Sizable electromagnetic forces in parallel-plate metallic cavity

TL;DR

This paper investigates electromagnetic forces in a parallel-plate metallic cavity across infrared and microwave frequencies, revealing resonance-enhanced forces significantly stronger than photon pressure, with different underlying mechanisms at different scales.

Contribution

It provides a comprehensive analysis of electromagnetic forces at multiple scales, introduces a simple transmission line model, and examines effects of surface features on force behavior.

Findings

Resonance significantly amplifies electromagnetic forces beyond photon pressure.

Different mechanisms drive strong forces at infrared and microwave scales.

Surface corrugation and roughness tend to induce attraction between plates.

Abstract

Using a boundary element method to calculate the electromagnetic fields and the Maxwell stress tensor method to compute the electromagnetic forces, we investigate electromagnetic wave induced forces acting on a pair of identical metal plates that forms an electromagnetic resonance cavity. Different frequency regimes are considered, from infrared frequencies with micron scale structures down to the microwave regime which involves millimeter scale structures. We found that at both length scales, the electromagnetic wave induced forces can be significantly stronger than the usual photon pressure exerted by a laser beam if the cavity is excited at resonance although the mechanisms that underlie the strong force are different at different length scales. In the infrared frequency regime, the strong force is induced by field penetration into the metal, whereas in the microwave regime, the electromagnetic force is induced by the leakage of electric field at the edges. At both frequency scales, we compare the results we obtained for Au metal plates with fictitious perfect electric conductor plates so as to understand the effect of field penetration. We also showed that a transmission line model can give simple expressions that can capture the essence of the physics. The effect of surface corrugation and surface roughness is also investigated, and we find that corrugation/roughness generally induces attraction between the plates.