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Accurate analysis of TEM horn antennas for pulse radiation 总被引:9,自引:0,他引:9
Shlager K.L. Smith G.S. Maloney J.G. 《Electromagnetic Compatibility, IEEE Transactions on》1996,38(3):414-423
In the past, various approximate theoretical models have been used to analyze TEM horn antennas. Because of the limitations of these approximate models, there has been, to date, only qualitative agreement of measurements for TEM horn antennas with the predictions of the theories. The finite-difference time-domain (FDTD) method is used to accurately analyze TEM horn antennas for pulse radiation. First, the metallic triangular-plate TEM horn antenna is considered. Computed results for the reflected voltage in the feeding transmission line and the time-varying radiated electric field are shown to be in very good agreement with new experimental measurements. Graphs of the electric field in the space surrounding the antenna (magnitude of field plotted on a color scale) are used to give a physical insight into the process of radiation. Next, the method is used to analyze two TEM horns that were previously designed for pulse radiation. The geometry and electrical properties of these antennas are more complicated than for the metallic, triangular-plate horn. One has shaped metallic plates with a resistive termination at the open end; the other has plates whose resistance varies continuously along their length. The computed results for these antennas are compared with previously made experimental measurements 相似文献
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时域有限差分法是电磁场领域中应用最为频繁的数值方法之一,它可以有效地处理复杂媒质中颗粒对电磁脉冲信号的散射问题,以及超宽带电磁脉冲信号在色散媒质中的传播问题。几乎所有介质,无论其在太赫兹(THz)波段是否有吸收峰,对太赫兹波的传播都有影响。研究太赫兹波在介质中的传播情况,对优化太赫兹系统,分析与设计太赫兹应用技术有重要意义。本文模拟了太赫兹波在散射介质中的传播,说明了太赫兹波在内弹道干涉测速应用中的可能性;模拟了太赫兹脉冲在色散介质中的传播情况,为太赫兹时域光谱系统中晶体选择提供依据。 相似文献
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在超宽带穿墙雷达接收机系统中,其关键的等效采样技术需要一种极窄脉宽高电压的脉冲触发采样门电路来对接收信号进行采样。介绍了超宽带取样脉冲产生技术,讨论并分析了几种常用超宽带脉冲产生方法的特点及其局限性。提出了新型的肖特基二极管脉冲整形网络,设计并实现了应用于等效采样接收机系统的新型亚纳秒取样脉冲产生器,很好地结合了雪崩晶体管与脉冲整形网络的优势,在显著减小脉宽的同时保持了较高的脉冲幅度。通过仿真分析和制作测试,获得了脉冲底宽为400 ps、幅度为6.46 V和波动水平为-14.7 dB的单极性窄脉冲,实测结果与设计数值一致性良好。这种简单高效廉价的电路十分符合超宽带穿墙雷达等效采样接收机取样脉冲的设计。 相似文献
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Finite difference time domain (FDTD) analysis has been successfully formulated for solving diffusion equation in biological tissues. Time-dependent diffusion equations are approximated by FDTD equations by assigning diffuse photon fluence rates and radiant flux defined in the diffusion equations to Yee meshes. At the boundary between scattering and no scattering material, FDTD equation including only fluence rate has been derived, which make it possible to calculate the fluence rate at the boundary. The formulation is useful to solve diffusion equations by iterative algebraic calculations in scattering media with inhomogeneous optical properties. The conditions to give stabilities for numerical solutions have been become clear in terms of scattering coefficients and mean cosine of scattering angles. Using the formulation, the reflectance of three-layered slabs containing a clear layer have been calculated. As a result, it has been found that absorption loss changes of the highly scattering medium beyond the clear layer are estimated from the time profiles of the reflectance. 相似文献
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Conformal mapping analysis of a modified TEM cell 总被引:1,自引:0,他引:1
Changhua Wan 《Electromagnetic Compatibility, IEEE Transactions on》1993,35(1):109-113
A modification procedure in which the inner conductor of the usual TEM cell is symmetrically finned with a pair of small vertical plates is proposed to obtain a more suitable uniform field. In such modified TEM cells, a fairly uniform field can be established just above the inner surface of the rectangular-shaped shield instead of in the central portion of the separation between the septum and the shield, and this uniform field can be used for EMC measurements without dielectric equipment support or on a ground screen. The usefulness of the proposed modification is illustrated by the conformal mapping analysis of a special modified TEM cell. A similar modification can also be made in a general TEM cell and GTEM cell for the aforementioned uses. Conclusions and discussions are given, and further work is suggested 相似文献
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Two-dimensional (2-D) TEM horns are modeled using the finite-difference time-domain (FDTD) method. The boundary walls are perfect electric conductors and one wall, which does not align with the Cartesian grid, is approximated using a staircased representation. By carefully comparing the FDTD results to those of the analytic solution, one can make conclusions about the coarseness with which a boundary can be represented. It is found that staircasing errors are small when the staircase diagonal (the hypotenuse of the right triangle created by the stairstep) is smaller than half a wavelength at the highest significant frequency in the excitation. This rule-of-thumb is put forward as a necessary condition for the discretization of general problems. Results are also provided for some simple FDTD schemes that are designed to reduce staircasing errors. By using large aspect-ratio cells, a grid can be constructed that satisfies the rule-of-thumb given above. While this approach eliminates general staircasing errors, some errors persist owing to the presence of step discontinuities immediately adjacent to the horn feed. These errors can be further reduced by using a cell-splitting approach. It is shown that the contour path FDTD technique can be used to eliminate nearly all staircasing errors, while some additional improvement is shown to be provided by using a stabilized contour path FDTD approach. Finally, a recently proposed conformal technique that permits simple implementation is shown to provide results comparable with those of the stabilized contour path approach 相似文献
