Magneto-optic parametric oscillation

We develop a model of large-signal steady-state magneto-optic parametric oscillation in the Faraday configuration of a singly resonant cavity. The conversion efficiency and the threshold and phase-matching conditions are discussed, and we show that tunable phase matching can be achieved by use of a static magnetic field, eliminating any walk-off effects.     

Multiband small zeroth-order metamaterial antenna

A novel resonant metamaterial antenna based on the Composite Right/Left-Handed (CRLH) transmission line (TL) model is presented. The proposed small antenna is designed to operate simultaneously over multiple wireless services (UMTS-WLAN-WIMAX)     

Faraday shield effects on a half-turn loop antenna used for ICRFplasma heating

The characteristics of a half-turn loop antenna having a Faraday shield (used for ion-cyclotron RF plasma heating) have been systematically investigated. The main interest is to clarify the Faraday shield effects on the near-zone electric field distribution. It has been confirmed that, in the presence of the Faraday shield, undesirable field components are sufficiently suppressed, and the heating component E _y, which otherwise is strongly localized as an end effect, has been found to be distributed uniformly along the antenna in the case of a short electric length. It is found that the shielding strips should be uniformly distributed over the entire region around the half-turn loop antenna     

Analytical model of a self-complementary connected antenna array on high impedance surface

This paper presents an analytical model to design a self-complementary connected antenna array above artificial materials like high impedance surfaces (HIS). The objective of this model is to perform parametric studies to facilitate deeper understanding of a complex antenna array with a significantly shorter computation time than with electromagnetic simulators. The model of the complete structure has been designed in receiving mode when structure is illuminated with a plane wave and using transmission line model and ABCD matrix. By applying an interesting property which gives equivalence between the input impedance in transmit mode and the surface impedance in receiving mode, the impedance match of the self-complementary connected antenna array can be quickly calculated. It is also simple to evaluate the influence of the incidence angle on the reflection coefficient of a self-complementary connected antenna array above perfect electric conductor (PEC) or HIS. PEC or artificial materials can modify the antenna array behavior by either increasing the bandwidth or by adding additional bandwidths. All these results have been verified to be accurate by numerical simulations done with Ansys HFSS.     

Multimode network analysis for dielectric leaky-wave antennas consisting of multilayer periodic structure with arbitrary dielectric distributions

The multimode network method is used to analyze the radiation characteristics of the leaky-wave antenna consisting of multilayer dielectric periodic structure with arbitrary dielectric distributions in each layer. The eigenfunction of each periodic layer is determined by Floquet theorem; and the mode matching combining with generalized transverse resonant method are used to derive the dispersion equation of the leaky-wave antenna. The complex transmission constant is calculated by Newton iterative method and the radiation characteristics of the antenna are obtained. Some antenna structures are analyzed and useful guidelines for design of the leaky-wave antennas are suggested.     

可调谐的低频连续引力波接收天线的研究

我们设计制造了共振频率在47.3Hz到60.5Hz之间连续可调谐的低频引力波四极天线。天线的重量为498kg,室温时在空气中加上调谐系统后Q值为4.4×10³。木文把天线的振动简化为在自由端附有—刚性质量的悬臂梁的振动。代替弹性力学的繁复计算,用材料力学的简单方法得到了可以满足要求的结果。本文对用机械方法调整频率的可能方案作了比较,并对把四极天线用于探测更低频的引力波的可能性进行了探讨。 关键词：     

Large enhancement of Faraday rotation by localized surface plasmon resonance in Au nanoparticles embedded in Bi:YIG film

A large enhancement of the Faraday rotation, which is associated with localized surface plasmon resonance (LSPR), was obtained in a sample with Au nanoparticles embedded in a Bi-substituted yttrium iron garnet (Bi:YIG) film. On a quartz substrate, Au nanoparticles were formed by heating an Au thin film, and a Bi:YIG film was then deposited on them. A sample containing the Au nanoparticles produced by 1000 °C heating showed a resonant attenuation with narrower bandwidth in the transmission spectrum than nanoparticles of other samples formed by low-temperature heating. The sharp resonant Faraday rotation angle was 4.4 times larger than the estimated intrinsic Bi:YIG film at the LSPR wavelength; the angular difference was 0.14°. A discrepancy in the bandwidth between the transmission attenuation and the resonant Faraday rotation is discussed.     

Measurement and study of the embedding impedance presented by the whisker antenna of a schottky diode corner cube mixer

A 250× scale model of a Schottky diode corner cube mixer designed for operation in the terahertz region has been built and tested. It has been successfully used to measure the embedding impedance presented to the diode at the whisker tip and also determine the impedance of the whisker antenna itself. The results have been input into a computer analysis to determine as to how the performance may be improved. With regards to improving the physical ruggedness of such mixers, a simple equivalent whisker structure has been determined and a new technique that may be used to fabricate a space qualifiable corner cube mixer intended for terahertz operation is disclosed.     

