基于粒子群结构寻优的电磁隐身微网格超表面

Electromagnetic Stealth Micro-Grid Metasurface Based on Particle Swarm Structure Optimization

针对电磁隐身超表面设计中寻求精确单元反射相位时存在的难点,提出一种将单元金属贴片区域网格化分割,并通过粒子群算法(Particle Swarm Optimization,PSO)自动寻优的设计方法,可自动生成符合预设反射相频特性的金属贴片图案.该方法将方形超表面单元的金属贴片区域划分为N×N网格(N为偶数,根据N和全对称条件可得到其中的自由网格数n),再用PSO对其自由网格的贴片编码进行训练,直至对应的贴片单元所构建的平面周期结构可实现预期反射相频特性(包括目标频率的反射相位精度及其邻域频段上相频曲线的平坦度).作为案例,在厘米波段和太赫兹波段,将寻优获得的反射相位相差约90°的4种单元,分别以90°和180°的相位梯度构建1 bit和2 bit超表面,全波仿真结果显示其在中心频率附近均可以得到-10 dB以上的RCS削减效果.验证了该方法可自动设计出具备特定反射相位的单元,并且跨频段适用,其所构建的超表面在获得特定频率雷达散射截面(Radar Cross Section,RCS)削减效果的同时,可兼顾有效削减的频段宽度.

A new design method of metasurface's unit cell for getting preset reflection phase-frequency characteristics is proposed,in which the metal patch area of the cells are splitted into small grids,whose patches schemes are trained by particle swarm optimization(PSO)algorithm.This is an effective solution to resolve the problem in the design of unit cells'reflection phase of electromagnetic stealth metasurface,in which the metal patch area of a square unit cell is splitted into N×N grids(N is an even number,the free grids number n can be derived by N and full symmetric condition),and the code string of the free grids'patch is trained by PSO,until the expected reflection phase-frequency characteristics(including the reflection phase's accuracy at target frequency and the flatness of phase-frequency curve in the neighborhood frequency band)obtain from the planar periodic structure constructed by the optimal unit cells.Taken as examples,in the centimeter band and terahertz band,four unit cells with a reflection phase difference of about 90°are given by PSO,and the 1-bit and 2-bit metasurfaces are constructed with phase gradients of 90°and 180°respectively,whose-10 dB RCS reduction effect near the target frequency are verified.It is verified that the unit cell with specific reflection phase can be designed automatically by this method,which is also universally applicable to different frequency bands,and the RCS reduction effect on a specific frequency and the bandwidth with satisfied reduction effect can both be obtained.