Abnormal enhancement of electric field inside a thin permittivity-near-zero object in free space

TL;DR

This paper demonstrates that a strong electric field enhancement occurs inside thin permittivity-near-zero objects in free space due to energy flow constraints, distinct from plasmonic resonance effects.

Contribution

It reveals a novel physical mechanism for electric field enhancement in permittivity-near-zero objects, emphasizing geometry and energy flow rather than resonance.

Findings

Electric field can be strongly enhanced inside permittivity-near-zero objects.

Enhancement increases as the object becomes thinner.

The mechanism differs from plasmonic resonance enhancement.

Abstract

It is found that the electric field can be enhanced strongly inside a permittivity-near-zero object in free space, when the transverse cross section of the object is small and the length along the propagation direction of the incident wave is large enough as compared with the wavelength. The physical mechanism is explained in details. The incident electromagnetic energy can only flow almost normally through the outer surface into or out of the permittivity-near-zero object, which leads to large energy stream density and then strong electric field inside the object. Meanwhile, the magnetic field inside the permittivity-near-zero object may be smaller than that of the incident wave, which is also helpful for enhancing the electric field. Two permittivity-near-zero objects of simple shapes, namely, a thin cylindrical shell and a long thin rectangular bar, are chosen for numerical illustration. The enhancement of the electric field becomes stronger when the permittivity-near-zero object becomes thinner. The physical mechanism of the field enhancement is completely different from the plasmonic resonance enhancement at a metal surface.