Acoustic Manipulation Research Articles

Microparticle concentration and separation inside a droplet using phononic-crystal scattered standing surface acoustic waves

Rapid particle and biocell concentration and separation are important for the development of miniaturized physical, biological, and chemical systems. In this study, the scattering of standing surface acoustic waves (SSAWs) in an acoustofluidic phononic crystal (PnC) device is used to actuate spatial concentration and separation of suspended microparticles with two different sizes in a sessile droplet. The simulation design of the device and manipulation mechanisms of the two distinct particles are presented and discussed. A surface acoustic wave (SAW) acoustofluidic device with a nickel pillar-type PnC electroplated on a piezoelectric substrate, 128°YX LiNbO3, is designed and fabricated. A 30-MHz SSAW field is scattered within the directional phononic bandgap of the PnC to generate simultaneously acoustic radiation force and acoustic streaming flow to concentrate and separate 2- and 20-μm polystyrene microparticles. Experiments are conducted to verify the device functions on concentrating and separating microparticles. The results also suggest the possibilities of regarding phononic crystals as an effective element to tailor the SAW field for building other innovative acoustofluidic devices to achieve novel concentration, separation, and acoustic manipulation of biocells and biomolecules in discrete microfluidic systems.

Highly Efficient Acoustic Metagrating with Strongly Coupled Surface Grooves

Typical acoustic refractive metasurfaces governed by generalized Snell law require several types of subwavelength subunits to provide an extra phase gradient along the surface. This design strategy, however, has several kinds of drawback. For instance, the inevitable viscous loss brought out by the complex subwavelength subunits, and the negligence of the coupling between adjacent subunits which leads to low-efficiency in wavefront manipulation, especially for large angles. To overcome these limitations, we propose a new type of refractive metasurface composed of only one straight channel and several surface-etched grooves per period. By harnessing the nonlocal coupling between the channel/grooves, and the evanescent modes inside them, superiorly feasible acoustic transmission manipulations can be achieved. Nearly perfect acoustic bending with transmission efficiency up to 95% is demonstrated with theory and experiments for an extremely large angle of 81 degree. The reported results introduce a novel concept of acoustic metasurfaces and offer a real leap towards the development of high-efficient acoustic devices for wavefront manipulation.

Near-field acoustic manipulation in a confined evanescent Bessel beam

We demonstrate the potential of using evanescent fields, instead of conventional propagating sound fields, to manipulate particles at micro or nano scale. We generate an evanescent acoustic Bessel beam in liquid above a thin, circular, asymmetrically excited plate. In the sub-MHz ultrasound domain, the resulting radiation force causes the particles to assemble at the pressure antinodes along concentric circles corresponding to the Bessel profile. By imposing an axial confinement in the evanescent region, the subwavelength two-plate sandwich system becomes resonant, increasing the radiation force magnitude. Resonances occur for some well-defined gaps for which whole numbers of antinodal circles are observed. Through fine tuning, particles as small as bacteria can be patterned. Further amplification can be obtained by trapping a microbubble in the Bessel beam axis. As we show, this resonant bubble, which acts as an acoustic magnet, can be used to efficiently capture or repel nearby micro-particles.

Multi-Channel Signal-Generator ASIC for Acoustic Holograms.

A complementary metal-oxide-semiconductor (CMOS) application-specific integrated circuit (ASIC) has been developed to generate arbitrary, dynamic phase patterns for acoustic hologram applications. An experimental prototype has been fabricated to demonstrate phase shaping. It comprises a cascadable 1 ×9 array of identical, independently controlled signal generators implemented in a 0.35- [Formula: see text] minimum-feature-size process. It can individually control the phase of a square wave on each of the nine output pads. The footprint of the integrated circuit is [Formula: see text]. A 128-MHz clock frequency is used to produce outputs at 8 MHz with a phase resolution of 16 levels (4 bits) per channel. A 6 ×6 air-coupled matrix array ultrasonic transducer was built and driven by four ASICs, with the help of commercial buffer amplifiers, for the application demonstration. Acoustic pressure mapping and particle manipulation were performed. In addition, a 2 ×2 array piezoelectric micromachined ultrasonic transducer (PMUT) was connected and driven by four output channels of a single ASIC, demonstrating the flexibility of the ASIC to work with different transducers and the potential for direct integration of CMOS and PMUTs.

