Electric and magnetic dipole couplings in split ring resonator metamaterials

In this paper, the electric and the magnetic dipole couplings between the outer and the inner rings of a single split ring resonator (SRR) are investigated. We numerically demonstrate that the magnetic resonance frequency can be substantially modified by changing the couplings of the electric and magnetic dipoles, and give a theoretical expression of the magnetic resonance frequency. The results in this work are expected to be conducive to a deeper understanding of the SRR and other similar metamaterials, and provide new guidance for complex metamaterials design with a tailored electromagnetic response.     

Metamaterial absorbers realized in an X-band rectangular waveguide

In this paper,we demonstrate six types of metamaterial absorbers(MMAs) by measuring their absorptivities in an X-band(8-12 GHz) rectangular waveguide.Some of the MMAs have been demonstrated previously by using the free space measurement method,and the others are proposed firstly in this paper.The measured results show that all of the six MMAs exhibit high absorptivities above 98%,which have similar absorbing characteristics to those measured in the free space.The numerically obtained surface current densities for each MMA show that the absorbing mechanism is the same as that under the free space conditions.Such a demonstration method is superior to the conventional free space measurement method due to the small-scale test samples required,the simple measure device,and its low cost.Most importantly,the proposed method opens a way to enable MMAs to be used in microwave applications such as matched terminations.     

Hybrid phase-locked loop with fast locking time and low spur in a 0.18-μm CMOS process

We propose a novel hybrid phase-locked loop(PLL) architecture for overcoming the trade-off between fast locking time and low spur. To reduce the settling time and meanwhile suppress the reference spurs, we employ a wide-band single-path PLL and a narrow-band dual-path PLL in a transient state and a steady state, respectively, by changing the loop bandwidth according to the gain of voltage controlled oscillator(VCO) and the resister of the loop filter. The hybrid PLL is implemented in a 0.18-μm complementary metal oxide semiconductor(CMOS) process with a total die area of1.4×0.46 mm2. The measured results exhibit a reference spur level of lower than-73 dB with a reference frequency of10 MHz and a settling time of 20 μs with 40 MHz frequency jump at 2 GHz. The total power consumption of the hybrid PLL is less than 27 mW with a supply voltage of 1.8 V.     

Highly Symmetric Planar Metamaterial Absorbers Based on Annular and Circular Patches

We present the simple designs of metamaterial absorbers which are composed of a periodic array of copper annular （or circular） patches, FR4 substrate, and copper film. With appropriate geometrical parameters, these metamaterials can provide the electric and magnetic resonances overlapping in the given frequency range, and the experiments demonstrate the absorptivities of 97.6% and 96.7% with only a single layer of the metamaterial absorber. The surface currents and field distributions of these metamaterials are discussed to look straight into the resonance mechanism. Furthermore, our numerical simulations confirm that these metamaterial absorbers could be operated at wide angles of incidence. The simple and highly symmetric structures of the metamaterial absorbers proposed would greatly accelerate the practical applications in optics and electromagnetics.     

Numerical Study of Low-Loss Cross Left-Handed Metamaterials at Visible Frequency

We present a numerical study of left-handed metamaterials （LHMs） composed of double cross pairs at visible frequency. The S-parameter retrieval method is adopted to confirm the negative refractive characteristic of this design. Compared with fishnet LHMs~ the proposed cross LHMs have a much lower loss, which will greatly facilitate practical applications. It is also found that, with the same size of resonant cells, the cross LHMs have a higher frequency than fishnet LHMs, which is explained using a simple effective LC circuit model.     

光波段多频负折射率超材料

从光波段圆孔形双鱼网结构的负折射材料模型出发,采用基于有限积分技术的CST软件系统研究了原胞结构的改变对负折射行为的影响.数值仿真结果表明,对原胞结构做微小调节也可获得负折射率频带的增大效应.将双鱼网结构改为阶梯形孔洞和半球形孔洞结构,可以在更多的频段里出现负折射率,并且谐振频率发生了一定的红移.半球形孔洞的双鱼网结构可以方便地用化学模板法制备,这为从实验上实现红外及可见光波段的多频负折射材料提供了一种简单可行的方法. 关键词： 负折射率 多频段 双鱼网结构     

一种基于开口空心球的声学超材料

提出了一种基于局域共振的开口空心球(spilt hollow spheres,SHS)模型,数值计算和声学透射实验结果表明基于该模型的声学超材料可以实现负的弹性模量.为了说明SHS的局域共振性质,研究了微结构SHS几何尺寸(例如开口孔径d和空心球直径D)变化时材料的透射性质,结果表明SHS的几何尺寸的改变对声学超材料的透射吸收峰频率有显著影响.另外,还研究了SHS不同排列方式对透射行为的影响,发现单层样品中SHS单元数目以及晶格常数的变化不会引起谐振频率的变化,但是随着SHS单元数目或者样品 关键词： 开口空心球(SHS) 声学超材料 吸收峰 等效弹性模量