Experimental investigation for field-induced interaction force of two spheres

An apparatus is developed to study the interaction forces between two spheres under an external ac electric field. The interaction forces of a pair of spheres as the function of interspherical spacing, electric field strength, and electric field frequency are measured precisely. The results reveal that much stronger interaction can be obtained for metal spheres and high-dielectric spheres compared with the spheres with a very low dielectric constant, such as glass and polymer. The measured forces increase very steeply as the gap of the spheres decreases, and become much larger than those of available theoretical predictions when the two single-crystalline spheres of SrTiO3 are closely spaced. The frequency dependence of the interaction force also shows an anomalous behavior. Our measurements indicate that a more accurate theoretical calculation should be performed to explain the experimental results. (C) 2003 American Institute of Physics