Multifunctional Asymmetric Sound Manipulations by a Passive Phased Array Prism

Asymmetric acoustic manipulations (AAMs) attract increasing attention for applications in integrated and architectural acoustics. However, because a planar phased array system has the same phase distribution on both sides, designing a monolayer device with asymmetric phase modulation is a real challenge. This work experimentally realizes four types of phased array prisms with different AAM effects arising from asymmetric phase distributions, created by different exit interfaces on either side of a prism. With broad bandwidth, multifunctional AAMs, passive structure, and easy fabrication, these prisms offer a fresh approach to creating $e.g.$ multifunctional acoustic rectifiers and diodes.

Observation of topological locally resonate and Bragg edge modes in a two-dimensional slit-typed sonic crystal

We present the design, analysis, fabrication and testing of the two topological edge states in a sub-wavelength two-dimensional sonic crystal (SC) system based on the mechanism of local resonance and Bragg scattering. The slit-typed SC consists of artificial meta-molecules embedded in the air with a triangle lattice, which is designed by introducing three coupled Helmholtz resonators. Frequency-tunable edge modes are obtained by adjusting the slit of the structure. Experimental results agree well with the theoretical calculations. Our works may enrich the designing of acoustic topological insulators in a sub-wavelength region and have potential applications in acoustic wave manipulation in general.

Reflected acoustic wavefront manipulation by an ultrathin metasurface based on three-dimensional generalized Snell’s law

We theoretically derive three-dimensional (3D) generalized Snell’s law which is demonstrated by reflected wavefront manipulations based on ultrathin quasi-3D acoustic metasurfaces. Acoustic metasurfaces with a deep subwavelength thickness of λ/10 are constructed with 16 unit cells composed of a straight pipe and two ring-like Helmholtz resonators. Based on the 3D generalized Snell’s law, many fascinating reflected wavefront manipulations in 3D space are realized separately, including anomalous reflections, point focusing, line focusing in two perpendicular directions, non-diffracting Bessel beam and self-bending beam. Our results provide a new design methodology for 3D sound wavefront manipulations and practical applications of 3D sound devices.

Acoustic patterning and manipulating microparticles using phononic crystal

Acoustic microparticles manipulations have attracted significant attention in recent years, which may have potential applications in the early detection and diagnosis of diseases. However, most of the current acoustic tweezers have only monotonous manipulation forms, which are limited by standing wave field patterning. Here, we introduce the phononic crystal structure to achieve acoustic patterning and manipulation. Phononic crystals can effectively control and modulate the acoustic pressure distribution, which can provide multiple modes to pattern the microparticles. We numerically investigate the microparticles trajectories under the given acoustic fields. The microparticles eventually exhibit a hollow-circle shape or a star shape, which are no longer merely linear arrangements. The results show that the phononic crystal structure is a useful tool to achieve microparticles manipulations with various patterns. Our study provides a new guide to manipulate the microparticles, which may have vast potential applications in microparticles array, orderly cell culture, and other biomedical areas.

Novel acoustic flat focusing based on the asymmetric response in parity-time-symmetric phononic crystals

We present a two-dimensional (2D) parity-time-symmetric (PT-symmetry) phononic crystals (PCs) with balanced gain and loss medium. Using the super cell method of rectangular lattice, we exhibit the thresholdless spontaneous PT-symmetry breaking in the band structure. The numerical results show that the asymmetric scattering properties obviously occur in a non-Hermitian system. At two specific incident frequencies, unidirectional reflectionless and perfect transmission behaviors exist individually in opposite directions, which are accompanied by a phase transition of π. Based on the generalized Snell’s law, combining such a PT-symmetric medium, we design a novel metamaterial crystal for PT-symmetric acoustic flat focusing. Its focus frequency can also be modulated by the gain/loss parameter. The novel flat focusing based on the PT-symmetry that we propose opens a new door for high-dimensional applications of non-Hermitian metamaterials in acoustic wave manipulation.

Floquet topological acoustic resonators and acoustic Thouless pumping.

