Acoustic Vortex Research Articles

Laser-generation of focused acoustic vortex with Fresnel spiral optoacoustic surfaces

We report a laser-based method to generate high central-frequency focused ultrasound vortices by introducing the Fresnel spiral for optoacoustic conversion. The formed broadband optoacoustic waves are coherently superimposed with each other, giving rise to acoustic vortices at different positions along the propagating axis according to their corresponding frequencies, while still maintaining the generation of focused vortex at the predetermined focal length. The laser-generated vortices show the typical vortex features including a helical wavefront and a central null pressure. A semi-parabolic focusing detection system is designed and constructed to scan the generated ultrasound vortices with high spatial resolution. The resulting acoustic vortices with the central frequency of about 3 MHz are presented in three dimensions, and agree well with the predictions. The flexibility of this scheme and its scalability to higher frequencies open tremendous perspectives in particle manipulation, ultrasonic therapy and so on.

Topologically crafted spatiotemporal vortices in acoustics

Vortices in fluids and gases have piqued the human interest for centuries. Development of classical-wave physics and quantum mechanics highlighted wave vortices characterized by phase singularities and topological charges. In particular, vortex beams have found numerous applications in modern optics and other areas. Recently, optical spatiotemporal vortex states exhibiting the phase singularity both in space and time have been described. Here, we report the topologically robust generation of acoustic spatiotemporal vortex pulses. We utilize an acoustic meta-grating with broken mirror symmetry which exhibits a topological phase transition with a pair of phase singularities with opposite topological charges emerging in the momentum-frequency domain. We show that these vortices are topologically robust against structural perturbations of the meta-grating and can be employed for the generation of spatiotemporal vortex pulses. Our work paves the way for studies and applications of spatiotemporal structured waves in acoustics and other wave systems.

Growth rates of harmonics in nonlinear vortex beams

Nonlinear effects in acoustical vortex beams were described originally in a numerical investigation by Marchiano et al. [Phys. Rev. E 77, 016605 (2008)]. The focus of the present investigation is the rate at which nonlinearly generated harmonics grow with distance in the field of a vortex beam radiated by a monofrequency or bifrequency source as a function of the topological charge. The motivation is a paper by Richard et al. [New J. Phys. 22, 063021 (2020)] suggesting that the rate of nonlinear distortion in the direction of the beam axis is increased in a vortex beam due to the lengthened propagation distance along the ray paths spiraling about the beam axis. In the present work, harmonic growth rate is characterized in terms of both amplitudes along different ray paths and total power across the beam. Growth rates are calculated and compared for harmonics generated in nonlinear vortex beams radiated by sources with different topological charges and amplitude distributions. Both unfocused and focused beams are considered. The likelihood of shock formations is also explored. [CAG is supported by the ARL:UT Chester M. McKinney Graduate Fellowship in Acoustics.]

Numerical investigation of acoustic streaming vortex and operating parameters in curved microchannel: driven by standing surface acoustic wave

Numerical investigation of acoustic streaming vortex and operating parameters in curved microchannel: driven by standing surface acoustic wave

Broadband high-efficiency acoustic vortices via a topology-optimized space-coiling-cavity metasurface

Acoustic vortices carrying orbital angular momentum are significant in wave-matter interactions, allowing for versatile devices with promising applications. However, current metasurface-based vortex generators have limited bandwidth, operating within a narrow frequency range. Here, we propose a broadband acoustic metasurface with four space-coiling-cavity units through the bottom-up topology optimization. These units have constant phase differences with high-efficiency transmission (>0.8) over a desired frequency range [3.0, 4.0] kHz, indicating the unique wideband vortex response of their assembled metasurfaces. Our simulations and experiments further demonstrate this excellent performance. This breakthrough in broadband vortices allows for the development of devices like acoustic tweezers, antennas, and spanners.

An asymmetric generator of acoustic vortex with high-purity

The asymmetric generation of acoustic vortex refers to the physical characteristics that pass the generated acoustic vortex in one direction while blocking it in the opposite direction. Such an effect has drawn much attention in acoustic vortex-based applications, but there is relatively little research about it. In this paper, we theoretically conceive an approach to realize asymmetric acoustic vortices with high purity by an asymmetric generator composed of a mode converter (MC) and a mode selector (MS). The underlying process is achieved with an integrated design combing vortex mode conversion and mode selection. The corresponding results of simulations and an experiment further confirmed the novel phenomenon. In addition, the designed configuration obtains unidirectional acoustic vortices with high purity, which may have potential in asymmetric acoustic communication.

