压差值的平方最小的声速即为管内平面波声速。该方法利用单频信号,在每一频率点均可测得声速,可以在任一种声管末端边界下进行测量,同时无需知道各水听器到边界的精确距离,在文中的3种边界下声速测量结果具有很好的一致性,实验操作简单、误差很小。该方法的仿真结果与管内声速的理论值吻合得很好,同时实验测量结果与仿真值之间的误差很小,证明了方法的准确性以及鲁棒性,为声管声速测量提供一个很好的思路。     

Investigation of sample size effects in impedance tube measurements

A series of careful impedance tube measurements using different sizes of glass fibre and felt samples have demonstrated that frame resonance effects result from slightly oversize samples. The appropriate size of a sample is investigated while also avoiding air leakage. Diameters of 0.5 or 1.0 mm less than the inner diameter of the tube are found to avoid these effects.     

An improved model for the acoustic radiation impedance of the mouth based on an equivalent electrical network

This paper proposes a model for acoustic radiation impedance of the mouth in the form of the equivalent electrical network. Five known models of radiation impedance are compared: radiation of a circular piston set in a spherical baffle: radiation of a circular piston set in an infinite baffle, the Flanagan model, the Wakita and Fant model, and the Stevens, Kasowski and Fant model. The proposed model most accurately approximates the radiation impedance of a circular piston set in a spherical baffle. Differences between the acoustic resistance and reactance calculated by the proposed model and the piston set in a spherical baffle of 9 cm radius are relatively small in the kr < 2 region. The deviations in calculated values of the acoustic resistance and the reactance are within ±0.023 × ρc/A_m and ±0.008 × ρc/A_m, respectively, where A_m denotes the area of the mouth aperture. The accuracy of the proposed model is demonstrated by vowel formant frequency calculations. Differences in formant frequencies calculated by applying the proposed model and the piston set in a spherical baffle model are less than 0.3%.     

微扰实验法测试螺旋线行波管耦合阻抗及模拟仿真

应用有限元仿真软件HFSS,建立了准确的3维螺旋线行波管耦合阻抗仿真模型。应用该模型,对微扰实验法在微扰杆内电场所做出的4个假设和近似,进行了定量的分析和讨论：电场在轴向是均匀的,忽略掉轴向高次空间谐波的存在;电场在角向是均匀的,忽略掉角向高次空间谐波的存在;忽略掉电场中TE波部分,认为电场角向分量为零;假设微扰前后的电场是相等的。同时,对微扰杆的尺寸和介电常数与耦合阻抗的依赖关系进行了模拟分析。结果表明：当微扰法所引入的假设和近似逐步消失后,微扰法的结果最后收敛于定义法。     

微扰实验法测试螺旋线行波管耦合阻抗及模拟仿真

 应用有限元仿真软件HFSS,建立了准确的3维螺旋线行波管耦合阻抗仿真模型。应用该模型,对微扰实验法在微扰杆内电场所做出的4个假设和近似,进行了定量的分析和讨论：电场在轴向是均匀的,忽略掉轴向高次空间谐波的存在;电场在角向是均匀的,忽略掉角向高次空间谐波的存在;忽略掉电场中TE波部分,认为电场角向分量为零;假设微扰前后的电场是相等的。同时,对微扰杆的尺寸和介电常数与耦合阻抗的依赖关系进行了模拟分析。结果表明：当微扰法所引入的假设和近似逐步消失后,微扰法的结果最后收敛于定义法。     

Simple sound transmission loss measurements using a modified impedance tube technique

A method of comparing the sound transmission characteristics of various materials, and combinations of materials, is presented, using a modified impedance tube technique. The procedure proved to be relatively quick and inexpensive in comparison with standard reverberation suite tests, and is therefore particularly useful for the qualitative ranking of multiple samples.The limitations of the technique are discussed in some detail, and particular emphasis is given to the problems of small sample size and method of mounting in the apparatus.     

Elastic characterization of closed cell foams from impedance tube absorption tests

A method is presented to determine the bulk elastic properties of isotropic elastic closed-cell foams from impedance tube sound absorption tests. For such foams, a resonant sound absorption is generally observed, where acoustic energy is transformed into mechanical vibration, which in turn is dissipated into heat due to structural damping. This article shows how the bulk Young's modulus, Poisson's ratio, and damping loss factor can be deduced from the resonant absorption. Also, an optimal damping loss factor yielding 100% of absorption at the first resonance is defined from the developed theory. The method is introduced for a sliding edge condition which is an ideal condition. Then, the method is extended to a bonded edge condition which is more easily achievable and additionally enables the identification of the Poisson's ratio. The method is experimentally tested on expanding closed-cell foams to find their elastic properties in both cases. Using the found properties, sound absorption predictions using an equivalent solid model with and without surface absorption are compared to measurements. Good correlations are obtained when considering surface absorption.     

