Measuring Electric Dipole Moments of Trapped Sub-mm Particles

Abstract

We present a method for measurements of electric dipole moments on (sub)-mm size (basalt) particles levitated in an acoustic trap and centered within a plate capacitor. If an electric field is applied the particles oscillate with specific frequencies due to their permanent dipole moments. We observe dipole moments on the order of $D_P = 10^{-15} ... 10^{-14} \rm \, C \, m $. The dipole moment increases in small aggregates with the number of grains and is larger for samples vibrated (tribocharged) before trapping. The basalt grains show no sign of change in their dipole moment during measurements, implying a timescale for charge mobility being at least larger than minutes.