Focused acoustic vortex-mediated sonochemotherapy for the amplification of immunogenic cell death combined with checkpoint blockade to potentiate cancer immunotherapy

Sonodynamic therapy (SDT) as an auxiliary modality of cancer immunotherapy enhances systemic anti-tumor immunity. However, the efficiency of SDT-mediated immunotherapy based on conventional focused ultrasound (FUS) is restricted by the tiny focal region of FUS. Focused acoustic vortex (FAV) possessing a larger focal region, can induce stronger cavitation and thermal effects than FUS with the same parameters, having the potential to overcome this issue. This research investigated the feasibility of FAV-mediated sonochemotherapy combined with the immune checkpoint blockade (ICB) to reshape immunosuppressive tumor microenvironment (TME), inhibit tumor growth and lung metastasis. Sonosensitizer chlorin e6 (Ce6) and chemotherapeutic agent doxorubicin (Dox) were co-loaded into microbubble-liposome complex to compose Ce6/Dox@Lip@MBs (CDLM) for “all-in-one” synergistic sonochemotherapy, whose main components were clinical approved. FAV-activated CDLM significantly enriched immunogenic cell death (ICD) inducers in tumors and amplified ICD of cancer cells compared with FUS-activated CDLM. Furthermore, the amplified-ICD combined with ICB increased the infiltration of cytotoxic T lymphocytes and natural killer cells, polarized M2 macrophages to M1 macrophages, and decreased regulatory T cells. This study provides a multifunctional strategy for enriching ICD inducers in tumors and amplifying ICD to ameliorate immunosuppressive TME and potentiate systemic anti-tumor immunity.

Acoustic Forceps Based on Focused Acoustic Vortices with Different Topological Charges.

For enhanced energy concentration with improved flexibility for object manipulation, a focused acoustic vortex (FAV) is designed using a sector planar piston transducer array and acoustic lens that can produce the effective concentration of the acoustic field to perform the focusing function. Compared to the Gaussian beam, which tends to cause the object to deviate from the axis of acoustic propagation, FAVs can form a central valley region to firmly bind the objects, thus preventing off-target effects. The heat energy in the paraxial region is transferred to the vortex center in the form of heat transfer so that the temperature-sensitive liposomes captured can quickly release drugs, which has a good effect on targeted drug administration. The focused acoustic wave stopped acting on the tissue (gel) for 2 s, the temperature of the vortex center continued to rise, reaching 41.5 °C at the moment of 3.7 s, at which point the liposomes began to release the drug. The FAVs capture the drug and use its thermal effect to achieve accurate and rapid treatment. The simulation results show that the drug release temperature of temperature-sensitive liposomes can be achieved by controlling the action time of the vortices. This study provides a reliable theoretical basis for the clinical application of targeted drugs.

Detecting acoustic chirality with matched metamaterial vortex wave antennas.

Acoustic communications often have limited data rates because of the intrinsically low frequencies. Exploring new spatial modes to increase data bandwidth at fixed frequency is a possible solution to this problem. Here, we demonstrate acoustic wave chirality transmission between two reciprocal metamaterial vortex wave antennas, generating and sensing transmitted acoustic wave chirality through the sub-wavelength geometry of the system. By adding an acoustic leaky wave surface to a ring resonator waveguide, acoustic vortex waves with positive or negative integer mode chirality are independently radiated and detected using a small number of microphones. Through computational simulation and experimental verification, using three-dimensional printed waveguides, we show that the vortex mode chirality can be transferred between two opposing acoustic vortex wave antennas across a small unguided air gap. We also show that emission into an external waveguide can provide long distance data transmission. This demonstrates the first use of metamaterial vortex wave antennas as chiral, mode multi-channel data transceivers.

Enhanced thermal ablation via an acoustic vortex with a large focal region

Focused ultrasound ablation provides a truly noninvasive tumor treatment option with clinically proven feasibility and safety. However, the frequently required long treatment duration hinders its clinical applicability. In this work, we compared the thermal ablation induced by conventional focused ultrasound (cFUS), split-focus ultrasound (sFUS), and acoustic vortex (AV) in tissue phantoms containing phase-change nanodroplets and mouse tumors. The results indicated that AV could substantially enhance the thermal ablation efficiency compared with cFUS, which was attributed to the larger focal region in the former. Additionally, the ablation region appeared as a unique cylindrical area with a smaller length-to-width ratio in AV than that in cFUS. Though the efficiency could also be improved in sFUS compared with cFUS, the ablation region was irregular and non-ablated tissues were present. Furthermore, in vivo experiments demonstrated that the tumor volume decreased faster and the mice survived longer after AV treatment compared with cFUS. The cavitation activity was also found to be more intense in AV ablation. The proposed method may solve the general issue of low efficiency often observed in cFUS ablation and further promote the development of other ultrasound treatments.

