Dielectrophoretic interaction of two spherical particles calculatedby equivalent multipole-moment method

A generalized equivalent multipole-moment theory is developed for the dielectrophoretic interactions between two arbitrarily oriented spherical dielectric particles in an external field. The method is based on the re-expansion technique: first, the electrostatic potential disturbance created by one of the dielectric spheres is expressed as a series of spherical harmonic terms with r^-(n+1)-dependence. This potential, having no singularities except at the center of the sphere, is then re-expanded about the center of the second sphere as a new series of spherical harmonics with rⁿ-dependence. Once this re-expansion is done, the effect of one sphere on its neighbor can be represented by an externally applied potential, and the interaction force thus calculated. The analytical results make it possible to investigate the strong angular dependence of the interaction force as particle spacing and permittivity are varied     

Dielectrophoretic detection of molecular bindings

The specificity of molecular binding between the "target" and the "probe" molecule, for example, between antigen and antibody or between two complementary deoxyribonucleic acid (DNA) sequences, is the principle of affinity assays. In the assay, the target is mixed with the fluorescence-labeled probe, so that the probe binds to the target to form a target-probe complex. Then, the bound complex is separated from the free (unbound) probe somehow (bound/free (BF) separation), and the fluorescence emission from the separated complex is measured to obtain the target concentration in the original sample. In this paper, the authors propose and experimentally demonstrate the use of dielectrophoresis (DEP) for such B/F separations. Using DEP chromatography, DEP characteristics of various biomolecules are measured, and: (1) separation of A-DNA (48.5 kbp) and oligonucleotide (22base); and (2) quantitative detection of antigen-antibody bindings, are demonstrated. Using the triple complex formation to facilitate DEP separation, a method is developed to detect B/F binding by a direct observation of the separation pattern on the microelectrode system. Et is applied for: (1) quantitative detection of alpha-fetoprotein, the diagnostic marker of liver cancer, through antigen-antibody reaction; and (2) the detection of DNA sequence through hybridization. The methods developed here are compatible with with micro fabrication, and suitable for affinity assays in micro-total analysis systems     

Multipole Corrections to Dielectrophoretic Force

Calculation of the dielectrophoretic (DEP) force on a neutral dielectric partide in a nonuniform electric field is simplified by using the effective dipole method. Once the instantaneous effective dipole moment peff(t) has been correctly identified using Gauss's law, then the expression (peff(t)?)E0(t) is used to determine the force on the particle. Recent work has demonstrated that the effective dipole method produces a result consistent with integration of the Maxwell stress tensor. In the present paper, the issues concerning identification of peff(t) are aired, and an alternate derivation of the DEP force on a conducting dielectric sphere immersed in a conducting dielectric fluid is offered. Then the effective dipole theory is generalized to account for higher order (multipole) contributions. This new effective multipole theory is restricted to spherical particles in a cylindrically symmetric cusped electric field, but the analysis leads to straightforward computation of the quadrupolar correction factor for the DEP force. A quantitative example is provided.     

Dielectrophoretic Levitation of Small Metallic Particles

Small uncharged metallic spheres have been levitated in a nonuniform electric field using a microprocessor-based active feedback control system. The particle is centered horizontally in an axisymmetric time-varying electric field. The vertical gravitational force is balanced by the dielectrophoretic force; however, the resulting equilibrium is unstable. To achieve stable levitation the vertical particle position is sensed optically and an error voltage is applied to the electrodes. Experimental results with the levitator are in good agreement with the equilibrium force balance model.     

Dielectrophoretic measurement of bacterial motor characteristics

Two methods of measuring bacterial motor characteristics using AC field effects in a microfabricated electrode system are presented. One is the measurement of the external force-velocity characteristics (F-v) of swimming bacteria. Electrostatic orientation of bacteria parallel to the field lines is used to guide the bacterial locomotion along a line. Dielectrophoresis is used to apply an external force, either forward or backward, to the swimming bacteria, and the velocity of locomotion is measured to obtain the F-v curve. The other approach is to measure torque-speed characteristics (T-w) of the motor. Electrorotation is used to apply external torque to the tethered cells, and by changing the applied torque and measuring the rotation speed, the T-ω curve is obtained. The results show that the motor generates approximately constant torque in the measured range of ω (0-100 Hz), regardless of the direction of rotation     

Dielectric Constant Measurements Using Dielectrophoretic Levitation

A dielectrophoretic levitation scheme is used to measure the dielectric constant of insulating dieletric liquids and small solid spherical particles. The fixed ring-disk electrode system is first calibrated against a known standard dielectric liquid by levitating a small gas bubble in the liquid at a fixed location. The measurements are then performed by measuring the voltage required to levitate a gas bubble in the unknown liquid at the same location with respect to the electrode structure. A similar procedure is used for solid spherical particles. The system is unique because it requires no detailed knowledge of the electric field. Fabrication of the electrodes does not require precision machining, and the structure is relatively insensitive to leveling. The size of the gas bubble or solid particle is not critical as long as it is much smaller than the electrode structure. The measurement precision is limited by the accuracy of the voltage measurements and by the accuracy to which the dielectric constant (of the standard) and the specific gravities (of the unknown and the standard) are known. The measurements presented support the contention that this method is a simple and reliable method of measuring the dielectric constant of insulating dielectric liquids.     

A Study of the Mechanisms of Particle Buildup on Single Rods in Dielectrophoretic Separation

A theoretical review of the particle buildup processes involved in dielectrophoretic capture of dielectric and conducting particles is presented. Trajectories are calculated, and the capture radius is plotted against the electric field and flow parameters. Photographic data of capture of barium titanate particulates are shown for the axial case, using a fine steel rod in laminar flow. A correlation for the radius of accumulation at saturation is obtained between the theoretical model and the experimental results.     

