基于一维声栅共振场的大规模微粒并行排列的实验研究

声操控微粒技术可以非接触无损伤地控制声场中的物体运动,其在精密制造、材料工程、体外诊断等领域具有广阔的应用前景.传统声操控微粒技术一般采用自由声场,如利用单个换能器或阵列换能器产生的聚焦声场、行波场或驻波场等.然而,一般单个换能器产生的声场仅能操控单个微粒;而阵列换能器的驱动系统复杂,导致操控器件成本高昂且难以微型化;因此,亟需研究新的声场形态实现多样性微粒操控.本工作中,采用单个换能器产生的平面波激发一维声栅的共振声场,实验实现了大规模泡沫微球的周期排列操控.其操控机制是由于声栅狭缝中法布里-珀罗谐振声场与声栅表面周期衍射场共振耦合,在声栅表面形成周期分布的局域梯度声场,导致微粒在平行于声栅表面受到声捕获力,在垂直于声栅表面受到指向表面的声吸引力,实现了微粒周期排列在声栅表面上.该工作为利用超声在空气中大规模排列微粒提供了理论基础和技术支持.     

基于亚波长管道增强的漩涡声场悬浮操控微粒和液滴的实验研究

声悬浮技术可以在无接触的情况下操控微粒和液滴,因此已被广泛应用于化学分析、液滴动力学和生物反应器等领域.目前声悬浮技术的主要工作是在开放环境中进行悬浮等操控.本文提出了亚波长管道增强型空气声镊的概念,利用亚波长声波导管进行声场操控及微粒和液滴悬浮.通过4个小型换能器激发有限长度亚波长圆波导管的单一低阶声学模态,可以在有限长度的波导管内产生漩涡声场.实验发现由于亚波长结构对声场的增强作用,亚波长管道增强的漩涡声场在径向和轴向悬浮力大小上均有较大提升,因此可对发泡聚苯乙烯颗粒和水滴实施悬浮和自转等操控.这项工作将亚波长声波导管的概念引入声场操控中,有望加深对声场和物质相互作用的物理理解,开发新型小型化悬浮微粒和液滴的声学操纵器件.     

零阶Bessel驻波场中任意粒子声辐射力和力矩的Born近似

声辐射力和声辐射力矩的计算是实现粒子精准操控的重要基础.基于经典声散射理论的偏波级数展开法较难直接用于复杂模型的研究,而纯数值的方法则不利于进行系统的参数化分析.基于Born近似的基本原理,推导了低频情况下零阶Bessel驻波场中心任意粒子的声辐射力和力矩表达式.在此基础上,以球形粒子、椭球形粒子和柱形粒子为例进行详细地计算,并考虑声参数的非均匀性对声辐射力和力矩的影响.仿真结果表明,在低频范围内Born近似具有很高的精度,随着频率的增加和粒子与流体的阻抗匹配变差,Born近似的精度逐渐下降.对于倾斜放置于零阶Bessel驻波场中的椭球形粒子和柱形粒子,非对称性会导致其受到声辐射力矩的作用.在粒子尺寸远小于波长的情况下,声辐射力特性与粒子的具体形状几乎无关,但声辐射力矩不然.最后,引入周围流体的黏滞效应并对声辐射力的表达式进行了修正.该研究预期可以为生物医学、材料科学等领域利用驻波场声镊子实现微小粒子的精准操控提供一定的理论指导.     

