共查询到20条相似文献,搜索用时 15 毫秒
1.
A dielectric grating leaky wave antenna with a substrate consisted of left handed material (LHM) is presented in this paper,
the case where the n = −1 space harmonic of TM mode radiating into the space is carefully investigated through the improved
perturbation analysis, which tremendously simplifies the analysis procedure with good calculation accuracy and brings considerable
physical insight into the overall behavior of the dielectric grating antenna. It has been found that the new leaky wave antenna
is of larger leakage constant than that of the traditional antenna with substrate of the right handed material (RHM). As a
result the dimension of the antenna could be largely reduced, which is of practical significance for some applications. Extensive
numerical results of the radiation characteristics are given to establish useful guidelines for the design of the new grating
antenna. 相似文献
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New double-layered electromagnetic absorbers are presented in this paper. The new absorbers composed of one lossy left-handed
material absorbing layer and one impedance matching layer consisted of lossless right-handed material. It is indicated that
the reflection loss of below −20dB can be obtained in the frequency range 7GHz–13GHz. Power attenuation achieving −50dB of
narrow frequency band electromagnetic absorbers can also be obtained by modulate permittivity of right-handed material. Furthermore,
the thickness of the whole absorbing structure is only 2mm, which is particularly helpful in some practical applications.
The presented results are of reference significance for accurate design of the new electromagnetic absorbers and of practical
prospects for stealth technology. 相似文献
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In this paper the electromagnetic similitudes for lossy and dispersive system are discussed. If both the geometric size of an object and incident wavelength are scaling-down simultaneously by analogy with microwave band, the inconsistencies exist for laser scattering in visible and near infrared bands. Another method of measurements and simulation for laser scattering in the geometric model is analyzed. That is, the geometric size of the object is only scaled down but the incident wavelength, material and configuration are keeping to not change. Although this way does not satisfy the principles of the electrodynamic similitude, it can overcome the electromagnetic inconsistencies for laser scattering. It is possible that the LRCS of the full-scale tested object are evaluated by those of the corresponding scaling-down model at identical frequency to establish theoretical models and data basis for LRCS of objects. 相似文献
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An-xue Zhang Hui Wu Chen Guo Yan-sheng Jiang 《International Journal of Infrared and Millimeter Waves》2008,29(10):946-952
For resolving the essential problem that the beam is too narrow in the application of the high-power UWB (Ultra-Wideband)
antenna with single-source, a novel wide-beam high-power parabolic antenna with dual-source has been designed, and the edge
of the paraboloid was cut in order to reduce the size of the antenna. Radiation properties of this proposed antenna are studied
with finite-difference time-domain (FDTD) numerical method. The radiation properties of the proposed antenna can be improved
by changing the structure of the parabolic antenna and adjusting the angle between the source and the axis of the antenna.
The result shows that the beam-width has been improved significantly under the precondition of maintaining the peak power,
and also the size of the antenna was minished by cutting the edge of the paraboloid. 相似文献
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Shakeel Ahmed 《Optics Communications》2008,281(23):5664-5670
