The Effect of Dissipation on the Torque and Force Experienced by Nanoparticles in an AC Field

TL;DR

This paper investigates how dissipation influences the electromagnetic force and torque on nanoparticles in an AC field, revealing conditions for particle rotation, resonance phenomena, and non-conservative forces due to absorption.

Contribution

It demonstrates that particle absorption is necessary for torque, explores resonance effects in multi-particle systems, and shows dissipation leads to non-conservative forces unlike classical models.

Findings

Torque requires particle absorption.

Multiple resonances depend on interparticle distance.

Dissipation causes non-conservative forces.

Abstract

We discuss the force and torque acting on spherical particles in an ensemble in the presence of a uniform AC electric field. We show that for a torque causing particle rotation to appear the particle must be absorptive. Our proof includes all electromagnetic excitations, which in the case of two or more particles gives rise to one or more resonances in the spectrum of force and torque depending on interparticle distance. Several peaks are found in the force and torque between two spheres at small interparticle distances, which coalesce to just one as the separation grows beyond three particle radii. We also show that in the presence of dissipation the force on each particle is non conservative and may not be derived from the classical interaction potential energy as has been done in the past.