Small Dielectric Spheres Research Articles

Dielectrophoretic levitation of spheres and shells

Under certain conditions, the dielectrophoretic force can be used to levitate particles or bubbles in dielectric liquids. The strength of the dielectrophoretic force depends on the effective dipole moment which is directly related to the induced dipole field. The situation of a small dielectric sphere or shell with finite conductivity submerged in dielectric liquid also of finite conductivity is considered. Under certain conditions, a cutooff frequency exists which determines the limit above or below which levitation is no longer obtainable. To test the theory, spheres and shells of various materials are levitated in ac and dc electric fields using a cusped electric field. A fixed electrode structure is calibrated using a dielectric liquid with known properties and the quantitative results of numerous levitation experiments are favorably compared to the theoretical model. The frequency-dependent behavior of glass microballoons is found to be generally consistent with the predictions of the model. Results with dc electric fields are inconclusive due to electroconvection, electrostatic repulsion, and long charge relaxation time constants.

Raman and fluorescent scattering by molecules embedded in small particles: Results for coherent optical processes

The work of the previous paper is extended to consider the effect upon coherent processes of embedment of inelastic scattering molecules within small dielectric spheres. In this case the scattered radiation field is obtained in analytic form by integrating the earlier result over the particle. Unlike the case for noncoherent inelastic processes, the scattering diagrams resemble qualitatively the main features of Lorenz-Mie scattering. The implications for developing coherent Raman techniques for diagnostic purposes are clear. Quantitative chemical analysis can only be carried out if the refractive index, the ratio of particle size to exciting and emitting wavelengths, and the scattering angle are specified.

Near-field centripetal scattering from dielectric spheres

The fields scattered from small dielectric spheres illuminated by a plane wave have been computed as part of a study of spherical dielectric antennas. Studies of scattering of 3 cm wavelength from a 6.6 cm diameter sphere of dielectric constant between 2 and 3 show large regions on the surface of the sphere where the Poynting vector is inwardly directed. These regions form sidelobes of inwardly directed power density between the sidelobes of outwardly directed power density in the principal planes. Away from the sphere the angular extent of the centripetal power flow is reduced until they disappear at 2-3 cm from the surface.

CHARACTERISTICS OF A TOROIDAL RESONATOR FOR PLASMA DIAGNOSTICS

In this paper an experimental investigation of the electric-field configuration in a toroidal resonator has been carried out by measuring the shift of the resonant frequency when a small dielectric sphere is introduced in the resonator. The good agreement between the experimental and the theoretical results shows that the assumptions concerning the electromagnetic-field configuration are correct and the method can be used in measuring the electrical conductivity of a plasma.

Blue Sun and Moon

Paul and Jones1, discussing the blue sun caused by selective absorption of a cloud of uniform spheres of radius r in light of wave-length λ, have considered the curve relating K (the ratio of effective to geometrical cross-section of a particle) and α, where α= 2πr/λ. They suggest a simple physical explanation of the maxima and minima of this curve on the basis of resonances. The maxima and minima, in the case of small dielectric spheres can also be explained from the principles of physical optics; this point of view was used by Van de Hulst2 in considering some aspects of the subject that could not so readily be treated by electromagnetic theory.

XL. An elementary theory of the scattering of light by small dielectric spheres

XL. <i>An elementary theory of the scattering of light by small dielectric spheres</i>