Proton transport through water-filled carbon nanotubes

Proton transfer along 1D chains of water molecules inside carbon nanotubes is studied by simulations. Ab initio molecular dynamics and an empirical valence bond model yield similar structures and time scales. The proton mobility along 1D water chains exceeds that in bulk water by a factor of 40, but is reduced if orientational defects are present. Excess protons interact with hydrogen-bonding defects through long-range electrostatics, resulting in coupled motion of protons and defects.     

双极性流对低阻抗器件的影响

 分析讨论了双极性流对平面二极管发射电流的影响,并利用PIC程序对平面二极管中的双极性流问题进行了数值对比。在此基础上模拟研究了具有径向发射特点的低阻抗高功率微波器件MILO中的双极性流问题。结果表明：双极性流的出现使器件偏离最佳工作点,使输出功率和效率降低,电压越高,器件偏离最佳工作点就会越远,当电压高到一定值以后会使器件的工作点移至B-H曲线以下,器件处于过绝缘状态,不能正常工作。     

采用伪随机信号激励的驻波管三点测量法

本文对伪随机信号激励的驻波管三点测量法(TPM)进行了讨论和误差分析,并与驻波比法(SWR)及双传声器传递函数法(TTF)进行了比较。结果表明,伪随机信号三点法具有较高的精度,与驻波比法所得结果吻合甚好,并很好地解决了双传声器传递函数法存在的缺陷,可用于实际测量。     

教学用光谱仪之改良

介绍一改良的教学用光谱仪（直视分光镜），利用发光二极体在完全黑暗的背景中标示谱线，并读出该位置谱线之刻度，进而求出其波长；克服了同类型教学用光谱仪之缺点（谱线位置之刻度难以精密测量、较暗谱线不易观察等）。     

An improved sonochemical reactor

The design and optimization of sonochemical apparatus are still open to advancement. Under high-intensity ultrasound reaction rates and yields are mainly influenced by the characteristics of transducer and reactor. Several useful improvements are introduced and described. In order to achieve uniformity of the acoustic field and optimal acoustic streaming in every part of the reaction vessel (a Teflon tube), the reactor can be made to rotate eccentrically around the horn axis and the probe to move alternatively up and down by a pre-determined excursion at a chosen speed. Continuous high-power irradiation is feasible without any time limit because the whole probe system is refrigerated by an oil forced-circulation circuit connected to a chiller. The apparatus can control a number of important reaction parameters: modified atmosphere, reaction temperature, tunable frequency and constant amplitude. Excellent performance was observed on several reactions, such as the chemical modification of chitosan, a poorly soluble biopolymer.     

An easily-prepared impedance matched Josephson parametric amplifier

An impedance matched parametric amplifier (IMPA) with Josephson junctions is fabricated and characterized. A hybrid structure containing coplanar and strip structures is implemented to realize an impedance taper line and a plate capacitor in an LC nonlinear resonator based on Josephson junctions. The upper plate of the capacitor is isolated with SiN_x without grounding as well as the strips. Such easily-prepared designs greatly reduce the requirements for lithography alignment and precision, which makes the fabrication process more reliable. The experimental results show that in such IMPA a gain higher than 25 dB with a bandwidth of about 100 MHz can be obtained. This broadband amplifier operates close to the quantum limit. By adjusting the working point, a higher bandwidth of about 400 MHz can be obtained with a gain of about 17 dB.     

An improved variational method

In order to improve the unitarity of the S-matrix, an improved variational formulism is derived by proposing new generating functionals and adopting proper asymptotic boundary conditions for trial relative wave functions. The formulas with the weighted line-column balance for the single-channel and multi-channel scatterings, where the non-central interaction is implicitly considered, are presented. A numerical check is performed with a soluble model in a four coupled channel scattering problem. The result shows that the high accuracy and the unitarity of the S-matrix are reached.     

An improved variational method

In order to improve the unitarity of the S-matrix, an improved variational formulism is derived by proposing new generating functionals and adopting proper asymptotic boundary conditions for trial relative wave functions. The formulas with the weighted line-column balance for the single-channel and multi-channel scatterings, where the non-central interaction is implicitly considered, are presented. A numerical check is performed with a soluble model in a four coupled channel scattering problem. The result shows that the high accuracy and the unitarity of the S-matrix are reached.