超薄宽带平面聚焦超表面及其在高增益天线中的应用

针对相位梯度超表面在灵活操控电磁波与提高天线增益中的潜在应用,提出一种新型的宽带超表面单元,实现了在较宽频带范围内操控电磁波波前与提高天线增益.本文首先设计了一种圆环十字形对称单元来控制反射波的相移量,单元厚度为1 mm,尺寸为0.3λ_0(λ_0=20 mm),工作频段15—18 GHz,而后验证了由该单元组成的相位梯度超表面在15—18 GHz范围内对电磁波的奇异反射与聚焦特性.最后将设计的反射聚焦超表面应用于提高天线增益中,仿真与测试结果均表明,天线最高增益在15—18 GHz内平均增加了11 d B且-1 dB增益带宽为15—18 GHz(相对带宽为18.2%).由于厚度薄、重量轻、频带宽,设计的该单元拓展了相位梯度超表面在微波领域的应用,有望为高增益天线的实现提供新的方法.     

单层超薄高效圆极化超表面透镜

针对超表面在透镜方面的应用, 本文设计了一种交叉极化透射聚焦超表面, 实现了将圆极化波转化为交叉极化波的同时聚焦电磁波的功能. 设计了一款旋转型单元, 单元为一层且厚度仅为1.5 mm, 分析了旋转型单元提供不同相移的原理并设计了相邻单元相移差为60°的相位梯度超表面, 在中心频率f=15 GHz附近发生奇异折射, 折射角与理论计算结果一致, 验证了设计单元的有效性, 基于该单元设计了尺寸为90 m mm×90 mm、单元数为15×15 的透射型聚焦超表面, 在中心频率f=15 GHz附近, 左旋圆极化平面波照射时, 透射波聚焦于L=40 mm 的实焦点且透射波为照射波的交叉极化波. 该超表面透镜效率高、厚度薄且为单层, 易于加工, 相对于传统透镜, 优势明显, 在操控电磁波、改善透镜性能方面有潜在应用价值.     

Single-layer broadband planar antenna using ultrathin high-efficiency focusing metasurfaces

Phase gradient metasurfaces(PGMS) offer a fascinating ability to control the amplitude and phase of the electromagnetic(EM) waves on a subwavelength scale, resulting in new applications of designing novel microwave devices with improved performances. In this paper, a reflective symmetrical element, consisting of orthogonally I-shaped structures, has been demonstrated with an approximately parallel phase response from 15 GHz to 22 GHz, which results in an interesting wideband property. For practical design, a planar antenna is implemented by a well-optimized focusing metasurface and excited by a self-designed Vivaldi antenna at the focus. Numerical and experimental results coincide well. The planar antenna has a series of merits such as a wide 3-d B gain bandwidth of 15–22 GHz, an average gain enhancement of 16 d B, a comparable aperture efficiency of better than 45% at 18 GHz, and also a simple fabrication process. The proposed reflective metasurface opens up a new avenue to design wideband microwave devices.     

Ultra-thin circularly polarized lens antenna based on single-layered transparent metasurface

Circularly polarized(CP) lens antenna has been applied to numerous wireless communication systems based on its unique advantages such as high antenna gain, low manufacturing cost, especially stable data transmission between the transmitter and the receiver. Unfortunately, current available CP lens antennas mostly suffer from high profile, low aperture efficiency as well as complex design. In this paper, we propose an ultra-thin CP lens antenna based on the designed singlelayered Pancharatnam–Berry(PB) transparent metasurface with focusing property. The PB metasurface exhibits a high transmissivity, which ensures a high efficiency of the focusing property. Launched the metasurface with a CP patch antenna at its focal point, a low-profile lens antenna is simulated and measured. The experimental results show that our lens antenna exhibits a series of advantages including high radiation gain of 20.7 dB, aperture efficiency better than 41.3%, and also narrow half power beam width(HPBW) of 13°at about 14 GHz. Our finding opens a door to realize ultra-thin transparent metasurface with other functionalities or at other working frequencies.     

