arXiv subjects

Glauber T. Silva

Publications and source records attributed to Glauber T. Silva.

At least 19 recordsLinked to original sources

arXiv2024

Scaterring of Massless Quasiparticles in the 3He-A Superfluid

In this work, we analyze the scattering of fermionic quasiparticles in the presence of radial disgyrations and symmetric vortices in the superfluid 3He-A. We consider a Volovik analog model for the description of these defects and investigate the scattering of fermionic quasiparticles in this background. Furthermore, we solve the massless Dirac equation employing this methodology to gain comprehensive insights into the scattering phenomena and its dependence on the geometric properties. These results validate the optical theorem and highlight the role of defect topology in the scattering process.

cond-mat.mes-hall↗

arXiv2024

Vortex Modes in Acoustofluidic Cylindrical Resonators

This paper presents a theoretical investigation of vortex modes in acoustofluidic cylindrical resonators with rigid boundaries and viscous fluids. By solving the Helmholtz equation for linear pressure, incorporating boundary conditions that account for no-slip surfaces and vortex and nonvortex excitation at the base, we analyze both single- and dual-eigenfunction modes near system resonance. The results demonstrate that single vortex modes generate spin angular momentum exclusively along the axial direction, while dual modes introduce a transverse spin component due to the nonlinear interaction between axial and transverse ultrasonic waves, even in the absence of vortex excitation. We find that nonlinear acoustic fields, including energy density, radiation force potential, and spin, scale with the square of the shear wave number, defined as the ratio of the cavity radius to the boundary layer depth. Theoretical predictions align closely with finite element simulations based on a thermoviscous model for an acoustofluidic cavity with adiabatic and rigid walls. These findings hold particular significance for acoustofluidic systems, offering potential applications in the precise control of cells and microparticles.

physics.flu-dyn↗

arXiv2023

Acoustic scattering-extinction cross section and the acoustic force of electrostatic type

The analysis of the secondary Bjerknes force between two bubbles suggests that this force is analogous to the electrostatic forces. The same analogy is suggested by the existence of a scattering cross section of an acoustic wave on a bubble. Our paper brings new arguments in support of this analogy. The study which we perform is dedicated to the acoustic force and to the scattering cross section at resonance in order to highlight their angular frequency independence of the inductor wave. Also, our study reveals that the angular frequency and the amplitude of the induction pressure wave are not related. Highlighting this analogy will allow us a better understanding of the electrostatic interaction if the electron is modeled as an oscillating bubble in the vacuum.

physics.gen-ph↗

arXiv2021

Mean-acoustic fields exerted on a subwavelength axisymmetric particle

The acoustic radiation force produced by ultrasonic waves is the "workhorse" of particle manipulation in acoustofluidics. Nonspherical particles are also subjected to a mean torque known as the acoustic radiation torque. Together they constitute the mean-acoustic fields exerted on the particle. Analytical methods alone cannot calculate these fields on arbitrarily shaped particles in actual fluids and no longer fit for purpose. Here, a semi-analytical approach is introduced for handling subwavelength axisymmetric particles immersed in an isotropic Newtonian fluid. The obtained mean-acoustic fields depend on the scattering coefficients that reflect the monopole and dipole modes. These coefficients are determined by numerically solving the scattering problem. Our method is benchmarked by comparison with the exact result for a subwavelength rigid sphere in water. Besides, a more realistic case of a red blood cell immersed in blood plasma under a standing ultrasonic wave is investigated with our methodology.

physics.flu-dyn↗

arXiv2020

Raman-acoustofluidic integrated system for single-cell analysis

Confocal Raman microscopy offers a particular pathway for monitoring chemical "fingerprints" of intracellular components like the cell membrane, organelles, and nucleus. Nevertheless, conventional Raman acquisitions of fixed or randomly dispersed cells on a substrate, such as a microscope slide, might be severely limited for biomedical investigations. Backscattered Raman signal is likely to be overshadowed by contributions from substrate fluorescence. Also, biological assays for drug discovery, infection, and tissue engineering may require monitoring live cells individually over a time interval spanning from a few hours to a few days. To meet the needs of cell assay monitoring, we propose an acoustofluidic device that forms a levitating cell aggregation (one layer) in a cylindrical chamber of 10 μL volume that operates at 1 MHz frequency. The integrated system comprises a lab-on-a-chip device and a confocal Raman microscope. In this setup, a cell can be selectively Raman-investigated with micrometre accuracy, without any substrate interference. Based on a set of carefully designed experiments, we demonstrate that polystyrene microparticles are assembled and held standstill, enabling a full Raman spectrum to be taken of a single particle in less than a minute. The signal-to-background ratio is improved by a thousandfold when compared with conventional Raman acquisition. The Raman-acoustofluidic system is showcased for obtaining the spectrum of a single cell among an enriched population of macrophages of mice. The obtained results confirm the method's robustness for applications in single-cell analysis.

