Acoustic Vortex Research Articles

Transfer of Orbital Angular Momentum to Freely Levitated High-Density Objects in Airborne Acoustic Vortices

Vortex-field acoustic levitation is an application of acoustic vortices that allows the manipulation of a wide range of materials in various media. However, to date, its levitation capability in air is limited to relatively low-density objects. Here, by optimizing an array-tube setup, we levitate iridium ($22.56\phantom{\rule{0.2em}{0ex}}\mathrm{g}/{\mathrm{cm}}^{3}$) in a first-order acoustic vortex in air. This technique makes it possible to observe the orbital angular momentum transfer carried by acoustic vortices to freely levitated high-density objects, of which the highest rotation speed reaches up to 6500 revolutions per second and increases with a decrease in the object size and an increase in the source amplitude. It is revealed that the thermal-viscous boundary layer dissipation is the dominant effect and leads directly to the rapid rotation of high-density objects. This work can expand the application scope of acoustic vortices, especially in the fields of containerless processing of various materials and rapid rotation of objects, and help to understand the mechanisms of orbital angular momentum transfer to matter.

Focused Acoustic Vortex-Regulated Composite Nanodroplets Combined with Checkpoint Blockade for High-Performance Tumor Synergistic Therapy.

The combination of checkpoint blockade with focused ultrasound (FUS) physical therapy can enhance antitumor immune response by improving the precision and efficiency of immunotherapy. However, one of the major disadvantages of conventional FUS treatment is the small lesion size, which prolongs treatment duration. We constructed a focused acoustic vortex (FAV) system with a hollow cylindrical focal region, which exhibited a larger focal region compared to conventional FUS of the same frequency. We developed an all-in-one synergistic therapy against metastatic breast cancer based on integrated FAV double combination sequence-regulated phase-transformation nanodroplets (CPDA@PFH) with checkpoint blockade immunotherapy. A single treatment with FAV + CPDA@PFH resulted in 2.25-fold higher inhibition of tumor growth compared to that with FUS + CPDA@PFH. In addition, FAV-regulated CPDA@PFH combined with ICB induced a systemic immune response that not only inhibited the growth of primary (98.41% inhibition rate) and distal (80.71%) 4T1 tumors but also reduced the progression of lung metastasis. In addition, the synergistic therapy achieved long-term immune memory that effectively prevented tumor growth and improved the survival time of mice. The long-term survival rate of 4T1 tumor-bearing mice treated with FAV + CPDA@PFH + Anti-PD-L1 was 57.14% on day 60 after treatment. Our study is a proof-of-concept of cascade-amplified synergistic tumor therapeutics based on ultrasonic-hyperthermia, cavitation, sonodynamic therapy (SDT), and checkpoint blockade immunotherapy through FAV-regulated CPDA@PFH phase-transformation nanodroplets.

Enhanced Detection in Droplet Microfluidics by Acoustic Vortex Modulation of Particle Rings and Particle Clusters via Asymmetric Propagation of Surface Acoustic Waves.

As a basis for biometric and chemical analysis, issues of how to dilute or concentrate substances such as particles or cells to specific concentrations have long been of interest to researchers. In this study, travelling surface acoustic wave (TSAW)-based devices with three frequencies (99.1, 48.8, 20.4 MHz) have been used to capture the suspended Polystyrene (PS) microspheres of various sizes (5, 20, 40 μm) in sessile droplets, which are controlled by acoustic field-induced fluid vortex (acoustic vortex) and aggregate into clusters or rings with particles. These phenomena can be explained by the interaction of three forces, which are drag force caused by ASF, ARF caused by Leaky-SAW and varying centrifugal force. Eventually, a novel approach of free transition between the particle ring and cluster was approached via modulating the acoustic amplitude of TSAW. By this method, multilayer particles agglomerate with 20 μm wrapped around 40 μm and 20 μm wrapped around 5 μm can be obtained, which provides the possibility to dilute or concentrate the particles to a specific concentration.

