超声波海水淡化装置的设计研究

针对我军海防士兵淡水补给困难的问题,以超声雾化为基础,结合半导体冷凝技术,提出了一种超声波海水淡化装置的设计思路.并利用Multisim和Matlab仿真软件研究了超声波发射器振荡频率与雾化水雾中盐度之间的关系,为相关设备的后续研制提供了可靠的理论依据.     

Application of laser ultrasonic technique for non-contact detection of drilling-induced delamination in aeronautical composite components

The detection of drilling-induced delamination in composite components is a vital and challenging task in aviation industry. Numerous key components of aircrafts are made of composite materials, and drilling is often a final operation during assembly. Drilling-induced delamination is a very serious defect that significantly reduces the structural reliability, but it is rather difficult to be detected effectively due to its special location. A novel application of laser ultrasonic technique for the detection of drilling-induced delamination in composites is presented in this paper. A carbon fiber reinforced plastic laminate with drilling holes was made as specimen. A laser ultrasonic system was constructed and experiments were performed to detect the drilling-induced delamination, based on propagation characteristic of ultrasonic waves generated by pulse laser with a wavelength of 1064 nm and pulse duration of 10 ns. A laser interferometer based on two wave mixing is used to measure ultrasonic wave signals, and the morphology features of the delamination are imaged clearly by laser ultrasonic C-scan testing. The results proved that the laser ultrasonic technique is a feasible and effective method for the detection of drilling-induced delamination in composite components.     

Sputtered ZnO film on aluminium foils for flexible ultrasonic transducers

Nanocrystalline ZnO films with both C-axis vertical grown and inclined angled grown were sputter-deposited onto aluminium foils (50 μm thick) and characterised for using as flexible ultrasonic transducers. As-deposited C-axis grown ZnO films were annealed at different temperatures up to 600 °C to enhance film crystallinity and reduce film stress. The C-axis grown ZnO film on the Al foil were bonded onto steel plates, and the pulse-echo tests verified a good performance (with dominant longitudinal waves) of the ultrasonic transducers made from both as-deposited and post-annealed films. Inclined angled ZnO films on the Al foil glued onto steel plates generated mixed shear and longitudinal waves in the pulse-echo test.     

Effect of trabecular bone material properties on ultrasonic backscattering signals

In this study, ultrasonic backscattering signals in cancellous bones were obtained by finite difference time domain （FDTD） simulations, and the effect of trabecular material properties on these signals was analyzed. The backscatter coefficient （BSC） and integrated backscatter coefficient （IBC） were numerically investigated for varying trabecular bone material properties, including density, Lame coefficients, viscosities, and resistance coefficients. The results show that the BSC is a complex function of trabecular bone density, and the IBC increases as density increases. The BSC and IBC increase with the first and second Lame coefficients. While not very sensitive to the second viscosity of the trabeculae, the BSC and IBC decrease as the first viscosity and resistance coefficients increase. The results demonstrate that, in addition to bone mineral density （BMD） and microarchitecture, trabecular material properties significantly influence ultrasonic backseattering signals in cancellous bones. This research furthers the understanding of ultrasonic backscattering in cancellous bones and the characterization of cancellous bone status.     

纵向带状裂隙形貌的逆时偏移超声成像

传统的工业超声成像方法通常只能确定缺陷的位置与横向尺寸,无法获得缺陷的形貌信息.一些特殊的缺陷,如纵向裂纹,是典型的例子.基于多阵元技术,开展了固体介质缺陷逆时偏移超声成像方法的数值与实验研究.针对铝块平底纵裂纹及内部纵裂纹两种传统方法无法有效成像的缺陷,首先开展了单分量逆时偏移成像方法研究,给出了基于数值仿真的逆时偏移成像结果以及基于多阵元超声成像实验系统实验测试的逆时偏移成像结果.进一步开展了基于多分量位移检测与转换横波分离的逆时偏移成像方法研究,并提出了基于新型多分量激光干涉仪进行检测的思路.数值仿真结果证实了多分量逆时偏移图像重建结果可以克服单分量方式的缺点,得到明显优于单分量检测时的图像.     

