Polarizability of conducting and dielectric agglomerates: theory and experiment

A method has been described for calculation of the dipole moment, when pola rized in an electric field, of agglomerates of spherical particles of any s pecified size and arrangement, and of both conducting and dielectric materi als. The polarization of each spherical component of an agglomerate of cond ucting spheres is represented by a real charge and a dipole moment in a gen eral direction. Within the constraints of zero net charge the problem can b e solved self-consistently. As a check on the validity of the method it is possible to plot contours of the constant potential surface for such an agg lomerate, and these are shown to coincide closely with the geometric surfac e. The theoretical predictions are, for the case of linear agglomerates of limited length, verified by direct measurement of force on large scale mode ls in spatially varying electric fields designed so that the polarization f orce is only weakly dependent on position. The theory is also applied to di electric agglomerates but in this situation no net charge develops on any o f the component spheres. The induced dipole moment, especially in the situa tion where the agglomerate is aligned parallel to the field, is much smalle r than that of a conductor with the same shape. The functional relationship of the induced dipole moment per unit volume of an infinitely long linear agglomerate aligned perpendicular to the field lies between the theoretical form for an isolated sphere and that for an infinitely long cylinder. That for a sheet of spheres lies between the form for an infinite cylinder and an infinite sheet of dielectric. (C) 2001 Elsevier Science B.V. All rights reserved.