In this paper, a broadband metamaterial absorber (MA) based on a multi-layer structure is presented. The advantages of this MA are the small periodic unit size, they are thin, have excellent polarization characteristics and are adaptive for wide angles of oblique incident electromagnetic waves. The unit cell of the broadband MA is composed of three dual-band sub-cells; each presents two resonant frequencies so as to form a wide absorptive spectrum when stacked. The sandwiched dual-band sub-cell is composed of one metallic annular patch and one metallic circular patch each etched on a lossy substrate. The radii of the metallic patches forming each sub-cell are different so as to appear to have different resonant frequencies. In the design of the unit cell there are metallic circular patches and an air layer at the bottom of each sub-cell to form magnetic coupling and avoid coupling between sub-cells. The broadband MA presents good absorptivity above 80% between 8.8 and 10.8 GHz, with a full width at half maximum (FWHM) absorption bandwidth of 2.3 GHz and a relative FWHM absorption bandwidth of 23%.

This paper presents a multi-band metamaterial absorber comprising three multi-gap split-ring resonators (SRRs) with different radii and ring widths, designed in combinatorial approach. Experiments demonstrate that it can perform absorption peaks at three resonant frequencies 7.10 GHz, 10.04 GHz, and 17.44 GHz with the absorption of 99.90%, 99.91%, and 99.68%, respectively. The physical mechanism of metamaterial absorber was explained through numerical calculation and simulation, which showed that three absorption peaks were caused respectively by the three four-gap SRRs. The absorber is insensitive to incident angles and polarization states, so it has broad prospect of application.

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