Constructing the topological states can serve as a promising approach for robust acoustic wave transports and manipulations. Here, the authors develop a scheme to realize acoustic topological states and adiabatic Thouless pumping in acoustic Floquet resonator systems. The directional acoustic wave can be robustly manipulated and pumped adiabatically from one side to the opposite side due to the non-trivial topological nature. The physical mechanism behind these phenomena can be understood by effective one-dimensional Aubry-André-Harper Hamiltonian, with an additional synthetic dimension originating from Floquet spatially periodic modulation. This Aubry-André-Harper acoustic resonator system can be regarded as a projection from a two-dimensional topological Hofstadter model for the integer quantum Hall effect. The authors' scheme provides a promising method for synthesizing acoustic topological states for efficient acoustic wave manipulations. Introducing the topological mechanism to the control wave will become an alternative method besides the conventional effective acoustic parameter methods.

Numerical Determination of the Secondary Acoustic Radiation Force on a Small Sphere in a Plane Standing Wave Field.

Two numerical methods based on the Finite Element Method are presented for calculating the secondary acoustic radiation force between interacting spherical particles. The first model only considers the acoustic waves scattering off a single particle, while the second model includes re-scattering effects between the two interacting spheres. The 2D axisymmetric simplified model combines the Gor’kov potential approach with acoustic simulations to find the interacting forces between two small compressible spheres in an inviscid fluid. The second model is based on 3D simulations of the acoustic field and uses the tensor integral method for direct calculation of the force. The results obtained by both models are compared with analytical equations, showing good agreement between them. The 2D and 3D models take, respectively, seconds and tens of seconds to achieve a convergence error of less than 1%. In comparison with previous models, the numerical methods presented herein can be easily implemented in commercial Finite Element software packages, where surface integrals are available, making it a suitable tool for investigating interparticle forces in acoustic manipulation devices.

Asymmetric coding metasurfaces for the controllable projection of acoustic images

The projection of acoustic images is of relevance for a wide range of applications, including acoustic communication and medical imaging. Various acoustic projection devices that use holograms have been proposed; however, they inevitably involve multiple basic elements and lack reconfigurability. In this paper, we demonstrate that an acoustic coding metasurface that consists of a single type of asymmetric acoustic unit (AAU) can be used to project the desired acoustic images. The AAU is constructed using a perforated panel and coating unit cell, which can be tunable in terms of the transmission coefficient and reflection phase asymmetry. Patterned in regular and inverse forms, the AAU can function as the coding elements ``0'' and ``1,'' respectively. We demonstrate, both numerically and experimentally, the efficient projection of complex acoustic images such as the letters ``N,'' ``J,'' and ``U.'' More importantly, we develop a simple composite metasurface system to achieve the controllable encryption and decryption of acoustic images. Our proposed approach provides a design methodology for the coding metasurface and may have applications in acoustic security, information storage, and wave manipulation.

All optical control of comb-like coherent acoustic phonons in multiple quantum well structures through double-pump-pulse pump-probe experiments.

We present an advancement in applications of ultrafast optics in picosecond laser ultrasonics - laser-induced comb-like coherent acoustic phonons are optically controlled in a In0.27Ga0.73As/GaAs multiple quantum well (MQW) structure by a high-speed asynchronous optical sampling (ASOPS) system based on two GHz Yb:KYW lasers. Two successive pulses from the same pump laser are used to excite the MQW structure. The second pump light pulse has a tunable time delay with respect to the first one and can be also tuned in intensity, which enables the amplitude and phase modulation of acoustic phonons. This yields rich temporal acoustic patterns with suppressed or enhanced amplitudes, various wave-packet shapes, varied wave-packet widths, reduced wave-packet periods and varied phase shifts of single-period oscillations within a wave-packet. In the frequency domain, the amplitude and phase shift of the individual comb component present a second-pump-delay-dependent cosine-wave-like and sawtooth-wave-like variation, respectively, with a modulation frequency equal to the comb component frequency itself. The variations of the individual component amplitude and phase shift by tuning the second pump intensity exhibit an amplitude valley and an abrupt phase jump at the ratio around 1:1 of the two pump pulse intensities for certain time delays. A simplified model, where both generation and detection functions are assumed as a cosine stress wave enveloped by Gaussian or rectangular shapes in an infinite periodic MQW structure, is developed in order to interpret acoustic manipulation in the MQW sample. The modelling agrees well with the experiment in a wide range of time delays and intensity ratios. Moreover, by applying a heuristic-analytical approach and nonlinear corrections, the improved calculations reach an excellent agreement with experimental results and thus enable to predict and synthesize coherent acoustic wave patterns in MQW structures.