Electromagnetic scattering of an incident uniform plane wave from a perfect electromagnetic conductor (PEMC) circular cylinder, coated with a metamaterial is investigated theoretically. In the analysis the coating layer may be double-positive (DPS), double-negative (DNG), epsilon-negative (ENG) or mu-negative (MNG). It is assumed that both PEMC cylinder and the coating layer are infinite along the cylinder axis. Both parallel and perpendicular polarization cases are considered for the analysis. Comparison between the monostatic and bistatic echo widths, of a PEMC cylinder coated with metamaterial and coated with ordinary dielectric material (DPS), is presented. The numerical results are compared with the published literature, and comparison is found to be in good agreement. 相似文献
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Bragg Reflectors and Resonators in Microstrip Technology Based on Electromagnetic Crystal Structures
Txema Lopetegi Francisco Falcone Mario Sorolla 《International Journal of Infrared and Millimeter Waves》1999,20(6):1091-1102
Recently, new promising two-dimensional (2-D) Photonic Bandgap Structures (PBG), or more properly Electromagnetic Crystal Structures, for microstrip lines have been proposed. In this paper, we analyze these structures in a manner like a Bragg reflector in optical wavelengths. Joining two of such Bragg like reflectors by means of a conventional microstrip transmission line allows one to design Bragg Resonators. The 2-D periodic pattern of the electromagnetic crystal structure is implemented with circles etched in the ground plane of the microstrip line by means of a numerical milling machine. Simulations have been performed by using HP
TM Momentum and MDS software, and in accordance with the measurements give, for the Electromagnetic Crystal Structures, new promising potential applications both in microwave and millimeter wave integrated circuits, and also in the experimentation of expensive short wavelength (including photonic) devices by using simpler and cheaper microwave down scaling. 相似文献
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Electromagnetic coupling reduction in dual-band microstrip antenna array using ultra-compact single-negative electric metamaterials for MIMO application 下载免费PDF全文
In this paper, an ultra-compact single negative(SNG) electric waveguided metamaterial(WG-MTM) is first investigated and used to reduce the mutual coupling in E H planes of a dual-band microstrip antenna array. The proposed SNG electric WG-MTM unit cell is designed by etching two different symmetrical spiral lines on the ground, and has two stopbands operating at 1.86 GHz and 2.40 GHz. The circuit size is very compact, which is only λ_0/33.6 ×λ_0/15.1(where λ_0 is the wavelength at 1.86 GHz in free space). Taking advantage of the dual-stopband property of the proposed SNG electric WG-MTM, a dual-band microstrip antenna array operating at 1.86 GHz and 2.40 GHz with very low mutual coupling is designed by embedding a cross shaped array of the proposed SNG electric WG-MTM. The measured and simulated results of the designed dual-band antenna array are in good agreement with each other, indicating that the mutual coupling of the fabricated dual-band antenna array realizes 9.8/11.1 d B reductions in the H plane, 8.5/7.9 d B reductions in the E plane at1.86 GHz and 2.40 GHz, respectively. Besides, the distance of the antenna elements in the array is only 0.35 λ_0(where λ_0 is the wavelength at 1.86 GHz in free space). The proposed strategy is used for the first time to reduce the mutual coupling in E H planes of the dual-band microstrip antenna array by using ultra-compact SNG electric WG-MTM. 相似文献
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基于电磁振动上料的茶梗和昆虫异物近红外光谱和荧光图像在线检测研究 总被引:1,自引:0,他引:1
茶叶是大众青睐的健康饮品之一,但茶叶在机器采收和加工过程中,容易混入茶梗和昆虫异物,污染茶叶、影响其质量安全,是未来应防范和检测的重点。X射线成像技术,根据食品基质和异物的密度差实施检测,广泛适用于金属异物并延伸至高密度塑料,但对于茶梗、昆虫这类低密度有机异物尚不适用,所以迫切需要研发新型无损检测技术和方法。针对片状茶叶重叠、遮掩异物的问题,提出了电磁振动上料辅助近红外光谱和荧光图像的检测方案,进行绿茶中的内源性异物茶梗和外源性异物昆虫的在线检测研究。通过电磁振动上料辅助近红外光谱和荧光成像系统,采集了600~1 050 nm范围的近红外光谱600条和RGB-N四通道图像各65幅。采用451条光谱进行建模,其余149条光谱作为预测集,评估模型的性能,比较了去趋势(Detrending)、多元散射校正(MSC)、标准正态变换(SNV)、变权重正态变换(VSN)、迭代自适应加权惩罚最小二乘法(airPLS)、不对称最小二乘法(ALS)、光程估计与校正(OPLEC)等不同光谱预处理方法的处理效果,其中OPLEC能较好地消除散射效应,偏最小二乘判别分析(PLS-DA)模型的正确识别率由78%提... 相似文献