Manipulation of acoustic vortex with topological dislocation states

Higher-order topological insulators as an exotic type of topological phases harboring fascinating topological corner or hinge states have attracted extensive attention recently. Dislocations are crystallinity-breaking defects in lattices that cannot be removed by local deformations due to nontrivial real-space topology. It is recently realized that dislocations can be used as a probe for higher-order topology. In this work, we propose a scheme to obtain acoustic dislocation states by introducing screw dislocations into higher-order topological insulators in a Kagome lattice. The topological dislocation states carry nonzero orbital angular momentum, which are locked to their propagation direction. We show that the screw dislocation states exist for both the tight binding model and the waveguide model as long as the system symmetry is preserved. By delicately designing the dislocation core, the dislocation states with selective angular momentum can be shifted into the bulk bandgap. Based on this in-gap dislocation states, filtering of acoustic vortex with a selective angular momentum is well achieved.

Acoustofluidic Stimulation of Functional Immune Cells in a Microreactor (Adv. Sci. 16/2022)

Acoustofluidic Stimulation of Functional Immune Cells In article number 2105809, Jinsoo Park, Hyung Jin Sung, Jessie S. Jeon, and co-workers employ surface acoustic waves to agitate fluid in a microreactor capable of dynamic cell culture in a controllable and contact-free manner. This microreactor prevents cellular damages that can be seen in the acoustic vortex by adjusting the duty cycle and applied power of the acoustical actuation. Using the microreactor, the functional changes of natural killer cells are observed upon the acoustical stimulation, namely, Ca2+ influx to the cells and their enhanced cell-mediated cytotoxicity to the tumor cells in the copresence of protein kinase C activator.

Beam alignments based on the spectrum decomposition of orbital angular momentums for acoustic-vortex communications

Given the enhanced channel capacity of wave chirality, acoustic communications based on the orbital angular momentum (OAM) of acoustic-vortex (AV) beams are of significant interest for underwater data transmissions. However, the stringent beam alignment is required for the coaxial arrangement of transceiver arrays to ensure the accuracy and reliability of OAM decoding. To avoid the required multiple measurements of the traditional orthogonality based algorithm, the beam alignment algorithm based on the OAM spectrum decomposition is proposed for AV communications by using simplified ring-arrays. Numerical studies of the single-OAM and OAM-multiplexed AV beams show that the error of the OAM spectrum increases with the translation distance and the deflection angle of the transceiver arrays. To achieve an ideal arrangement, two methods of the single-array translation alignment and the dual-array deflection alignment are developed based on the least standard deviation of the OAM spectrum (SD-OAM). By decreasing the SD-OAM towards zero using transceiver arrays of 16 transmitters and 16 receivers, accurate beam alignments are accomplished by multiple adjustments in three dimensions. The proposed method is also demonstrated by experimental measurements of the OAM dispersion and the SD-OAM for misaligned beams. The results demonstrate the feasibility of the rapid beam alignment based on the OAM spectrum decomposition by using simplified transceiver ring-arrays, and suggest more application potentials for acoustic communications.

Chirality-switchable acoustic vortex emission via non-Hermitian selective excitation at an exceptional point

Artificial structures provide an efficient method to generate acoustic vortices carrying orbital angular momentum (OAM) essential for applications ranging from object manipulation to acoustic communication. However, their flexibility in terms of chirality control has thus far been limited by the lack of reconfigurability and degrees of freedom like spin–orbit coupling. Here we show that this restriction can be lifted by controlling the individual on–off states of two coherent monopolar sources inside a passive parity-time-symmetric ring cavity at an exceptional point where the counter-propagating waves coalesce into one chiral eigenmode. One of the sources satisfies the chirality-reversal condition, generating a travelling wave field fully decoupled from and opposite to the chiral eigenmode, while the other source is phase-shifted such that the wave generated by the first source can be canceled out, and the remaining sound field circulates in the same direction as the chiral eigenmode. Such non-Hermitian selective excitation enables our experimental realization of acoustic vortex emission with switchable OAM but free of system reconfiguration. Our work offers opportunities for chiral sound manipulation as well as integrated and tunable acoustic OAM devices.

