由同时具有磁谐振和电谐振结构组成的左手材料

为了在同一结构中同时实现负介电常数和负磁导率(双负),采用一种“巨”字形结构,利用丝网印刷技术在氧化铝基板上进行加工制作,并通过仿真和实验测试证实了这种结构的“双负”特性. 与利用磁谐振器和电谐振器组阵实现左手材料的方法相比,这种单一结构可以同时实现负介电常数和负磁导率,制作方便,等效电路简单,双负频段较宽. 利用丝网印刷技术进行样品的制作,工艺简单,成本低廉. 关键词： 左手材料 磁谐振 电谐振     

An improved fishnet three-dimensional metamaterial with multiband left-handed characteristics at terahertz frequencies

We present the design of a multiband left-handed three-dimensional (3D) metamaterial based on improved fishnet structure at terahertz frequencies. The design realizes a three-dimensional material by mechanical stacking of multiple layers. The electromagnetic properties of the metamaterial have been investigated by numerical simulation. The results show that simultaneously negative values of permittivity, permeability and refractive index are found around the frequencies of 0.73, 0.85 and 1.12 THz for the electromagnetic wave normal incidence. The proposed metamaterial with independent polarization and compact effect offers a way to develop THz 3D materials and devices suitable for multifrequencies.     

A novel structure for broadband left-handed metamaterial

A low absorptivity broadband negative refractive index metamaterial with multi-gap split-ring and metallic cross (MSMC) structure is proposed and investigated numerically and experimentally in the microwave frequency range. From the numerical and experimental results, the effective media parameters were retrieved, which clearly show that there exists a very wide frequency band where the permittivity and permeability are negative. The influence of the structure parameters on the magnetic response and the cut-off frequency of the negative permittivity are studied in detail. This metamaterial would have potential application in designing broadband microwave devices.     

A novel structure for a broadband left-handed metamaterial

A low absorptivity broadband negative refractive index metamaterial with a multi-gap split-ring and metallic cross (MSMC) structure is proposed and investigated numerically and experimentally in the microwave frequency range. The effective media parameters were retrieved from the numerical and experimental results, which clearly show that there exists a very wide frequency band where the permittivity and permeability are negative. The influence of the structure parameters on the magnetic response and the cut-off frequency of the negative permittivity are studied in detail. This metamaterial would have potential application in designing broadband microwave devices.     

Low losses left-handed materials with optimized electric and?magnetic resonance

We propose that the losses in left-handed materials (LHMs) can be significantly affected by changing the coupling relationship between electric and magnetic resonance. A double bowknot shaped structure (DBS) is used to construct the LHMs. And the magnetic resonance of the DBS, which resonated in the case of lower and higher frequencies than the electric resonant dip, is studied in simulation and experiment by tailoring the structural parameters. The case of magnetic resonance located at low electric resonance frequencies band is confirmed to have relatively low losses. Using full wave simulation of prism shaped structure composed of DBS unit cells, we prove the negative refraction behavior in such a frame. This study can serve as a guide for designing other similar metal–dielectric–metal (MDM) in low losses at terahertz or higher frequencies.     

单方环结构左手材料微带天线

设计了一种简单的双面单方环结构左手材料,在4.8–5.25 GHz频率范围内该材料的等效介电常数和等效磁导率同时为负.将此单方环左手材料作为覆盖层,置于中心工作频率为5.0 GHz的微带天线之上. 仿真和实验研究表明:相对普通微带天线而言,覆层微带天线的性能得到了明显改善, E面和H面的半功率波束宽度分别收缩了25°和20°,定向性得到了提高, 5 GHz处的增益提高了3 dB, -10 dB带宽增加了600 MHz. 关键词： 单方环结构 左手材料 微带天线     

A very compact Mach-Zehnder interferometer with left-handed material

A very compact Mach-Zehnder interferometer (MZI) composed of two parallel straight waveguides with left-handed material (LHM) layers is proposed. The operating principle and characteristics of the MZI with electro-optic material (EOM) core are analyzed by using the supermode theory and coupled mode theory. The result shows that regardless of material loss, a very compact MZI of only 0.87 mm × 0.022 mm can be achieved by utilizing EOM with ultrahigh electro-optic coefficient, which means a new way to fulfill a very compact electro-optic modulator or optical switch. The absorption effect of the proposed MZI is also analyzed by perturbation method which is generated by lossy LHM layers.     