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准确及时的检测原油含水率对注水策略调整、原油开采能力评估、油井开发寿命预测等均具有重要意义。然而,当前我国大多数油田均已进入高含水的开发中晚期,含水率测量难度大且准确率不高。在此背景下,开展了高含水情况下利用近红外光谱进行原油含水率测量的研究。 首先介绍了目前原油含水率检测的常用方法,分析了它们的优劣。理论上,由于水的近红外光吸收带与原油中C-H键的吸收带有明显区别,根据Lambert-Beer吸收定律和吸光度线性叠加定律可知,不同含水率高含水原油近红外光谱会存在较强响应差异。为此,对高含水原油进行近红外光谱检测,建立原油含水率与近红外光谱响应间的非线性映射模型,可实现高含水原油含水率的精确测量。为了验证该方法的有效性,搭建了近红外光谱数据采集实验装置:采用白炽灯作为光源,经过光路调节成平行光后垂直射入样品池,用近红外光谱仪(海洋光学NIR512)采集光谱用于分析。其中,接收光谱仪带宽为900~1 700 nm,平均分成512个波段。光谱数据利用光谱仪配套软件储存在电脑中。样本采用相同厚度不同比例的油水混合物,样本含水率范围为70%~99%,共采集数据60组,每组重复3次取平均值。得到原始数据后,先进行原始数据预处理,以减少数据采集时来自高频随机噪音及温度不稳定、样本不均匀、基线漂移、光散射等不利因素的影响。分别选用了S-G滤波、一阶导数和S-G滤波+一阶导数作为数据预处理的方法,利用连续投影算法(SPA)对光谱数据进行降维,并利用偏最小二乘法(PLS)和多元线性回归(MLR)进行建模,模型精度通过计算均方根误差值(RMSE)和相关系数(r)来验证。对比发现,使用S-G滤波+一阶导数建立的模型RMSE值最小(RMSE=0.007 0,r=0.998 3)。使用SPA降维后的模型要优于全波段PLS模型(RMSE=0.083 3,r=0.920 6)与MLR模型(RMSE=0.099 9,r=0.967 1)。利用SPA提取出的31个特征波长建立的模型仅占全波段的6.05%,并获得了较好的精度。证明了利用光谱检测高含水原油含水率可行性,并且得到了满意的精度,为高含水原油的含水率检测提供了新的方法, 为进一步利用近红外光进行高含水原油的快速检测与在线监测提供参考。 相似文献
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针对国际电工委员会1996年制定的IEC61000-2-9和美国国防部1999年修定的MIL-STD-461E标准提出的高空核爆电磁脉冲波形,研制了一台新型纳秒高压脉冲源。其产生的双指数波脉冲前沿小于3ns,脉宽58ns,幅度可达4kV,此外还可产生前沿小于2ns、幅度最高为4kV的脉冲方波;两种脉冲均可实现单次和间歇可调输出。介绍了脉冲源的电路设计和调试结果,通过实验对比了MIL-STD-461E与MIL-STD-461D两种双指数波形条件下某测控系统模块的干扰耦合效应。 相似文献
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示差折光检测-高效液相色谱内标法测定虫草中的甘露醇 总被引:2,自引:0,他引:2
研究了用示差折光检测 ,高效液相色谱内标法测定虫草中甘露醇的方法。虫草样品中的甘露醇用水超声振荡浸取 ,浸取液用 ZORBAX- C18固相萃取小柱预分离 ,以海藻糖为内标物 ,ZORBAX钙型阳离子交换柱为固定相 ,0 .0 5 g/L EDTA钙钠水溶液为流动相 ,示差折光仪为检测器检测虫草样品中的甘露醇含量。检出限在微克级 ,方法用于几种虫草样品的测定 ,结果令人满意。 相似文献
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偏硼酸锂固体及其熔体结构的高温Raman光谱研究 总被引:2,自引:0,他引:2
本文对偏硼酸锂(LiBO2)从室温到1673K进行了Raman光谱测试,得到了其在不同温度下的Raman谱图。通过分析,阐述了常温下的链状BO3三角形结构在熔化后逐渐转变为六角环(B3O6)^3-,即相变过程;以及在1273K后,由长链和六角环结构转化为CRN(Continuous Ruleless Network,BO3单元组成的连续无规网络)的新的相平衡移动过程。通过各谱峰在相平衡移动过程中相 相似文献
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It is a challenging issue to get satisfied results in terms of 3D imaging for shiny surface with fringe projection profilometry (FPP), as the wide variation of surface reflectance for shiny surface will lead to bad exposure, which requires the high dynamic range imaging (HDRI) technique. HDRI with monochromatic illumination and single-shot raw data of the color camera is presented in this paper. From the single-shot raw data, 4 monochrome sub-images corresponding to R, G, G and B channels can be separated respectively. After the attenuation ratios between R&G, G&B channels are calibrated, an image with higher dynamic range can be synthesized with the 4 sub-images, which can help to avoid the impact of bad exposure and improve the accuracy of phase calculation. Experiments demonstrate the validity of proposed method for shiny surface. 相似文献
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High gain and circularly polarized substrate integrated waveguide cavity antenna array based on metasurface 下载免费PDF全文
Two substrate integrated waveguide (SIW) cavity antenna arrays based on metasurface are proposed in this paper. By rotating the metasurface element, circularly polarized and high gain antennas are achieved respectively. Firstly, multi-mode resonance theory is employed to broaden the bandwidth of the slot antenna. And then, an SIW cavity composed of 4×4 cornercut elements is added on the top of the slot antenna to achieve the circular polarization and improve the front-to-back ratio. Thirdly, the metasurface elements are sequentially rotated and a high gain antenna with 2-dBi enhancement on average in the operation band is obtained. Based on the two antenna units, two 2×2 antenna arrays are designed. The circularly polarized and high gain antenna arrays are both fabricated to verify the correctness. Furthermore, the novel wideband phase shifter is employed in the circularly polarized antenna to obtain an operating bandwidth of 38% (4.05 GHz-5.95 GHz) and AR bandwidth of 24.9% (4.4 GHz-5.65 GHz). The bandwidth of the high gain antenna can reach 42.7% (3.95 GHz-6.1 GHz) and with the gain enhancement of 2 dBi compared with that of the circularly polarized antenna. The gain remains steady in most of operating band within a variation of 1 dBi. It is remarkable that the rotating of the metasurface element has a great influence on the antenna performance, which provides a new explication for the multi-function antenna design. 相似文献