The viscous strip approach to simplify the calculation of the surface acoustic wave generated streaming

In recent decades,the importance of surface acoustic waves,as a biocompatible tool to integrate with microfluidics,has been proven in various medical and biological applications.The numerical modeling of acoustic streaming caused by surface acoustic waves in microchannels requires the effect of viscosity to be considered in the equations which complicates the solution.In this paper,it is shown that the major contribution of viscosity and the horizontal component of actuation is concentrated in a narrow region alongside the actuation boundary.Since the inviscid equations are considerably easier to solve,a division into the viscous and inviscid domains would alleviate the computational load significantly.The particles'traces calculated by this approximation are excellently alongside their counterparts from the completely viscous model.It is also shown that the optimum thickness for the viscous strip is about 9-fold the acoustic boundary layer thickness for various flow patterns and amplitudes of actuation.

Theoretical and experimental characterizations of gigahertz acoustic streaming in microscale fluids

Even as gigahertz(GHz) acoustic streaming has developed into a multi-functional platform technology for biochemical applications, including ultrafast microfluidic mixing, microparticle operations, and cellar or vesicle surgery, its theoretical principles have yet to be established. This is because few studies have been conducted on the use of such high frequency acoustics in microscale fluids. Another difficulty is the lack of velocimetry methods for microscale and nanoscale fluidic streaming. In this work, we focus on the basic aspects of GHz acoustic streaming,including its micro-vortex generation principles, theoretical model, and experimental characterization technologies. We present details of a weak-coupled finite simulation that represents our current understanding of the GHz-acoustic-streaming phenomenon. Both our simulation and experimental results show that the GHzacoustic-induced interfacial body force plays a determinative role in vortex generation. We carefully studied changes in the formation of GHz acoustic streaming at different acoustic powers and flow rates. In particular,we developed a microfluidic-particle-image velocimetry method that enables the quantification of streaming at the microscale and even nanoscale. This work provides a full map of GHz acoustofluidics and highlights the way to further theoretical study of this topic.

A NEW PHENOMENON OF ACOUSTIC STREAMING

This paper describes a new phenomenon of acoustic streaming which takes place when a Helmholtz resonator is excited by an inside sound source with resonant frequency,and takes the form of a strong turbulent jet.The flow visualizations,hot wire and LDV measurements are combined to investigate the process of acoustic streaming.It is found that this kind of acoustic streaming results from the contribution of Reynolds stress.

Manipulations of micro/nanoparticles using gigahertz acoustic streaming tweezers

Contactless acoustic manipulation of micro/nanoscale particles has attracted considerable attention owing to its near independence of the physical and chemical properties of the targets,making it universally applicable to almost all biological systems.Thin-film bulk acoustic wave(BAW)resonators operating at gigahertz(GHz)frequencies have been demonstrated to generate localized high-speed microvortices through acoustic streaming effects.Benefitting from the strong drag forces of the high-speed vortices,BAW-enabled GHz acoustic streaming tweezers(AST)have been applied to the trapping and enrichment of particles ranging in size from micrometers to less than 100 nm.However,the behavior of particles in such 3D microvortex systems is still largely unknown.In this work,the particle behavior(trapping,enrichment,and separation)in GHz AST is studied by theoretical analyses,3D simulations,and microparticle tracking experiments.It is found that the particle motion in the vortices is determined mainly by the balance between the acoustic streaming drag force and the acoustic radiation force.This work can provide basic design principles for AST-based lab-on-a-chip systems for a variety of applications.

