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图 1和图 2是本文中提出的基于二氧化钒材料的可调谐吸波器的单元结构示意图。图 1是金属谐振单元的示意图。图 2是侧视图。由图可知,该结构单元包括两种介质基板、两种谐振单元以及金属反射板,共10层。自下而上,第1层为金属反射板(材料为金,电导率σ=4.561×107S/m), 第2层为SiO2介质基板(相对介电常数ε=3.9,无损耗),第3层、第5层、第7层、第9层为Y2O3(相对介电常数ε=3.06,无损耗)介质基板,第4层为金属谐振单元(材料为金), 第6层、第8层、第10层为VO2谐振单元。金属反射板的边长p=70μm,厚度h1=0.1μm。SiO2介质基板和第3层Y2O3介质基板的边长p=70μm,厚度h2, h3分别为2μm和1.8μm,第5层、第7层、第9层Y2O3介质基板的尺寸分别是第2层介质基板尺寸的(1-k)倍,(1-2k)倍, (1-3k)倍(k=0.01)。金属谐振单元和VO2谐振单元形状相同、尺寸不同,都由一个蛇形线结构、4个正方形谐振环和一个正方形谐振单元构成,第6层、第8层、第10层VO2谐振单元尺寸分别是金属谐振单元尺寸的(1-k)倍, (1-2k)倍, (1-3k)倍。金属谐振单元中,蛇形线的外边长a=66μm,线宽和线间距离b=2μm,缝隙g=10μm,正方形谐振环的线宽c=0.2μm,线间距离d=3.8μm,由外至内,第1个正方形谐振环的边长e=60.2μm,第2个正方形谐振环的边长f=56.4μm,第3个正方形谐振环的边长i=52.6μm,第4个正方形谐振环的边长j=48.8μm,正方形谐振单元的边长m=10μm,厚度h4=1μm。其它结构参量如表 1所示。电磁波波矢方向为沿-z方向垂直入射。本文中将TE波定义为:电场E平行于y轴,磁场H平行x轴。吸波器的吸收率A(ω)可以表示为A(ω)=1-R(ω)-T(ω)-S(ω),其中R(ω)为反射率,T(ω)为透射率,S(ω)为散射率。由于本文中设计的吸波器的最底层为金属反射板,所以透射率T(ω)=0,散射率S(ω)不考虑,那么吸收率将写为A(ω)=1-R(ω)。
Table 1. Parameters of the absorber
parameters a b c d value/μm 66 2 0.2 3.8 parameters e f g i value/μm 60.2 56.4 10 52.6 parameters j k m p value/μm 48.8 0.01 10 70 parameters h1 h2 h3 h4 value/μm 0.1 2 1.8 1
一种基于二氧化钒材料的可调谐吸波器设计
Design of a tunable microwave absorber based on vanadium dioxide
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摘要: 为了在THz波段获得TE波下的可调谐吸收频谱, 采用全波仿真的方法, 设计了一款基于二氧化钒材料的可调谐THz吸波器, 对该吸波器的吸收频谱、电场图、表面电流图以及能量损耗图进行分析, 并讨论了结构参量h4, k以及入射角度θ对吸收频域和吸收带宽的影响。结果表明, 通过外部温控的方式改变二氧化钒谐振单元的物理特性可以获得可调谐的吸收频谱并改善吸波器的吸收性能, 该吸波器在温度T≥68℃时, 可以实现在2.70THz~3.36THz频段的宽带吸收(吸收率在90%以上), 相对带宽达到21.8%;在T<68℃时, 可以实现多个单频点的吸收; 改变结构参量h4, k可以改变吸收频点的位置以及吸收带宽, 改变入射角度θ可以影响吸波器的吸收效果。该研究对可调谐太赫兹器件的进一步探究是有帮助的。Abstract: In order to obtain the tunable absorption spectrum of TE wave in THz band, a tunable THz absorber based on vanadium dioxide was designed by full-wave simulation. Absorption spectrum, electric field, surface current and energy loss of the absorber were analyzed. The effects of structural parameters h4, k and incident angle θ on absorption frequency domain and absorption bandwidth were discussed. The simulation results show that, tunable absorption spectrum can be obtained and absorption performance of the microwave absorber can be improved by changing the physical characteristics of vanadium dioxide resonator unit through external temperature control. When T≥68℃, broadband absorption of microwave absorber can be achieved in 2.70THz~3.36THz band. Absorption rate is above 90% and relative bandwidth can reach 21.8%. When T < 68℃, multiple single frequency points can be absorbed. The position of absorption frequency point and absorption bandwidth can be changed by changing the structural parameters h4 and k. The absorption effect can be affected by changing incident angle θ. This study is helpful for further research of tunable terahertz devices.
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Key words:
- physical optics /
- phase-changed material /
- THz microwave absorber /
- tunable property
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Figure 4. Distribution of electric field of the absorber at different frequencies
a—side view of electric field distribution at 2.77THz b—side view of electric field distribution at 3.18THz c—electric field distribution of metal resonant unit at 2.77THz d—electric field distribution of metal unit at 3.18THz
Table 1. Parameters of the absorber
parameters a b c d value/μm 66 2 0.2 3.8 parameters e f g i value/μm 60.2 56.4 10 52.6 parameters j k m p value/μm 48.8 0.01 10 70 parameters h1 h2 h3 h4 value/μm 0.1 2 1.8 1 -
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