自由空间中球形粒子的负向声辐射力

针对一定声场作用下自由空间中的球形粒子,首先分析了声散射过程中的吸收声功率、散射声功率和损失声功率以及三者之间的关系,并通过计算发现了由于参数选取不当导致的负吸收现象。接着从动量守恒定律出发推导了声辐射力的一般表达式,阐释了声辐射力与声能流之间的关系,并从理论和计算两方面验证了负向声辐射力的存在。当负向声辐射力产生时,声波的背向散射被抑制。在此基础上,进一步研究了粒子的偏心特性和流体的黏度这两种常见因素对负向声辐射力的影响。利用球函数的加法公式推导了偏心球的散射系数和声辐射力公式,结果显示偏心距离、粒子的材料等都会显著改变负向声辐射力的产生条件。在低频近似下,由于流体黏度附加的正向声辐射力是否能完全抵消原来的负向声辐射力将决定最终的声辐射力方向。该结果对利用负向声辐射力制成单行波声学镊子来实现对特定粒子的操控有着理论指导意义。      

平面行波场中多个粒子受到的声辐射力*

从粒子在行波场中的声散射出发,研究当声场中存在稀疏分布的多个粒子时粒子受到的声辐射力,并且给出了适用于声场中任意位置的粒子声辐射力计算公式。由于声辐射力为非线性力,当声场中存在多个粒子时,直接计算粒子受到的声辐射力非常复杂。结果表明,当声场中存在多个稀疏分布的粒子时,这一多粒子系统可以视为多个单独的双粒子系统的叠加,只需要分别计算各个双粒子系统的声辐射力就可以通过叠加得到声场中任意粒子的声辐射力。这一结果有助于利用声辐射力对微小粒子进行精细操控。     

利用k-Wave计算超声在腹壁组织的声辐射力*

随着科学技术的发展,声辐射力在生物医学领域得到了更为广泛的应用,尤其是在弹性成像领域。为了使弹性成像技术更加精准,对声辐射力的预测至关重要。该文基于腹壁组织图像,利用k-Wave对超声波在腹壁组织区域传播时的声场进行数值模拟,获得了其声场分布,进而求得了组织中声辐射力分布情况,同时对面阵换能器的阵元宽度、间距、阵元个数以及工作频率等参量对声辐射力的影响进行了计算与分析。结果表明,腹壁组织的声场分布受其非均匀性的影响,声辐射力的分布情况依赖于换能器参量的选择。该研究为声辐射力在弹性成像技术中的应用奠定了基础,为其技术的改进提供了重要依据。     

空气中一维声栅对微粒的声操控

本文对一维空气声栅表面微粒受到的声辐射力进行了详细的理论研究.首先采用有限元方法研究一维声栅的透射性质及表面声场分布,然后将有限元与动量张量积分结合研究处于一维声栅表面微粒受到的声辐射力特征.声栅共振透射增强是表面周期衍射波与狭缝Fabry-Perot共振耦合形成的,并且与声栅周期和厚度密切相关.研究发现,当共振波长与声栅周期相当时,微粒在其表面可受到指向声栅板面的声吸引力;当共振波长为声栅周期的二倍及以上,微粒可受到指向狭缝中的吸引力,且强度远小于第一种情况的吸引力.因此,在声栅处于共振波长与周期相当的共振模式时,可以在空气中利用声栅表面操控、吸引和排列微粒.     

准高斯声束对超声造影剂的声辐射力研究*

超声造影剂的定向输运在超声医学成像领域有着极为重要的意义,而声辐射力作用是实现该过程的关键,相比于高斯声束,准高斯声束是无源亥姆霍兹方程的精确解,可以使用标准波分解法简化计算。因此,本文研究了准高斯声束对超声造影剂的声辐射力作用。文章首先分析了准高斯声束与高斯声束之间的相关性;随后通过数值计算求得了准高斯声束对超声造影剂模型的声辐射力函数与无量纲频率之间的关系;最后,本文研究了不同造影剂气泡情况下的声辐射力。研究结果表明:声辐射力函数随无量纲频率变化将在不同位置出现共振峰,不同的波束宽度值将改变辐射力强度,但不改变共振峰的位置。相关结果可为利用声辐射力定向输运超声造影剂至靶向位置提供理论参考。     