Controllable blood–brain barrier(BBB)regulation based on gigahertz acoustic streaming

The blood–brain barrier(BBB)is a structural and functional barrier necessary for brain homeostasis,and it plays an important role in the realization of neural function and in protecting the brain from damage by circulating toxins and pathogens.However,the extremely dense BBB also severely limits the transport of molecules across it,which is a great hindrance to the diagnosis and treatment of central nervous system(CNS)diseases.This paper reports a new method for controllable opening of the BBB,based on the gigahertz acoustic streaming(AS)generated by a bulk acoustic wave resonant device.By adjusting the input power and working distance of the device,AS with tunable flow rate can be generated to disrupt tight junction proteins(TJs)between endothelial cells.The results obtained with this method show that the gigahertz AS promotes the penetration of dextran molecules with different molecular weights across the BBB.This work provides a new platform for studying the mechanical regulation of BBB by fluid shear forces and a new method for improving the efficiency of drug delivery.

Quantitative Visualization of Two-Phase Acoustic Streaming Emitted from Ultrasonic Scaler

This study experimentally investigated two-phase acoustic streaming and droplet properties of aerosols, which were generated by a dental ultrasonic scaler. The velocity field of acoustic streaming was measured using particle image velocimetry with the generated liquid droplets as tracers, and the shadowgraph technique was adopted to measure the droplet diameter. In the PIV measurement of the gas-liquid two-phase flow, the injection of oil smoke substantially suppressed the number of invalid vectors. The acoustic streaming of the ultrasonic scaler showed maximum velocity at a region away from the scaler tip, and the maximum velocity increased with an increase in the liquid flow rate. The droplets of the ultrasonic scaler were generated by capillary waves and had a diameter on the order of tens of micrometers. These droplets effectively enhanced the velocity of the acoustic streaming in the two-phase case compared to the single-phase case without the droplets.

Distribution pattern of acoustic and streaming field during multi-source ultrasonic melt treatment process

The ultrasonic melt treatment(UMT)is widely used in the fields of casting and metallurgy.However,there are certain drawbacks associated with the conventional process of single-source ultrasonic(SSU)treatment,such as the fast attenuation of energy and limited range of effectiveness.In this study,the propagation models of SSU and four-source ultrasonic(FSU)in Al melt were respectively established,and the distribution patterns of acoustic and streaming field during the ultrasonic treatment process were investigated by numerical simulation and physical experiments.The simulated results show that the effective cavitation zone is mainly located in a small spherical region surrounding the end of ultrasonic horn during the SSU treatment process.When the FSU is applied,the effective cavitation zone is obviously expanded in the melt.It increases at first and then decreases with increasing the vibration-source spacing(Lv)from 30 mm to 100 mm.Especially,when the Lv is 80 mm,the area of effective cavitation zone reaches the largest,indicating the best effect of cavitation.Moreover,the acoustic streaming level and flow pattern in the melt also change with the increase of Lv.When the Lv is 80 mm,both the average flow rate and maximum flow rate of the melt reach the highest,and the flow structure is more stable and uniform,with the typical morphological characteristics of angular vortex,thus significantly expanding the range of acoustic streaming.The accuracy of the simulation results was verified by physical experiments of glycerol aqueous solution and tracer particles.

Rotational manipulation of massive particles in a 2D acoustofluidic chamber constituted by multiple nonlinear vibration sources

Rotational manipulation of massive particles and biolo gical samples is essential for the development of miniaturized lab-on-a-chip platforms in the fields of chemical,medical,and biological applications.In this paper,a device concept of a two-dimensional acoustofluidic chamber actuated by multiple nonlinear vibration sources is proposed.The functional chamber enables the generation of acoustic streaming vortices for potential applications that include strong mixing of multiphase flows and rotational manipulation of micro-/nano-scale objects without any rotating component.Using numerical simulations,we find that diversified acoustofluidic fields can be generated in the chamber under various actuations,and massive polystyrene beads inside can experience different acoustophoretic motions under the combined effect of an acoustic radiation force and acoustic streaming.Moreover,we investigate and clarify the effects of structural design on modulation of the acoustofluidic fields in the chamber.We believe the presented study could not only provide a promising potential tool for rotational acoustofluidic manipulation,but could also bring this community some useful design insights into the achievement of desired acoustofluidic fields for assorted microfluidic applications.