Acoustic Funnel and Buncher for Nanoparticle Injection

Acoustics-based techniques are investigated to focus and bunch nanoparticle beams. This allows to overcome the prominent problem of the longitudinal and transverse mismatch of particle stream and x-ray beam in single-particle/single molecule imaging at x-ray free-electron lasers (XFEL). It will also enable synchronised injection of particle streams at kHz repetition rates. Transverse focusing concentrates the particle flux to the (sub)micrometer x-ray focus. In the longitudinal direction, focused acoustic waves can be used to bunch the particle to the same repetition rate as the x-ray pulses. The acoustic manipulation is based on simple mechanical recoil effects and could be advantageous over light-pressure-based methods, which rely on absorption. The acoustic equipment is easy to implement and can be conveniently inserted into current XFEL endstations. With the proposed method, data collection times could be reduced by a factor of $10^4$. This work does not just provide an efficient method for acoustic manipulation of streams of arbitrary gas phase particles, but also opens up wide avenues for acoustics-based particle optics.

Acoustic Splitting and Bending with Compact Coding Metasurfaces

Acoustic metasurfaces have drawn great interest for their flexibility in acoustic field manipulation, but are being held back in practice by their complex configurations and narrow frequency range. This study uses hornlike helices in the logical units of a compact coding metasurface that yields broadband acoustic bending and splitting. Such a simple, aperiodic design in compact coding metasurfaces could promote innovative techniques of acoustic wave control.

Switchable omnidirectional acoustic insulation through open window structures with ultrathin metasurfaces

We theoretically propose and experimentally realize two types of open window structures that exhibit an unusual functionality of switchable omnidirectional acoustic insulation in two different ways. Both types of open window structures consist of an array of blades that are attached with ultrathin metasurfaces on both sides. Based on the acoustic manipulation ability of the metasurfaces, omnidirectional acoustic insulation can be realized in the open windows. Interestingly, such an effect is switchable by simply changing the configuration of the blade array. For the first type, omnidirectional acoustic insulation can be switched on or off by adjusting the distance between two adjacent blades. For the second type in which the open window structure is composed of an alternative arrangement of two types of blades, acoustic insulation can be controlled by moving one kind of blade horizontally. The proposed open windows have the advantage of broadband omnidirectional acoustic insulation and convenient switching mechanisms. Our work opens up a new approach for acoustic insulation in open structures, with potential applications in a variety of fields, such as noise control and architectural acoustics.

Vocal Fundamental Frequency and Sound Pressure Level in Charismatic Speech: A Cross-Gender and -Language Study

Charismatic leaders use vocal behavior to persuade their audience, achieve goals, arouse emotional states, and convey personality traits and leadership status. This study investigates voice fundamental frequency (f0) and sound pressure level (SPL) in female and male French, Italian, Brazilian, and American politicians to determine which acoustic parameters are related to cross-gender and cross-cultural common vocal abilities, and which derive from culture-, gender-, and language-specific vocal strategies used to adapt vocal behavior to listeners' culture-related expectations. Speech corpora were collected for two formal communicative contexts (leaders address followers or other leaders) and one informal communicative context (dyadic interaction), based on the persuasive goals inherent in each context and on the relative status of the listeners and speakers. Leaders' acoustic voice profiles were created to show differences in f0 and SPL manipulation with respect to speakers' gender and language in each communicative context. Cross-gender and cross-language similarities in manipulation of average f0 and in f0 and SPL ranges occurred in all communicative contexts. Patterns of f0 manipulation were shared across genders and cultures, suggesting this dimension might be biologically based and is exploited by leaders to convey dominance. Ranges for f0 and SPL seemed to be affected by the communicative context, being wider or narrower depending on the persuasive goal. Results also showed language- and speaker-specific differences in the acoustic manipulation of f0 and SPL over time. These findings are consistent with the idea that specific charismatic leaders' vocal behaviors depend on a fine combination of vocal abilities that are shared across cultures and genders, combined with culturally- and linguistically-filtered vocal strategies.

