摘要
近年来,基于超材料的电磁吸波器件由于其宽带、易制备等优势而备受各国研究者的广泛关注.本文为实现宽带电磁低可探测,提出一种渐变电阻膜-介质复合结构的超材料吸波器.基于传输线理论和阻抗匹配原理,对强吸波条件进行了分析.在单元结构设计方面,采用遗传算法在多变量域内全局搜索最优解,快速地确定出能够兼顾低频与宽带吸波性能的超材料单元结构与电阻参数,并对器件吸波性能与吸波机理进行了深入的探讨.仿真结果表明,在垂直入射下,所设计的超材料吸波器对1.62-19.16 GHz(相对带宽168.8％)之间的入射波吸收率均大于90％,有效地向L和K波段拓展了吸收带宽.虽然在部分频段测试和仿真结果之间存在一定偏差,但两种类型的曲线随频率的变化趋势基本一致,这充分证明了所设计的超材料吸波器在低频宽带吸波领域具有潜在应用价值.
Abstract
In recent years,electromagnetic(EM)wave absorbing devices based on metamaterials have attracted widespread attention,due to their advantages such as broadband,easy preparation,and flexibility to tailor EM waves.Nevertheless,a review of the existing research reveals that the inherent sub-wavelength characteristics of metamaterials and metasurfaces impose certain constraints on their applications in low-frequency ranges.In order to achieve low detectability that takes into account both low-frequency and broadband absorbing performance,this work,presents a metamaterial absorber based on 5-layer gradient resistance film and dielectric composite structure,as shown in Fig.(a).To begin with,we introduce the structural design of the initial element,and based on this,the transmission line theory and impedance matching principle are used to analyze the strong wave absorption conditions of the absorber element.In terms of the element structure optimization,the genetic algorithm is adopted to globally search for the optimal solution in the multi-variable domain,resulting in the rapid determination of metamaterial elements'configurations and resistance parameters that meet the design goals.In the simulation,the wave absorption performance and mechanism of the designed absorbing element are also investigated in an in-depth manner.Simulation results show that the designed metamaterial absorber can achieve more than 90％EM wave absorption in a frequency range of 1.62-19.16 GHz(with a relative bandwidth of 168.8％)under normal incidence of linearly polarized plane waves,which effectively expands the absorption bandwidth to the L band and K band.In addition,the simulations for oblique incidence at different polarizations provide strong evidence for the device's insensitivity to both polarization and angle.The radar cross section(RCS)curves obtained by the time domain(TD)simulation illustrate that the novel structure can achieve more than 10 dB RCS reduction in a frequency range of 1.7-20 GHz.In the device's performance verification process,a metamaterial absorber with 20 x 20 elements and dimensions of 1.566 λl× 1.566 λl × 0.113 λl is fabricated and tested by using the bow method reflectivity test system.The absorptivity curves under 5° oblique incidence of different polarizations,show that the proposed metamaterial absorber can realize more than 80％EM absorption in an entire frequency range from 2 to 18 GHz,the test results of different polarizations are basically consistent.The test results at oblique incidence(θ ≥ 30°)show that although the measured and simulated curves exhibit discrepancies in certain frequency bands due to human error or material dispersion characteristics,the overall experimental results are consistent with our expectations,which fully proves that the designed metamaterial absorber has potential application value in the field of low-frequency and broadband EM absorption.
维普
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