Acoustic Manipulation Research Articles

Multibody dynamics in acoustophoresis.

Determining the trajectories of multiple acoustically and hydrodynamically interacting as well as colliding particles is one of the challenges in numerical acoustophoresis. Although the acoustic forces between multiple small spherical particles can be obtained analytically, previous research did not address the particle-particle contacts in a rigorous way. This article extends existing methods by presenting an algorithm on displacement level which models the hard contacts using set-valued force laws, hence allowing for the first time the computation of a first approximation of complete trajectories of multiple hydrodynamically and acoustically interacting particles. This work uses a semi-analytical method to determine the acoustic forces, which is accurate up to the dipole contributions of the multipole expansion. The hydrodynamic interactions are modeled using the resistance and mobility functions of the Stokes' flow. In previous experimental work particles have been reported to interact acoustically, ultimately forming stacked lines near the pressure nodes of a standing wave. This phenomenon is examined experimentally and numerically, the simulation shows good agreement with the experimental results. To demonstrate the capabilities of the method, the rotation of a particle clump in two orthogonal waves is simulated. The presented method allows further insight in self-assembly applications and acoustic particle manipulation.

Acoustic Manipulation of a Liquid-filled Spherical Shell Activated with an Internal Spherical Oscillator

Acoustic Manipulation of a Liquid-filled Spherical Shell Activated with an Internal Spherical Oscillator

Metamaterial bricks and quantization of meta-surfaces

Controlling acoustic fields is crucial in diverse applications such as loudspeaker design, ultrasound imaging and therapy or acoustic particle manipulation. The current approaches use fixed lenses or expensive phased arrays. Here, using a process of analogue-to-digital conversion and wavelet decomposition, we develop the notion of quantal meta-surfaces. The quanta here are small, pre-manufactured three-dimensional units—which we call metamaterial bricks—each encoding a specific phase delay. These bricks can be assembled into meta-surfaces to generate any diffraction-limited acoustic field. We apply this methodology to show experimental examples of acoustic focusing, steering and, after stacking single meta-surfaces into layers, the more complex field of an acoustic tractor beam. We demonstrate experimentally single-sided air-borne acoustic levitation using meta-layers at various bit-rates: from a 4-bit uniform to 3-bit non-uniform quantization in phase. This powerful methodology dramatically simplifies the design of acoustic devices and provides a key-step towards realizing spatial sound modulators.

Observation of Metal Nanoparticles for Acoustic Manipulation.

Use of acoustic trapping for the manipulation of objects is invaluable to many applications from cellular subdivision to biological assays. Despite remarkable progress in a wide size range, the precise acoustic manipulation of 0D nanoparticles where all the structural dimensions are much smaller than the acoustic wavelength is still present challenges. This study reports on the observation of metal nanoparticles with different nanostructures for acoustic manipulation. Results for the first time exhibit that the hollow nanostructures play more important factor than size in the nanoscale acoustic manipulation. The acoustic levitation and swarm aggregations of the metal nanoparticles can be easily realized at low energy and clinically acceptable acoustic frequency by hollowing their nanostructures. In addition, the behaviors of swarm aggregations can be flexibly regulated by the applied voltage and frequency. This study anticipates that the strategy based on the unique properties of the metal hollow nanostructures and the manipulation method will be highly desirable for many applications.

Hybrid optothermal and acoustic manipulations of microbubbles for precise and on-demand handling of micro-objects

Manipulating specific micro-objects (e.g., colloidal particles and microorganisms) precisely and selectively in liquid medium is of great importance in myriad engineering fields. We here develop a hybrid technique for micromanipulation of micro-objects by incorporating optothermally and acoustically excited bubble on-demand. The integrated strategy combines strengths of optothermal (e.g., precise size control in bubble creation and easy delivery of micro-objects into target position) and acoustical (e.g., on-demand capturing and precise sorting of micro-objects) strategies. Microbubbles can be optothermally generated, and their size can be regulated by tuning the illumination time and power of a laser beam. The bubbles can be delivered into a preferred position an optothermocapillary flow. Sequentially, micro-objects with two different sizes can be selectively separated, and then only micro-objects with a specific size can be collected through a secondary acoustic radiation and a streaming flow generated from an acoustically oscillating bubble. To emulate on-demand manipulation of bio-objects in technological applications, we examine a full-step manipulation process of micro-objects, which consists of generating bubbles and sorting/capturing/carrying/releasing of desired micro-objects under optothermal and acoustical actuation. The hybrid manipulation technique can be a good alternative technology to conventional ones and thus can be utilized in biological applications and micro-device assembly.

