瞬变电磁场模拟中的CPML吸收边界条件

提出用于瞬变电磁法(TEM)模拟的时域有限差分(FDTD)算法中的卷积完全匹配层(CPML)吸收边界条件.首先,在磁场散度方程显式处理条件下,计算磁场z分量时,构造出一种计算时域卷积项的方法,并详细推导计算磁场z分量的表达式.而后,对均匀半空间模型进行数值计算.结果表明,提出的CPML吸收边界条件在保证计算精度的前提下,实现了瞬变电磁法时域有限差分高效正演计算.     

Ultra-wideband circular-polarization converter with micro-split Jerusalem-cross metasurfaces

An ultrathin micro-split Jerusalem-cross metasurface is proposed in this paper, which can efficiently convert the linear polarization of electromagnetic(EM) wave into the circular polarization in ultra-wideband. By symmetrically employing two micro-splits on the horizontal arm(in the x direction) of the Jerusalem-cross structure, the bandwidth of the proposed device is significantly extended. Both simulated and experimental results show that the proposed metasurface is able to convert linearly polarized waves into circularly polarized waves in a frequency range from 12.4 GHz to 21 GHz, with an axis ratio better than 1 d B. The simulated results also show that such a broadband and high-performance are maintained over a wide range of incident angle. The presented polarization converter can be used in a number of areas, such as spectroscopy and wireless communications.     

Ultra-broadband and polarization-independent planar absorber based on multilayered graphene

We propose an ultra-broadband and polarization independent planar absorber comprising multilayered graphene. The bandwidth of the proposed absorber is extended by increasing the number of layers of graphene, and it is polarization independent due to its symmetrical unit structure. The full wave simulation results show that an absorber with three graphenebased layers can efficiently harvest an electromagnetic wave with random polarization from 17.9 GHz to 188.7 GHz(i.e.,covering frequency regimes from K to D bands and relative bandwidth of ~ 165%). The physical absorption mechanism of ultra-broadband absorption has been elaborated upon using the destructive interference method and multiple resonances approach in a multilayered medium. The proposed absorber can be used in many applications such as medical treatment,electromagnetic compatibility, and stealth technique.     

层状介质时域有限差分方法斜入射平面波引入新方式

应用二维时域有限差分方法分析层状介质中的目标散射时,在总场-散射场边界斜入射平面波源用常规方法难以引入,因为在总场-散射场边界处设置的入射波实际上包含了入射脉冲以及各分层界面的反射和多次反射.为解决这个问题,提出了斜入射平面波的混合引入方式,即对总场-散射场的四个边界面采取不同的处理方式.对于总场-散射场的纵向侧边界,用含有斜入射角度的修正一维时域有限差分方法,只要在自由空间位置加入入射脉冲就会自行产生由各分层界面形成的反射波,包括多次反射.同时,把纵向总场-散射场侧边界向下延伸,使得总场-散射场下边界位于完全匹配层内,这样透射波和散射波均为外向行波而被吸收.对于总场-散射场的上边界,由于完全位于自由空间中,边界上各点的入射波将是总场-散射场纵向边界角点处入射波的带有时间延迟的复制.数值模拟结果表明了本文所提出方法的正确性和有效性. 关键词： 时域有限差分 层状介质 斜入射平面波 修正一维麦克斯韦方程     

分层背景2维FDTD中斜入射平面波的引入

 对于分层介质中目标散射的时域有限差分（FDTD）计算,在分层背景中引入斜入射平面波源是一个难点。在2维Maxwell方程基础上,导出TM和TE模下含有斜入射角度的１维Maxwell方程,并用它在分层介质中连接边界上模拟斜入射平面波源,克服了分层背景时域有限差分计算斜入射平面波引入的困难。对熔石英表面覆盖薄膜的分层光学元件进行平面波斜入射时域有限差分计算结果表明,电磁波在各层内形成完好的平面波推进,验证了这种斜入射平面波添加方式的正确性。并通过对含气泡的缺陷模型的计算,来阐述这种入射波添加方式的应用。     

高功率速调管TE_(11)-HE_(11)模式变换器的设计及实验验证

基于模式匹配法编制了分析内壁刻槽TE11-HE11圆波导模式变换器数值计算程序;采用该程序为工作频率为30.5GHz的高功率速调管设计了一半径为16mm的TE11-HE11模式变换器。计算表明该变换器在2.6%的带宽内转换效率在98.8%以上,实验结果表明该变换器性能良好。     