Acoustic manipulation of microparticle in a cylindrical tube for 3D printing

Purpose The capability of microparticle/objects patterning in the three-dimensional (3D) printing structure could improve its performance and functionalities. This paper aims to propose and evaluate a novel acoustic manipulation approach. Design/methodology/approach A novel method to accumulate the microparticles in the cylindrical tube during the 3D printing process is proposed by acoustically exciting the structural vibration of the cylindrical tube at a specific frequency, and subsequently, focusing the 50-μm polystyrene microparticles at the produced pressure node toward the center of the tube by the acoustic radiation force. To realize this solution, a piezoceramic plate was glued to the outside wall of a cylindrical glass tube with a tapered nozzle. The accumulation of microparticles in the tube and printing structure was monitored microscopically and the accumulation time and width were quantitatively evaluated. Furthermore, the application of such technology was also evaluated in the L929 and PC-12 cells suspended in the sodium alginate and gelatin methacryloyl. Findings The measured location of pressure and the excitation frequency of the cylindrical glass tube (172 kHz) agreed quite well with our numerical simulation (168 kHz). Acoustic excitation could effectively and consistently accumulate the microparticles. It is found that the accumulation time and width of microparticles in the tube increase with the concentration of sodium alginate and microparticles in the ink. As a result, the microparticles are concentrated mostly in the central part of the printing structure. In comparison to the conventional printing strategy, acoustic excitation could significantly reduce the width of accumulated microparticles in the printing structure (p < 0.05). In addition, the possibility of high harmonics (385 and 657 kHz) was also explored. L929 and PC-12 cells suspended in the hydrogel can also be accumulated successfully. Originality/value This paper proves that the proposed acoustic approach is able to increase the accuracy of printing capability at a low cost, easy configuration and low power output.

Axial acoustic radiation force on a spherical particle in a zero-order Mathieu beam.

In this paper, an expression for the acoustic radiation force on a sphere located on the axis of a zero-order Mathieu beam propagating in an ideal fluid is obtained. The simulation results of different kinds of spherical particles, including rigid spheres, fluid spheres, and elastic spheres, are presented to illustrate the theory. Curves of the acoustic radiation force function versus ka are obtained for different half-cone angles β and ellipticity parameters q of the Mathieu beam. The simulation results reveal that β and q have a direct effect on the acoustic radiation force exerted on a spherical object in an ideal fluid. The acoustic radiation force has negative values for a fluid sphere in a zero-order Mathieu beam when the half-cone angle is β≥60°. The value of the half-cone angle β also affects the direction of the acoustic radiation force for an elastic sphere. When the half-cone angle is set as a constant, the greater the ellipticity parameter is, the slower the decrease in the value of the acoustic radiation force function for a spherical particle. The conclusions of this work may be helpful for the design of acoustic tweezers and may also extend the potential applications of acoustic manipulation technology.

Realizing passive direction-bias for mechanical wave propagation using a nonlinear metamaterial

The possibility of realizing amplitude-activated passive direction-bias in longitudinal elastic wave propagation using a nonlinear acoustic metamaterial is demonstrated. Applying the method of multiple scales, approximate analytical solutions are derived for the dispersion curve and bandgap shifts due to the presence of nonlinear hardening local oscillators within the metamaterial using its lumped parameter effective-mass model. The configuration for a structural waveguide consisting of a tuned combination of a nonlinear and a linear acoustic metamaterial that takes advantage of these shifts to produce amplitude-activated direction-bias in propagation was postulated and verified using discrete element simulations. A numerical routine to generate root profile geometries that enable contact-based hardening response in tip-loaded cantilever beam resonators was developed and implemented. Utilizing a hybrid fabrication process involving additively manufactured and machined components, a prototype test article was constructed. Experiments using a structural waveguide test rig verify the existence and extent of bandgaps and provide evidence for the passive direction-bias phenomenon. Follow-on investigations on configurations with different types of nonlinearities could pave the way for development of additional passive acoustic wave manipulation devices with enriched dynamics.