球共振声学法测量普适气体常数

设计和建立了高精度的球共振声学法气体音速测量装置,分析了实际的球共鸣器的结构对共振频率的影响,并给予了相应的修正.测量了温度为29315K,压力在02MPa—08MPa范围内氩气的音速,并根据音速数据确定了普适气体常数.实验温度、压力和普适气体常数的不确定度分别为±14mK,±2kPa和±00036%.最终确定的普适气体常数R为831439±000030J·mol-1·K-1. 关键词： 普适气体常数 音速 球共振器 声学法     

丙烷气相音速与理想气体比热的实验研究

用球共鸣声学法测量了工质丙烷（Ｒ２９０）在温度分别为２９３．４８ Ｋ、３０２．９６Ｋ、３１３．２１Ｋ和３２３．１９Ｋ时,压力从２００ｋＰａ～７００ｋＰａ范围内的四条等温线共２８个音速数据。温度、压力和气体音速测量的不确定度分别为±１４ｍＫ、２．０ｋＰａ和±０．００３７％．根据实验数据,由热力学关系式得到了Ｒ２９０在四个温度下的理想气体比热和第二音速维里系数．同时根据现有的高精度实验数据拟合Ｒ２９０的理想气体比热方程．这些研究为Ｒ２９０在工程上的应用提供了必需的热物理性质基础数据．     

自发布里渊散射法异丙醚音速的实验测量

本文研制了一套基于自发布里渊散射法的流体音速测量实验系统,分析得到该实验系统温度、压力测量的不确定度分别为0.02 K,10 kPa,音速测量的扩展不确定度为0.5%。测量了标准物质正戊烷310 K到470 K饱和液体和350 K到470 K饱和气体的音速,与文献值比较得到,该实验测量值的测量偏差为2.5%左右,验证了本实验系统的可靠性与稳定性。在温度为303.15 K~453.15 K,压力达5.5 MPa范围内,对燃料添加剂异丙醚的饱和液体和过冷液体的音速进行了测量,并依据实验数据给出了异丙醚音速的经验关联式,关联式的计算偏差为0.51%(饱和液体)和0.54%(过冷液体)。     

一种新型的水下低频共鸣器*

该文旨在宽开口的共鸣腔内嵌入聚氨酯泡沫来设计一种新型的水下低频共鸣器。首先通过水池实验测定聚氨酯泡沫板的声速。然后基于此建立镶嵌聚氨酯泡沫共鸣器的理论模型获得声阻抗率,通过与直口结构以及棒纵振动模型对比,验证理论模型的正确性,并建立集中参数系统,分析内嵌聚氨酯泡沫能够降低共鸣器共振频率的原因。最后通过有限元仿真软件进行计算,检验理论模型的正确性,与无聚氨酯泡沫镶嵌的共鸣器相比,镶嵌聚氨酯泡沫的共鸣器在维持较低品质因素的同时实现了共振频率大幅降低。     

基于石英音叉增强型光谱技术(QEPAS)的实时探测系统研究

利用石英音叉增强型光谱技术(QEPAS)结合基于Lab-VIEW设计的数字 频率锁定技术建立了一套气体实时探测系统, 该方案使用3f信号作为误差反馈信号, 将激光器锁定在待测气体吸收峰的中心位置, 保证了长时间测量的准确度并且提高了探测效率. 实验中采用中心波长位于1.396 μm的DFB半导体激光器作为光源, 选择常压下空气中的水汽作为研究对象, 对系统性能进行了测试, 并对影响影响系统探测灵敏度的主要因素进行了分析. 实验结果表明, 该系统可以将激光器稳定在± 0.001 cm^-1范围内, 对激光器长时间工作时的波长漂移起到了很好的抑制作用, 系统的检测限约为1 ppm, 该方案可以直接应用于工业气监测、痕量污染物实时测量等领域.     

