声学与海洋

在各种辐射形式中,声波在海水中的传播为最佳,在混浊和含盐的海水中,无论光波或电磁波的衰减都远较声波的衰减为大。 海洋及其边界的详细特征对声传播的影响是非常复杂的,声速是温度、深度和盐度的函数,而温度又是深度、季节、地理位置(纬度)和气候条件的函数。海洋表面有时是非常     

声波多次往返叠加对相位比较法测量声速的影响

相位比较法测量声速实验中,由于声波在传输过程中存在衰减、反射以及在收、发换能器之间多次反射叠加,当收、发换能器间距较小时,发射信号和接收信号合成的李萨如图形变化规律与理论不一致,即,接收器移动1个波长的距离,示波器中观察到合成直线段在同相和反相区域分别连续出现多次,该现象影响了学生对实验现象的判断和实验测量.本文通过理论计算分析,声波在收、发换能器之间的多次往复反射叠加次数增加,声波传输衰减小和换能器表面反射系数大会增大该现象产生的强度和持续的空间范围,理论计算直观地说明了接收器接收的声压信号与空气振动信号之间的关系和利用相位比较法测量声速的合理性.     

Ultrasonic Study on Jahn-Teller Distortions in La1=3Sr2=3CoO3

系统研究了La1=3Sr2=3CoO3单相多晶样品在低温下的电磁输运性质和超声特性．电阻率测量表明，La1=3Sr2=3CoO3在整个温区内都表现出金属特性，并且在235 K处电阻率-温度曲线的斜率发生了变化，同时伴随着铁磁相变．超声声速在铁磁相变温度以下出现软化，并在120 K附近达到最小，之后，随着温度的进一步降低，声速开始硬化，同时出现了一个宽大的超声衰减峰．分析认为，该超声异常可能起源于中等自旋态Co3+的Jahn-Teller效应．     

利用SHC-Ⅱ型声波测试仪进行声波特性测量

声学测量在科学技术和生产实践中应用越来越广泛．声行波的特性包括波长，波速，多普勒效应，干涉，衍射以及传播过程中的衰减、吸收、反射、折射、声场中强度分布、相位分布等等．作者利用本校研制的SHC-Ⅱ型声波特性测试仪近行了声波的部分特性测量。     

垂直载荷下湿玻璃珠样品的声速和衰减测量及非线性声学响应

为了分析垂直载荷下颗粒物质的声速、声衰减系数、谐波非线性等特性,本工作采用飞行时间法测量了不同含水量下声速随压强的变化规律,并利用傅里叶变换法分析了干、湿玻璃珠样品的声衰减和非线性声学特性。结果表明:干、湿玻璃珠样品中的声速、声衰减系数以及谐波非线性均随压强呈幂律变化;湿颗粒样品中随着液体含量增多,声速逐渐增加,超声波透过湿颗粒样品时的能量耗散和非线性逐渐减小。分析原因表明,压强和孔隙流体改变了颗粒之间的接触分布,使得颗粒体系的声速、声衰减以及谐波非线性等特性都随之发生变化。     

利用SHC－Ⅱ型声波测试仪进行声波特性测量

利用ＳＨＣ－Ⅱ型声波测试仪进行声波特性测量青岛海洋大学物理系吕振洪，杨振华，李振庄声学测量在科学技术和生产实践中应用越来越广泛．声行波的特性包括波长，波速，多普勒效应，干涉，衍射以及传播过程中的衰减、吸收、反射、折射、声场中强度分布、相位分布等等．作...     

Nd0.5Ca0.5Mn1-xAlxO3 (x=0,0.03)体系中电荷有序态的超声研究

系统研究了Nd0．5Ca0．5Mn1-xAlxO3(x=0,0．03)单相多晶样品在低温下的电磁性质和超声特性．电阻和磁化率测量表明,Nd0．5Ca0.5O3体系在TCO-257 K处发生了电荷有序相变．超声声速从室温开始随着温度的降低逐渐减小,并在TCO附近达到最小,之后,随着温度的进一步降低,声速急刷增加,同时伴随着一个尖锐的超声衰减峰出现.TCO附近的超声异常表明体系中存在着强烈的电-声子相互作用,该电-声子耦合来源于Mn3 的Jahn-Teller效应．在低温下,出现了另一个超声衰减峰,它的出现归结为反铁磁相与顺磁相之间的相分离现象.随着Al在Mn位的掺入,超声声速的最低点和衰减峰向低温移动,表明体系中的电荷有序态和反铁磁相均被部分抑制,     