Measurement of the effects of Faraday shields on ICRH antennacoupling

Compact loop antennas are being applied to several fusion experiments, including DIII-D, the Advanced Toroidal Facility, Tore Supra, and the Tokamak Fusion Test Reactor. Although individual configurations vary, all of these antennas generally comprise a current strap in a recessed box and a Faraday shield. The coupling characteristics of cavity antennas that have current straps with the previously evaluated cross-sectional shapes are tested with several Faraday shields. The coupling is purely a measure of the magnetic flux linkage at relevant ion-cyclotron resonance heating (ICRH) frequencies and does not include plasma spectral effects. Impedances and relative fields are measured for various combinations of the current strap and Faraday shield. The experiments show that the fractional reduction in the magnetic flux linkage to the plasma resulting from the addition of any particular Faraday shield is virtually independent of the shape of the current strap. This is true in spite of the fact that the same mechanism which is responsible for the reduction in flux is also responsible for a significant redistribution of the antenna current on the current strap. Thus the process of optimizing antennas is reduced to that of separately optimizing the current strap and Faraday shield     

Design and implementation of dual-band antennas based on a complementary split ring resonators

A simple dual-band antenna design and implementation method is proposed in this work, based on the equivalent media properties inspired by resonant metamaterial elements. The equivalent circuit model of dual-band patch antennas based on a complementary split ring resonator (CSRR) is presented and validated. The dual-band patch antenna is designed etching a CSRR in the patch of a conventional rectangular microstrip patch antenna. The first resonance is governed by the quasi-static resonance of the CSRR while the second resonance is originated by the rectangular patch. The fact of etching a CSRR on a rectangular patch antenna also produces a miniaturization of a conventional patch antenna. The equivalent circuit model proposed in this letter is sound in order to understand the functionality of dual-band patch antennas based on a CSRR. Good agreement between simulation, equivalent circuit model and experimental results is shown and discussed. These results lead the equivalent circuit model to become a simple and straightforward tool for the design of this type of multiband antennas, of low cost and versatile operation for a broad range of wireless communication systems.     

Faraday Rotation of Overdense Magnetized Plasma

In this study, we investigate Faraday rotation of electromagnetic waves that are anomalously transmitted through an over‐dense magnetized plasma layer. Here, magnetized plasma indicates that the plasma layer is immersed in a uniform magnetic field. Firstly, normally opaque over‐dense magnetized plasma is shown to be transparent to obliquely incident electromagnetic waves. This high transparency can be achieved by providing conditions for resonant excitations of plasmonic modes. The resonant characteristics of the transmission coefficient of the considered structure are determined and discussed. The conditions under which the magnetized plasma behaves as a complete reflector are also obtained. Faraday rotation is shown to be enhanced under high transparency conditions. The reflected wave also exhibits Faraday rotation and is enhanced under total reflection conditions. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

可调频高功率宽谱微波的产生和辐射

 设计了一种可调谐频率的高功率宽谱微波辐射装置,装置由可调谐长度的1/4波长低阻同轴谐振器、环形开关、电容耦合器和宽谱辐射天线组成,中心频率调谐为200～400 MHz。低阻传输线与环形开关构成1/4波长短路谐振器,它产生的宽谱微波振荡通过耦合器耦合到宽谱辐射天线上辐射,而耦合器由集中电容与分布电感组成,实现宽谱微波在频率调谐范围内以较为一致的耦合度提取微波能量。通过转动螺杆滑动安装在同轴谐振器内芯上的环形开关,达到改变谐振频率的目的。最后,将可调频宽谱辐射装置与输出电压为500 kV的Tesla变压器脉冲功率源联试,得到200～400 MHz宽谱微波辐射,辐射因子为95～130 kV,频谱百分比带宽为10%～30%。     

Magnetic field effects on coherent backscattering of light

We have studied the influence of magneto-optical Faraday rotation on coherent backscattering of light experimentally, theoretically and by computer simulations of Monte-Carlo type. The consistency of these three approaches reveals new aspects of the propagation of vector waves in turbid media with and without Faraday rotation. Experimentally, we have demonstrated that the Faraday rotation may almost completely destroy the reciprocity of light paths. However, as shown by the simulations, the cone of coherent backscattering may not only be destroyed but also shifted off the exact backscattering direction, parallel to the magnetic field, as long as the amount of circular polarization is not completely destroyed by the multiple scattering. The relationship between coherent backscattering, depolarization and Faraday rotation are explained by a simple path model of vector waves. This leads to a new characteristic correlation length required to properly describe the influence of Faraday rotation on multiple light scattering. Received 28 January 2000     

Properties of Carbon Nanotube Optical Antennae

The properties of carbon nanotube as optical antennae have been studied. The equation of current distribution on a single antenna has been obtained by using conventional transmission line theories. The re-radiation lobe pattern of a single antenna and an antenna arrays have been gained by computer simulation.     