Lapillus bug : 音響浮揚操作に基づいた粒子の生物的表現とインタラクション

lapillus bug : 音響浮揚操作に基づいた粒子の生物的表現とインタラクション

Omnidirectional broadband acoustic deflector based on metamaterials

We report a theoretical, numerical, and experimental work on the design of an omnidirectional acoustic deflector capable of redirecting an incident wave to propagate along a predesigned direction over a broad frequency range, regardless of the incidence angle. An implementation by metamaterials is demonstrated both in simulation and experiment, with both showing the effectiveness of our scheme as long as the effective medium approximation stands. With the capability of omnidirectional broadband deflection and the flexibility of a controllable tuning angle, our design opens a route to the development of wave-steering devices and has great application potentials in various situations such as on-chip acoustic manipulations.

Mathematical operations for acoustic signals based on layered labyrinthine metasurfaces

Acoustic devices such as acoustic diodes, switches, and logic gates can manipulate acoustic signals extraordinarily and show potential in acoustic engineering. However, pioneering works suffer from the limitations of simple functionality, high losses, and geometrical complexity. Here, we present an acoustic analog computing system based on acoustic metasurfaces constructed from layered labyrinthine metamaterials. The system can perform complex mathematical operations, such as spatial differentiation, integration, and convolution on acoustic signals. The proposed system offers a practical, efficient, and flexible solution of designing compact devices for acoustic computing applications, signal processing, and acoustic wave manipulations.

Acoustic manipulation of particles by a resonant one-dimensional grating in air

It is well known that acoustic wave carries momentum and energy. An object in a sound field, which absorbs or reflects sound energy, can be subjected to the acoustic radiation force (ARF), and thus can be manipulated in the contactless and noninvasive manners. This effect has potential applications in the fields of environment monitoring, microbiology, food quality control, etc. Obtaining a tunable trapping or pushing ARF should enable the design of an incident beam profile. However, the conventional acoustic manipulation system with plane wave, standing waves or Gaussian beams, which is usually generated directly by acoustic transducer, cannot be redesigned easily, nor can the corresponding ARF be modulated efficiently. Phononic crystals, which are artificial periodic structure materials, exhibit great advantages in modulating the propagation and distribution of acoustic wave compared with conventional materials, and thus have potential applications in tunable particle manipulation. Here, we present a theoretical study of the ARFs exerted on a cylindrical polystyrene foam particle near the surface of a one-dimensional (1D) grating in air. By using the finite element method (FEM) to investigate the transmission spectra and field distribution of the 1D grating and the FEM combined with momentum-flux tensor to obtain the ARF on the particle, we find that there are two resonance modes in the 1D grating, which origin from the coupling between the diffractive waves excited from the export of periodic apertures and the Fabry-Perot resonance mode inside the apertures. In addition, it can be seen from field distribution that in the first resonant mode, the resonance wavelength is approximate to the period of grating, and the enhanced spatial confinement of acoustic wave is located at the surface of the plate besides in the aperture. In the second resonant mode, the corresponding wavelength is more than twice the period of grating, and the enhanced spatial confinement of acoustic wave is mainly located in the aperture. Moreover, due to the gradient field distribution at the surface of slits and plate in these resonance modes, particles at the surface can be under the action of tunable negative ARFs. In the first resonance mode, the particle can be trapped on the surface of grating. While in the second resonance mode, the particle can be trapped in the aperture, and the amplitude of ARF of this mode is far smaller than that of the first mode. Thus, this system in the first resonance mode may have potential applications in air acoustic manipulation, aligning, and sorting micro-particles.

Visual and acoustic information supporting a happily expressed speech-in-noise advantage

There was an advantage found for recognizing happily expressed audio and audio-visual speech-in-noise relative to speech spoken with neutral or sad expressions. The advantage of happily expressed speech was explored in a set of visual and acoustic manipulations designed to isolate the potential contributions from each signal. For this research, a replication of previous research with the happily expressed speech advantage was completed with a novel inclusion of a learning paradigm. Additional experiments directly investigated the role of the fundamental frequency of the voice for affect, and the affective facial components with the eyes and mouth. We found that the happily expressed speech advantage persisted despite constraints to the amount of frequency modulation and with distortions to the talker's face. These findings seem largely attributable to the influences of affect on low-level acoustical and articulatory information, with only a very subtle role of approach/withdrawal motivation.

