A High-Temperature and Frequency-Reconfigurable Multilayer Frequency Selective Surface Using Liquid Metal

Abstract

A high-temperature and frequency-reconfigurable multilayer frequency selective surface (FSS) based on liquid metal is proposed in this work. After construction of a multilayer dielectric cavity with specific dielectric-shaped pillars and the injection of liquid metal (EGaIn) into each layer of the cavity, the liquid metal and dielectric pillars form a slot-type bandpass FSS, and frequency reconfiguration is realized by switching the injection layer. A prototype of the proposed FSS was designed, fabricated and measured. The measured results validated the design well. The good conductivity and fluidity of the liquid metal are utilized to realize the reconfigurable electromagnetic performance of the proposed FSS. This works in the C-band (5 GHz) and Ku band (13 GHz) and has a frequency switching time between 13.1 to 14.2 s. Moreover, due to the good thermal conductivity of liquid metal, the flowing liquid metal can take away heat, and the multilayer FSS can work as cooling plate. The heat transfer performance was investigated by numerical simulations. A 1000 • plane heat source was set on the bottom surface of the double-layer FSS. The average temperature on the top surface was 62.2 • , when the liquid metal fluid in the FSS had a speed of 1 m/s. The proposed multilayer FSS has strong potential for applications in some special application fields involving stealth and hypersonic aircraft.INDEX TERMS Multilayer FSS, frequency reconfiguration, liquid metal, heat transfer.

Switchable and optically transparent ultrawide stopband frequency selective surface for electromagnetic shielding

“…入射到其上的电磁波呈现出独特的空间滤波特性 [1] ，在吸波材料 [2,3] 、天线罩 [4,5] 、 电磁干扰(EMI)抑制 [6,7] 等多个领域内具有广泛应用。与金属网屏蔽相比，FSS 电磁屏蔽结构更轻便且具有频率选择性，可应用于特定场所以满足其电磁安全或 健康需求，如重症监护室(ICU) 、数据中心、安全装置、军事设施和关键基础设 施等 [8][9][10][11][12][13][14] 。由于外部高频电磁波穿透混凝土墙壁时衰减严重，主要通过玻璃门窗 进入建筑物内部，因此在提供电磁屏蔽的同时，需要考虑光学透明性和美观。随 着无线技术和雷达技术的不断发展，对超宽带电磁屏蔽结构的需求日益增加。因 此，设计一种透明的超宽带电磁屏蔽体具有重要应用价值。 近年来，已有许多研究致力于电磁干扰(EMI)抑制的光学透明频率选择表 面(FSS)结构设计 [15][16][17][18][19][20] 。一种常用策略是应用透明导电材料，例如通过银纳米 线(Ag NW)或氧化铟锡(ITO)来实现透明屏蔽。Yang 等人使用银纳米线透明 油墨设计了具有 81.6%透明度的 FSS 结构，在 0.71 ~ 1.25 GHz 和 1.73 ~ 2.16 GHz 的测量范围内产生良好反射，实现了 GSM 频段 EMI 的有效屏蔽 [15] 。Zhang 等人 利用 ITO 制作 FSS 吸收体，通过吸收电磁波实现从 7.8 GHz 到 18.0 GHz 的透明 宽带屏蔽 [18] 。 另一种方式则是将 FSS 结构设计中常用的介质基板更换为透明基板， 通过设计图案未覆盖区域实现光学透明。例如，Dewani 等人利用丝网印刷技术 将基于电阻性油墨的 FSS 结构印刷在玻璃上，在 1.5 至 2.5 GHz 频段实现理想的 屏蔽 [20] 。因此，当前光学透明 FSS 设计可以有效抑制特定频段或双频甚至三频段 的 EMI，但尚缺乏能够抑制超宽带范围(包含 P、L、S、C、X 以及 Ku 波段) EMI 的电磁屏蔽设计。 随着无线新技术的不断发展，对多功能电磁屏蔽结构提出了新要求，超宽带 电磁屏蔽、电磁性能动态可调等成为电磁屏蔽设计的重要功能特点。对于宽带电 磁屏蔽的研究，目前主要基于小型化、多层技术实现宽带电磁特性 [21][22][23][24] 。 Habib S 等人通过多层及卷曲 FSS 方形和圆形环路元件实现了 S、C、X 频段的宽带带 阻 [21] ， Xu, S J 等人则通过三层级联 FSS 结构实现了小型化及 7.34 GHz ~ 15.0 GHz 的宽阻带抑制 [22] 。电磁性能动态可调通常分为可开关和可调谐两种 [25][26][27][28][29][30][31][32] ，可开关 [25] ；也可以利用液态 金属注入与否实现开关功能，切换 FSS 结构的滤波功能，例如 Ghosh S 等人将 EGaIn 注入 FSS 结构微通道，实现全通到带通(TE 极化)/带阻(TE、TM 极化) 的切换 [32] FSS ...…”

Dual-Polarized Metal Vivaldi Array Using Independent Structural Elements

“…Wideband or multi-band antennas are very valuable for improving the performance of wireless communication systems, especially for multi-functional integrated communication systems [ 1 , 2 , 3 , 4 , 5 ]. Since Gibson first proposed the Vivaldi antenna in 1979, it has been demonstrated to be a critical technology for providing a wide operating bandwidth and has been widely utilized in various systems [ 6 ].…”