纳秒脉冲下典型钳压型浪涌防护元件的响应特性

为研究以压敏电阻和瞬态抑制（TVS）二极管为代表的典型钳压型浪涌防护元件的纳秒脉冲响应特性,为电磁脉冲干扰防护元件的选型提供科学依据,分别基于百ns和2 ns上升前沿电磁脉冲直接注入的方式,实验测试并对比分析两类元件在不同脉冲上升沿时间、电压幅值等情况下的响应差异,并阐明产生过冲响应差异的物理机理。结果表明:两类防护元件的响应时间均与注入纳秒脉冲上升沿时间有关,且随着上升沿的增加而变长,其中TVS二极管在相同上升脉冲情况下具有更为敏感的响应速度;当注入脉冲电压幅值增加时,PN结热积累加快,击穿速度加快,元件响应时间更短,相比于TVS稳定的钳位幅值,压敏电阻在钳位幅值附近处振荡明显;当快速脉冲到达时,压敏电阻和TVS二极管响应曲线在钳位幅值稳定前均发生过冲现象,并且两类防护元件的过冲电压均随着注入脉冲幅值的增加而增加;尽管钳位电压幅值由自身防护特性决定,但在相同注入脉冲条件下,同类不同型号的防护元件过冲电压几乎相同,通常压敏电阻过冲电压小于钳位电压,而TVS二极管则相反,并且随着钳位幅值变小,过冲电压与钳位电压的比值变大,这意味着过冲现象对低压TVS二极管性能影响更为严重。     

An ultra-wideband pattern reconfigurable antenna based on graphene coating

An ultra-wideband pattern reconfigurable antenna is proposed. The antenna is a dielectric coaxial hollow monopole with a cylindrical graphene-based impedance surface coating. It consists of a graphene sheet coated onto the inner surface of a cylindrical substrate and a set of independent polysilicon DC gating pads mounted on the outside of the cylindrical substrate. By changing the DC bias voltages to the different gating pads, the surface impedance of the graphene coating can be freely controlled. Due to the tunability of graphene's surface impedance, the radiation pattern of the proposed antenna can be reconfigured. A transmission line method is used to illustrate the physical mechanism of the proposed antenna. The results show that the proposed antenna can reconfigure its radiation pattern in the omnidirectional mode with the relative bandwidth of 58.5% and the directional mode over the entire azimuth plane with the relative bandwidth of 67%.     

回旋速调管变周期TE01-TE11模式变换器

针对蛇形圆波导变换器尺寸大和带宽窄的不足,提出了变周期蛇形圆波导模式变换器,以实现TE01到TE11模式的高效率转换。根据耦合波方程,编制了优化计算程序,对工作于30.5 GHz、半径为16 mm的变周期以及传统蛇形变换器几何结构分别进行了优化计算,得到了可实现最高模式变换效率的几何参量。计算结果表明:传统结构变换器最优长度长达1 056.97 mm,转换效率98.1%,90%以上转换带宽也仅为3.3%;变周期变换器最优长度为769.53 mm,转换效率为99.3%,90%以上转换带宽为5.9%。变周期结构相对于传统结构的模式变换器具有尺寸小和带宽宽的明显优势。测试表明所提出的模式变换器具有良好的模式变换性能。     

一种基于石墨烯的超宽带吸波器

隐身技术对降低飞行器目标的雷达散射截面、提高飞行器目标的生存能力具有重要的意义和价值, 而在飞行器目标上引入吸波器结构是一种重要的隐身手段. 然而, 目前已有吸波器的研究主要集中在单频或多频窄带方面. 为了拓展吸波器工作频带, 基于石墨烯材料提出了一种工作于S/C波段的新型超宽带吸波器模型单元, 其中包含一个用石墨烯材料设计的方圆形双环周期结构. 调节石墨烯的表面阻抗, 使得吸收率超过90%的频带范围为2.1-9.0 GHz, 相对带宽约为124%, 实现了超宽带的吸波特性; 鉴于模型的高度对称性, 提出的吸波器模型表现出对入射波极化不敏感的吸波特性; 在不改变模型结构情况下, 调节石墨烯的静态偏置电场, 亦可调控吸波器谐振在2.0-9.0 GHz频带范围内的任意频率点处, 且达到超过99%的吸收效果. 最后采用等效电路模型方法和波的干涉理论对其吸波机理进行深入研究与分析: 从等效电路角度来讲, 方形和圆形环分别引入高、低吸波谐振频率, 二者优化叠加拓展了吸波带宽; 从干涉理论方面来看, 吸波器表面处的首次反射波与透射波的多次出射波形成较强的干涉相消现象, 有效减少了吸波器的反射回波.