Manipulation Of Small Particles Research Articles

Acoustophoresis in suspensions with local and time-discrete sound fields based on the time reversal technique

Abstract. In this paper, a new approach of three-dimensional acoustic particle manipulation (acoustophoresis) in closed and liquid-filled vessels based on the time reversal technique is discussed. Based on simulation studies, this work investigates the technical prerequisites to achieve appropriate acoustic radiation forces (ARFs) for the manipulation of small particles with the time reversal method by utilizing multiple reflections in a closed vessel. The time-discrete and localized acoustic pressure field required for this purpose is generated by a time reversal mirror composed of 24 piezoceramic transducers. The paper also gives an outlook on practical evaluation of the simulation results based on a demonstrator setup.

Born approximation of acoustic radiation force and torque for an arbitrary particle in a zero-order standing Bessel beam

The calculation of acoustic radiation force and acoustic radiation torque is an important basis for the precise manipulation of particles. It is difficult to directly apply the partial-wave series expansion method based on the classical acoustic scattering theory to the study of complicated models, while pure numerical methods are not conducive to the parametric analyses of the system. Based on the basic principle of Born approximation, the expressions of acoustic radiation force and torque acting on an arbitrary particle located in the center of a zero-order Bessel standing wave field are derived at low frequencies. On this basis, the numerical simulations are systematically performed by taking spherical, spheroidal and cylindrical particles as examples. The effects of inhomogeneity on the acoustic radiation force and torque are also investigated. The simulation results show that the Born approximation method has a high accuracy in the low frequency range. As the frequency increases and the impedance matching between the particle and the fluid becomes worse, the accuracy of Born approximation will gradually decrease. An acoustic radiation torque caused by asymmetry will be exerted on spheroidal and cylindrical particles obliquely positioned in a zero-order Bessel standing wave field. When the particle size is much smaller than the wavelength, the acoustic radiation force is nearly independent of the particle shape, but this is not the case for acoustic radiation torque. Finally, viscous effect of the surrounding fluid is introduced and the expression of acoustic radiation force is corrected accordingly. The study is expected to provide a theoretical guide for the precise manipulation of small particles using standing wave acoustic tweezers in biomedicine and material sciences.

Polarization-controlled generation and superposition of surface plasmon polariton vortices with a plasmonic metasurface

Optical vortex that carries orbital angular momentum has shown great potential in various applications, including high-density optical communication, quantum information, and manipulation of small particles. Here, an approach to design a plasmonic metasurface that can control both the generation and superposition of surface plasmon polariton (SPP) vortices is proposed and demonstrated. Under circularly polarized light incidence, the SPP vortices with different topological charges can be generated depending on the spin of the incidence, and the superposition state can be achieved when the polarization of incident light turns to linear polarization. Furthermore, it is demonstrated that the superposition of SPP vortices can be accurately controlled by the polarization states of the incidence. This proposed approach is quite versatile for generating and controlling SPP vortices and provides a feasible way to design miniaturized photonic devices for on-chip optical micromanipulation, sensing, and other related applications.

Formulation of resonant optical force based on the microscopic structure of chiral molecules.

Optical manipulation, exemplified by Ashkin's optical tweezers, is a promising technique in the fields of bioscience and chemistry, as it enables the non-destructive and non-contact selective transport or manipulation of small particles. To realize the separation of chiral molecules, several researchers have reported on the use of light and discussed feasibility of selection. Although the separation of micrometer-sized chiral molecules has been experimentally demonstrated, the separation of nanometer-sized chiral molecules, which are considerably smaller than the wavelength of light, remains challenging. Therefore, we formulated an optical force under electronic resonance to enhance the optical force and enable selective manipulation. In particular, we incorporated the microscopic structures of molecular dipoles into the nonlocal optical response theory. The analytical expression of optical force could clarify the mechanism of selection exertion of the resonant optical force on chiral molecules. Furthermore, we quantitatively evaluated the light intensity and light exposure time required to separate a single molecule in a solvent. The results can facilitate the design of future schemes for the selective optical manipulation of chiral molecules.

Optical Forces and Torques on Eccentric Nanoscale Core–Shell Particles

The optical trapping and manipulation of small particles is an important tool for probing fluid properties at the microscale. In particular, microrheology exploits the manipulation and rotation of micron-scale particles to probe local viscosity, especially where these properties may be perturbed as a function of their local environment, for example in the vicinity of cells. To this end, birefringent particles are useful as they can be readily controlled using optically induced forces and torques, and thereby used to probe their local environment. However the magnitude of optical torques that can be induced in birefringent particles is small, and a function of the particle diameter, meaning that rotational flow cannot readily be probed on length scales much small than the micron level. Here we show modelling that demonstrates that eccentric spherical core-shell nanoparticles can be used to generate considerable optical torques. The eccentricity is a result of the displacement of the centre of the core from the shell. Our results show that, for particles ranging from 90~nm to 180~nm in diameter, we may achieve rotation rates exceeding 800~Hz. This fills a missing size gap in the rotation of microparticles with optical forces. The diameter of particle we may rotate is almost an order of magnitude smaller than the smallest birefringent particles that have been successfully rotated to date. The rotation of eccentric core-shell nanoparticles therefore makes an important contribution to biophotonics and creates new opportunities for rheology in nanoscale environments.