physics.app-ph↗

arXiv2020

Acoustic radiation force and torque on spheroidal particles in an ideal cylindrical chamber

We theoretically investigate how the acoustic radiation force and torque arise on a small spheroidal particle immersed in a nonviscous fluid inside an ideal cylindrical chamber. The ideal chamber comprises a hard top and bottom (rigid boundary condition), and a soft or hard lateral wall. By assuming the particle is much smaller than the acoustic wavelength, we present analytical expressions of the radiation force and torque caused by an acoustic wave of arbitrary shape. Unlike previous results, these expressions are given relative to a fixed laboratory frame. Our model is showcased for analyzing the behavior of an elongated metallic microspheroid (with a 10 : 1 aspect ratio) in a half-wavelength acoustofluidic chamber with a few millimeters diameter. The results show the radiation torque aligns the microspheroid along the nodal plane, and the radiation force causes a translational motion with a speed of up to one body length per second. At last, we discuss the implications of this study to propelled nanorods by ultrasound.

physics.flu-dyn↗

arXiv2020

Nonlinear interaction of acoustic waves with a spheroidal particle: radiation force and torque effects

The nonlinear interaction of a time-harmonic acoustic wave with an anisotropic particle gives rise to the radiation force and torque effects. These phenomena are at the heart of the acoustofluidics technology, where microparticles such as cells and microorganisms are acoustically manipulated. We present a theoretical model considering a generic acoustic beam interacting with a subwavelength spheroidal particle in a nonviscous fluid. Concise analytical expressions of the radiation force and torque are obtained in the scattering dipole approximation. The radiation force is given in terms of a gradient and scattering force; while the radiation torque has two fundamental contributions, namely, the momentum arm and acoustic spin (spin-torque effect). As a practical example, we use the theory to describe the interaction of two crossed plane waves and a prolate spheroidal particle. The results reveal the particle is transversely trapped in a pressure node and is axially pushed by the radiation force. Also, the momentum arm aligns the particle in the axial direction. At certain specific positions, only the spin-torque occurs. Our findings are remarkably consistent with finite-element simulations. The success of our model enables its use as an investigation tool for the manipulation of anisotropic microparticles in acoustofluidics.

physics.app-ph↗

arXiv2020

Acoustic spin transfer to a subwavelength spheroidal particle

We demonstrate that the acoustic spin of a first-order Bessel beam can be transferred to a subwavelength (prolate) spheroidal particle at the beam axis in a viscous fluid. The induced radiation torque is proportional to the acoustic spin, which scales with the beam energy density. The analysis of the particle rotational dynamics in a Stokes' flow regime reveals that its angular velocity varies linearly with the acoustic spin. Asymptotic expressions of the radiation torque and angular velocity are obtained for a quasispherical and infinitely thin particle. Excellent agreement is found between the theoretical results of radiation torque and finite element simulations. The induced particle spin is predicted and analyzed using the typical parameter values of the acoustical vortex tweezer and levitation devices. We discuss how the beam energy density and fluid viscosity can be assessed by measuring the induced spin of the particle.

physics.class-ph↗

arXiv2020

Subwavelength beam focusing using a ball-shaped lens for ultrasound imaging

Ultrasonic superresolution images can be generated by means of (super) focusing acoustic beams to subwavelength dimensions or using algorithm-based methods. Here, we demonstrate that ultrasonic pulses which are superfocused by a ball-shaped lens can be used to produce superresolution images. The imaging system is comprised of a circular flat transducer with an operation frequency of $1$ MHz, and a ball lens centered in the beam axis of symmetry. The corresponding wavelength in water is $λ_0 = 1.53$ mm. The system resolution is $0.6λ_0$ in the focal plane at one wavelength away from the lens. The superresolution method is compared with a conventional ultrasonic system based on a spherically focused transducer. Our method presents twice more resolution with a shorter depth-of-field of $2λ_0$. Possible applications that take advantage of these features are discussed, as well as some limitations of the proposed technique.

physics.app-ph↗

arXiv2019

Acoustic radiation torque exerted on a subwavelength spheroidal particle by a traveling and standing plane wave

