High-confinement ultra-wideband bandpass filter using compact folded slotline spoof surface plasmon polaritons

A novel bandpass filter(BPF)based on spoof surface plasmon polaritons(SSPPs)using a compact folded slotline structure is proposed and experimentally demonstrated.The proposed novel SSPPs structure compared with a conventional plasmonic waveguide with slot line SSPPs unit structure at the same size,the considerable advantages in much lower asymptotic frequency with tight field confinement,which enable the proposed filter to be more miniaturization.A high-efficient mode conversion structure is designed to transition from TE-mode to SSPPs-mode by gradient slotline lengths.The low-frequency stop-band can be committed with microstrip to slotline evolution on both sides of the dielectric,while the high-frequency cutoff band is realized by the proposed SSPPs structure.The influence of dispersion relation,electric field distribution,surface current,and structural parameters on the transmission characteristics of the proposed BPF are analyzed by finite difference time domain(FDTD).To validate the design concept,the prototype of the miniaturized SSPPs BPF has been manufactured and measured.The experimental results show high performance of the fabricated sample,in which the working in a range of 0.9 GHz-5.2 GHz with the relative bandwidth is 142%,the insertion loss less than 0.5 dB,the reflection coefficient less than-10 dB,and the group delay is less than one ns.This works provides a mirror for realizing the miniaturization of waveguides,and the application and development of high-confinement SSPPs functional devices in the microwave and THz regimes.     

Ultra-wideband surface plasmonic bandpass filter with extremely wide upper-band rejection

An ultra-wideband bandpass filter (BPF) with a wide out-of-band rejection based on a surface plasmonic waveguide (SPW) slotline with ring grooves is designed and analyzed. A paired microstrip-to-slotline transition is designed for quasi-TEM to TM mode conversion by using a microstrip line with a circular pad and the slotline with the same circular slot. The mode conversion between the TM and the surface plasmon polariton (SPP) mode is realized by using a gradient slotline with ring grooves and an impedance matching technique. The upper cut-off frequencies of the passband can be adjusted by using these proposed SPP units, while the lower frequencies of the passband are created by using the microstrip-to-slotline transitions to give an ultra-wideband BPF. The dispersion curves of SPP units, electric field distribution, and the transmission spectra of the proposed ultra-wideband bandpass filter are all calculated and analyzed by the finite-difference time-domain (FDTD) method. The simulated results show that the presented filter has good performance including a wide 3-dB bandwidth of 149% from 0.57 GHz to 3.93 GHz, an extremely wide 40-dB upper-band rejection from 4.2 GHz to 18.5 GHz, and low loss and high selectivity in the passband. To prove the design validity, a prototype of the BPF has been manufactured and measured, showing a reasonable agreement with simulation results. The unique features of the proposed BPF may make it applicable for integrated circuit and plasmonic devices in microwave or THz frequency ranges.     

基于塔姆激元-表面等离极化激元混合模式的单缝加凹槽纳米结构的增强透射

金属单缝纳米结构因为结构简单、易于集成,常用在基于表面等离极化激元(surface plasmon polaritons,SPPs)的纳米结构中构建光源.但是,金属亚波长单缝结构一直存在透射率低的问题,如何提高其透射率一直是研究的重点.为了更好地提高金属亚波长单缝的透射率,本文对之前文献提出的分布式布拉格反射镜(distributed bragg reflector,DBR)和金属银薄膜纳米缝结构进行改进,在金属银薄膜两侧设计凹槽.当TM偏振光由DBR侧入射至DBR-银纳米缝结构时,DBR-银膜界面上和银膜入射侧凹槽一起激发的塔姆激元(Tamm plasmon polaritons,TPPs)和SPPs,以及纳米缝和银膜出射侧凹槽对的SPPs同时激发,利用凹槽激发的SPPs和银膜表面处的TPPs-SPPs混合模式的干涉相长耦合作用,通过塔姆激元的局域场增强效应和两侧凹槽与单纳米缝的干涉相长耦合作用进一步提高了表面等离极化激元模式的激发效率,再加上纳米缝中的类法布里-珀罗腔共振效应,使纳米缝的透射率得到增强.本文采用有限元方法研究了DBR-银纳米缝结构上单纳米缝加凹槽的透射特性.经过一系列参数优化,使DBR-银纳米缝凹槽结构的最大透射率增加到0.22,相对于TiO_2-银纳米缝结构的透射率(0.01)提高了22倍,比文献[23]得到的最大透射率0.166有所提高.研究结果在纳米光源设计、光子集成电路和光学信号传输等相关领域具有一定的应用价值.     