Switching of radiation pressure acting on microparticles by using T-type photochromic reactions

Manipulation of small particles can be achieved by using the radiation pressure of a laser beam. The strength and direction of the radiation pressure depends on the dielectric constant of target materials. It can therefore be expected to induce mechanical motions of small materials in optical trap by changing their optical property by chemical reactions. Along this line, we recently demonstrated switching of radiation pressure acting on single optically trapped microparticles by using photochromic molecules (Refs. 3, 4). To explore more flexible mesoscopic motions synchronizing photochemical reactions, we have investigated in the present study the micromechanical motion of optically trapped particles containing a T-type photochromic molecule, naphthopyran (NP), with multiple thermal back-reaction rates. The single microparticle with NP was optically trapped with CW 532-nm laser and the photochromic reaction was induced by UV irradiation, resulting in the modification of the optomechanical responses of the particle under laser trapping.

Long-range interacting pendula: A simple model for understanding complex dynamics of charged particles in an electronic curtain device

In this paper, we investigate the equilibrium and non-equilibrium properties of a model that shares several important characteristics with charged particles interacting in an Electric Curtain (EC) device. An EC comprises a periodic array of parallel electrodes, applied to each is an alternating electric potential. Depending on the applied potentials and the geometry of the electrodes, a wide variety of field structures above the plane of the electrodes are possible. The EC has multiple applications in the control and manipulation of small particles, but is under utilized in industry and science because of difficulties in predicting and understanding the particle dynamics. One particular challenge in understanding the dynamics is the many-body coulomb interactions. To better understand the role of the interactions, we study a one-dimensional analytically tractable model that encapsulates their long-range nature. Specifically, we study a Hamiltonian similar to that of the Hamiltonian mean field model but with the inclusion of an index dependent phase in the interaction term that, as we show, reflects the periodic structure of an EC field. We solve for the canonical partition function and also investigate some of the non-equilibrium behaviors. In the study of the non-equilibrium behaviors, we find an interesting property, namely that a quasistationary (lifetime diverges as the number of particles is increased) clustered state can exist when an initial configuration is ordered by the particle indices.

Lateral forces on circularly polarizable particles near a surface.

Optical forces allow manipulation of small particles and control of nanophotonic structures with light beams. While some techniques rely on structured light to move particles using field intensity gradients, acting locally, other optical forces can ‘push' particles on a wide area of illumination but only in the direction of light propagation. Here we show that spin–orbit coupling, when the spin of the incident circularly polarized light is converted into lateral electromagnetic momentum, leads to a lateral optical force acting on particles placed above a substrate, associated with a recoil mechanical force. This counterintuitive force acts in a direction in which the illumination has neither a field gradient nor propagation. The force direction is switchable with the polarization of uniform, plane wave illumination, and its magnitude is comparable to other optical forces.

Compact Optical systems for Micromanipulation

AbstractHighly focused laser beams offer exciting possibilities for the handling and manipulation of small particles. Even though the technique of “optical tweezing” has been discussed and applied in research labs for more than 40 years a breakthrough in industrial applications has not taken place so far. Major obstacles result from the complex systems used to generate the necessary focus distribution. Our latest research indicates that optical tweezers based on compact and integrated optical systems are feasible. Such systems could open the field to a wide variety of new applications.

Dynamic array generation and pattern formation for optical tweezers

The generalised phase contrast approach is used for the generation of optical arrays of arbitrary beam shape, suitable for applications in optical tweezers for the manipulation of biological specimens. This approach offers numerous advantages over current techniques involving the use of computer-generated holograms or diffractive optical elements. We demonstrate a low-loss system for generating intensity patterns suitable for the trapping and manipulation of small particles or specimens.

From Micro- to Nanoparticle Manipulation

The precise manipulation of small particles is not a trivial task. In a first effort, a nanorobot system was built based on a robot with vision feedback and a micromachined gripper. It was suitable for handling particles down to 100 μ with submicron accuracy in a normal environment. For smaller particles stiction effects prohibit the release of the particles in a controlled way. Stiction effects are avoided in a fluid environment. As an example, a system of channels is described in detail that is able to feed micron sized particles in a fluid environment to the desired places.

Particle micromanipulator consisting of two orthogonal channels with travelling-wave electrode structures

Abstract In the paper experimental and numerical results for a simple particle micromanipulator fabricated in silicon technology are presented. It consists of three orthogonal liquid filled channels above meander-shaped planar electrode strips. By applying appropriate alternating, rotating or travelling electric fields in the chamber dielectric forces acting on particles suspended in the liquid are induced allowing trapping, movement and separation of them. The efficient manipulation of small particles with typical dimensions of several micrometers using electrogradient techniques (EGT) requires electrode structures of the same size. Due to the complex electrode geometry a numerical procedure is used for calculation of particle trajectories and optimising the design. In the micro range small fabrication defects are likely to cause large changes of the properties of the manipulator. Therefore, a test procedure based on electrode processes in aqueous media and the pH-dependent fluorescence intensity of a marker solution which enabled us to visualise the working states, surface coatings and fabrication defects of microstructured electrodes via a microscope is introduced.

Simple Models for Particle Aggregation, Deposition and Segregation

ABSTRACTMost conventional and experimental methods for the formation of ceramic objects involve the manipulation of small particles and/or structures comprised of these particles. Consequently, a better understanding of the physics and chemistry of small particles could contribute to the development of better ceramics. Here the results of some recent computer simulation studies of processes such as particle aggregation, deposition and segregation are surveyed. More realistic models are needed to represent accurately the behavior of most real systems.

Comments on "The large-scale manipulation of small particles"

Comments on "The large-scale manipulation of small particles"