制冷工质PVT实验系统研制及HFC-227ea蒸气压测量

本文介绍了一套自行研制的制冷工质PVT实验系统。该系统的温度控制采用改进的增量式数字PID算法,由自行开发的测控软件进行计算机实时测控。实验结果表明,在整个适用温度范围内温度测量精度可达±5mK。压力测量系统最大不确定度为±1.5 kPa。利用本装置,测量了HFC-227ea的蒸气压,并拟合了一个Wagner型蒸气压方程,结果与文献值吻合很好。     

圆柱定程干涉法声速测量原理与实验系统研制

气相声速是日前可测量的最精确的热物性之一,圆柱定程干涉法是极有应用前景的测量方法.本文分析了圆柱定程干涉法测量气相声速的实验原理,在此基础上研制了一套新的实验系统,由共鸣腔、压力仓、共振频率测量系统、温度和压力测量系统以及数据采集与控制系统组成.实验系统综合考虑了多种非理想因素的影响,提高了共振频率测量的信噪比,降低了...     

京胡和二胡的共鸣器

本文主要是对京胡和二胡共鸣器的理论分析。从膜与琴筒内声波的耦合振动出发,给出共振频率和共振响应的近似解,并与实验结果进行比较。对于二胡的共鸣器,由实验的声压分布推算琴筒开口格板的声阻抗率作为格板的影响。文中还给出共鸣器辐射场声压频率特性的例子。     

基于莫尔信号的精密位移测量与控制的研究

应用光衍射理论分析了一种纳米级位移分辨率的双级衍射光栅测量系统,建立了衍射莫尔信号与对应位移的数学模型,并通过计算机仿真对莫尔信号的位移特性进行了研究。在此基础上构建了一套精密位移测量与控制装置,取差动零次激光莫尔信号为控制信号,由微机控制实现高精度位移检测及全自动精密定位。实验结果表明,基于激光莫尔信号的精密检测与控制装置可获得得5nm的位移分辨率及±0.4μm的定位精度。     

激光干涉任意转角测量信号的获得及误差补偿技术

采用信号处理的方法对激光干涉测角系统的特性进行线性化处理,需要产生两路正交信号。采用空间互相垂直的两套干涉系统获得信号难免会使系统复杂、调整困难,因此提出了一种插值处理方法,可以利用测量得到的一路信号获得线性输出信号。输出信号的非线性误差较处理前大大减小了,但是无法满足高精度测量的要求。还提出了针对误差产生的原因进行的误差补偿技术。实验结果表明,提出的方法可以实现任意转角的高精度测量,光程差的测量误差小于±0 2μm,对应的转角测量误差为0 63″。     

Precision measurement of the speed of sound and thermodynamic properties of gases

Conclusions  The main significance of this paper is to evidence that the speedu of an acoustic wave propagating through a fluid provides nearly exhaustive information about its thermodynamic state. In recent years a substantial improvement of the experimental techniques and the associated theoretical models have made it possible to measureu with outstanding precision and accuracy (some parts in 10⁶). Thus, even if the thermodynamic quantities of interest are determined indirectly from the acoustic data, their ultimate accuracy favourably compares with that characteristic of traditional non-acoustic techniques. Among the wide variety of applications of speed-of-sound measurements, the result of major scientific relevance is the re-determination of the universal gas constantR. The revision of thermodynamic temperature scales and determinations of densities and heat capacities for pure gases and mixtures with accuracy of 0.1% also represent important results. The speed of sound is experimentally determined measuring the resonance frequencies of cavities (resonators) of spherical or cylindrical geometry, the choice depending on the order of accuracy demanded and the particular application of interest. Future improvements of the technique would require either an improved method for the determination of the resonator dimensions as a function of temperature, or different methods for excitation and detection of sound. These should have such design characteristics to extend the accessible range of experimental temperatures and pressures while maintaining or improving the signal-to-noise ratio. Substitution of conventional electro-acoustic transducers with non-contact optical techniques is under study and looks as a promising alternative.     