A compact polarization splitter utilizing directional coupler with left-handed material

A compact polarization splitter (PS) with left-handed material (LHM) sandwiched between two right-handed material (RHM) waveguides of a directional coupler (DC) is proposed. Its operation is by setting the coupling length of TM polarization be half that of TE polarization. Theoretic analysis exhibits that the PS with a very small size of 138.4 μm × 18.6 μm can be realized due to the inclusion of LHM even when the RHM with small birefringence is used.     

Enhancement of magnetic field intensity with a left-handed metamaterial tunnel resonator for obstacle sensing

A narrow metal strip inspired by the left-handed metamaterial and sensitive LC resonator structure has been released in this work where the narrow metal strip is presented as a tunnel structure which can enhance electric and magnetic properties. A commercially available electromagnetic simulator CST Microwave Studio is utilized to design and investigate the eSRR (electric split-ring resonator) and tunnelled LC resonator structures. Furthermore, ADS (Advance Design software) is used to determine the scattering parameters of the equivalent circuit. The proposed metamaterial structure is employed as a sensor operating in the C-band (6.88 GHz) of the microwave region, and its sensing properties are tested using glossy paper as an obstacle. The designed metamaterial tunnelling structure exhibits very high sensitivity toward dielectric obstacles at different rotational angles and thus can be potentially used in various sensing applications. The field enhancement effects on sensing application are verified by measured obtained results for eSRR and tunnelled LC resonator structures.     

A new double negative metamaterial for multi-band microwave applications

This paper reveals the design and analysis of a new split-H-shaped metamaterial unit cell structure that is applicable for multi-band frequency range, and it shows negative permeability and permittivity at those frequency bands. In the basic design, the two separate split square resonators have been added by a metal link to form H-shape unit structure. Moreover, the analyses and comparison of the 1 × 1-array, 2 × 2-array structures and 1 × 1, 2 × 2 unit cell configurations have been investigated. All these configurations demonstrate its multi-band operating frequency (S-band, C-band, X-band, K _u -band) with double negative characteristics. The equivalent circuit model for the unit cell is presented to demonstrate the validation of the resonant behavior. The commercially available finite-difference time-domain based simulation software CST microwave studio has been used to get the reflection and transmission parameters of the unit cell. In summation, the material also exhibits single negative characteristics in the multi-band frequency range if it is projected on the 20 × 20 mm² substrates. The simplicity, scalability, double negative characteristics, and multi-band operations have made this design novel in the electromagnetic paradigm.     

A compact warm ring for industrial applications

The ultrafast, high brightness X-ray free electron laser (XFEL) sources of the future have the potential to revolutionize the study of time-dependent phenomena in the natural sciences. These linear accelerator (linac) sources will generate femtosecond (fs) X-ray pulses with peak flux comparable to conventional lasers, and far exceeding all other X-ray sources. The Stanford Linear Accelerator Center (SLAC) has pioneered the development of linac science and technology for decades, and since 2000 SLAC and the Stanford Synchrotron Radiation Laboratory (SSRL) have focused on the development of linac based ultrafast electron and X-ray sources.     

A GaAs planar Schottky varactor diode for left-handed nonlinear transmission line applications

The left-handed nonlinear transmission line(LH-NLTL) based on monolithic microwave integrated circuit(MMIC) technology possesses significant advantages such as wide frequency band,high operating frequency,high conversion efficiency,and applications in millimeter and submillimeter wave frequency multiplier.The planar Schottky varactor diode(PSVD) is a major limitation to the performance of the LH-NLTL frequency multiplier as a nonlinear component.The design and the fabrication of the diode for such an application are presented.An accurate large-signal model of the diode is proposed.A 16 GHz-39.6 GHz LH-NLTL frequency doubler using our large-signal model is reported for the first time.The measured maximum output powers of the 2nd harmonic are up to 8 dBm at 26.4 GHz,and above 0 dBm from 16 GHz to 39.6 GHz when the input power is 20 dBm.The application of the LH-NLTL frequency doubler furthermore validates the accuracy of the large-signal model of the PSVD.     