Generation and steering of airborne acoustic vortices with broadband electro-active spiral gratings

Acoustic beam shaping technology has flourished in the last decade, motivated by its important applications. For example, in the context of contactless manipulation, the use of structured ultrasonic fields has led to significant advances, such as the development of the acoustic tweezers based on the use of ultrasonic vortex beams. In this work, we present a powerful and efficient technique to structure acoustic fields based on the use of planar electro-active diffraction gratings, which can be tailored in practically arbitrary shapes. For this purpose, a lower electrode with the desired shape is printed on a circuit board and covered with an active ferroelectret film, whose metallized top surface acts as a continuous upper electrode. Importantly, these devices can be operated within a broad spectral range of ultrasonic frequencies. Two kinds of structured fields are demonstrated: a focused acoustic vortex and the simultaneous generation of multiple acoustic Bessel beams of different topological charges, well separated among each other along the propagation axis. In both cases, the main parameters of the field can be finely and continuously tuned by setting the operation frequency, which allows an axial steering of the vortices. Experimental results exhibit very good agreement with theoretical analysis and numerical simulations.

Implementation of an ultrasonic fluid manipulation experiment on the International Space Station

The International Space Station (ISS) provides a unique opportunity to investigate acoustic radiation force interactions with a minimal interference from gravity. There are many design considerations to make when creating an experiment that is suited for use on board the ISS. NASA’s primary concerns with all experiments implemented in the ISS are with the safety of the crew and the success of the mission. Acoustic experiments are surprisingly rare on the ISS and present additional unique design challenges. This is especially true for experiments operated under water. Our work implements a high-intensity acoustic vortex beam under water for single droplet tractoring and capture operated inside the Microgravity Science Glovebox (MSG) on the ISS. The experiment payload consists of a signal generator, an amplifier module, and a sealed water chamber. A secondary fluid immiscible with water is injected into the chamber for acoustic manipulation, and the results of the experiment are recorded as high-definition video.

Acoustic vortex beam reflection, refraction, and orbital Hall effect

Some of our recent work concerned the interactions of twisted wave fronts of acoustic vortex beams with boundaries and inhomogeneities of media. Experimental measurements and numerical simulations were conducted to investigate vortex beam reflection from a water-air interface and vortex beam refraction when travelling in an inhomogeneous medium or through an acoustic metasurface. The results reveal spatial evolution of the wave fields and the carried angular momenta. In particular, the investigation observed a reversal of orbital angular momentum in the reflected wave field [Zou et al., Phys. Rev. Lett. 125(7), 074301 (2020)], and a shift of beam center and an asymmetric vortex pattern in the refracted wave field in the direction transverse to the plane of incidence [Fan et al., Phys. Rev. Res. 1(3), 032014 (2019); 3(1), 013251 (2021)]. The shift relates to conservation of angular momenta and coupling of the twisted wave fronts with the refraction and is termed as acoustic orbital Hall effect.

Coupled Focused Acoustic Vortices Generated by Degenerated Artificial Plates for Acoustic Coded Communication

AbstractAcoustic vortices (AVs) show great significance in acoustic communication. However, the lack of confidentiality and the cross‐talks in communications based on traditional AVs remain problems. Here, a degenerated centrosymmetric circular hole plate (DCHP) is designed to generate coupled focused acoustic vortices (CFAVs) with pure orbital angular momentums (OAMs) in both air and water. When an acoustic plane wave transmits through DCHP, two focused acoustic vortices (FAVs) with opposite topological charges are produced simultaneously, and the coupling between them results in a focused acoustic petal beam (FAPB). The OAM of the CFAV can be simply modulated by the angular interval of the adjacent holes on DCHP and the CFAV can be focused at any distances by adjusting the positions of holes. The DCHPs are demonstrated to be able to generate FAPBs numerically and experimentally. Furthermore, 8 FAPBs with different OAMs are set as 8 bases to represent 8 bits of ASCII binary code, and the information encoding and decoding for acoustic communication are realized in water using them. The proposed DCHP provides a convenient method to achieve CFAVs, which may be helpful to enhance the security, reduce the false information, and increase the information capacity in acoustic communication.

Asymmetric Generation of Acoustic Vortex Using Dual-Layer Metasurfaces.

In this Letter, we introduce a new paradigm for achieving robust asymmetric generation of acoustic vortex field through dual-layer metasurfaces by controlling their intrinsic topologic charges and the parity of geometry design. The underlying physics is contributed to the one-way process of orbital angular momentum (OAM) transition ensured by the broken spatial symmetry and the external topologic charge from the vortex diffraction. We further experimentally demonstrate this novel phenomenon. Our findings could provide new routes to manipulate the asymmetric response of vortex fields, including one-way excitation and propagation, and promise potential applications in passive OAM-based diodes.

