Multi-particle trapping and manipulation by a high-frequency array transducer

Red blood cell trapping using single-beam acoustic tweezers in the Rayleigh regime

Acoustic tweezers (ATs) are a promising technology that can trap and manipulate microparticles or cells with the focused ultrasound beam without physical contact. Unlike optical tweezers, ATs may be used for in vivo studies because they can manipulate cells through tissues. However, in previous non-invasive microparticle trapping studies, ATs could only trap spherical particles, such as beads. Here, we present a theoretical analysis of how the acoustic beam traps red blood cells (RBCs) with experimental demonstration. The proposed modeling shows that the trapping of a non-spherical, biconcave-shaped RBC could be successfully done by single-beam acoustic tweezers (SBATs). We demonstrate this by trapping RBCs using SBATs in the Rayleigh regime, where the cell size is smaller than the wavelength of the beam. Suggested SBAT is a promising tool for cell transportation and sorting.

An analytical study of spatial resolution enhancement for a dual-frequency acoustic beamformer

In this paper, we address an acoustic directed-self-assembly (DSA) problem for aiming to pattern particles based on creating an appropriate acoustic field by the fine adjustment of transducer operating parameters. The proposed idea is to incorporate the DSA problem with multi-frequency beamforming techniques. First, the boundary element method (BEM) is implemented for the direct modeling of the proposed DSA problem. Then, it is integrated with the concept of dual-frequency beamforming. In this study, the influence of changing excitation frequency is investigated on the spatial resolution enhancement of the pressure field. Also, the optimal frequency difference is calculated theoretically to produce two adjacent pressure traps with maximum separability and, therefore, maximum spatial resolution in a two-frequency acoustic beamformer without any restriction on the chamber shape. The performance of the proposed Dual-Frequency Beamforming (DFB) method is evaluated by simulations based on the finite element method (FEM) and compared with conventional Delay-And-Sum (DAS), Eigen Vector-Based (EigVec-based), and Bessel Beam techniques. Several evaluation metrics such as Full Width at Half Maximum (FWHM), Peak Side-lobe Level (PSL), Contrast Ratio (CR), Positioning Accuracy (PA), and processing time are considered for comparisons. Simulation results indicate the superiority of the proposed DFB method over the mentioned methods in separability and focusing precision when the two pressure traps are close to each other.

Electrolyte Solvation Structure Design for Sodium Ion Batteries

Sodium ion batteries (SIBs) are considered the most promising battery technology in the post-lithium era due to the abundant sodium reserves. In the past two decades, exploring new electrolytes for SIBs has generally relied on the "solid electrolyte interphase (SEI)" theory to optimize the electrolyte components. However, many observed phenomena cannot be fully explained by the SEI theory. Therefore, electrolyte solvation structure and electrode-electrolyte interface behavior have recently received tremendous research interest to explain the improved performance. Considering there is currently no review paper focusing on the solvation structure of electrolytes in SIBs, a systematic survey on SIBs is provided, in which the specific solvation structure design guidelines and their consequent impact on the electrochemical performance are elucidated. The key driving force of solvation structure formation, and the recent advances in adjusting SIB solvation structures are discussed in detail. It is believed that this review can provide new insights into the electrolyte optimization strategies of high-performance SIBs and even other emerging battery systems.

Tailoring Ince-Gaussian arrays based on a computer-generated hologram

The continually expanding interest in Ince-Gaussian modes has arisen due to their highly complex and widely varying spatial structures, which allow these fascinating diverse light modes to be significant to various topics. In this paper, we propose a technique for generating beam arrays that contain four Ince-Gaussian modes. By utilizing a single digital hologram, the intensity distributions of each mode in the array can be manipulated independently and flexibly. This work provides a feasible method to realize the controllable multiplexing of Ince-Gaussian modes, which has potential application in numerous important areas.

Acoustic trapping of particles using a Chinese taiji lens

Focused acoustic vortex (FAV) beams can trap particles in a contactless and non-destructive way and the method has thereby attracted much attention. In contrast to the traditional complex and expensive transducer array, we propose a fast and cheap method to generate FAV beams in water using an ultrasonic holographic lens engraved with the Chinese taiji pattern. This method can obtain high transmission efficiency, and hence the strong trapping force makes the particles trapped stably in a straight line. The formation of the FAV beams derives from a superposition of the spiral phase of a Laguerre Gaussian beam and the focusing phase. Because of the phase singularity of this beam, the intensity of the ultrasonic field on the beam axis is zero, thereby forming a strong gradient surround the beam axis. The trapping and manipulation of polystyrene particles with a radius of 150 μm is realized in the gradient field of the FAV beam. The proposed single beam acoustic trapping method does not depend on the reflector, making it more suitable for the manipulation of cells in vivo.

