A novel four-legged loaded element thick-screen frequency selective surface with a stable performance

<正>A thick-screen frequency selective surface(FSS) has not only a broad bandwidth but also the advantages of overcoming the multilayer FSS shortcoming of complex structure and low transmittance of centre frequency due to the cascade of FSSs,and this means it could potentially be applied in a stealth curved streamlined radome.However,there is an unsteadiness of centre frequency in a wide range of incident angles and another unsteadiness of polarization in a big incident angle.In order to solve these problems,in this paper we provide a novel four-legged loaded element thick-screen FSS.The structure is analysed and simulated using the mode matching method and moment method.The centre frequency,the transmittance of centre frequency,and bandwidth of the structure are investigated when some parameters including the polarization at a big incident angle and the incident angles of TE & TM waves are changed. The novel four-legged loaded element thick-screen FSS has better transmission properties with a better steadiness of polarization and incident angle independence.The novel structure of the four-legged loaded element thick-screen FSS provides a valuable reference for their application in a stealth curved streamlined radome.     

一种性能稳定的新Y形单元厚屏频率选择表面

厚屏频率选择表面(FSS) 能克服双层或多层薄屏FSS级联引起的结构复杂和中心频率透过率容易降低的不利影响, 并且在拓展FSS带宽方面具有优势, 这使其在曲面隐身雷达天线罩应用方面有潜在的价值. 但是, 当电磁波以大范围角度入射时, 中心频率可能会随入射角度的变化而漂移, 而且在大角度入射时不易实现极化稳定性. 本文针对此问题, 设计了一种新Y形单元厚屏FSS, 利用模式匹配法对此结构进行分析计算, 并研究TE, TM波入射时角度变化及大角度入射时极化变化对通带带宽、 中心频率及其透过率的影响. 仿真实验结果表明: 新Y形单元厚屏FSS的中心频率在TE, TM波入射时均能实现角度稳定性和大角度入射时的极化稳定性. 这为FSS在曲面隐身雷达天线罩上的应用提供了一种借鉴.     

Effect of NO annealing on charge traps in oxide insulator and transition layer for 4H-SiC metal–oxide–semiconductor devices

The effect of nitric oxide(NO) annealing on charge traps in the oxide insulator and transition layer in n-type4H–Si C metal–oxide–semiconductor(MOS) devices has been investigated using the time-dependent bias stress(TDBS),capacitance–voltage(C–V),and secondary ion mass spectroscopy(SIMS).It is revealed that two main categories of charge traps,near interface oxide traps(Nniot) and oxide traps(Not),have different responses to the TDBS and C–V characteristics in NO-annealed and Ar-annealed samples.The Nniotare mainly responsible for the hysteresis occurring in the bidirectional C–V characteristics,which are very close to the semiconductor interface and can readily exchange charges with the inner semiconductor.However,Not is mainly responsible for the TDBS induced C–V shifts.Electrons tunneling into the Not are hardly released quickly when suffering TDBS,resulting in the problem of the threshold voltage stability.Compared with the Ar-annealed sample,Nniotcan be significantly suppressed by the NO annealing,but there is little improvement of Not.SIMS results demonstrate that the Nniotare distributed within the transition layer,which correlated with the existence of the excess silicon.During the NO annealing process,the excess Si atoms incorporate into nitrogen in the transition layer,allowing better relaxation of the interface strain and effectively reducing the width of the transition layer and the density of Nniot.     

低品位菱锰矿浸出锰的工艺条件研究

对低品位菱锰矿浸出工艺条件进行了研究,发现还原剂(绿矾、煤粉及双氧水)、硫酸、液固比、pH值、浸出温度及时间等因素对锰浸出率存在重要影响.通过单因素分析试验,得出最优工艺条件:当矿酸比为1∶ 0.324、温度为90℃、液固比为6:1、pH值为4.50、浸出时间为5h时,锰的实际浸出率可达80%以上.该工艺具有能源消耗低,生产成本低,锰的回收率高等优点.     

一种介质-金属加载圆孔单元厚屏频率选择表面

厚屏频率选择表面能较好地改善FSS带宽性能,是实现隐身雷达天线罩的有效手段.为了全面掌握厚屏FSS的传输特性,给FSS的工程应用提供可靠依据,本文设计了一种介质-金属加载圆孔单元的厚屏频率选择表面.采用矩量法对此结构进行分析计算,主要研究了加载金属直径、加载介质厚度、电磁波入射角等几个参数对厚屏FSS传输特性的影响规律.仿真实验结果表明:带宽、中心频率及其透过率都对填充介质直径、加载金属直径、加载介质厚度、电磁波入射角和不同排列方式有不同程度的敏感性,可以通过合理调整加载金属直径及加载介质厚度来获得较宽的通带和较高的透过率.这为实现厚屏FSS在曲面隐身雷达天线罩上的应用提供了一种有价值的借鉴.