Acoustic helical dichroism in a one-dimensional lattice of chiral resonators

Circular dichroism and helical dichroism are intriguing chiroptical phenomena with broad applications in optical sensing and imaging. Here, we generalize one of the phenomena-helical dichroism-to acoustics. We show that a one-dimensional lattice of chiral resonators with loss can induce differential absorption of helical sounds (i.e., acoustic vortices) carrying opposite orbital angular momentum (OAM). This acoustic helical dichroism strongly depends on the rotation symmetry of the chiral resonators. Breaking the ${C}_{4}$ rotation symmetry can induce coupling between the opposite chiral dipole modes of the resonators. This leads to OAM band gaps and non-Hermitian exceptional points near the Brillouin-zone center and boundaries, which together give rise to significantly enhanced helical dichroism. The underlying physics can be well captured by an effective Hamiltonian that quantitatively reproduces the complex band structures. The acoustic helical dichroism can find important applications in acoustic OAM manipulations and chiral sound-matter interactions.

Quasi-Bessel Acoustic-Vortex Beams Constructed by the Line-Focused Phase Modulation for a Ring Array of Sectorial Planar Transducers.

Acoustic Bessel beams are commonly used as ideal sources to study the characteristics for acoustic-vortex (AV) beams, exhibiting prosperous perspectives in contactless object manipulations and acoustic communications. However, accurate Bessel beams are difficult to construct using 2-D arrays in practical applications. By integrating active phase control and passive phase modulation to a ring array of sectorial planar transducers, quasi-Bessel AV (QB-AV) beams of arbitrary order are built by the line focus of AV fields in the current study. Based on Snell's refraction law, a circular sawtooth lens of phase modulation is designed to converge incident waves toward the beam axis at the same deflection angle. QB-AV beams constructed by the main lobes of the sectorial sources are demonstrated by theoretical derivations, numerical simulations, and quality evaluations, while those created by the sidelobes are neglected to avoid the pressure fluctuations in the near field. Experimental measurements for AV beams of different orders coincide basically with the simulations, demonstrating that line-focused QB-AV beams can be generated along the beam axis across the pressure peak. With the increase of the topological charge, the peak pressure of the beam decreases accordingly with a reduced effective axial range. The favorable results prove that, as a special kind of diffraction sources, the adjustable QB-AV beams may enable more important biomedical applications where Bessel beams are necessary, especially for the line-focused manipulation of biological and drug particles.

A simple acoustofluidic device for on-chip fabrication of PLGA nanoparticles.

Miniaturization of systems and processes provides numerous benefits in terms of cost, reproducibility, precision, minimized consumption of chemical reagents, and prevention of contamination. The field of microfluidics successfully finds a place in a plethora of applications, including on-chip nanoparticle synthesis. Compared with the bulk approaches, on-chip methods that are enabled by microfluidic devices offer better control of size and uniformity of fabricated nanoparticles. However, these microfluidic devices generally require complex and expensive fabrication facilities that are not readily available in low-resourced laboratories. Here, a low-cost and simple acoustic device is demonstrated by generating acoustic streaming flows inside glass capillaries through exciting different flexural modes. At distinct frequencies, the flexural modes of the capillary result in different oscillation profiles that can insert harmonic forcing into the fluid. We explored these flexural modes and identified the modes that can generate strong acoustic streaming vortices along the glass capillary. Then, we applied these modes for fluid mixing using an easy-to-fabricate acoustofluidic device architecture. This device is applied in the fabrication of poly(d,l-lactide-co-glycolide) (PLGA) nanoparticles. The acoustic device consists of a thin glass capillary and two polydimethylsiloxane adaptors that are formed using three-dimensional printed molds. By controlling the flow rates of the polymer and water solutions, PLGA nanoparticles with diameters between 65 and 96 nm are achieved with polydispersity index values ranging between 0.08 and 0.18. Owing to its simple design and minimal fabrication requirements, the proposed acoustofluidic mixer can be applied for microfluidic fluid mixing applications in limited resource settings.