Inter-Particle Effects with a Large Population in Acoustofluidics

The ultrasonic manipulation of cells and bioparticles in a large population is a maturing technology. There is an unmet demand for improved theoretical understanding of the particle–particle interactions at a high concentration. In this study, a semi-analytical method combining the Jacobi–Anger expansion and two-dimensional finite element solution of the scattering problem is proposed to calculate the acoustic radiation forces acting on massive compressible particles. Acoustic interactions on arrangements of up to several tens of particles are investigated. The particle radius ranges from the Rayleigh scattering limit (ka«1) to the Mie scattering region (ka≈1). The results show that the oscillatory spatial distribution of the secondary radiation force is related to the relative size of co-existing particles, not the absolute value (for particles with the same radius). In addition, the acoustic interaction is non-transmissible for a group of identical particles. For a large number of equidistant particles arranged along a line, the critical separation distance for the attraction force decreases as the number of particles increases, but eventually plateaus (for 16 particles). The range of attraction for the formed cluster is stabilized when the number of aggregated particles reaches a certain value.

A new strategy to capture single biological micro particles at the interface between a water film and substrate by ultrasonic tweezers

Controlled capture of single biological micro particles, with effective capture function, little heat damage to and good stability of captured samples simultaneously, has been a technological challenge in the area of micro manipulation. This paper presents an ultrasonic tweezers based new strategy to meet the challenge. In the strategy, being different from the other ultrasonic methods, the MMP (micro manipulating probe), which vibrates elliptically, is in contact with the substrate. Single yeast cells with a diameter of 3-7 μm and Chlorella vulgaris powders with a diameter of 2-10 μm near the MMP can be sucked onto the MMP's tip. The captured particle can be transferred to a desired location at the interface between the water film and substrate by moving the ultrasonic tweezers. The temperature rise in the capture region is less than 0.1 °C, and the sucking distance can be up to 20 μm. The captured particle is in contact with the MMP's tip, which results in a good stability of the captured particle. The experiments also show that it is possible to use multiple MMPs to individually capture single cells. The finite element analyses indicate that acoustic radiation force generated by the ultrasonic field around the MMP is responsible for the capture. Moreover, the effects of the orthogonal vibration components, tilt angle and length of the MMP on the capture capability are clarified.

A One-Sided Acoustic Trap for Cell Immobilization Using 30-MHz Array Transducer

Biological studies often involve the investigation of immobilized (or trapped) particles and cells. Various trapping methods without touching, such as optical, magnetic, and acoustic tweezers, have been developed to trap small particles. Here, we present the manipulation of a single cell or multiple cells using ultrasound-array-based single-beam acoustic tweezers (UA-SBATs). In SBATs, only a one-sided tightly focused acoustic beam produces a high acoustic gradient force-a mechanism that mirrors that of optical tweezers. As a result, targeted cells can be attracted to the beam center and immobilized within its trapping zone. Since an array transducer allows acoustic beam steering and scanning electronically instead of mechanical translation, it can manipulate cells more simply and quickly compared with single-element transducers, especially in biocompatible setup. In this experiment, a customized 30-MHz array transducer with an interdigitally bonded (IB) 2-2 piezocomposite was employed to immobilize MCF-12F cells. Cells were attracted to the center of the beam and laterally displaced with the array transducer without any damages to the cells. These findings suggest that UA-SBAT can be a promising tool for cell manipulation and may pave the way for exploring new biological applications.

Generating Bessel beams with broad depth-of-field by using phase-only acoustic holograms

We report zero-th and high-order acoustic Bessel beams with broad depth-of-field generated using acoustic holograms. While the transverse field distribution of Bessel beams generated using traditional passive methods is correctly described by a Bessel function, these methods present a common drawback: the axial distribution of the field is not constant, as required for ideal Bessel beams. In this work, we experimentally, numerically and theoretically report acoustic truncated Bessel beams of flat-intensity along their axis in the ultrasound regime using phase-only holograms. In particular, the beams present a uniform field distribution showing an elongated focal length of about 40 wavelengths, while the transverse width of the beam remains smaller than 0.7 wavelengths. The proposed acoustic holograms were compared with 3D-printed fraxicons, a blazed version of axicons. The performance of both phase-only holograms and fraxicons is studied and we found that both lenses produce Bessel beams in a wide range of frequencies. In addition, high-order Bessel beam were generated. We report first order Bessel beams that show a clear phase dislocation along their axis and a vortex with single topological charge. The proposed method may have potential applications in ultrasonic imaging, biomedical ultrasound and particle manipulation applications using passive lenses.