Acoustic streaming induced by ultrasonic quasi-lamb waves in a plate

The speed of the streaming flow in the liquid layer loaded on a thin plate, in which Lamb waves are propagating, was calculated. The results are good agreement with Moroney's experiment

Large Amplitude Dust Ion Acoustic Solitons and Double Layers in Dusty Plasmas with Ion Streaming and High-Energy Tail Electron Distribution

Large amplitude dust ion acoustic （DIA） solitons as well as double layers （DLs） are studied in a dusty plasma having a high-energy-tail electron distribution. The influence of electron deviation from the Maxwellian distribution and ion streaming on the existence domain of solitons is discussed in the （M, f） space using the pseudo-potential approach. It is found that in the presence of streaming ions and for a fixed f, solitons may appear for larger values of M. This means that in the presence of ion streaming, high values of the Mach number are needed to have soliton. The DIA solitary waves profile is highly sensitive to the ion streaming speed. Their amplitude is found to decrease with an increase of the ion streaming speed. In addition, we find that the ion streaming effect may lead to the appearance of double layers. The results of this axticle should be useful in understanding the basic nonlinear features of DIA waves propagating in space dusty plasmas, especially those including a relative motion between species, such as comet tails and solar wind streams, etc.

基于氧化锌薄膜声表面波器件的细胞富集方法

针对常见的铌酸锂等压电单晶在高温易碎裂且不能弯曲等问题,提出了一种区别于传统压电单晶富集细胞的方法。通过磁控溅射技术在硅衬底上制备了厚度为3.83μm的氧化锌薄膜,并用扫描电子显微镜与X射线衍射表征了薄膜性能,在薄膜表面制备了频率为195 MHz的叉指换能器,插入损耗为-33.8 dB,且仿真分析了该器件的声场。结果表明,表面波声束集中在换能器声孔径处,液滴位于声束边缘。实验结果表明,该器件能够驱动液滴产生3.9×10^(-3)m/s流速的涡旋,并在20 s内富集了悬浮于液滴中的微球和人体淋巴细胞,将液滴中细胞的浓度提升55倍。

基于声流的非接触超声电机理论分析与试验研究

针对传统超声电机存在严重的摩擦磨损及难以长时间连续工作的问题,本文中基于声流原理设计了1种新型的非接触式超声电机.建立电机定子谐响应有限元分析模型,获得其工作频率及结构振型,并对悬浮间隙内的声流场进行建模,采用雷诺应力法求解声流场驱动力,分析不同激励电压下转子转速以及驱动力的变化规律.为验证模型的合理性,搭建试验测试系统并进行性能测试对比分析.结果表明,该电机在声流驱动下能够稳定地运转,转速随着电压的升高而单调上升,驱动电压为1430 V时,转子转速可以达到28 r/min.理论结果与试验结果具有较好的一致性,验证了模型的合理性.

盘型声流超声电机驱动机理分析及实验研究

针对传统超声电机定子与转子表面存在严重摩擦磨损导致系统性能降低的问题,提出了一种新型非接触悬浮式声流超声电机。该电机结构紧凑,能够利用声悬浮原理实现定子和转子的非接触驱动,消除传统超声电机存在的严重摩擦磨损。基于连续性方程,建立了悬浮间隙介质流体分析模型,并采用有限元法进行求解。搭建实验台进行转动特性测试实验,分析了新型电机的工作机理,研究了不同槽型及运转状态下的声流分布。研究结果表明:转子表面刻槽导致间隙内圆周方向产生了压力梯度,进而形成了驱动转子的转矩;随着驱动电压升高,定子盘的振动幅值及转子转速均增大,当驱动电压为1 430 V时,定子盘振动幅值为9.8μm,转子转速达到74 r·min^(-1);相较于光滑转子,刻槽型转子在槽域附近的声流场发生了明显改变。此研究可为非接触超声电机的研究提供参考,也能进一步扩展超声电机的应用领域。

