音频声速测量仪的研制

设计制作了音频声速测量仪,传输信号是可以连续调节频率的音频信号,发声喇叭和拾音喇叭分别安装在圆管的两端,距离保持不变,拾音喇叭的信号经放大后连接到数字电压表,把发声喇叭的激励信号和拾音喇叭的输出信号都接到示波器上.通过连续改变喇叭的发声频率,利用共振干涉法和相位比较法测量声速.     

基于MATLAB的变频定距法测量声速的研究

利用声卡和matlab设计了一套变频定距法测量声速的装置,喇叭和麦克风放在共鸣管的一端,保持共鸣管水面高度不变,通过matlab软件控制声卡改变喇叭的发声频率,当反射波和入射波信号发生相遇时,可以从频谱图上看出干涉加强或干涉相消时的频率,从而得到声速。实验结果和理论声速相比较,百分偏差最大为1.66%。     

水中声速的测量

将空气中声速测量实验拓展至水中声速的测量,将NaCl溶于水中,制成不同浓度的盐水来模拟海水,对不同盐分的"海水"中的声速进行了测量.结果表明,随着海水盐度的增加,声速也增加.     

相位比较法测声速原理的剖析

研究了用相位比较法测超声声速问题 ,对其原理进行严格的分析和解释。     

基于光学信息处理的液体内声速测量

采用光学信息处理的方法获取相位物体的可见像,使相位物体的对比度从0提高到人眼可见的0.1以上,通过直接测量声光栅的光栅常量得到液体中的声速.该方法与采用衍射方法测量的结果基本符合.     

空气比热容比之声速测量法

介绍了声速公式的理论推导;提出了用声速测量方法测空气比热容比的实验方法;将声速测量方法和FD-NCD型空气比热容比测定仪测得的空气比热容比的误差进行了比较。     

应用时差法测量声速

共振干涉法和相位比较法是大学物理实验中常用的测量声速的方法,但工程应用很广泛的时差法测量声速却很少在大学物理实验内容中涉及。在文中实验用时差法测量声速的实验结果和理论值相符较好,并对实验结果进行讨论和分析。     

超声干涉法测量液体声速

研究了声速测量 ,介绍超声干涉测量液体声速的原理和技术。     

圆柱定程干涉法声速测量系统的实验测试

研究了圆柱腔体共振频率的测量方法,测试了新建立的声速实验系统,结果显示圆柱共鸣腔具有较高的信噪比,共振频率的测量不确定度小于5×10^-6。采用Ar气（99.999%）标定了声速共鸣腔的有效长度,不确定度为1.8×10^-5。开展了303～333 K下CO₂的气相声速实验研究,实验结果表明,当实验工质具有较高的纯度（>99.995%）时,气相声速的测量精度优于0.01%。     

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...     

Measuring the speed of sound of quintessence

Quintessence, a time-varying energy component that may account for the accelerated expansion of the universe, can be characterized by its equation of state and sound speed. In this paper, we show that if the quintessence density is at least 1% of the critical density at the surface of last scattering the cosmic microwave background anisotropy can distinguish between models whose sound speed is near the speed of light versus near zero, which could be useful in distinguishing competing candidates for dark energy.     

利用智能手机居家测量声速和重力加速度

利用两部智能手机,借助手机软件phyphox在家进行了多普勒效应实验.两部手机分别作为接收器和声源,让接收器和声源分别做自由落体运动,测得了接收频率和运动速度随时间的变化曲线,通过对数据的处理得到了声速和重力加速度值,并和理论值进行了对比,验证了用手机进行多普勒效应实验的可靠性,为以后实验的进行以及数据处理提供了参考.     

基于 LabVIEW 声速测量系统研究声速与温湿度的关系

利用USB独立声卡结合虚拟仪器软件LabVIEW开发了声速测量系统,研究了声速与空气的温度、湿度之间的关系,得到了温湿度修正的声速经验公式。     

Low frequency sound produced by a ventilated supercavitating vehicle

An analytical investigation is made of the low frequency noise produced by gas jet impingement on the gas-water interface of a ventilated supercavity. Enclosure within a supercavity enables an underwater vehicle to attain high-speed forward motion. Whereas high frequency components of the cavity self-noise can interfere with the vehicle guidance system, low frequency sound tends to radiate in the water to large distances from the cavity. A canonical mathematical problem is examined that extends a previous study by Foley et al. (Journal of Sound and Vibration329 (2010) 415-424.) of sound generation by a specially modified, model scale supercavitating vehicle involving gas jet impingement at normal incidence to the interface. Our analysis determines the influence on low frequency sound production of cavity aspect ratio and the manner in which the efficiency of sound production increases with decreasing distance of the jet impact region from the circular ‘cavitator’ at the vehicle nose, where the supercavity is formed.     

Multiple-order derivatives of a waveguide acoustic field with respect to sound speed, density, and frequency

An adjoint perturbative method is used to derive expressions for the first- through third-order derivatives of a pressure field with respect to sound speed, density, and frequency, for the restricted case of a laterally homogenous waveguide in which environmental parameters are only a function of depth. By using a normal-mode Green's function, the three-dimensional spatial correlation required by the standard acoustic adjoint equation can be reduced to a set of one-dimensional depth integrals. The resulting expressions for the first-order derivative are similar to those obtained by previous perturbative approaches based on the depth-separated wave equation, but the approach followed here permits straightforward extension to higher-order derivatives. Explicit evaluations of the expressions for a representative shallow-water waveguide model are in excellent agreement with numerical finite-difference computations. An analysis of the expressions as a function of source-receiver range finds the contributions to the mode amplitude derivatives to be non-negligible at ranges less than a few modal interference lengths, for parameters associated with the ocean bottom. Therefore, linear perturbative inversion methods that perturb only horizontal wavenumbers and not mode amplitudes should either be used with caution or modified to incorporate the expressions presented here.     

电阻法间接测量居里温度

在磁性材料的实际应用中有时需要测量居里温度．采用电阻法测量在升温过程中电阻的变化从而来推算居里温度．结果表明．一般情况下．随着温度的升高电阻是增大的．当温度在居里点附近．电阻或者处于一稳定值或者有明显偏小现象．根据温度对电阻的影响可知居里点就在此范围内．     

Determination of sound speed in biological tissues based on frequency analysis of pulse response.

The sound speed in biological tissues provides important diagnostic and treatment planning information. Conventional methods of sound-speed determination generally require that transducers make physical contact with specimens in order to measure thickness and travel time in the time domain. The physical contact may cause deformation and affect blood flow and the measurement of travel time in the time domain may be sensitive to waveform distortion due to tissue inhomogeneity and surface roughness. A method for determination of the sound speed is proposed in which the sound travel time in the sample and the difference in total travel time from the transducer to the rigid reflector due to the presence of the sample are estimated in the frequency domain and which does not require physical contact of ultrasonic probes to living or freshly excised tissue specimens. Ultrasonic speed measurements in silicone rubber and acrylic resin specimens verified the method validity. The standard deviation of the measurements over a 10- x 10-mm area is less than 4 m/s. Sound-speed distribution measurements of porcine muscle are in agreement with previously published results.     

Solar models with a helioseismic sound speed profile

The problem of computation of the present Sun model with a given sound speed profile in the solar radiation zone is considered. It is shown that the chemical composition is still a free parameter, but the entropy of the adiabatic part of the convective zone is determined by the simulation procedure. The parameters of the models are compared with the helioseismic calibration of the solar envelope and a disagreement is revealed. Study of the seismic properties of the model cores indicates that the best model shows closeness to the standard solar model.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 10, pp. 1199–1203, October, 1996.