Retrieval of the effective constitutive parameters from metamaterial absorbers*

Abstract

The equivalent medium theory of metamaterials provides a way to obtain their effective constitutive parameters. However, because of its non-reciprocity, the complexity of the electromagnetic coupling, and a metallic bottom layer, it has been challenging to retrieve them from a metamaterial absorber. In this paper, we propose a method without any approximation to obtain them, in which the non-reciprocity and the strong electromagnetic coupling are included. Compared with the three methods such as symmetric metamaterial method, asymmetric metamaterial method and metasurface method, our method can reveal the metamaterial absorber’s electrical and magnetic resonance and show its electromagnetic coupling coefficients. To deal with a metamaterial absorber with a metallic bottom layer, four corners of the metallic bottom layer in the unit cell are removed, making it possible to retrieve the electromagnetic parameters. Surprisingly, these results show that the metamaterial absorber with a metallic bottom layer in our example operates in a negative refraction state at the half absorption frequencies, which helps further understand the absorbing mechanism of these metamaterial absorbers.

A compact ultra-broadband metamaterial absorber for Ku-, K-, and Ka- band applications

“…The retrieval method proposed by Smith et al [46,47] cannot successfully retrieve the parameters. However, this design can be achieved by creating openings in the metallic bottom layer [48]. As shown in figure 3, the permittivity and permeability curves are relatively smooth between 16.22 GHz and 30.03 GHz.…”