Study of Power Coupling through an Electrostatic Shield on a Loop Antenna for ICRF Heating of EBT-S

The effects of electrostatic shields around the antenna used for ICRF heating in the EBT-S fusion experiment on the efficiency of power transfer from the antenna to the plasma were studied in bench tests using resonant coupling loops placed near the antenna to simulate plasma behavior. For the frequency range of interest in these experiments, the length of the antenna was much shorter than the free-space wavelength. Coupling efficiencies in excess of 90 percent were obtained under best conditions. There was a reduction in coupling efficiency due to the presence of the shield, which was found to be dependent on the proximity of the loop to the antenna and on the Q of the loop. The change in coupling efficiency of the antenna with the shield compared to the antenna without a shield was greater the farther the loop was removed from the antenna and the lower the Q of the loop. In general, the reduction in coupling efficiency due to the shield is probably tolerable, with the advantages of having an electrostatic shield outweighing the disadvantage of a lower power coupling efficiency.     

一体化GPS磁窗天线的设计与实验研究

设计了一种用于减缓高超声速飞行器通信中断的、中心频率为1.575GHz、一体化GPS磁窗天线,并开展了静态验证实验。设计的磁窗天线由贴片微带天线和永磁体一体化组成,结构尺寸为100mm×100mm×75mm,并设计了防护结构。磁窗天线的贴片微带天线不会对永磁体磁场产生影响,而永磁体也不会改变贴片微带天线谐振频率;设计的磁场防护装置对天线轴向的磁场强度没有减弱,对非传播方向完全屏蔽,起到了保护作用。针对厚度为25.5mm、电子密度为6×1010~1×1011 cm-3的等离子体,设计的磁窗天线能将1.575GHz电磁波透射系数从-19~-23.5dB提高到-11~-16dB。研究结果表明:设计的一体化GPS磁窗天线能够一定程度减缓电子密度为6×1010~1×1011cm-3的等离子体对1.575GHz电磁波通信影响,且实现了磁窗天线的小型化,并提高了安全性。     

Faraday effect in alkali-metal vapors in a strong bichromatic field of laser light

Results of a numerical study of the Faraday effect arising upon propagation of the light beams with the frequencies ω _L1 (resonant to the nS _1/2-nP _{1/2, 3/2} transitions) and ω _L2 (resonant to the nP _{1/2, 3/2}-(n+2)S _1/2 transitions) through alkali-metal vapors are presented. Characteristics of the magneto-optical rotation spectra at each of the frequencies are strongly affected by the second intense radiation field resonant to the adjacent transition. When the atoms interact with two strong light waves, resonant to adjacent transitions, and with a magnetic field, the shape of the Faraday rotation spectra depends on the energy shifts of the atomic states that arise due to the dynamic Stark effect and the Zeeman effect (the Paschen-Back or an intermediate-type effect), as well as due to the difference of populations of these states caused by the interaction of the atoms with the fields. The results obtained show that in the frequency selection method, based on the resonance Faraday effect, the frequency of the generated narrow-band beam can be tuned by the intensity of the strong wave, resonant to the transition between the excited states.     

Resonances of the Faraday Effect in Nanostructured Iron Garnet Films

Magnetic nanostructures make it possible to enhance magneto-optical effects by many times owing to the excitation of optical resonances. A new type of magnetic structure is proposed, which is a two-dimensional all-dielectric bismuth-substituted iron garnet grating. Enhancement of the Faraday effect in such a structure caused by the excitation of waveguide modes is described analytically, and the conditions for the resonant enhancement are revealed. The resonant enhancement of the Faraday effect in all-dielectric magnetic nanostructures has been experimentally demonstrated for the first time.

     

Optical limitation in resonant Faraday media

Optical limitation in resonant Faraday media sandwiched between crossed polarizers is analyzed both theoretically and experimentally. In this technique resonant Faraday rotation permits a net transmission at low intensity levels, whereas the setup transmission is quenched at higher intensities when the active transition is completely saturated. This technique offers many advantages, such as a very low fluence threshold (~12 nJ/cm(2) in cesium vapor), a high intensity range (more than 4 orders of magnitude for polarizer losses of 10(-5)), and quasi invulnerability to optical damage, which make this technique attractive for the protection of fixed-wavelength operated detectors.     

Fabry–Pérot-like phenomenon in the surface plasmons resonant transmission of metallic gratings with very narrow slits

The general role of the surface plasmons in the transmission of the metallic grating with very narrow slits has been numerically described using the finite difference time domain method. The straightforward evidence of the surface plasmons existing in the sharp transmission peak has been given by the near-field distribution of the electrical fields normal components. The Fabry–Pérot-like behavior has also been found in the transmission of surface plasmons resonant mode versus the grating depth. It is concluded that whether the peak of surface plasmons resonant transmission emerge or not is mainly determined by the grating depths. Based on the approximate resonant transmission equation proposed in our work, it is revealed that the different physical mechanisms of two resonant modes root in the difference in the power-coupled processes. PACS 42.79.Dj; 71.36.+c; 73.20.Mf; 78.66.Bz