Simulated and experimental studies of a multi-band symmetric metamaterial absorber with polarization independence for radar applications

We develop a simple new design for a multi-band metamaterial absorber (MTMA) for radar applications. Computer Simulation Technology (CST) Studio Suite 2018 was used for the numerical analysis and absorption study. The simulated results show four high peaks at 5.6 GHz, 7.6 GHz, 10.98 GHz, and 11.29 GHz corresponding to absorption characteristics of 100%, 100%, 99%, and 99%, respectively. Furthermore, two different structures were designed and compared with the proposed MTMA. The proposed structure remained insensitive for any incident angle and polarization angle from 0° to 60°. Moreover, negative constitutive parameters were retrieved numerically. To support the simulated results, the proposed design was fabricated by using a computer numerical control-based printed circuit board prototyping machine and tested experimentally in a microwave laboratory. The absorption mechanism of the proposed MTMA is presented through the surface current and electric field distributions. The novelties of the proposed structure are a simple and new design, ease of fabrication, low cost, durability, suitability for real-time applications and long-term stability given the fabrication technique and non-destructive measurement method and very high absorption. The proposed structure has potential applications in C and X band frequency ranges.     

A dual-mode microwave resonator for double electron-electron spin resonance spectroscopy at W-band microwave frequencies

We present a dual-mode resonator operating at/near 94 GHz (W-band) microwave frequencies and supporting two microwave modes with the same field polarization at the sample position. Numerical analysis shows that the frequencies of both modes as well as their frequency separation can be tuned in a broad range up to GHz. The resonator was constructed to perform pulsed ELDOR experiments with a variable separation of "pump" and "detection" frequencies up to Δν=350 MHz. To examine its performance, test ESE/PELDOR experiments were performed on a representative biradical system.     

A magnetic resonance spectrometer for FIR frequencies; Measurement on LiErF4

A magnetic resonance spectrometer is described with an HCN laser and an optically pumped FIR laser as radiation sources. The latter enables us to measure magnetic resonances at many frequencies throughout the FIR range. High magnetic fields up to 35 T are generated by means of a capacitor discharge with 10 ms pulse duration. The results of our measurments on LiErF₄ are in good agreement with resonance conditions calculated from parameters found by Hansen et al[10]. Different aspects of FIR magnetic resonance spectroscopy are discussed.     

局域共振型声学超材料薄板带隙特性的能量解法

研究局域共振型声学超材料的带隙特性时,面临的首要问题是寻求一种带隙特性的高效解法。为此,本文以局域共振型声学超材料薄板为研究对象,提出了一种基于能量泛函变分原理及正交多项式级数展开的带隙计算方法。该方法通过合并基体板及共振子的动、势能及外力功建立元胞的能量泛函,经过变分运算得到元胞的振动控制方程,进而引入第一类Chebyshev正交多项式作为基函数将控制方程进行离散。为克服无法直接对离散控制方程中的广义坐标施加周期边界条件的困难,该方法将连续边界条件弱化到若干选定的配点上以离散方式实现,并将对应的一组线性约束条件通过拉格朗日乘子法施加到系统中。仿真结果表明,该方法具有较高的计算精度和效率,并可应用于\     

基于感兴趣区域的海洋卫星遥感图像压缩算法

针对海洋监视卫星遥感图像的特点,提出了一种基于感兴趣区域的自适应遥感图像近无损压缩算法。该算法利用红-黑小波提升方法检测出目标的边缘,采用阈值法将目标和背景分割,使用外接矩形来描述目标,从而自动确定感兴趣区域。感兴趣区域采用Rice无损熵编码方法,背景区域采用比特平面编码的有损压缩方法。实验结果表明,该算法能有效地划分感兴趣区域,其压缩比较无损压缩有了很大提高,目标无失真,整幅图像的峰值信噪比都在40dB以上。算法的计算复杂度较低,易于硬件实现,而且还具有自适应性和数据包独立的优点,适合于海洋监视卫星遥感图像近无损压缩应用。     

A compact automatic wavemeter for use with tunable infrared diode lasers

We have studied the magnetic-dipole and electric-quadrupole contributions to second-harmonic generation (SHG) of centro-symmetric media. It can be shown that the phenomenological parameters , , can be arranged to form an effective -tensor, which describes dipole-forbidden SHG as the effect of a surface layer upon excitation with a single plane electromagnetic wave. An experimental technique is proposed allowing a determination of the usually very small term due to magnetic-dipole interaction using coherent compensation of its contribution by a coverage with an appropriate dye monolayer.     

A compact continuous-wave green laser with line beam for laser projection

An efficient and compact continuous-wave green laser with line beam using LBO crystal was developed. The maximum output power was 6.5 W. The optical-to-optical conversion efficiency was as high as 31%. The compact size of the line beam green laser was 2 cm×5 cm×8.8 cm. Reliability and stability of the green laser were evaluated.