Dielectrophoresis dielectrophoretic force

Dielectrophoresis is the translational motion of neutral matter owing to polarization effects in a non-uniform electric field. Depending on matter or electric parameters, different particle populations can exhibit different behavior, e.g. following attractive or repulsive forces. DEP can be used for mixing of charged or polarizable particles by electrokinetic forces [48], In particular, dielectric particles are mixed by dielectrophoretic forces induced by AC electric fields, which are periodically switched on and off. 

ABSTRACT A brief history of the behavior of materials in nonuniform electrical fields is presented, followed by a theory of dielectrophoretic force and the derivation of the general force equation. Attention is paid to the several classes of polarization which lead to the experimental considerations of induced cellular dielectrophoresis. A distinction between batch and continuous methods is discussed, with a focus on a new microtechnique. While dielectrophoresis can induce aggregation of materials, i.e., cells, other orientational applications exist. Cell division, cellular spin resonance, and pulse-fusion of cells form topics appropriate to the realm of high-frequency electrical oscillations and are discussed in the context of living material. 

One further point might be made for clarity. As we have seen, dielectrophoresis is the translational motion evoked by a nonuniform electric field. In the case of some solid materials and in certain semisolid ones (e.g., liquid crystals) there is seen still another mechanical response of a neutral body to an electric field, that of a distortion. This is electrostriction, and refers to the distortional response or strain resulting from an imposed electrical stress. Electrostrictive strains are used in sound transducers, for example. Historically speaking the two effects, translational (dielectrophoresis) and distortional (electrostriction), where both at times referred to as electrostriction with resultant confusion. Modem usage has tended to restrict the term electrostriction to the discussion of distortional strain that has been induced electrically. For the sake of brevity, we shall frequently use the abbreviation DEP response as that referred to properly as dielectrophoresis. One can, of course, couple a moment arm to the dielectrophoretic force (e.g., DEP force) producing a torsion, and possibly a realignment of the body in the field. 

Dielectrophoresis is the translational motion of a neutral particle by induced polarization in a nonuniform electric field. The magnitude and direction of the induced dielectrophoretic force are dependent on the characteristics of the applied electric field as well as the dielectric properties of the surrounding medium and of the particle itself. 

Dielectrophoretic forces, though, can be induced by means other than an applied electric signal through electrodes. Optical tools can be implemented to modify an applied electric field, making these methods more susceptible for dynamic as opposed to static manipulation of electric fields with surface electrodes. Dielectrophoresis applications are not limited to particulate manipulation either. With properly configured surface-electrode geometry, it is possible to induce fluid motion and create nanoliter-sized droplets. Additionally, dielectrophoretic forces can be utilized to manipulate particles to buUd micro- and nanostructures such as wires. 

An electrode-less approach to induce localized dielectrophoretic forces can be created by light illumination in optically induced dielectrophoresis. This technique utilizes low-power optical beams to manipulate particles and cells. Consider an AC electric signal applied across two parallel electrodes with a film of photocon-ductive layer in between. This generates a uniform electric field across the film however,... 

In AC and DC dielectrophoresis, the dielectrophoretic force acting on the polarized particle causes it to move either up or down the induced electric field gradient, which is created by (a) nonuniform electrode geometry in AC fields or by (b) a nonuniform insulator geometry of obstacles in an otherwise uniform DC field or DC-offset AC field. This spatially nonuniform field or gradient dotted with the polarized particle dipole yields a net dielectric force ... 

Dielectrophoresis, Fig. 6 (a) Schematic diagram of the interdigitated electrode array in a microfluidic system, (b) Plot of the direction of the dielectrophoretic force for the... 

Recently, the theory of dielectrophoresis was applied to explain the microscopic physics of the movement of pigments in electrophoretic image displays and to prove the discrepancies between theory and measurement [9], Dielectrophoresis is induced by the interaction of the electric field and the induced dipole and is used to describe the behavior of polarizable particles in a locally nonuniform electric field. For example, the phenomenon of the delay time can be explained by the principle of dielectrophoresis. In electrophoresis, when the backplane voltage is switched, the particles on the electrode have to move instantaneously under a given electric field. However, the particles need a removal time which results in a delay time in the switching process. The time constant to obtain an induced dipole from a particle at rest is derived by Schwarz s formula [10] and used to compute the dielectrophoretic force at its steady-state value. The force and the velocity fields under a nonuniform electric field due to the presence of pigments also help to estimate realistic values for physical properties. 

Reservoir-Based Dielectrophoresis, Fig. 1 Contour (the darker, the larger magnitude) of the electric field, E (a) contour and arrow of the induced dielectrophoretic force, Fdep (b) and particle velocity analyses (c) at the... 

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