非线性声参量B/A的参量阵成象

非线性声参量B／A描述了有限振幅声波在媒质中传播的非线性特性,有可能成为生物组织定征的一个新参量,有重要的应用前景。本文在声与声相互作用的理论基础上,研究了参量阵的非线性声参量成象,用滤波边投影算法对无损及损耗样品模型进行了计算机模拟成象,在成象过程中讨论了声波衰减对重建象的影响,并提出了衰减修正办法。     

基于混合气体分子复合弛豫模型的一氧化碳浓度检测算法

研究了声波通过混合气体时，复合弛豫声吸收和声速与气体各成分浓度和声频率之间的依赖关系.以一氧化碳气体、水蒸气、氮气和氧气的混合气体为例，分别建立了弛豫声吸收和声速与气体浓度的三维模型，以及弛豫声吸收与声频率的二维模型.完成了通过测量弛豫声吸收和声速计算一氧化碳气体浓度的算法推导，提出了一种依据弛豫声吸收和声速检测气体浓度的简化算法.仿真实验结果不仅证明了算法的理论可行性，还给出了算法的最佳适用声频率范围，并估计了将算法应用于实验的误差原因，证明了算法具有实际可行性. 关键词： 气体浓度声学检测 一氧化碳浓度检测 复合弛豫声吸收 声速     

声管测量系统的宽带复合型换能器

提出了一种纵向换能器与Ⅳ型弯张换能器相结合的复合型换能器,推导了换能器的等效电路,根据等效电路分析了纵向换能器和弯张换能器之间的耦合作用;应用有限元方法进行了结构优化,使换能器能够发射较高频率声波的同时兼顾低频发射.研制了宽带复合型换能器实验样机,对在声管中所建立的驻波声场特性进行了实验研究,并成功利用该脉冲声管系统进...     

Acoustic properties of multiferroic BiFeO<Subscript>3</Subscript> over the temperature range 4.2–830 K

The longitudinal acoustic wave velocity and attenuation in BiFeO₃ ceramics have been measured by ultrasonic pulse-echo technique at a frequency of 10 MHz in the temperature range from 4.2 K to 830 K. The anomalies observed in the sound velocity and attenuation behavior versus temperature are attributed to the assumed relaxation in the temperature range 200–500 K and antiferromagnetic phase transition at higher temperatures. Order parameter fluctuations along with magnetostriction are discussed as the factors determining the acoustic wave velocity anomaly in the vicinity of the antiferromagnetic phase transition point.     

The attenuation coefficient of an acoustic wave propagating in a turbulent flow in a long pipeline

Results of experiments on measuring the attenuation coefficient for acoustic waves propagating in long oil and petroleum product pipelines are presented. A comparison of experimental results with theory is performed. An approximate dependence of the attenuation coefficient on the dimensionless parameter of the flow is proposed.     

Acoustic properties of multiferroic PbFe1/2Ta1/2O3

The longitudinal acoustic wave velocity and attenuation in PbFe_1/2Ta_1/2O₃ ceramics have been measured by pulse-echo technique in the temperature range from 4.2 to 530 K. The anomalies observed in the sound velocity and attenuation behavior versus temperature were correlated with Burns temperature, temperature range of the coexistence of relaxor ferroelectric and antiferromagnetic states, and a suggested second antiferromagnetic phase transition at low temperatures.     

Temperature dependent ultrasonic properties of aluminium nitride

Hexagonal wurtzite structured aluminium nitride has been characterized by the theoretical calculation of ultrasonic attenuation, ultrasonic velocity, higher order elastic constants, thermal relaxation time, acoustic coupling constants and other related parameters in temperature range 200-800 K for wave propagation along the unique axis of the crystal. Higher order elastic constants of AlN at different temperatures are calculated using Lennard-Jones potential for the determination of ultrasonic attenuation. A decrease in ultrasonic velocity with temperature has been predicted, which is caused by reduction in higher order elastic constants with temperature. The temperature dependent ultrasonic properties have been discussed in correlation with higher order elastic constants, thermal relaxation time, thermal conductivity, acoustic coupling constants and thermal energy density. Anomalous behaviour of the attenuation is found at 400 K. On the basis of attenuation, the ductility and performance of AlN have been studied.     