沿海声层析数据在印尼巴厘海峡的同化研究

沿海声层析(Coastal Acoustic Tomography,简称CAT)是利用高频声信号实现近海大范围流场观测的有效手段,但其直接观测范围仍然有限。海洋数值模式提供了一种存在仿真误差的大范围海洋背景场,将CAT观测结果与海洋背景结果同化,可以提高流场结果的分辨率和准确度。本文提出一种利用流函数拟合海洋模式流场结果并使用集合卡尔曼滤波算法同化CAT数据的方法,获得更大范围的海洋水平二维流场结果。同化研究以非结构化网格有限体积海洋数值模式(Finite-Volume Community Ocean Model,简称FVCOM)作为背景场,以2016年6月1日至3日在印度尼西亚巴厘海峡(Bali Strait)进行的4站CAT实验作为观测数据。经过背景场流函数拟合和CAT数据同化,获得巴厘海峡二维流场。同化结果分别与同期观测结果和潮位数据对比,发现流函数拟合同化后的流场能更准确地描述巴厘海峡涨落潮和流量情况,通过引入CAT数据与流场的函数关系,可以有效地降低海洋模式的误差和原观测数据的稀疏性。

高能超声作用下金属基复合材料的制备

综述了高能超声复合法制备金属基复合材料的研究现状,包括高能超声复合法的原理、工艺、制备材料的种类及存在的问题,并展望其发展前景。

高能超声在颗粒/金属熔体体系中的声学效应

讨论并分析了600℃的SiCp/ZA27熔体中超声的作用机理和有效作用范围。研究结果表明:在实验所用超声处理条件下(20kHz,1kW),ZA27合金熔体中声空化效应引发的熔体局部高压最大可达105MPa,局部高温可达1.77×104K;声流在熔体体系各个部位的作用强度不同,要获得优质的复合材料就必须在工艺上保证熔体的各个部位均能受到超声的有效作用。高能超声之所以能够制备出颗粒均匀分布、界面结合良好的SiCp/ZA27复合材料是高能超声在金属熔体中产生的声空化与声流共同作用的结果。

超声波强化超滤的研究进展

本文综述了超声波强化超滤的作用机理,声冲流和空化作用在超声波强化超滤中起到主要作用。文章还综述了超声波强化超滤的实验方法、超声波辐射对超滤膜的影响及超声波强化清洗超滤膜等方面的研究进展。

高能超声制备金属基复合材料的研究进展与展望

简要介绍了高能超声制备金属基复合材料的原理和研究现状,分析了高能超声改善润湿性,促进分散,除气除渣的作用机理。指出用高能超声制备纳米增强金属基复合材料是未来发展的重点,提出了改善高能超声作用的有效途径。

超声波强化超滤过程

本文综述了超声波强化超滤的实验方法、超声波对超滤膜结构的影响及超声波强化清洗超滤膜等方面的研究进展。论述了超声波强化超滤的作用机理,声冲流和空化作用在超声波强化超滤中起到主要作用。

液体媒质超声波电机特性与饱和流速的研究

与一般超声波电机依靠定转子之间的摩擦来传递能量不同,非接触型超声波电机的定转子不直接接触,克服了接触型超声波电机的易磨损、不能长时间工作等缺点,是超声波电机领域的一个新的研究方向。该文介绍了一种基于液体媒质的非接触型超声波电机,其转子浸于液体之中,不与定子直接接触,定子振动所产生的能量,通过液体传递给转子,从而驱动电机旋转。文章给出了电机的结构及工作原理,并且简要介绍了电机驱动电路的实现。该 文实验验证了电机的基本运行特性,测定了电机转速、驱动频率和驱动电压之间的关系。实验中发现,在一定范围内,电机中液体旋转速度随定子振动速度的增大而增大,而当电机定子圆环振动速度超过某一特定值后,电机中液体的转速出现了饱和流速现象。文章中对液体饱和流速问题进行了理论分析,证明了液体中声场的非线性是导致饱和流速的主要因素,并通过实验测出了饱和流速与液面高度、液体浓度和非线性参数之间的关系,实验结果与理论分析结果一致。