水下高斯界面背向散射超声散斑场的相位奇异

为了精确描述超声散斑场的特性,提出了采用计算机模拟产生超声散斑场的方法.利用模拟产生的高斯相关随机表面,获得了这类表面远场超声散斑场,同时得到了声强分布和相位分布.与实验产生的散斑场进行对比,建立了超声散斑场接收的实验系统,取与计算模拟相同的参数,获得了实验散斑场.通过对比发现:计算机模拟产生的超声散斑场相位存在奇异点,奇异点周围相位分布类似漩涡,计算机模拟产生的散斑场与实验得到的散斑场强度分布相似,强度值比实验产生的散斑场强度大,携带有用信息的高亮散斑较多,暗点较少,更利于研究和分析.     

厚度模压电超声换能器无源声学材料研究进展*

厚度模压电超声换能器作为超声波发射、接收以及电信号间转换的载体,是超声成像与检测系统的核心器件,一般由压电层、匹配层和背衬层3部分组成。超声换能器的性能一定程度上决定着整体超声设备的性能,影响了其在工业、医学、军事等领域的应用。该换能器的关键性能指标(带宽、灵敏度)除了受到压电层的影响,还与匹配层、背衬层等无源声学材料的设计密切相关。该文综述了近年来厚度模压电超声换能器无源声学材料(匹配层、背衬层和声透镜)的研究进展,提出了当前该类材料面临的难题和解决途径,并对其未来发展方向进行了展望。     

New ultrasonic assisted technology of freezing,cooling and thawing in solid food processing: A review

Solid foods include fish, shrimp, shellfish, and other aquatic products, fruits, and vegetables. These products are commonly used for food freezing, cooling, and thawing. However, traditional freezing, cooling, and thawing of solid food technologies have limitations in quality, such as protein denaturation and water loss in food. Ultrasound-assisted technology has become a useful method in solid food processing due to improved preservation quality of solid food. This paper comprehensively reviews the mechanism and application of ultrasonic in solid food processing technology. Although the application of ultrasound-assisted ultrasound in solid food processing is relatively comprehensive, the energy saving of food cold processing is essential for practical application. This paper analyzes the optimization of ultrasonic in solid food processing, including orthogonal/multi-frequency technology and the combination of ultrasonic and other technologies, which provides new ideas for freezing, cooling, and thawing of solid food processing.     

超声波专题设计性实验

在测量超声波在空气中传播速度实验基础上,开设了超声波专题设计性实验,分别增加了测量压电换能器的共振频率、超声波在空气中的损耗系数、超声波在水中的传播速度等实验内容,丰富了大学物理实验教学内容,拓展了学生视野.     

Development and study of novel non-contact ultrasonic motor based on principle of structural asymmetry

The article presents novel design of non-contact rotary ultrasonic motor consisting of ring-shaped stator vibrating in in-plane flexural mode and rotor provided with blades. In contrast to other motors with similar design proposed motor relies on the use of standing ultrasonic waves. This simplifies design and electronic control of motor and becomes possible due to introduction of artificial asymmetry, for example by tilting one or several blades of the rotor relative to the surface normal. Operating principle of the proposed motor is based on acoustic radiation torque exerted on rotor by ultrasonic waves propagating in air or fluid gap between rotor and stator. This torque is calculated using finite element method by means of COMSOL Multiphysics software. Dynamics of rotor is studied using MathCad software and general theory of nonlinear conservative oscillators. Role of asymmetry is explained on the basis of comparative analysis of potential functions and phase trajectories for symmetric and asymmetric cases. It is shown that direction of rotation is determined by structural parameters of motor, particularly tilting direction (clockwise or counter-clockwise) of the blades. Conceptual design of motor with bidirectional rotation is described. Direction and velocity of rotation in the proposed conceptual design can be potentially controlled by changing excitation frequency of stator.