Coupled Membranes with Doubly Negative Mass Density and Bulk Modulus

TLDR

The system’s symmetry allows separately tunable monopolar and dipolar resonances, enabling broadband double negativity. The authors present a structurally simple acoustic double‑negative metamaterial composed of two coupled membranes. The metamaterial is characterized by a homogenization scheme that uses measured surface displacement fields to determine effective mass density and bulk modulus beyond the long‑wavelength regime. Double negativity is achieved between 520 Hz and 830 Hz, and transmission and reflection predictions using the effective parameters agree remarkably well with the experiment.

Abstract

We present a structurally and conceptually simple acoustic double negative metamaterial comprising two coupled membranes. Owing to its symmetry, the system can generate both monopolar and dipolar resonances that are separately tunable, thereby making broadband double negativity possible. A homogenization scheme is implemented that enables the exact characterization of our metamaterial by the effective mass density and bulk modulus even beyond the usual long-wavelength regime, with the measured displacement fields on the sample's surfaces as inputs. Double negativity is achieved in the frequency range of 520-830 Hz. Transmission and reflection predictions using effective parameters are shown to agree remarkably well with the experiment.