Bessel驻波对椭球形液滴的声辐射转矩

在实际的声操控中,由于声辐射力、表面张力和重力的共同作用,液滴往往呈现出椭球的形状,在螺旋声场中会受到力矩的作用而发生转动。从声波的散射理论出发,根据部分波展开法求解得到了椭球形液滴在Bessel驻波场中的声散射系数,并给出了其受到的声辐射转矩的解析式。在此基础上,对椭球形不可压缩液滴和椭球形可压缩液滴分别进行数值计算。仿真结果表明,不可压缩液滴的声辐射转矩与声束半锥角的关系更密切,而可压缩液滴则更依赖于特定的频率;提升Bessel驻波场的阶数有利于增强声辐射转矩的峰值,但在中低频处较难对可压缩液滴产生明显的力矩。该研究结果预期对利用螺旋声场进行液滴的操控具有理论指导作用。      

光学微操纵过程的轴平面显微成像技术

光学俘获技术利用光与物质相互作用产生的光势阱效应来实现对微粒的操控,已经成功应用于生物医学、材料科学等交叉领域.在对微粒进行三维俘获时,传统的宽场光学显微技术只能观测到某一平面内微粒的横向运动,对微粒沿轴向运动的观测受到很大限制.本文将轴平面显微成像技术引入光学微粒操控研究中,利用45?倾斜的反射镜把微粒的轴向运动信息转换到横向平面进行观测,与传统宽场显微成像技术相结合,实现了对二氧化硅小球俘获过程横向和轴向运动的同步观测.该成像方法无需扫描和数据重构,具有实时快速等优点,在新型光束光镊、厚样品三维观测和成像等领域具有潜在的应用价值.     

Particle separation in microfluidics using different modal ultrasonic standing waves

Microfluidic technology has great advantages in the precise manipulation of micro and nano particles, and the separation of micro and nano particles based on ultrasonic standing waves has attracted much attention for its high efficiency and simplicity of structure. This paper proposes a device that uses three modes of ultrasonic standing waves to continuously separate particles with positive acoustic contrast factor in microfluidics. Three modes of acoustic standing waves are used simultaneously in different parts of the microchannel. According to the different acoustic radiation force received by the particles, the particles are finally separated to the pressure node lines on both sides and the center of the microchannel. In this separation method, initial hydrodynamic focusing and satisfying various equilibrium constraints during the separation process are the key. Through numerical simulation, the resonance frequency of the interdigital transducer, the distribution of sound pressure in the liquid, and the relationship between the interdigital electrode voltage and the output sound pressure are obtained. Finally, the entire separation process in the microchannel was simulated, and the separation of the two particles was successfully achieved. This work has laid a certain theoretical foundation for the rapid diagnosis of diseases in practical applications.     

Precise micro-particle and bubble manipulation by tunable ultrasonic bottle beams

This paper reports a method to generate tunable bottle beams using an ultrasonic lens, by which the bottle position can be precisely adjusted with the change of the acoustic frequency. Therefore, the position of a single particle or bubble in liquid can be manipulated without using phased array which is costly and huge with complex circuits. Furthermore, we introduced this method to multiple bubble manipulation using acoustic holography. The bottle properties against frequency are theoretically and experimentally analyzed. It is shown that the bottle position depends almost linearly on the operating frequency, which provides a basis for the precise manipulation of bubbles and particles. In addition, the relationship between the acoustic radiation force and the drag force under different incident acoustic pressures is considered, establishing a limit on the moving velocity of the trapped particles. The ultrasonic field observation is further demonstrated by Schlieren imaging system. The proposed method has potential biomedical applications, such as more flexible cell manipulation and targeted drug delivery in vivo, as well as potential applications in the study of chemical reactions between micro objects.     

