关键词: 超材料, 吸波材料, 柔性材料, 电磁防护

Abstract: With the advancement of science and technology, electromagnetic protective materials are no longer confined to traditional flexible electromagnetic shielding materials. The emergence of electromagnetic metamaterial functional devices has enabled effective manipulation of electromagnetic waves. In the fabrication of metamaterial absorbers, a majority of them are constructed as three-layer structures on rigid substrates. Flexible metamaterials not only enable the conformal wrapping of objects but also contribute to the electromagnetic properties of materials.
Traditional metamaterial structures consist of three layers, namely, a metal-dielectric-metal structure. The top layer is used for providing impedance matching, the middle layer attenuates electromagnetic waves through absorption, and the bottom layer is employed to block transmitted waves. Researchers have designed and prepared flexible absorbing materials that achieve efficient absorption at specific frequencies and within a wide frequency range, with polyimide (PI) being a commonly used flexible medium. Researchers replaced the metal resonator in the top layer of the absorbing material with a resistive film to optimize impedance matching. Studying flexible electromagnetic metamaterial absorbing materials with different material combinations is crucial for addressing complex electromagnetic wave environments and coping with multi-frequency band communication systems.
Subsequently, researchers began to design flexible electromagnetic metamaterial absorbing materials based on structures with more than three layers. The materials mainly achieve absorption at different frequencies by combining the electromagnetic characteristics of multiple layers, thus providing a broader absorption spectrum. Among them, flexible electromagnetic metamaterial absorbing materials based on indium tin oxide (ITO) not only achieve high absorption rates, but also maintain good optical transparency. This type of structure has greater design flexibility and resonance intensity. Therefore, such materials can achieve precise and extensive impedance matching, demonstrating broadband absorption characteristics.
Compared to planar structures, flexible electromagnetic metamaterial absorbing materials based on three-dimensional structures have significant potential applications. These materials can absorb electromagnetic waves in multiple frequency bands simultaneously and adapt to surfaces of various shapes and curvatures to meet various engineering and design requirements.
In general, the research scope of flexible electromagnetic metamaterial absorbers is extensive, involving diverse fabrication techniques employing multiple structures. The optimization and enhancement of electromagnetic performance are achieved through meticulously layered designs. In-depth exploration and practical experimentation in the aforementioned research directions may potentially offer novel insights and methodologies for the preparation and application of flexible electromagnetic metamaterial absorbers. The future applications of flexible metamaterial absorbers are expected to continually expand across various domains.

Key words: metamaterials, wave absorbing materials, flexible materials, electromagnetic protection