Boundary-layer effects on electromagnetic and acoustic extraordinary transmission through narrow slits

TL;DR

This paper extends existing theories of extraordinary wave transmission through narrow slits by incorporating boundary-layer effects such as dissipation and viscosity, providing accurate analytical models validated by experiments.

Contribution

It introduces a boundary-layer analysis for electromagnetic and acoustic wave transmission through narrow slits, accounting for dissipation and viscous effects, and generalizes previous idealized models.

Findings

Analytical approximations match experimental data.

Electromagnetic-acoustic analogy is maintained with a single parameter.

Boundary-layer effects significantly influence transmission resonance.

Abstract

We study the problem of resonant extraordinary transmission of electromagnetic and acoustic waves through subwavelength slits in an infinite plate, whose thickness is close to a half-multiple of the wavelength. We build on the matched-asymptotics analysis of Holley & Schnitzer (Wave Motion, 91 102381, 2019), who considered a single-slit configuration assuming an idealised formulation where dissipation is neglected and the electromagnetic and acoustic problems are analogous. We here extend that theory to include thin dissipative boundary layers associated with finite conductivity of the plate in the electromagnetic problem and viscous and thermal effects in the acoustic problem, considering both single-slit and slit-array configurations. By considering a distinguished boundary-layer scaling where dissipative and diffractive effects are comparable, we develop accurate analytical approximations that are generally valid near resonance; the electromagnetic-acoustic analogy is preserved up to a single physics-dependent parameter that is provided explicitly for both scenarios. The theory is shown to be in excellent agreement with GHz-microwave and kHz-acoustic experiments in the literature.