Single-channel acoustic vortex tweezer with attachable fan-shaped holographic lens

The utilization of acoustic vortices presents a promising technique for contactless particle manipulation. However, existing methods for generating acoustic vortices typically rely on complex active driving systems and array ultrasound transducers. Therefore, more simplified and robust approaches to inducing acoustic vortices should be considered. With inspiring the fact that acoustic vortices can be generated by the differences in the height of adjacent sectors in conventional four-panel transducers, we aim to develop a single-channel acoustic vortex tweezer with a simplified driving system by incorporating attachable fan-shaped polydimethylsiloxane (PDMS) holographic lens. This passive lens structure with different heights in adjacent sectors can generate phase-modulated ultrasonic waves. Therefore, the interaction of phase-modulated waves passing through the lens is expected to result in a vortex-like beam. The available materials of fan-shaped lens are not limited to the PDMS. This lens type can be appropriately fabricated with an understanding of the sound of speed within the desired material and predetermined thickness, inducing π/2 phase difference in the adjacent lobes. As a result, the excited acoustic waves propagated through the lens were under mutual interaction without any active electrical setup, forming a null pressure region enveloped by four distinct acoustic lobes. We systemically investigated the tweezing potential using vortex-like waves. Several types of bioparticles were utilized in these investigations: microbubbles, polystyrene (PS) beads, and cancer cells. Our findings demonstrate that the transducer with lens is sufficiently capable of spatial manipulation of bioparticles. Remarkably, the microbubbles traveling at a flow velocity of 32 cm/s in a blood vessel-mimicking phantom were feasibly trapped in the proposed transducer. Furthermore, the spatial control of PS and cells with higher acoustic impedance was also feasible in static conditions. Consequently, the proposed transducer offers an economically and practically viable solution for various biomedical applications, such as drug delivery and cell-based bioengineering.

Acoustic dark lattices generated by composite spiral plates for multi-particle trapping

The interactions of two Bessel acoustic vortices (BAVs) with different topological charges (TCs) have been investigated in detail. The theoretical results show that, with changing the TCs of two BAVs, the intensity distributions of the coupled-BAVs can switch among the petal mode, the acoustic dark lattice (ADL) mode, and the crescent mode, where the positions of the dark spots coincide with the phase singular points. We concentrate on the ADL modes and a composite spiral plate (CSP) is well designed to realize them. It is shown both numerically and experimentally that the CSP can create the ADL modes in air, which also exhibit strong self-healing. Additionally, the CSP is employed to generate ADLs in water. Four-order and six-order ADLs produced by two steel CSPs are used, respectively, to achieve multi-particle trappings in water experimentally. The capacity of the ADLs generated by the simple CSPs to trap multiple micro-particles in desired positions may find applications in biomedicine, including microarrays, tissue engineering, and regenerative medicine.

Spatiotemporal Acoustic Vortex Beams with Transverse Orbital Angular Momentum.

Recently, the discovery of optical spatiotemporal (ST) vortex beams with transverse orbital angular momentum (OAM) has attracted increasing attention and is expected to extend the research scope and open new opportunities for practical applications of OAM states. The ST vortex beams are also applicable to other physical fields that involve wave phenomena, and here we develop the ST vortex concept in the field of acoustics and report the generation of Bessel-type ST acoustic vortex beams. The ST vortex beams are fully characterized using the scalar approach for the pressure field and the vector approach for the velocity field. We further investigate the transverse spreading effect and construct ST vortex beams with an ellipse-shaped spectrum to reduce the spreading effect. We also experimentally demonstrated the orthogonality relations between ST vortex beams with different charges. Our study successfully demonstrates the versatility of the acoustic system for exploring and discovering spatiotemporally structured waves, inspiring further investigation of exotic wave physics.

Design and simulation of acoustic vortex wave arrays for long-range underwater communication

The formation and propagation of acoustic vortex waves have been of increasing interest for multiple applications, namely, underwater acoustic communications. Several methods have been presented to form these vortices in underwater environments; however, their performance and propagation over long distances is largely unstudied. Understanding the long-distance propagation of these waves is vital to enhancing their usefulness as an added degree of freedom in underwater acoustic communications systems. In this work, the ray tracing algorithm of bellhop is used to investigate the design parameters of vortex wave transducer and receiver arrays consisting of multiple rings of independently controlled transducers and simulate their performance.

Pseudospin-layer coupled edge states in an acoustic topological insulator

The acoustic pseudospin edge states characterized by backscattering immunity and unidirectional transport provide a basis for designing devices with unconventional functions. In this Letter, we report pseudospin-layer coupled acoustic topological edge states realized by two layers of coupled honeycomb sonic crystals. With the additional layer degree of freedom, we define two distinctly different topological invariants that collectively determine the direction of the acoustic vortex and the layer polarization. We achieve an interesting phase diagram and explore the edge states between different phases. Additionally, we extend the topological edge states to the heterostructure and experimentally verify its capability to focus acoustic waves and convert layer polarization. Our work may provide a feasible platform for the manipulation of acoustic waves and could have promising applications in various areas, such as acoustic signal transmission and splitting.

