Levitation electrostatic

Electrostatic levitation Electrostatic fields A few nanolitres to 100 pi No Capable of carrying electrostatic charge Investigations in single drops II6-II8... 

In order to stably levitate an object, the net force on it must be zero, and the forces on the body, if it is perturbed, must act to return it to its original position. The object must be at a local potential minimum that is, the second derivatives with respect to all spatial coordinates of the potential must be positive. This may seem, at first sight, to be trivial to arrange. However, any system whose potential is a solution to Laplace s equation is automatically unstable A statement in words of Laplace s equation is that the sum of the second partial derivatives of the potential is zero, and so not all can be simultaneously positive. This has long been known for electrostatic potentials, having been stated by Earnshaw(n) Millikan s scheme for suspending charged particles is thus only neutrally stable, since the fields within a Millikan capacitor provide no lateral constraint. 

The classical electrostatic balance is the Millikan condenser, which was first used to measure the charge on the electron in the famous Millikan oil-drop experiment. In principle, the device can be used to levitate a small charged mass by using the electrical field generated by two flat plates to... 

Rhim, W.-K. and Chung, S. K. (1990). Isolation of crystallizing droplets by electrostatic levitation. Methods 1, 118-127. 

In contrast to most levitation techniques such as levitation in electrostatic or magnetic fields, acoustic levitation requires no specific properties of the sample, so almost every substance, whether solid or liquid, can be acoustically levitated. The maximum possible diameter for a levitated sample is a function of the ultrasonic wavelength and turns out to be about one-half the wavelength under ambient atmospheric conditions. Usually, levi-tators are operated by ultrasound frequencies between 15 and 100 kHz resulting in wavelengths from 2.2 to 0.34 cm. 

Levitation of Cs atoms in the evanescent field has been demonstrated in Ref. [Hammes 2002], where the the optical dipole potential created by 1 W-laser has been utilized for trapping the atoms far from the surface. The exponential profile of the potential decreases at a half-wave length A/,/w,/2 250 nm. At these distances the optical field compensates for the long-range attraction induced by the electrostatic polarization and the Casimir-Polder potential... 

Kelton, K.F. Lee, G.W. Gangopadhyay, A.K. Hyers, R.W. Rathz, T.J. Rogers, J.R. Robinson, M.B. Robinson, D.S. First X-ray scattering studies on electrostatically levitated metallic liquids demonstrated influence of local icosahe-dral order on the nucleation barrier. Phys. Rev. Lett. 2003, 90 (19), 195504 1. ... 

In contrast to contacting particles, an isolated particle of charge Q that interacts with a local field Eis simply evaluated from the relationship f =Q E. Such electrostatic forces for isolated particle can be simply evaluated by levitation, i.e., utilizing gravitational forces and steady-state experiments (Colver, 1976 Jones, 1986, Tombs and Jones, 1990, 1993). Charged droplets have been levitated for the studies of surface tension and viscosity (Rhim and... 

A.C. Rudack, L.B. Levit, and A. Williams, Mask damage by electrostatic discharge a reticle print ability evaluation, Proc. SPIE 4691, 1340 1347 (2002). 

Fig. 1.3 A time-temperature-transformation diagram for the Vitreloy 1 glass-forming liquid (a, obtained using electrostatic levitation , obtained using carbon crucibles) (from Busch (2000) courtesy of TMS).

W. K. Rhim and K. Osaka, Thermophysical properties measurement of molten silicon by high-temperature electrostatic levitator density, volume expansion, specific heat capacity, emissivity, surface tension and viscosity, J Ciyst Grovrtft 208, 313-321 (2000). 

In contact-free platforms, various force fields, such as electrostatic, magnetic or pneumatic, are used to create a cushion on which the part levitates. The forces of these fields need to be directionally dependent in order to drive the part s manipulation on the workplane (e.g. the directed air streams for a pneumatic system). The main advantage of the contact-free microconveyor platforms is low friction, while the drawback is their high sensitivity to the cushion thickness (load-dependent), which can be quite difficult to control. 

The relatively recent development of contactless processing, such as aerodynanuc [32], aero-acoustic [42], and electrostatic [38] levitation techniques has enabled the structural determination of amorphous materials that were previously experimentally challenging or even unachievable. Levitation methods have been used for both in situ structural measurements [9, 23] and ex situ for atypical sample preparation this includes sample purification [43, 47] and single crystal growth [6], but is perhaps most often applied to the fabrication of new glasses which are unobtainable by other methods. 

The sample stability in row A is that reported by Greaves et al. [5], although this is significantly lower than those reported for aerodynamic levitation [2] and combined aerodynamic and electrostatic [9] levitation shown in row B. Row C is an intermediate sample stabdity which stiU causes a significant error in the transmission... 

Containerless processing techniques have been developed to a great extent for space experiments i.e. these are electromagnetic [9], electrostatic [10], aerodynamic [11] and aero-acoustic levitations [12]. Containerless processing assures measurements of thermophysical properties of molten semiconductors usually it... 

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