Enhancement of absorption bandwidth of magnetic microwave absorbers via embedding metamaterials

Traditional microwave absorbers are typically made of ferrite powders and/or ferromagnetic metal powders and rely on ferromagnetic relaxation in the powders. These absorbers can show strong absorption over a relatively wide frequency range if the thickness is sufficiently large, and for a given absorption level the frequency bandwidth usually decreases with a reduction in the thickness. One can also make microwave absorbers by using metamaterials that consist of metallic patterns on a back-grounded dielectric substrate. The perfect metamaterial absorber can achieve near unity absorption and can be easily adjusted by changing the structure parameters. That brings a new way to improve the absorption property of the traditional magnetic absorber, especially in low frequency range under the condition of limited thickness. In this paper, we presented the method of increasing the low-frequency bandwidth of absorption of magnetic microwave absorber almost without increasing the thickness via embedding a thin metamaterial layer into the absorber.