探测器频带对光声成像分辨率的影响研究

 为了研究探测器频带对光声成像分辨率的影响,采用有限元仿真实验,得出不同探测器频带与分辨率之间的经验公式,即对于mm量级的吸收体,探测器的截止频率大于2 MHz时,重建图像分辨率变化不明显,当探测器的截止频率小于2 MHz时,分辨率降低非常明显。该研究结果对光声成像探测器的选择、成像效果评估具有参考价值。     

基于磁谐振器加载的宽频带超材料吸波体的设计

基于加载集总元件的磁谐振器设计了一种宽频带、极化不敏感和宽入射角的超材料吸波体.该吸波体的结构单元由加载集总元件的磁谐振器、介质基板和金属背板组成.仿真得到的加载集总元件和不加载集总元件情况下一维阵列结构吸波体的吸收率表明,相对于不加载集总元件的情况,加载集总元件的一维阵列结构吸波体能够实现宽频带吸波.仿真得到的集总电阻和集总电容取不同值时一维阵列结构吸波体的吸收率表明,集总电阻和集总电容都存在一个最佳值,此时吸波体的吸收率最高、吸收带宽最宽.仿真得到的基板有耗和无耗情况下一维阵列结构吸波体的吸收率表明, 关键词： 磁谐振器 集总元件 宽频带 超材料吸波体     

基于DGS和双层SRRs结构的左手介质微带线的设计

基于DGS结构和双层SRRs结构，提出了一种工作于双频段的微带线结构的新型左手介质，它除了频带宽和损耗小外，还具有体积小、结构简单便于加工的优点. 基于电磁波在微带线上的传输和反射数据，分别计算了左手介质微带线的有效介电常数和有效磁导率，并进一步得到了电波在微带线上传播时的波数随频率的变化曲线，结果表明文中讨论的左手介质微带线确实在较宽的频段上表现出后向波特性，从而证实了左手介质的存在. 关键词： 左手介质 宽频带 电小单元 后向波效应     

改进的5.1通路环绕声三扬声器虚拟重发系统

提出一种改进的5．1通路环绕声的三扬声器虚拟重发系统。本文首先指出,现有的两扬声器虚拟重发存在听音区域窄、声像稳定性差等缺陷。通过理论分析和心理声实验证明,采用一对布置在前方±30°的全频带扬声器和一个前方0°的高频中置扬声器组成5．1通路环绕声虚拟重发系统,不但可提高重发声像的稳定性,且扬声器布置实际可行,信号处理相对简单。因此所提出的虚拟系统及其扬声器布置是适合于电视和多媒体计算机的应用。     

Ka波段宽频带行波管放大器线性化研究

线性化器是毫米波通信系统中的关键器件,在改善放大器的线性指标及提高通信质量等方面起着至关重要的作用。现阶段国内行波管放大器（TWTA）线性化技术尚不完善,无法满足通信技术发展的应用需求,因此线性化技术的研究刻不容缓。本文提出了一种新的宽频带模拟预失真线性化器结构,用来改善Ka波段TWTA的非线性特性。仿真结果表明,在26～30 GHz频率范围内,输入功率为?20～10 dBm,线性化器的增益扩张≥5.08 dB,相位扩张≥64.81 °。将线性化器与TWTA进行级联测试,中心频率的增益压缩≤3.12 dB,相位压缩≤2.31 °,三阶互调（IMD3）显著提高。     

基于发卡式开口谐振环的柔性双频带超材料

本文设计了一种基于开口谐振环(split ring resonator, SRR)混合排列单元格的小型化双频带超材料(metamaterial, MM). 该MM的单元结构为发卡式SRR, 所设计的双频带MM可以应用于无线局域网(2.4 GHz) 和全球微波互联接入(3.5GHz)系统. 并且, 采用柔性介质作为基板增加了MM的柔韧度和普适性, 实验和测试结果表明: 双频带MM的中心频率可以通过调节SRR的尺寸进行控制. 此外, 本文也对MM在不同入射角的情况进行了分析, 结果表明MM对入射角度不敏感.最后, 通过MM的表面电流分布情况研究, 进一步解释了其双频带谐振频率的产生原理.     

Designing analysis of the polarization beam splitter in two communication bands based on a gold-filled dual-core photonic crystal fiber

We design a novel kind of polarization beam splitter based on a gold-filled dual-core photonic crystal fiber （DC-PCF）. Owing to filling with two gold wires in this DC-PCF, its coupling characteristics can be changed greatly by the second-order surface plasmon polariton （SPP） and the resonant coupling between the surface plasmon modes and the fiber-core guided modes can enhance the directional power transfer in the two fiber-cores. Numerical results by using the finite element method show the extinction ratio at the wavethlengths of 1.327 μm and 1.55 μm can reach -58 dB and -60 dB and the bandwidths as the extinction ratio better than -12 dB are about 54 nm and 47 nm, respectively. Compared with the gold-unfilled DC-PCF, a 1.746-mm-long gold-filled DC-PCF is better applied to the polarization beam splitter in the two communication bands of λ = 1.327 μm and 1.55 μm.     

低射频窄通带高温超导滤波器设计

本文在双面YBCO高温超导薄膜上设计了12节低射频窄通带超导带通滤波器.中心频率385MHz,相对带宽1.3%,考虑到窄带滤波器对衬底介电常数的敏感性,采用MgO基片以避免基片孪晶造成的介电常数非均匀性带来的影响.为了能在不大于2英寸的基片上制备出如此低频的高性能超导滤波器,设计中选用了1/4波长的螺旋形谐振结构.设计结果的带边陡峭度达到了50dB/MHz,带内插损小于0.014dB,带外抑制达到100dB,二倍频处抑制度优于130dB.     

Suppression of Anti-resonant Effect in Presence of Band Overlap

By exact resolution of coupled ideal chains connecting an extra side site, we show that the so-called ＂anti-resonant effect＂ is suppressed when the electron energy is inside the overlap region of extended bands of the ideal tight-binding chains. When the electronic energy is outside the band overlap region, the existence of ＂anti-resonant effect＂ is tuned by details of local connectivity around the extra side site and can be suppressed by introduction of magnetic flux.     

Polarization sensitivity contributes to multiple band spectra of one mid-infrared absorber

The emerging perfect-absorber metamaterials （PAMs） provide an alternative material approach for the next generation of electromagnetic detection at any frequency band of interest. One type of dual cross-shaped PAMs is developed to obtain multiplex-band spectrum absorption at mid-infrared region. Three distinct absorption peaks are attributed to the polarization sensitivity excitation of the plasmonic resonance. The charge density distributions, which are excited by resonant electromagnetic waves passing through the PAMs medium, provide insights into the observed absorption behavior. We find that the retrieved optical properties of the PAMs including permittivity and permeability are still consistent with the sum of the Drude and Lorentz type models at wavelengths ranging from 2.0 to 10.0μm. Such multiplex-band absorption properties enable the proposed PAMs a powerful tool for the direct detection of multiple molecular vibrational structures, and for multiple spectra infrared detection.