Stealth technology includes shape stealth, material stealth, and electronic countermeasure technology, which achieve the purpose of stealth by absorbing or losing electromagnetic wave energy. Material stealth refers to a stealth technology that uses absorbing materials to absorb and detect electromagnetic waves, and is currently the most important stealth approach. The absorbing material can convert electromagnetic interference into heat and dissipate it, thereby realizing electromagnetic shielding. Absorbing materials with superior performance require strong absorption, wide frequency bandwidth, light weight and good overall performance. Traditional absorbing materials include ferrite, barium titanate, silicon carbide, graphite, conductive fiber, etc. They usually have the shortcomings of narrow absorption band or high density.
Research in recent years has found that electromagnetic metamaterials have peculiar and adjustable electromagnetic effects and can achieve high absorption of electromagnetic waves. This has opened up a new field for the research of absorbing materials and has become a hot spot in the field of absorbing materials. The so-called metamaterial is a new academic vocabulary that has appeared in the field of physics in the 21st century. It refers to some artificial composite structures or composite materials that have supernormal physical properties that natural materials do not have. Metamaterial absorber is a kind of composite absorber composed of metamaterial structure and dielectric substrate.
Compared with traditional absorbing materials, metamaterial absorbers have many advantages such as thin thickness, light weight, strong absorption, adjustable frequency bands, and designable electromagnetic parameters of materials. They have shown important potential in the fields of stealth, imaging, and detection. Value. By optimizing the structural model and adjusting the electrical resonance and magnetic resonance of the unit, the metamaterial absorber can achieve impedance matching with free space, reduce the reflectivity of incident electromagnetic waves, and use the dielectric loss and ohmic loss of the structural unit to achieve strong absorption of electromagnetic waves . This mechanism overcomes the thickness limitation imposed by the diffraction effect on traditional absorbing materials, and meets the design requirements of light and thin absorbing materials.
Another significant advantage of this material is that it does not need to load a lumped resistance as a loss layer to achieve a wave absorption rate close to 100%. Metamaterials can prepare multi-band and broadband absorbers. According to reports, a metamaterial absorber composed of dual-band electric harmonic oscillators has an absorption rate of 85% at 1.4THz and an absorption rate of 94% at 3THz. It is also reported that through the superposition of resonant structures of different sizes, three resonant peaks can be merged into a broadband absorption band in the terahertz frequency band. The bandwidth of the absorber with an absorption rate greater than 60% is 1.86 THz.
There is also a report of a wide-band metamaterial absorber based on lumped elements. The absorber has an absorption rate of over 90% in the low frequency band of 2.5 to 4.46 GHz, and a good absorption characteristic of 70% in the FWHM. The study also shows that the metamaterial absorber based on the double-layer hexagonal close-packed dendritic structure can obtain an absorption rate higher than 90% in the frequency range of 9.79～11.72GHz through optimized design.
Metamaterials can be used as absorbing materials alone, or they can be combined with traditional absorbing materials. For example, by covering a layer of metamaterials on the surface of traditional absorbing materials, not only can the absorption rate of traditional absorbing materials be enhanced, but also the influence of polarization on traditional absorbing materials can be improved.