Washizu M, Jones T B, Kaler K V
Department of Electrical Engineering, Seikei University, Tokyo, Japan.
Biochim Biophys Acta. 1993 Aug 20;1158(1):40-6. doi: 10.1016/0304-4165(93)90094-o.
Experiments with certain new micro-electrode structures used to achieve passive dielectrophoretic levitation of small particles and biological cells reveal a pronounced size-dependent effect not anticipated by the conventional dipole-based model. The conventional theory fails to predict this size effect because it neglects higher-order moments such as the quadrupole, hexapole, and octupole. These higher-order moments are in fact responsible for the levitation force achieved by azimuthally periodic electrode structures because, in such geometries, the electric field is zero along the axis so that the induced dipole moment must be zero. For example, the planar quadrupole levitates particles passively along the central axis through the interaction of its field with the induced quadrupolar moment of the particle. The size effect reported with this structure is readily explained in terms of this quadrupolar component of the ponderomotive force exerted on the particle.
使用某些新型微电极结构实现小颗粒和生物细胞被动介电泳悬浮的实验表明，存在一种明显的尺寸依赖性效应，这是传统基于偶极子的模型所未预料到的。传统理论无法预测这种尺寸效应，因为它忽略了诸如四极子、六极子和八极子等高阶矩。实际上，这些高阶矩是由方位角周期性电极结构实现的悬浮力的原因，因为在这种几何结构中，沿轴的电场为零，所以感应偶极矩必须为零。例如，平面四极子通过其场与粒子感应四极矩的相互作用，沿中心轴被动悬浮粒子。用施加在粒子上的有质动力的这种四极分量很容易解释这种结构所报告的尺寸效应。