Generation of acoustic vortices and acousto-optic interactions with acoustic vortex beams.

We demonstrate the generation of acoustic vortex beams with the aid of an acoustic spiral phase plate and an acoustic grating having a fork-like bifurcation of its slits. The acoustic vortex beam generated in this manner influences the particles floating on a water surface and rotates them. Our experiments show that the intensity of the acoustic vortex beam increases from zero in its center to a certain maximal value near the shell of the beam. The phase of the beam changes by the angle 2π whenever the azimuthal angle is changed by the same value. We also study acousto-optic diffraction of the optical beam by the acoustic beam bearing a vortex and demonstrate that each of the appropriate diffraction maxima are split into two maxima. The latter correspond to diffraction by the elementary acoustic rays which are close to the opposite edges of the acoustic vortex beam. A dark region between the maxima appears due to destructive interference of the elementary optical rays originated from the diffraction by the opposite sides of the acoustic vortex beam, which are phase-shifted by π.

Broadband achromatic acoustic vortex generator based on integrated-resonant meta-atoms

Acoustic vortex generator based on metamaterials is of great importance in acoustic communication, particle manipulation, and other applications. However, most of these applications are limited by narrow bandwidth due to strong dispersion. In this work, we numerically and experimentally present a broadband achromatic acoustic vortex generator (BAAVG) based on integrated-resonant meta-atoms (IRMs). The proposed IRMs, composed of a straight channel with side-loaded resonators and a large cavity, demonstrate linear phase shifts with high transmission efficiency and guarantee the existence of broadband vortex resulting from constant phase difference between adjacent IRMs. Based on the proposed BAAVG, conversion from plane wave to high purity vortex (with average purity 0.9) is demonstrated from 2187 to 2787 Hz. Good agreement between numerical and experimental results verifies the effectiveness of the proposed BAAVG. The high vortex purity of BAAVG exhibits broadband conversion properties quantitatively compared with traditional acoustic vortex generator. Our study provides an avenue to construct broadband achromatic acoustic vortex generators, which advances the capability of designing broadband acoustic vortex beams for versatile applications.

Sound Waveguiding by Spinning: An Avenue toward Unidirectional Acoustic Spinning Fibers

Although optical fiber has revolutionized modern life, creating a corresponding fiber as a waveguide for airborne sound has proven difficult, due to the scarcity of high-index acoustic materials. In this study the authors utilize spinning of the air inside a metamaterial tube to create an acoustic fiber. Their simulations demonstrate nonreciprocal propagation resulting from the acoustic equivalent of the Zeeman effect, which leads to robust waveguiding in the proposed fiber. This contribution may open avenues for studying the physics of acoustic vortex beams and nonreciprocal phenomena.

Tunable Broadband Acoustic Vortex Generator with Multiple Orders Based on Mie Resonances Structure

AbstractAcoustic vortices are intensely researched in metasurfaces for their potential application in acoustic communication and particle manipulation. By elaborately designing acoustic metasurfaces with phase profiles, an acoustic vortex is obtained. However, most existing studies are limited to the single working frequency and the specific topological charge. To address these limitations, a tunable broadband acoustic vortex generator is designed to generate acoustic vortices with multiple orders. For this purpose, an annulus subwavelength Mie resonator is theoretically proposed first. In the Mie resonator, the multipole mode is excited by coupling eccentric monopole sources at related resonance frequencies. Then coupling the Mie resonance structure and two eccentric monopole sources can realize the multipole crossing, thus generating acoustic vortices with topological charge m of ±1, ±2, ±3, ±4, and ±5. Numerical simulations and an experiment further confirm the theory. In addition, frequency tunability, broadband characteristics, and system robustness are quantitatively studied. The designed vortex generator performs well on these characteristics, which may have potential applications in acoustic communication for multiplexing and demultiplexing.

Helical particle manipulation based on power-exponent-phase acoustic vortices generated by a sector transducer array

The characteristics of traditional acoustic vortices (AVs) were verified by the cross-sectional axisymmetric pressure distributions with perfect phase spirals around the center pressure null. In order to generate a non-axisymmetric pressure distribution, the concept of power-exponent-phase was first introduced into the formation of AV beams, named “power-exponent-phase acoustic vortices (PAVs)” in this paper. Based on a ring-array of sector transducers, the helical distribution of the low-pressure valley in cross-sections of PAVs, which enables particles to move from a distant position to the center low-potential well along a certain spiral passageway, was proved theoretically. The particle manipulation behavior for PAVs with a power order of 2 is numerically modeled and experimentally confirmed. The results show that PAVs with a non-axisymmetric spiral pressure distribution can be used to realize the directional transport of particles in an enlarged scope, suggesting prospective application potential in biomedical engineering.