Thin Film PZT-Based PMUT Arrays for Deterministic Particle Manipulation

Lead zirconate titanate (PZT)-based piezoelectric micromachined ultrasonic transducers (PMUTs) for particle manipulation applications were designed, fabricated, characterized, and tested. The PMUTs had a diaphragm diameter of 60 [Formula: see text], a resonant frequency of ~8 MHz, and an operational bandwidth (BW) of 62.5%. Acoustic pressure output in water was 9.5 kPa at 7.5 mm distance from a PMUT element excited with a unipolar waveform at 5 V_pp . The element consisted of 20 diaphragms connected electrically in parallel. Particle trapping of 4 [Formula: see text] silica beads was shown to be possible with 5 V_pp unipolar excitation. Trapping of multiple beads by a single element and deterministic control of particles via acoustophoresis without the assistance of microfluidic flow were demonstrated. It was found that the particles move toward diaphragm areas of highest pressure, in agreement with literature and simulations. Unique bead patterns were generated at different driving frequencies and were formed at frequencies up to 60 MHz, much higher than the operational BW. Levitation planes were generated above the 30 MHz driving frequency.

Dual-Phase Transmit Focusing for Multiangle Compound Shear-Wave Elasticity Imaging

Shear-wave elasticity imaging (SWEI) enables the quantitative assessment of the mechanical properties of tissue. In SWEI, the effective generation of acoustic radiation force is of paramount importance. Consequently, several research groups have investigated various transmit beamforming and pulse-sequencing methods. To further improve the efficiency of the shear-wave generation, and therefore, to increase the quality of SWEI, we introduce a technique referred to as "multiangle compound SWEI" (MAC-SWEI), which uses simultaneous multiangular push beams created by dual-phase transmit focusing. By applying a constant phase offset on every other element of an array transducer, dual-phase transmit focusing creates both main and grating lobes (i.e., multiangular push beams for pushing) to simultaneously generate shear waves with several wavefront angles. The shear waves propagating at different angles are separated by multidirectional filtering in the frequency domain, leading to the reconstruction of multiple spatially co-registered shear-wave velocity maps. To form a single-elasticity image, these maps are combined, while regions associated with known artifacts created by the push beams are omitted. Overall, we developed and tested the MAC-SWEI method using Field II quantitative simulations and the experiments performed using a programmable ultrasound imaging system. Our results suggest that MAC-SWEI with dual-phase transmit focusing may improve the quality of elasticity maps.

Formation of high-order acoustic Bessel beams by spiral diffraction gratings

The formation of high-order Bessel beams by a passive acoustic device consisting of an Archimedes' spiral diffraction grating is theoretically, numerically, and experimentally reported in this paper. These beams are propagation-invariant solutions of the Helmholtz equation and are characterized by an azimuthal variation of the phase along its annular spectrum producing an acoustic vortex in the near field. In our system, the scattering of plane acoustic waves by the spiral grating leads to the formation of the acoustic vortex with zero pressure on axis and the angular phase dislocations characterized by the spiral geometry. The order of the generated Bessel beam and, as a consequence, the size of the generated vortex can be fixed by the number of arms in the spiral diffraction grating. The obtained results allow for obtaining Bessel beams with controllable vorticity by a passive device, which has potential applications in low-cost acoustic tweezers and acoustic radiation force devices.

Acoustic Interaction Forces and Torques Acting on Suspended Spheres in an Ideal Fluid

In this paper, the acoustic interaction forces and torques exerted by an arbitrary time-harmonic wave on a set of N objects suspended in an inviscid fluid are theoretically analyzed. We utilize the partial-wave expansion method with translational addition theorem and re-expansion of multipole series to solve the related multiple scattering problem. We show that the acoustic interaction force and torque can be obtained using the farfield radiation force and torque formulas. To exemplify the method, we calculate the interaction forces exerted by an external traveling and standing plane wave on an arrangement of two and three olive-oil droplets in water. The droplets' radii are comparable to the wavelength (i.e., Mie scattering regime). The results show that the acoustic interaction forces present an oscillatory spatial distribution which follows the pattern formed by interference between the external and rescattered waves. In addition, acoustic interaction torques arise on the absorbing droplets whenever a nonsymmetric wavefront is formed by the external and rescattered waves' interference.