Residue-free acoustofluidic manipulation of microparticles via removal of microchannel anechoic corner

Surface acoustic wave (SAW)-based acoustofluidics has shown significant promise to manipulate micro/nanoscale objects for biomedical applications, e.g. cell separation, enrichment, and sorting. A majority of the acoustofluidic devices utilize microchannels with rectangular cross-section where the acoustic waves propagate in the direction perpendicular to the sample flow. A region with weak acoustic wave intensity, termed microchannel anechoic corner (MAC), is formed inside a rectangular microchannel of the acoustofluidic devices where the ultrasonic waves refract into the fluid at the Rayleigh angle with respect to the normal to the substrate. Due to the absence of a strong acoustic field within the MAC, the microparticles flowing adjacent to the microchannel wall remain unaffected by a direct SAW-induced acoustic radiation force (ARF). Moreover, an acoustic streaming flow (ASF) vortex produced within the MAC pulls the particles further into the corner and away from the direct ARF influence. Therefore, a residue of particles continues to flow past the SAWs without intended deflection, causing a decrease in microparticle manipulation efficiency. In this work, we introduce a cross-type acoustofluidic device composed of a half-circular microchannel, fabricated through a thermal reflow of a positive photoresist mold, to overcome the limitations associated with rectangular microchannels, prone to the MAC formation. We investigated the effects of different microchannel cross-sectional shapes with varying contact angles on the microparticle deflection in a continuous flow and found three distinct regimes of particle deflection. By systematically removing the MAC out of the microchannel cross-section, we achieved residue-free acoustofluidic microparticle manipulation via SAW-induced ARF inside a half-circular microchannel. The proposed method was applied to efficient fluorescent coating of the microparticles in a size-selective manner without any residue particles left undeflected in the MAC.     

Hypersonic‐Induced 3D Hydrodynamic Tweezers for Versatile Manipulations of Micro/Nanoscale Objects

Developing microrobots for precisely manipulating micro/nanoscale objects has triggered tremendous research interest for various applications in biology, chemistry, physics, and engineering. Here, a novel hypersonic‐induced hydrodynamic tweezers (HSHTs), which use gigahertz nano‐electromechanical resonator to create localized 3D vortex streaming array for the capture and manipulation of micro‐ and nanoparticles in three orientations: transportation in a plane and self‐rotation in place, are presented. 3D vortex streaming can effectively pick up particles from the flow, whereas the high‐speed rotating vortices are used to drive self‐rotation simultaneously. By tuning flow rate, the captured particles can be delivered, queued, and selectively sorted through the 3D HSHTs. Through numerical simulations and theoretical analysis, the generation of the 3D vortex and the mechanism of the particles manipulation by ultrahigh frequency acoustic wave are demonstrated. Benefitting from the advantages of the acoustic and hydrodynamic method, the developed HSHTs work in a precise, noninvasive, label‐free, and contact‐free manner, enabling wide applications in micro/nanoscale manipulations and biomedical research.     

Agglomeration of particles by a converging ultrasound field and their quantitative assessments

The acoustic radiation force resulting from acoustic waves have been extensively studied for the contact-free generation of organized patterning arrays. The precise arrangement of microscopic objects clustered at the pressure nodes is critical to the development of functional structures and patterned surfaces. However, the size of the clusters is restricted by the saturation limit of the acoustic nodes. Here, we present a bulk acoustic wave (BAW) platform, which employs a two-dimensional acoustic wave to propel particles of various sizes. Experimentally, when particles are large, significant acoustic energy is scattered and partly absorbed by the matched layers in front of the sensors. The acoustic radiation force from a convergent acoustic pressure field agglomerates the large polystyrene (PS) particles towards the central region instead of the pressure nodes. The parametric analysis has been performed to assess the transition in the particles from clustering at the organized nodal arrays to agglomerating in the central region, which is a function of particle size, particle concentration, and load voltage. Statistically, the particles can agglomerate with a cluster ratio greater than 70%, and this ratio can be improved by increasing the load power/voltage supplied to the transducers. With its ability to perform biocompatible, label-free, and contact-free self-assembly, this concept offers a new possibility in the fabrication of colloidal layers, the recreation of tissue microstructure, the development of organoid spheroid cultures, the migration of microorganisms, and the assembly of bioprinting materials.     

