A Circuit-based Model for the Interpretation of Perfect Metamaterial Absorbers

TL;DR

This paper presents a transmission line model for perfect metamaterial absorbers, providing analytical formulas to understand and optimize their absorption characteristics, bandwidth, and angular stability.

Contribution

It introduces a circuit-based analytical model that explains the absorption mechanism and guides the design of tunable, broadband, and angularly stable metamaterial absorbers.

Findings

Moderate substrate losses enable perfect absorption through impedance matching.

Highly capacitive elements maximize absorption bandwidth.

Low capacitive elements achieve high frequency selectivity.

Abstract

A popular absorbing structure, often referred to as Perfect Metamaterial Absorber, comprising metallic periodic pattern over a thin low-loss grounded substrate is studied by resorting to an efficient transmission line model. This approach allows the derivation of simple and reliable closed formulas describing the absorption mechanism of the subwavelength structure. The analytic form of the real part of the input impedance is explicitly derived in order to explain why moderate losses of the substrate is sufficient to achieve matching with free space, that is, perfect absorption. The effect of the constituent parameters for tuning the working frequency and tailoring the absorption bandwidth is addressed. It is also shown that the choice of highly capacitive coupled elements allows obtaining the largest possible bandwidth whereas a highly frequency selective design is achieved with low capacitive elements like a cross array. Finally, the angular stability of the absorbing structure is investigated.