Vortex shedding from In-line tube banks on acoustic resonance

In the present paper the attention is focused on relation between acoustic resonance and vortex shedding from in-line tube banks. We have examined the characteristics of acoustic resonance generated from tube banks with tube pitch ratio of 4.0-1.4 in the flow direction. At the tube pitch ratio in the flow direction of 4.0-2.8, the acoustic resonance of low order mode in the transverse direction occurred. The resonance Strouhal number agreed well with the vortex shedding Strouhal number. At the tube pitch ratio in the flow direction of 2.0-1.4, the resonance Strouhal number did not agree with the vortex shedding Strouhal number. The acoustic resonance occurred at the lower frequencies of vortex shedding frequency. As the number of rows of tubes increased, the acoustic resonance of transverse mode occurred. We discussed the prediction formula of Strouhal number at the tube pitch ratio in the flow direction of 2.0-1.4.

Generation of acoustic and optical vortices in the course of mechanical bending and collinear acousto-optic diffraction

Generation of acoustic and optical vortices in the course of mechanical bending and collinear acousto-optic diffraction

Generation of acoustic vortices in crystals by conical electric field: a collinear acousto-optic diffraction

Generation of acoustic vortices in crystals by conical electric field: a collinear acousto-optic diffraction

3-D Ultrafast Ultrasound Imaging of Microbubbles Trapped Using an Acoustic Vortex.

Increasing the local concentration of microbubbles (MBs) within the blood flow plays a crucial role in several medical applications, but there are few imaging modalities available for volumetric tracking of the aggregated MBs in real time. Here we describe a device integrating acoustic vortex tweezers (AVTs) and ultrasound plane-wave imaging (PWI) to achieve the goal of controlling the spatial distribution of MBs in blood vessels and simultaneously monitoring this process using the same probe. Experiments were conducted using a 5-MHz 2-D array ultrasound probe (with three cycles of excitation at an acoustic pressure of 2000 kPa) and 1.2- [Formula: see text]-diameter MBs at a flow rate of 20 mm/s. The AVT waveform was produced by modulating the repetition frequency of the transmitted pulse asymmetrically (4 and 8 kHz at the inflow and outflow ends, respectively). In order to simultaneously capture MBs and carry out imaging with the same probe, the asymmetric AVT pulse signal and the ultrasound-imaging pulse signal were arranged in a staggered series, and the imaging was carried out using plane-wave pulses at nine angles (-7° to 7°) in compounded PWI (volume rate: 200 Hz). Microscopy observations showed that freely suspended MBs could indeed be gathered by the asymmetric AVT in the flow field to form an MBs cluster with a spot size of about [Formula: see text], which could resist the flow to remain at a fixed location for about 22 s. After the asymmetric AVT signal and the ultrasound-imaging pulse signal were turned on for 1 s, the ultrasound 3-D image showed that the signal intensity of the MB clusters increased by 13.1 dB ± 2.9 dB in relation to the background area. These results show that the proposed strategy can be used to accumulate flowing MBs at a desired location and to simultaneously observe this phenomenon. This tool could be used in the future to improve the outcomes of MB-related treatments for various diseases.

Compact acoustic monolayered metadecoder for efficient and flexible orbital angular momentum demultiplexing

Detecting the orders of an orbital angular momentum (OAM)-carrying beam is of fundamental interest and practical importance in wave physics. Yet accurate and fast demultiplexing of free-space OAM beams within physical space comparable to wavelength still remains challenging. Here, a passive monolayered metadecoder with compactness, high efficiency and flexibility is designed systematically and demonstrated experimentally for real-time demultiplexing of multiple OAM modes in free space. A simple yet effective mechanism of simultaneously untwisting and reshaping the synthesized vortex beams is presented to remarkably downsize the device and arbitrarily modulate the propagation path of output beam with amplified intensity and intact information, whose detection needs no sensor array or postprocessing. Consequently, the resulting device features the ultra-compact size, enhanced signal-to-noise ratio, high spectral and spatial selectivity, controllable detection locations, and furthermore, the compatibility to existing multiplexing methods. The effectiveness of proposed mechanism is demonstrated numerically and experimentally via parallel and real-time demultiplexing of a synthesized acoustic vortex using a planar metadecoder much more compact than existing devices in all three dimensions. The realization of metadecoder offers the possibility of high-capacity and miniaturized passive devices harnessing OAM and may promise important applications, including advances in high-speed underwater communication and optical on-chip signal process.