边界层效应对定程干涉法声速测量的影响

定程干涉法是精度最高的气相声速测量方法,本文再现了定程干涉法共振频率的导出过程,在此基础上复现了边界层修正式的导出过程。最后以声速数据丰富的Ar为例,分析了边界层对这两种定程干涉法测量的影响规律。结果表明:边界层对定程干涉法声速测量有着显著的影响;边界层的影响随温度升高而增大、随压力升高而降低;适当增加共鸣腔体的几何尺寸有利于减小边界层效应的影响。     

Study of ferrobielastic twinning in quartz under conditions of uniaxial pressure by the compound acoustic resonator method

The compound acoustic resonator method is used to study the phenomenon of the ferrobielastic transition in single crystals of quartz subjected to uniaxial pressure. Toward this end, a layered structure consisting of an aluminum film/zinc oxide film/aluminum film sandwich was deposited on one of the surfaces of an X-cut plane-parallel quartz plate. This structure served as an electromechanical transducer in such a way that the entire system acted as a multifrequency acoustic resonator. Uniaxial pressure was applied perpendicular to the direction of propagation of the acoustic waves and caused a growth of the frequencies of the resonance peaks of the structures, indicating a change in the velocity of the acoustic waves. The ferrobielastic phase transition, which arises at some threshold pressure (the ferrobielastic switching effect), is characterized by a discontinuous drop in the frequencies of the resonance peaks. The variation of the resonator frequency both below and above the switching threshold correlates with the variation of the so-called “natural” sound velocity determined by the pressure-dependent elasticity constants of the material. The observed frequency jump of the resonance peaks is due mainly to the relatively abrupt change in the dimensions of the crystal. The results of the acoustic measurements allow reliable recording of the switching effect and a study of its properties. Fiz. Tverd. Tela (St. Petersburg) 39, 290–294 (February 1997)     

Air-coupled MUMPs capacitive micromachined ultrasonic transducers with resonant cavities

This work reports performance improvements of air-coupled capacitive micromachined ultrasonic transducers (CMUTs) using resonant cavities. In order to perform this work, we have designed and manufactured a CMUT employing multi-user microelectromechanical systems (MEMS) processes (MUMPs). The transducer was designed using Helmholtz resonator principles. This was characterised by the dimensions of the cavity and several acoustic ports, which had the form of holes in the CMUT plate. The MUMPs process has the advantage of being low cost which allows the manufacture of economic prototypes. In this paper we show the effects of the resonant cavities and acoustic ports in CMUTs using laser Doppler vibrometry and acoustical measurements. We also use Finite Element (FE) simulations in order to support experimental measurements. The results show that it is possible to enhance the output pressure and bandwidth in air by tuning the resonance frequency of the plate (f_p) with that of the Helmholtz resonator (f_H). The experimental measurements show the plate resonance along with an additional resonance in the output pressure spectrum. This appears due to the effect of the new resonant cavities in the transducer. FE simulations show an increase of 11 dB in the output pressure with respect to that of a theoretical vacuum-sealed cavity MUMPs CMUT by properly tuning the transducer. The bandwidth has been also analyzed by calculating the mechanical Q factor of the tuned CMUT. This has been estimated as 4.5 compared with 7.75 for the vacuum-sealed cavity MUMPs CMUT.     

Suppression of Helmholtz resonance using inside acoustic liner

When a Helmholtz resonator is exposed to grazing flow, an unstable shear layer at the opening can cause the occurrence of acoustic resonance under appropriate conditions. In this paper, in order to suppress the flow-induced resonance, the effects of inside acoustic liners placed on the side wall or the bottom of a Helmholtz resonator are investigated. Based on the one-dimensional sound propagation theory, the time domain impedance model of a Helmholtz resonator with inside acoustic liner is derived, and then combined with a discrete vortex model the resonant behavior of the resonator under grazing flow is simulated. Besides, an experiment is conducted to validate the present model, showing significant reduction of the peak sound pressure level achieved by the use of the side-wall liners. And the simulation results match reasonably well with the experimental data. The present results reveal that the inside acoustic liner can not only absorb the resonant sound pressure, but also suppress the fluctuation motion of the shear layer over the opening of the resonator. In all, the impact of the acoustic liners is to dampen the instability of the flow-acoustic coupled system. This demonstrates that it is a convenient and effective method for suppressing Helmholtz resonance by using inside acoustic liner.     