The nonlinear interaction of ultrasonic waves with a nonspherical particle may give rise to the acoustic radiation torque on the particle. This phenomenon is investigated here considering a rigid prolate spheroidal particle of subwavelength dimensions that is much smaller than the wavelength. Using the partial wave expansion in spheroidal coordinates, the radiation torque of a traveling and standing plane wave with arbitrary orientation is exactly derived in the dipole approximation. We obtain asymptotic expressions of the torque as the particle geometry approaches a sphere and a straight line. As the particle is trapped in a pressure node of a standing plane wave, its radiation torque equals that of a traveling plane wave. We also find how the torque changes with the particle aspect ratio. Our findings are in excellent agreement with previous numerical computations. Also, by analyzing the torque potential energy, we determine the stable and unstable spatial configuration available for a particle.

physics.flu-dyn↗

arXiv2016

Acoustic radiation force and torque exerted on a small viscoelastic particle in an ideal fluid

We provide a detailed analysis on the acoustic radiation force and torque exerted on a homogeneous viscoelastic particle in the long-wave limit (the particle radius is much smaller than the incident wavelength) by an arbitrary wave. We assume that the particle behaves as a linear viscoelastic solid, which obeys the fractional Kelvin-Voigt model. Simple analytical expressions for the radiation force and torque are obtained considering the low- and high-frequency approximation in the viscoelastic model. The developed theory is used to describe the interaction of acoustic waves (traveling and standing plane waves, and zero- and first-order Bessel beams) with a low- and high-density polyethylene particle chosen as examples. Negative axial radiation force and torque are predicted when the ratio of the longitudinal to shear relaxation times is smaller than a constant that depends on the speed of sound in the particle. In addition, a full 3D tractor Bessel vortex beam acting on the high-density polyethylene is depicted. These predictions may enable new possibilities of particle handling in acoustophoretic techniques.

physics.class-ph↗

arXiv2014

Designing single-beam multitrapping acoustical tweezers

The concept of a single-beam acoustical tweezer device which can simultaneously trap microparticles at different points is proposed and demonstrated through computational simulations. The device employs an ultrasound beam produced by a circular focused transducer operating at 1 MHz in water medium. The ultrasound beam exerts a radiation force that may tweeze suspended microparticles in the medium. Simulations show that the acoustical tweezer can simultaneously trap microparticles in the pre-focal zone along the beam axis, i.e. between the transducer surface and its geometric focus. As acoustical tweezers are fast becoming a key instrument in microparticle handling, the development of acoustic multitrapping concept may turn into a useful tool in engineering these devices.

physics.flu-dyn↗

arXiv2014

Acoustic radiation force and torque on an absorbing compressible particle in an inviscid fluid

Exact formulas of the acoustic radiation force and torque exerted by an arbitrary time-harmonic wave on an absorbing compressible particle that is suspended in an inviscid fluid are presented. It is considered that the particle diameter is much smaller than the incident wavelength, i.e. the so-called Rayleigh scattering limit. Moreover, the particle absorption assumed here is due to the attenuation of compressional waves only. Shear waves inside and outside the particle are neglected, since the inner and outer viscous boundary layer of the particle are supposed to be much smaller than the particle radius. The obtained radiation force formulas are used to establish the trapping conditions of a particle by a single-beam acoustical tweezer based on a spherically focused ultrasound beam. In this case, it is shown that the particle absorption has a pivotal role in single-beam trapping at the transducer focal region. Furthermore, it is found that only the first-order Bessel vortex beam can generate the radiation torque on a small particle. In addition, numerical evaluation of the radiation force and torque exerted on a benzene and an olive oil droplet suspended in water are presented and discussed.

physics.class-ph↗

arXiv2014

Acoustic interaction forces between small particles in an ideal fluid

We present a theoretical expression for the acoustic interaction force between small spherical particles suspended in an ideal fluid exposed to an external acoustic wave. The acoustic interaction force is the part of the acoustic radiation force on one given particle involving the scattered waves from the other particles. The particles, either compressible liquid droplets or elastic microspheres, are considered to be much smaller than the acoustic wavelength. In this so-called Rayleigh limit, the acoustic interaction forces between the particles are well approximated by gradients of pair-interaction potentials with no restriction on the inter-particle distance. The theory is applied to studies of the acoustic interaction force on a particle suspension in either standing or traveling plane waves. The results show aggregation regions along the wave propagation direction, while particles may attract or repel each other in the transverse direction. In addition, a mean-field approximation is developed to describe the acoustic interaction force in an emulsion of oil droplets in water.

physics.flu-dyn↗

arXiv2014

Exact computations of the acoustic radiation force on a sphere using the translational addition theorem