Symbolic manipulation of transfer functions and state spacerealizations

In this paper several applications on the use of symbolic computation to control system design are discussed. These applications are of educational value to control engineering courses. The routines developed here provide a quick way to formulate control design problems, ranging from calculating elementary transfer functions to automating the construction of state space realization. This paper also gives detailed discussion on the symbolic computational process of the programs being developed. Examples of symbolic calculation of generalized plant state space realization for use in H_∞/H₂ optimal control are presented     

基于径向偏振光束的微粒捕获与操控

因为空间变化的偏振分布及独特的聚焦特性,径向偏振光束在粒子捕获及操控方面有独特的应用价值。从理论和实验方面研究了基于径向偏振光束的微粒捕获与操控。首先,介绍了捕获力的计算方法,重点基于光线理论模型计算了径向偏振光束的轴向及横向捕获效率,并与切向偏振光和圆偏振光的捕获效率进行了比较;然后,基于倒置显微镜和空间光调制器搭建了光学捕获与操控系统,采用两种不同的成像物镜实现了对直径为10μm左右的酵母菌细胞及直径为1μm的苯乙烯小球的捕获和操控,根据预定的轨迹实现了粒子的稳定移动,体现了该类型光镊较为宽阔的应用前景;最后,简要分析了影响粒子捕获及操控的若干因素,为系统改进提供了指导意见。     

Multi-axis maglev nanopositioner for precision manufacturing and manipulation applications

We present a six-axis magnetic-levitation (maglev) stage capable of precision positioning down to several nanometers. This stage has a simple and compact mechanical structure advantageous to meet the performance requirements in the next-generation nanomanufacturing. It uses the minimum number of linear actuators required to generate all six axis motions. In this paper, we describe the electromechanical design, modeling, and control, and the electronic instrumentation to control this maglev system. The stage has a light moving-part mass of 0.2126 kg. It is capable of generating translation of 300 /spl mu/m in the x, y, and z axes, and rotation of 3 mrad about the three orthogonal axes. The stage demonstrates position resolution better than 5 nm rms and position noise less than 2 nm rms. Experimental results presented in this paper show that the stage can carry, orient, and precisely position a payload as heavy as 0.4 kg. The pull-out force was found to be 8.08 N in the vertical direction. Furthermore, under a load variation of 0.14 N, the nanopositioner recovers its regulated position within 0.6 s. All these experimental results match quite closely with the calculated values because of the accurate plant model and robust controller design. This device can be used as a positioning stage for numerous applications, including photolithography for semiconductor manufacturing, microscopic scanning, fabrication and assembly of nanostructures, and microscale rapid prototyping.     

Agglomeration of particles by ac corona discharge

Improving the collection efficiency for particles smaller than 1 μm on every precipitator is important. We sought to improve the collection of these particles on an ESP due to particle agglomeration. Particles are charged by ac corona discharge in a precharger and agglomerated by a dc electric field in an agglomerator downstream of the precharger. Diesel exhaust particles were used as particulate matter for the experiments. The distribution of particle size was measured using a particle counter and a scanning electron microscope. By these methods, particles as small as 0.01 μm could be counted. Results showed the agglomeration between particles at ac corona discharge operating mode. The concentration of particles smaller than approximately 0.35 μm decreases, and that of particles larger than approximately 0.35 μm increases in the agglomerator. The agglomeration rate increases with increasing applied voltage, then saturates. These results may be due to the size distribution and to decrease of concentration by agglomeration. © 1999 Scripta Technica, Electr Eng Jpn, 130(1): 30–37, 2000     

On the dielectrophoretic separation of solid particles

An analysis of an idealized high-gradient dielectrophoretic separator that is simply a metal circular filament placed in a uniform electric field between two parallel plates is presented. The analysis is aimed at determining the spatial distribution of the electric field inside the volume of the separator, so that the dielectrophoretic force on a dielectric particle can be evaluated. The conditions necessary for producing dielectrophoretic forces comparable to those in electrostatic separators are determined     

History of optical trapping and manipulation of small-neutralparticle, atoms, and molecules

Reviews the history of optical trapping and manipulation of small-neutral particles, from the time of its origin in 1970 up to the present. As we shall see, the unique characteristics of this technique are having a major impact on the many subfields of physics, chemistry, and biology where small particles play a role     

Multiple fields manipulation on nitride material structures in ultraviolet light-emitting diodes

As demonstrated during the COVID-19 pandemic, advanced deep ultraviolet (DUV) light sources (200–280 nm), such as AlGaN-based light-emitting diodes (LEDs) show ...     

Unipolar charging of cylindrical insulating particles nearelectrode surfaces

Numerous papers have discussed the ionic charging of insulating spheres in uniform electric fields. However, in certain electrostatic technologies, such as separation and flocking, the particles are often cylindrical in shape, and they get charged on the surface of an electrode or in its proximity, so that existing formulas cannot be used. This paper addresses this problem from both a computational and an experimental point of view. The charge acquired by cylindrical particles of various dielectric constants was evaluated with an original computer program, based on the boundary-element method of field analysis. The computed results show that the position of the particle with respect to the electrodes changes the value of the saturation charge. The experimental setup simulated the charging conditions in a roll-type electrostatic separator. The unipolar space charge was generated by a needle-type electrode. An electrometer was used to measure the charge acquired by millimeter-size calibrated cylinders of polyethylene and polyvinyl chloride on a rotating roll electrode. The experimental results, which were in good agreement with the theoretical predictions, put forward a particle self-discharge effect, at field intensities beyond a well-defined threshold. This kind of information may guide the design of the electrostatic technologies based on the corona charging of granular matter