Investigation of Acoustic Manipulation by Layered Periodic Composites

Investigation of Acoustic Manipulation by Layered Periodic Composites

Subwavelength diffractive acoustics and wavefront manipulation with a reflective acoustic metasurface

Acoustic metasurfaces provide useful wavefront shaping capabilities, such as beam steering, acoustic focusing, and asymmetric transmission, in a compact structure. Most acoustic metasurfaces described in the literature are transmissive devices and focus their performance on steering sound beam of the fundamental diffractive order. In addition, the range of incident angles studied is usually below the critical incidence predicted by generalized Snell's law of reflection. In this work, we comprehensively analyze the wave interaction with a generic periodic phase-modulating structure in order to predict the behavior of all diffractive orders, especially for cases beyond critical incidence. Under the guidance of the presented analysis, a broadband reflective metasurface is designed based on an expanded library of labyrinthine acoustic metamaterials. Various local and nonlocal wavefront shaping properties are experimentally demonstrated, and enhanced absorption of higher order diffractive waves is experimentally shown for the first time. The proposed methodology provides an accurate approach for predicting practical diffracted wave behaviors and opens a new perspective for the study of acoustic periodic structures. The designed metasurface extends the functionalities of acoustic metasurfaces and paves the way for the design of thin planar reflective structures for broadband acoustic wave manipulation and extraordinary absorption.

Acoustic Holographic Rendering with Two-dimensional Metamaterial-based Passive Phased Array.

Acoustic holographic rendering in complete analogy with optical holography are useful for various applications, ranging from multi-focal lensing, multiplexed sensing and synthesizing three-dimensional complex sound fields. Conventional approaches rely on a large number of active transducers and phase shifting circuits. In this paper we show that by using passive metamaterials as subwavelength pixels, holographic rendering can be achieved without cumbersome circuitry and with only a single transducer, thus significantly reducing system complexity. Such metamaterial-based holograms can serve as versatile platforms for various advanced acoustic wave manipulation and signal modulation, leading to new possibilities in acoustic sensing, energy deposition and medical diagnostic imaging.

Musical mind control: Acoustic convergence to background music in speech production

Talkers adjust their speech to resemble that of their interlocutors—a phenomenon known as speech convergence. Broadly defined, convergence describes automatic synchronization to some external source, and this effect has been recognized in various linguistic domains (e.g., syntactic structuring, morphological choices, and vowel production). Using a speech-in-noise reading-task, this paper explores whether or not speech production also converges with non-linguistic signals: Specifically, might a speaker’s rhythm, pitch or intensity be influenced by fluctuations in background music? Participants read passages aloud while music was presented at ~45 dB(A) via headphones. Music was composed with relatively flat envelopes in the domains of interest, and in test-conditions only Pitch, Tempo, or Intensity was altered. Manipulation was gradual (linear function) and would similarly return to the point of origin after reaching a target (Pitch = -200 cents; Amp = + 6dB; Tempo = -20 beats per minute). Control conditions (i.e., no acoustic manipulation) broke up test conditions. Analyzing data from 25 English speakers identifies significant convergence effects in the Pitch condition (tempo and intensity analyses have not yet been conducted). Using Generalized Additive Mixed Models, the predicted Time by Condition interactions were observed, suggesting that environmental noise may constantly be influencing speech production.

Demonstration of acoustic holographic rendering with two-dimensional metamaterial-based passive phased array

Acoustic holograms in analogy with optical holograms are useful for a variety of applications, such as multi-focal lensing, multiplexed sensing and synthesizing three-dimensional complex sound fields. We previously presented the designs and simulation results of several metamaterial-based acoustic holograms (J. Acoust. Soc. Am. 138, 1751 (2015)). Here, we demonstrate the experimental realization of two of them: one projects a complex pattern on the image plane, while the other focus energy onto multiple circular spots of different sizes. We showcase the holographic reconstruction measurements carried out in an anechoic chamber. The demonstrated passive holograms, without phase-shifting circuitry and transducer arrays, are advantageous for applications where simplicity, robustness, and small footprint are preferred over adaptive control. We also discuss the higher frequency versions of such holograms and their applications in robotic sensing and wireless power transfer. Such metamaterial-based holograms can serve as versatile platforms for various advanced acoustic wave manipulation and signal modulation, leading to new possibilities in acoustic sensing, imaging and energy deposition.

Quantised acoustic meta-surfaces using metamaterial bricks

Acoustic meta-surfaces offer an extremely successful way of transforming an input acoustic wave into almost any diffraction-limited field. This is typically achieved by encoding a phase delay function on the unit cells that form the meta-surface, which is then manufactured by rapid prototyping. One of the limits of current technology is that meta-surfaces built in this way are targeted to a single, specific application. In this work, we present a method of building acoustic meta-surfaces using metamaterial bricks, designed to operate at 40 kHz and quantized both in the space and in the phase domains. First, we present finite-elements simulations and experiments to discuss key parameters of our bricks as frequency response, directivity, impedance. Second, our metamaterial bricks are used here to achieve some key beam transformations like steering and focusing, but also more complex fields like an acoustic tractor beam. We use the latter to levitate one or more polystyrene beads and diffraction theory to explain some of the findings. Our method, where the phase in a specific position may be changed by changing the specific brick, may find applications in loudspeaker design, ultrasound imaging/therapy, or acoustic particle manipulation.