Measurements of attenuation and electromechanic coupling constant of piezoelectric films in microwave resonators

It was found that for arbitrary high overtone and thin film microwave resonators the results of the measurements of the difference between frequencies of resonance and antiresonance on any harmonic of the resonator together with the measurement of the frequency difference between the peculiarities on the frequency dependence of imagine part of the electric impedance of the resonator give a simple way of the evaluation of the losses in the materials composing resonator structures and of the evaluation of the electromechanical constant of the piezoelectric film exciting acoustic waves.     

高次谐波体声波谐振器机械品质因数的测量*

高次谐波体声波谐振器(HBAR)具有高的机械品质因数(Q_M)和多模谐振谱特性,其在频率控制系统中具有重要应用。对制备的Al/Zn O/Au/Sapphire结构HBAR器件进行了Q_M的测定,从实际的测试系统出发,给出了它的等效电路,通过一系列分析处理得到了Q_M随频率的变化曲线。结果表明,Q_M随频率增加逐渐减小。     

光声池径向共振模式耦合系数理论分析

光声光谱法是基于红外吸收光谱原理的一种高灵敏度的微量气体探测技术。它使用声共振腔来实现微弱声信号的共振放大。通过调节激光的调制频率,当它等于腔的某个共振频率时,在腔内形成声驻波,而腔本身的作用相当于一声放大器。共振腔的放大作用取决于当前被激活的共振模式、腔的品质因素、声传感器的状态以及电磁辐射与腔共振模式的耦合作用。值得关注的是,红外激光相对于声共振腔的入射方位不同则激励产生的光声信号幅值也不同。采用理论推导与数值计算相结合的方法,以圆柱形光声池为例,研究了径向共振模式下耦合系数受激光入射方位的影响。研究表明,激光入射角在0～π/2范围变化时耦合系数存在2个零点和2个极大值：入射角为0或tan-1(0.859 2×2R/L)时,耦合系数为零而径向共振失效;入射角为tan-1(0.556 8×2R/L)或tan-1(2R/L)时,耦合系数极大而径向共振最强。此处R为池径而L为池长。结果可用于指导光声池结构优化设计与安装调试,增强光声法检测微量气体的信号幅值,提高检测灵敏度。     

Improvements to the methods used to measure bubble attenuation using an underwater acoustical resonator

Active acoustic techniques are commonly used to measure oceanic bubble size distributions, by inverting the bulk acoustical properties of the water (usually the attenuation) to infer the bubble population. Acoustical resonators have previously been used to determine attenuation over a wide range of frequencies (10-200 kHz) in a single measurement, corresponding to the simultaneous measurement of a wide range of bubble sizes (20-300 μm radii). However, there is now also considerable interest in acquiring measurements of bubbles with radii smaller than 16 μm, since these are thought to be important for ocean optics and as tracers for near-surface flow. To extend the bubble population measurement to smaller radii, it is necessary to extend the attenuation measurements to higher frequencies. Although the principles of resonator operation do not change as the frequency increases, the assumptions previously made during the spectral analysis may no longer be valid. In order to improve the methods used to calculate attenuation from acoustical resonator outputs, a more complete analysis of the resonator operation is presented here than has been published previously. This approach allows for robust attenuation measurements over a much wider frequency range and enables accurate measurements from lower-quality spectral peaks.     

应用于流管实验装置的声源控制方法

流管试验中由于管道响应不同频率下声压起伏很大,影响测量精度,为此在流管实验装置中发展了一种声源反馈控制方法,以管道内的声压信号为反馈信号,通过改变声源系统中信号源输出信号来调节不同频率下管道内的声压大小。本文分析了反馈次数,反馈信号采集卡量程以及反馈采样时间等因素对反馈控制结果的影响。该方法原理简单,易于实现,其控制思想可应用于其他实验装置的声源控制中。