In this paper, the translational addition theorem for spherical functions is employed to exactly calculate the acoustic radiation force produced by an arbitrary shaped beam on a sphere suspended in an inviscid fluid. The radiation force is given in terms of the beam-shape and the scattering coefficients. Each beam-shape coefficient (BSC) is the complex weight of a multipole mode in partial-wave expansion of the incident beam. Moreover, they depend on the choice of the reference frame which is defined by the sphere's center. On the other hand, the scattering coefficients are obtained from the acoustic boundary conditions across the sphere's surface. Given a set of known BSCs, the translational addition theorem can be used to obtain the new coefficients relative to the sphere's position. Such approach is particularly useful when no closed-form expression of the incident pressure is known, but its BSCs are available. This is the case of a spherically focused ultrasound beam, for which we compute the radiation force on an absorbing compressible sphere arbitrarly placed in the fluid. The analysis is carried out in the Rayleigh and the resonant scattering regimes. It is shown that the focused beam may trap a spherical particle in the Rayleigh scattering regime.

physics.class-ph↗

arXiv2012

Difference-frequency generation in nonlinear scattering of acoustic waves by a rigid sphere

In this paper, the partial-wave expansion method is applied to describe the difference-frequency pressure generated in a nonlinear scattering of two acoustic waves with an arbitrary wavefront by means of a rigid sphere. Particularly, the difference-frequency generation is analyzed in the nonlinear scattering with a spherical scatterer involving two intersecting plane waves in the following configurations: collinear, crossing at right angles, and counter-propagating. For the sake simplicity, the plane waves are assumed to be spatially located in a spherical region which diameter is smaller than the difference-frequency wavelength. Such arrangements can be experimentally accomplished in vibro-acoustography and nonlinear acoustic tomography techniques. It turns out to be that when the sphere radius is of the order of the primary wavelengths, and the downshift ratio (i.e. the ratio between the fundamental frequency and the difference-frequency) is larger than five, difference-frequency generation is mostly due to a nonlinear interaction between the primary scattered waves. The exception to this is the collinear scattering for which the nonlinear interaction of the primary incident waves is also relevant. In addition, the difference-frequency scattered pressure in all scattering configurations decays as $r^{-1} \ln r$ and $1/r$, whereas $r$ is the radial distance from the scatterer to the observation point.

physics.class-ph↗

arXiv2012

Off-axial acoustic radiation force of pressor and tractor Bessel beams on a sphere

Acoustic Bessel beams are known to produce an axial radiation force on a sphere centered on the beam axis (on-axial configuration) that exhibits both "pressor" and "tractor" behaviors. The pressor and the tractor forces are oriented along the beam's direction of propagation and opposite to it, respectively. The behavior of the acoustic radiation force generated by Bessel beams when the sphere lies outside the beam's axis (off-axial configuration) is unknown. Using the 3D radiation force formulas given in terms of the partial wave expansion coefficients for the incident and scattered waves, both axial and transverse components of the force exerted on a silicone-oil sphere are obtained for a zero- and a first-order Bessel vortex beam. As the sphere departs from the beam's axis, the tractor force becomes weaker. Moreover, the behavior of the transverse radiation force field may vary with the sphere's size factor $ka$ (where $k$ is the wavenumber and $a$ is the sphere radius). Both stable and unstable equilibrium regions around the beam's axis are found depending on $ka$ values. These results are particularly important for the design of acoustical tractor beam devices operating with Bessel beams.

physics.class-ph↗

arXiv2012

Deconvolution of vibroacoustic images using a simulation model based on a three dimensional point spread function

Vibro-acoustography (VA) is a medical imaging method based on the difference-frequency generation produced by the mixture of two focused ultrasound beams. VA has been applied to different problems in medical imaging such as imaging bones, microcalcifications in the breast, mass lesions, and calcified arteries. The obtained images may have a resolution of 0.7--0.8 mm. Current VA systems based on confocal or linear array transducers generate C-scan images at the beam focal plane. Images on the axial plane are also possible, however the system resolution along depth worsens when compared to the lateral one. Typical axial resolution is about 1.0 cm. Furthermore, the elevation resolution of linear array systems is larger than that in lateral direction. This asymmetry degrades C-scan images obtained using linear arrays. The purpose of this article is to study VA image restoration based on a 3D point spread function (PSF) using classical deconvolution algorithms: Wiener, constrained least-squares (CLSs), and geometric mean filters. To assess the filters' performance, we use an image quality index that accounts for correlation loss, luminance and contrast distortion. Results for simulated VA images show that the quality index achieved with the Wiener filter is 0.9 (1 indicates perfect restoration). This filter yielded the best result in comparison with the other ones. Moreover, the deconvolution algorithms were applied to an experimental VA image of a phantom composed of three stretched 0.5 mm wires. Experiments were performed using transducer driven at two frequencies, 3075 kHz and 3125 kHz, which resulted in the difference-frequency of 50 kHz. Restorations with the theoretical line spread function (LSF) did not recover sufficient information to identify the wires in the images. However, using an estimated LSF the obtained results displayed enough information to spot the wires in the images.

cs.CV↗