Acoustic manipulation of active spherical carriers: Generation of negative radiation force

This paper examines theoretically a novel mechanism of generating negative (pulling) radiation force for acoustic manipulation of spherical carriers equipped with piezoelectric actuators in its inner surface. In this mechanism, the spherical particle is handled by common plane progressive monochromatic acoustic waves instead of zero-/higher- order Bessel beams or standing waves field. The handling strategy is based on applying a spatially uniform harmonic electrical voltage at the piezoelectric actuator with the same frequency of handling acoustic waves, in order to change the radiation force effect from repulsive (away from source) to attractive (toward source). This study may be considered as a start point for development of contact-free precise handling and entrapment technology of active carriers which are essential in many engineering and medicine applications.     

Manipulation with sound and vibration: A review on the micromanipulation system based on sub-MHz acoustic waves

Manipulation of micro-objects have been playing an essential role in biochemical analysis or clinical diagnostics. Among the diverse technologies for micromanipulation, acoustic methods show the advantages of good biocompatibility, wide tunability, a label-free and contactless manner. Thus, acoustic micromanipulations have been widely exploited in micro-analysis systems. In this article, we reviewed the acoustic micromanipulation systems that were actuated by sub-MHz acoustic waves. In contrast to the high-frequency range, the acoustic microsystems operating at sub-MHz acoustic frequency are more accessible, whose acoustic sources are at low cost and even available from daily acoustic devices (e.g. buzzers, speakers, piezoelectric plates). The broad availability, with the addition of the advantages of acoustic micromanipulation, make sub-MHz microsystems promising for a variety of biomedical applications. Here, we review recent progresses in sub-MHz acoustic micromanipulation technologies, focusing on their applications in biomedical fields. These technologies are based on the basic acoustic phenomenon, such as cavitation, acoustic radiation force, and acoustic streaming. And categorized by their applications, we introduce these systems for mixing, pumping and droplet generation, separation and enrichment, patterning, rotation, propulsion and actuation. The diverse applications of these systems hold great promise for a wide range of enhancements in biomedicines and attract increasing interest for further investigation.     

Proposed method of partial discharge allocation with acoustic emission sensors within power transformers

Employing acoustic emission sensors for detection of partial discharge, PD, introduces many advantages. Besides easy installation and replacement, they are non-invasive and immune to electromagnetic noise and interference and their sensitivity does not vary with object capacitance. For PD allocating utilizing AE sensors, distance calculations are based on the arrival time of acoustic waves to the sensors. Considering structure-borne waves of higher speed, the peaks of some of indirect path AE signals with significant contribution are mistakenly considered as peaks of direct path AE signals. Furthermore, the acoustic signals are propagating through certain parts of the transformer, such as the windings, and this complicates the partial discharge detection and allocation. These would imply an incorrect distance between the source and sensor. A method based on a heuristic algorithm has been proposed which considering all possible indirect paths with the relevant propagation times and all the barriers on the travel path of acoustic signal, calculates the more precise arrival times to sensors. A test chamber has been utilized and artificial PD signals are produced at various points. Output results of algorithm have been compared with results of classic method. It has been shown that proposed method significantly reduces the positioning errors.     

Acoustic source localization

In this article different techniques for localizing acoustic sources are described and the advantages/disadvantages of these techniques are discussed. Some source localization techniques are restricted to isotropic structures while other methods can be applied to anisotropic structures as well. Some techniques require precise knowledge of the direction dependent velocity profiles in the anisotropic body while other techniques do not require that knowledge. Some methods require accurate values of the time of arrival of the acoustic waves at the receivers while other techniques can function without that information. Published papers introducing various techniques emphasize the advantages of the introduced techniques while ignoring and often not mentioning the limitations and weaknesses of the new techniques. What is lacking in the literature is a comprehensive review and comparison of the available techniques; this article attempts to do that. After reviewing various techniques the paper concludes which source localization technique should be most effective for what type of structure and what the current research needs are.     

高精度声学模拟系统简介

介绍了一套声学模拟系统。系统用采计算机控制,主要由高精度定位子系统、信号收发子系统、环境与目标模拟子系统以及配套软件组成,初步具备开展水声学模拟实验和超声实验的能力。