基于十字连通形环形谐振腔金属-介质-金属波导的折射率传感器和滤波器

提出了由十字连通形环形谐振腔耦合两个金属-介质-金属(metal-insulator-metal, MIM)波导的结构,并用有限元法数值研究了表面等离极化激元在结构中的传输特性.通过对透射谱的研究,系统地分析了MIM结构的传感特性.结果表明,在透射光谱中有三个共振峰,即存在三种共振模式,其中透射峰与材料的折射率呈线性关系.通过对结构参数的优化,得到了折射率灵敏度(S)高达1500 nm/RIU的理论值,相应的传感分辨率为1.33×10~(-4)RIU.更重要的是,灵敏度不受结构参数变化的影响,这意味着传感器的灵敏度不受制造偏差的影响.此外,谐振波长与环形腔中心半径成线性关系,该器件在较大波长范围内实现可调谐带通滤波.透射强度随着波导与环形腔间距的增大而减小,透射带宽同时减小,因此,可以通过控制环形腔与波导的耦合距离来调谐透射强度及透射带宽.研究结果对高灵敏度纳米级折射率传感器和带通滤波器的设计以及在生物传感器方面的应用都具有一定的指导意义.     

求解结构矩阵低秩逼近的交替投影方法

结构矩阵低秩逼近在图像压缩、计算机代数和语音编码中有广泛应用.首先给出了几类结构矩阵的投影公式,再利用交替投影方法计算结构矩阵低秩逼近问题.数值试验表明新方法是可行的.     

O2/CO2气氛下污泥/煤混燃中半挥发性重金属的释放特性

在固定床焚烧实验装置上,采用正交实验法研究了焚烧温度(t_c)、污泥掺混比(X_s)、O_2体积分数(φ_(O2))、初始含水率(φ_(H2O))、焚烧时间(τ)和含氯量(φ_(Cl))六个因素对O_2/CO_2气氛下污泥/煤混燃中半挥发性重金属(Zn、Pb、Cd、Cu、Ni和Cr)释放特性的影响。结果表明,六种因素对重金属释放率影响程度排序为t_cX_sφ_(H2O)φ_(O2)≈τφ_(Cl)。相同焚烧工况下,Zn释放率最大,Pb和Cd次之,Cu、Ni和Cr较小。提高温度会促进重金属释放,且高温(1000-1100℃)对重金属释放的影响显著强于低温(700-900℃)。随着温度由700℃升高至1100℃,Zn和Pb释放率分别由36.1%和12.2%上升至70.9%和63.5%,Cd在900℃下达到40.0%的最大释放率,而Cu、Ni和Cr释放率大都维持在20.0%以下,温度对重金属释放率影响程度排序为PbZnCdCuCrNi。重金属释放率随着污泥掺混比增加逐渐下降,却随着初始含水率增加呈现波浪式变化趋势,且在30%O_2体积分数下重金属释放率取得最小值。焚烧时间和含氯量对Pb释放的影响程度显著强于其他五种重金属。O_2/CO_2气氛下污泥/煤混燃的最佳工况为:焚烧温度为900-1000℃、污泥掺混比为25%左右、O_2体积分数为30%、初始含水率小于10%,并尽可能的缩短焚烧时间。