The recent rise of metacomposites offered a new research strategy for electromagnetic shielding materials owing to their negative electromagnetic parameters, such as negative permittivity. Herein, we prepared silver/silicon nitride (Ag/Si₃N₄) metacomposites with tunable negative permittivity by a facile impregnation-calcination process, and explored their electrical conductivity, permittivity and electromagnetic shielding properties. As the Ag content increased, formative metal networks in the composites rendered their conductivity characteristic changing from a hopping conductivity to a metal-like conductivity. Tunable negative permittivity behavior combined with enhanced shielding effectiveness (SE) was observed at 2-18 GHz in the metacomposites with high Ag contents. The plasma-like negative permittivity was accounted for by a low frequency plasmonic state of free electrons in the inductive Ag networks, and the frequency band and absolute magnitude of negative permittivity could be adjusted by controlling Ag content, which was well described by Drude model. The average total SE of our obtained metacomposite could reach ∼30 dB, and the reflection was the primary shielding mechanism, which was attributed to the intense impedance mismatching stemmed from the negative permittivity. Our work opens up the possibility of designing metacomposites for promising electromagnetic shielding materials, promoting their application in microwave field.

由于金属复合材料的负电磁参数，例如负介电常数，近来兴起的复合材料为电磁屏蔽材料提供了一种新的研究策略。在这里，我们通过一种容易的浸渍-煅烧过程制备了具有可调的负介电常数的银/氮化硅（Ag / Si ₃ N ₄）超复合材料，并研究了它们的电导率，介电常数和电磁屏蔽性能。随着Ag含量的增加，复合材料中的形成性金属网络使其电导率特性从跳跃电导率变为类金属电导率。可调的负介电常数行为与增强的屏蔽效果（SE在2至18 GHz的高Ag含量的复合材料中观察到）。电感式Ag网络中自由电子的低频等离激元态解释了类等离子体的负介电常数，并且可以通过控制Ag的含量来调节负介电常数的频带和绝对大小，这在Drude模型中得到了很好的描述。我们获得的超复合材料的平均总SE可以达到约30 dB，并且反射是主要的屏蔽机制，这归因于负介电常数引起的强烈阻抗失配。我们的工作为设计有前途的电磁屏蔽材料的超复合材料开辟了可能性，并促进了它们在微波领域的应用。