Sb2O3/BiVO4/WO3异质结构建及光电催化合成过氧化氢

采用溶剂热法-旋涂法构建了Sb₂O₃/BiVO₄/WO₃半导体异质结,并采用X射线衍射、扫描电子显微镜、X射线光电子能谱等手段表征了其物化性质。在1.23 V(vs RHE)电位下,BiVO₄/WO₃的光电流密度相对于BiVO₄提高了2倍。进一步复合Sb₂O₃之后,虽然Sb₂O₃/BiVO₄/WO₃薄膜的光电流密度有所下降,但其光电催化产H₂O₂的法拉第效率和产生速率得到明显提升。在1.89V(vs RHE)电位下,3c-Sb₂O₃/BiVO₄/WO₃薄膜产H₂O₂的法拉第效率提高到约19%;1c-Sb₂O     

Ultra-thin two-dimensional transmissive anisotropic metasurfaces for polarization filter and beam steering application

We propose an anisotropic planar transmitting metasurface, which has the ability to manipulate orthogonally-polarized electromagnetic waves in the reflection and refraction modes respectively. The metasurface is composed of four layered rectangular patches spaced by three layered dielectric isolators each with a thickness of 0.15λ0 at 15 GHz. By tailoring the sizes of the patches, the metasurface functions as a band-stop filter for the y-polarzied wave and a band-pass filter for the x-polarized wave operating from 14 GHz to 16 GHz. Moreover the phases of the transmitting x-polarized wave can be modulated at about 15 GHz, which contributes to beam steering according to the general refraction law. Experimental results are in good accordance with the simulated ones, in which the reflection efficiency is almost 100% while the transmission efficiency of the x-polarized wave reaches 80% at 15 GHz. Besides, the transmitted x-polarized wave is effectively manipulated from 14 GHz to 16 GHz.     

高极化纯度的超表面透镜设计与应用

针对超表面在透镜方面的应用,基于各向异性超表面单元设计了一款高极化纯度的聚焦超表面透镜,并探讨了其在高增益高极化纯度天线方面的应用.设计了一款具有极化滤波特性的各向异性超表面单元,单元对x极化波保持高透性的同时,对y极化波保持近乎为零的透射率.利用该型单元设计了焦距为30 mm、阵列大小为105 mm×105 mm、单元数为21×21的聚焦超表面透镜.根据光路可逆原理,焦点处发出的球面波被超表面透镜有效转化为平面波,从而达到提高天线增益的目标.实验中分别用不同极化形式的球面波照射聚焦超表面来研究超表面对不同极化波的控制特性.结果表明,x极化波照射时,超表面工作于透镜模式,球面波转化为平面波,天线增益大大提高;y极化波照射时,超表面类似于金属板,将入射波全部反射;x/y极化混合波照射时,天线增益大大提高,且极化隔离度高于25 dB,充分说明设计的聚焦超表面在提高x极化波增益的同时可高效滤除y极化波,达到了高增益高极化纯度的目标.     

Sb2O3/BiVO4/WO3异质结构建及光电催化合成过氧化氢

采用溶剂热法-旋涂法构建了Sb₂O₃/BiVO₄/WO₃半导体异质结,并采用X射线衍射、扫描电子显微镜、X射线光电子能谱等手段表征了其物化性质。在1.23 V(vs RHE)电位下,BiVO₄/WO₃的光电流密度相对于BiVO₄提高了2倍。进一步复合Sb₂O₃之后,虽然Sb₂O₃/BiVO₄/WO₃薄膜的光电流密度有所下降,但其光电催化产H₂O₂的法拉第效率和产生速率得到明显提升。在1.89V(vs RHE)电位下,3c-Sb₂O₃/BiVO₄/WO₃薄膜产 H₂O₂的法拉第效率提高到约 19%;1c-Sb₂O₃/BiVO₄/WO₃薄膜 H₂O₂产生速率从约2.1 μmol·h^-1·cm^-2提高到约3.6 μmol·h^-1·cm^-2。此外,Sb₂O₃的复合显著提高了BiVO₄/WO₃电极材料的光电催化稳定性。