Temperature dependent ultrasonic characterization of biological media

Quantitative ultrasound (QUS) is an imaging technique that can be used to quantify tissue microstructure giving rise to scattered ultrasound. Other ultrasonic properties, e.g., sound speed and attenuation, of tissues have been estimated versus temperature elevation and found to have a dependence with temperature. Therefore, it is hypothesized that QUS parameters may be sensitive to changes in tissue microstructure due to temperature elevation. Ultrasonic backscatter experiments were performed on tissue-mimicking phantoms and freshly excised rabbit and beef liver samples. The phantoms were made of agar and contained either mouse mammary carcinoma cells (4T1) or chinese hamster ovary cells (CHO) as scatterers. All scatterers were uniformly distributed spatially at random throughout the phantoms. All the samples were scanned using a 20-MHz single-element f/3 transducer. Quantitative ultrasound parameters were estimated from the samples versus increases in temperature from 37 °C to 50 °C in 1 °C increments. Two QUS parameters were estimated from the backscatter coefficient [effective scatterer diameter (ESD) and effective acoustic concentration (EAC)] using a spherical Gaussian scattering model. Significant increases in ESD and decreases in EAC of 20%-40% were observed in the samples over the range of temperatures examined. The results of this study indicate that QUS parameters are sensitive to changes in temperature.     

重塑砂质含气沉积物的声响应特性与模型预测分析

海洋沉积物中气泡的存在对沉积物的声学特性有显著影响.为实现在实验室内对不同初始应力条件下含气沉积物的声学特性测量,研制了一套可用于土工三轴仪的双探针声学测量系统,基于CT扫描试验获得重塑含气砂样品中气泡群的尺寸分布,确定其共振频率范围.试验结果表明:细砂沉积物声速随气体含量的增加呈指数型降低,衰减系数随气体含量的增加呈...     

声波在含气泡液体中的线性传播

为了探讨含气泡液体对声波传播的影响, 研究了声波在含气泡液体中的线性传播. 在建立含气泡液体的声学模型时引入气泡含量的影响,建立气泡模型时引用 Keller的气泡振动模型并同时考虑气泡间的声相互作用,得到了经过修正的气泡振动方程. 通过对含气泡液体的声传播方程和气泡振动方程联立并线性化求解,在满足 (ω R₀)/c << 1 的前提下,得到了描述含气泡液体对声波传播的衰减系数和传播速度. 通过数值分析发现,在驱动声场频率一定的情况下,气泡含量的增加及气泡的变小均会导致衰减系数增加和声速减小;气泡的体积分数和大小一定时, 驱动声场频率在远小于气泡谐振频率的情况下,声速会随驱动频率的增加而减小; 气泡间的声相互作用对声波传播速度及含气泡液体衰减系数的影响不明显.最终认为气泡的大小、 数量和驱动声场频率是影响声波在含气泡液体中线性传播的主要因素. 关键词： 含气泡液体 线性声波 声衰减系数 声速     

Thermal effect on the acoustic behavior of an axisymmetric lined duct

This paper deals with the effect of the temperature and the frequency on the acoustic behavior of lined duct partially treated with usual material used in acoustic insulation.First, the effect of frequencies and temperature on the acoustic impedance of usual materials used in lined duct such as glass or rock wools in order to reduce acoustic level is investigated.Secondly, the variational formulation of the acoustic duct problem taking into account velocity and temperature effects is established. Then, a numerical model is derived which permits to compute the reflection and the transmission coefficients of such duct for different temperatures and several flow velocities. The acoustic power attenuation is then computed from these coefficients and the effect of the temperature and flow velocities on this energetic quantity is evaluated.The numerical results are obtained for three configurations of a lined duct treated for different temperature ranges and several velocities. Numerical coefficients of transmission and reflection as well as the acoustic power attenuation show the relative influence of temperature.     

Properties of sound attenuation around a two-dimensional underwater vehicle with a large cavitation number

Due to the high speed of underwater vehicles,cavitation is generated inevitably along with the sound attenuation when the sound signal traverses through the cavity region around the underwater vehicle.The linear wave propagation is studied to obtain the influence of bubbly liquid on the acoustic wave propagation in the cavity region.The sound attenuation coefficient and the sound speed formula of the bubbly liquid are presented.Based on the sound attenuation coefficients with various vapor volume fractions,the attenuation of sound intensity is calculated under large cavitation number conditions.The result shows that the sound intensity attenuation is fairly small in a certain condition.Consequently,the intensity attenuation can be neglected in engineering.     

Anisotropy of the phonon-phason dynamics and the pinning effect in icosahedral AlPdMn quasicrystals

A minimal model of the phonon-phason dynamics in icosahedral quasicrystals with inclusion of the pinning effect is suggested. Resonant attenuation of low-frequency acoustic waves in the temperature range corresponding to thermal activation of phasons is considered. In the long-wave length limit, the velocity of acoustic phonons is isotropic; however, the phonon-phason coupling causes anisotropy of the velocity and of the attenuation of acoustic waves with small wave vectors. These effects manifest themselves most strongly at an acoustic wave frequency close to the inverse relaxation time of phasons with the same wave vector. The pinning effect can cause a significant decrease in the anisotropy of the velocity and of attenuation of acoustic waves.