Non-contact acoustic manipulation in microchannel

Noncontact micromanipulation technique is needed in micromachine technology, biotechnology, and other fields. In the present paper, a standing wave field is generated in a microchannel and a geometric space, and it is possible to trap small objects at nodes of the sound pressure distribution in the medium. A microchannel and a geometric space were made at the center of a glass plate of 50 mm x 50 mm x 5 mm. In the experiment, when the liquid water containing alumina particles was injected into the microchannel on glass plate irradiated by ultrasound, the particles flowed along several layers in the microchannel. In the geometric space, the particles were trapped in the sound pressure nodes of the standing wave field. By changing the frequency, the geometric pattern of particles aggregation interestingly changed. When the geometric space is a triangular space, the particle moved toward the top from the base of the triangle. When the microchannel is branched at the half circular geometric space, it was able...

Axial acoustic radiation force on rigid oblate and prolate spheroids in Bessel vortex beams of progressive, standing and quasi-standing waves

The analysis using the partial-wave series expansion (PWSE) method in spherical coordinates is extended to evaluate the acoustic radiation force experienced by rigid oblate and prolate spheroids centered on the axis of wave propagation of high-order Bessel vortex beams composed of progressive, standing and quasi-standing waves, respectively. A coupled system of linear equations is derived after applying the Neumann boundary condition for an immovable surface in a non-viscous fluid, and solved numerically by matrix inversion after performing a single numerical integration procedure. The system of linear equations depends on the partial-wave index n and the order of the Bessel vortex beam m using truncated but converging PWSEs in the least-squares sense. Numerical results for the radiation force function, which is the radiation force per unit energy density and unit cross-sectional surface, are computed with particular emphasis on the amplitude ratio describing the transition from the progressive to the pure standing waves cases, the aspect ratio (i.e., the ratio of the major axis over the minor axis of the spheroid), the half-cone angle and order of the Bessel vortex beam, as well as the dimensionless size parameter. A generalized expression for the radiation force function is derived for cases encompassing the progressive, standing and quasi-standing waves of Bessel vortex beams. This expression can be reduced to other types of beams/waves such as the zeroth-order Bessel non-vortex beam or the infinite plane wave case by appropriate selection of the beam parameters. The results for progressive waves reveal a tractor beam behavior, characterized by the emergence of an attractive pulling force acting in opposite direction of wave propagation. Moreover, the transition to the quasi-standing and pure standing wave cases shows the acoustical tweezers behavior in dual-beam Bessel vortex beams. Applications in acoustic levitation, particle manipulation and acousto-fluidics would benefit from the results of the present investigation.

An Experimental Study on the Influence of Soundscapes on People’s Behaviour in an Open Public Space

Several studies have investigated how environmental sounds and music can modulate people’s behaviours, particularly in marketing research. However, there are relatively few examples of research about such relationships with a focus on the management of urban public spaces. The current study investigated an open public space used mainly as a pedestrian crossing to analyse the relationship between the audio stimuli and peoples’ behaviours. An experiment relying on covert behavioural observation was performed. During the experiment, three different music stimuli and a control condition (i.e., no music) were reproduced in order to find out firstly whether music compared to no music could elicit an increase in the number of people stopping in the investigated area, and secondly whether music is associated with a longer duration of stay for those who stop. Results showed that the presence of music had no effect on the number of people stopping in the area, but it had a statistically significant effect on the duration of stay for those who stopped. The above findings support the idea that people felt more invited to stay in the area with music rather than with no music, and suggest that the acoustical manipulation of the existing sound environment could provide soundscape strategies capable of promoting social cohesion in public spaces.

Contactless Acoustic Manipulation and Sorting of Particles by Dynamic Acoustic Fields.

This paper presents a contactless, acoustic technique to manipulate and sort particles of varying size in both liquid and air media. An acoustic standing wave is generated by the superposition of counterpropagating waves emitted by two opposing emitters. The acoustic radiation force traps the smallest particles at the pressure nodes of the acoustic standing wave. The position of the particles can be manipulated by dynamically changing the phase difference between the two emitters. By applying a dynamic acoustic field (DAF), it is demonstrated that particles can be manipulated spatially and sorted according to size. The discrimination (sorting dynamic range) capability is initially demonstrated in liquid media by separating three different sets of polystyrene particles, ranging in size from 5 to 45μm in diameter. The separation between particles was performed up to a ratio of 5/6 in diameter (20% diameter difference). Finally, the scalability of the DAF method is demonstrated by sorting expanded polystyrene particles of 2 and 5 mm diameter in air.