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Water is one of the most promising dielectric materials for microwave absorption due to its superior broadband dielectric loss. Inspired by the mechanism of traditional metamaterials, we have designed a water-based dielectric loss microwave absorber based on 3D-printing technology. Through stepwise structural optimization, the fabricated flexible water-based metamaterial experimentally demonstrated an ultra-broadband absorption in the frequency range 5.9–25.6 GHz with a thickness of 4 mm. Meanwhile, its angular tolerance also demonstrated wide-angle absorption capability. All these properties make it suitable for practical electromagnetic applications such as microwave radiation protection technology and microwave shielding boxes.

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Fishnet metamaterials have shown their excellent absorption at terahertz and optical frequencies. Here, we experimentally demonstrate an ultra-broadband and lightweight microwave absorber by fabricating a conventional magnetic absorbing material into a fishnetlike structure. Compared with the pure absorbing material, the broadest absorption bandwidth (less than −10 dB) of the fishnet-like absorber is extended from 7.4-11 GHz to 4.8-20.7 GHz. Meanwhile, the high surface density, which is a important shortcoming for the magnetic absorbing materials, has been reduced clearly because a large part of magnetic microwave absorption material has been removed. The ultra-broadband absorption is a result of the structure-induced strong magnetic resonances and electric confinement excited by the magnetic loop, which made the effective impedance of our structure matched well with the free space within the absorption bandwidth. Our results may provide a method for further improving the performance of the pure microwave absorbing materials.

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Bayberry-like, needle array-like and urchin-like NiCo2O4 hierarchical structures were synthesized by simple hydrothermal reactions.

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