Enhancing low-frequency performance of thin-layer magnetic microwave absorbing materials via phase gradient metasurface

• A phase gradient metasurface (PGM) working in low-frequency range (2–6 GHz) is designed, realizing abnormal reflection and surface wave conversion. • Through placing the PGM under the 1 mm thick magnetic microwave absorbing material, the low-frequency performance is significantly improved, achieving −10 dB absorption band of 2.8–6.2 GHz. • The surface density of the whole absorber is only 7.24 kg/m 2 . Magnetic composites are the most widely-used microwave absorbing materials (MAMs), but for low-frequency absorption, their heavy weight caused by the increasing thickness has always been the major drawback. Recently, the flexible manipulation on reflected/refracted wave realized by phase gradient metasurfaces (PGMs) has attracted much attention. Here, this manipulation ability is applied to enhance low-frequency performance of thin-layer magnetic MAMs. The −10 dB absorption band of the 1 mm thick MAM here is 8.4–13.6 GHz. A polarization conversion PGM working in low-frequency range is achieved by designing a sub-cell that contains an anchor-shaped metallic pattern. Six sub-cells with different sizes are properly arranged to ensure 2π phase change of the formed super-cell. With this PGM, the incident wave can be abnormally reflected when f > 4.17 GHz and coupled into surface wave when f < 4.17 GHz. Through placing the PGM under the 1 mm MAM, the low-frequency performance can be significantly improved, achieving −10 dB absorption band of 2.8–6.2 GHz. A corresponding sample with surface density of only 7.24 kg/m 2 was fabricated and the experimental result agrees with the simulation result. This work provides an effective approach to enhance low-frequency performance of thin-layer magnetic MAMs with light weight, which has important application value.