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皮秒脉冲光源是量子密钥分配系统核心器件。为了实现皮秒脉冲光源的国产化,基于国产芯片研制了一种千兆皮秒脉冲激光器模块。该模块采用比例-积分-微分算法控制温度,使光波长漂移在0.01nm以内,使用外部光电二极管探测光功率,反馈调整激光管驱动电流,进行了实验验证。结果表明,利用国产单片机精确控制恒流源和窄脉冲电路驱动激光管发光,输出光脉冲频率达到1.25GHz,脉冲宽度约为50ps,光功率为-3dB对应的谱宽小于0.2nm,输出光波长和功率稳定。此研制的国产化皮秒脉冲激光器模块可满足量子密钥分配系统对光源稳定性的要求。 相似文献
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Luebbers R. Kumagai K. Adachi S. Uno T. 《Electromagnetic Compatibility, IEEE Transactions on》1993,35(1):90-94
The application of the finite-difference-time-domain (FDTD) method to propagation through a highly conductive nonlinear magnetic material is described. The FDTD calculations will require changing the permeability of the material at each time step based on the value of the magnetic field at the previous time step. The effects of the high conductivity and magnetic material nonlinearity on the stability of the FDTD calculation is investigated. Stability requires reduction of the time-step size to well below the Courant limit. Accuracy is demonstrated by comparison with previously published results 相似文献
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薄膜材料透射电镜截面样品的简单制备方法 总被引:1,自引:0,他引:1
针对薄膜材料透射电镜截面样品制备过程复杂、制样成功率低的问题,本文详细介绍了一种操作简单、实用性强的制备方法,采用该方法可以成功制备出脆性衬底上薄膜材料的TEM截面样品。 相似文献
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David Dubuc Olivier Mazouffre Clément Llorens Thierry Taris Mary Poupot Jean-Jacques Fournié Jean-Baptiste Begueret Katia Grenier 《Analog Integrated Circuits and Signal Processing》2013,77(2):135-142
This paper presents an innovative biosensing technique, based on the interaction between biomaterial and microwave electromagnetic (EM) waves, which probes the bio-parameters of investigated biological samples. Thanks to the microtechnologies, this approach is able to sense biomaterials down to living cells size without invasivity. The broadband dielectric spectroscopy of living cells suspensions is therefore demonstrated, sketching a rich EM signature, “rich” in terms of biological information’s such as cells’ proliferation and cells’ viability. Capacitive contrasts of 4 and 12 % between the cells suspension and their pure medium are measured at 20 and 40 GHz respectively, which demonstrate the ability of such a technique to detect (and quantify) living cells non-invasively. Moreover, we demonstrate a capacitive contrast of 5 % at 30 GHz between living and dead cells. Such a result is based on the ability of the microwaves to penetrate into the cells and sense their intracellular content, and then to carry viability information’s of biomaterials out. Finally, we present the feasibility of on-chip microwave signals processing, which points out that integrated circuit for data processing can be integrated together with a nano-liter range microfluidic bio-sample manipulation and a microwave-based biosensor. Such a work consequently permits to envision promising Lab-on-Chip applications such as cells’ drug screening for personalized medicine notably. 相似文献
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Huaping Liu 《Communications Letters, IEEE》2003,7(11):531-533
In this paper, the error performance of an ultra-wideband (UWB) system with a hybrid pulse amplitude and position modulation (PAPM) scheme over indoor lognormal fading channels is analyzed. In the PAPM UWB system, input data is modulated onto both the pulse amplitudes and pulse positions. The receiver employs a RAKE to combine energy contained in the resolvable multipath components. Derivation of closed-form error rate expressions of the system in lognormal fading channels is based on approximating a sum of independent lognormal random variables (RV) as another lognormal RV using the Wilkinson method. Given the same delay spread of the channel, the proposed PAPM scheme can provide a higher throughput than the binary pulse amplitude or pulse position modulation scheme. 相似文献
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The finite-difference time-domain (FDTD) method is used to analyze a dielectric leaky-wave antenna comprising metal strips etched on a rectangular dielectric rod. The radiation patterns of the leaky-wave antenna with and without the transition are determined by using FDTD. The effects of the launching discontinuity on the performance of the antenna are discussed. In addition, the application of the perfectly matched layer (PML) technique to the three-dimensional (3-D) dielectric waveguide and its performance, compared to those of the Mur's (1981) first-order and super-absorbing Mur's first-order absorbing boundary conditions (ABCs) are described. In addition, the effects caused by perturbation on the wave propagation characteristics of dielectric waveguide are also discussed. The FDTD results are verified by a W-band experiment and found to be in good agreement 相似文献
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Yaguchi T Suzuki M Watabe A Nagakubo Y Ueda K Kamino T 《Journal of electron microscopy》2011,60(3):217-225
An environmental cell for high-temperature, high-resolution transmission electron microscopy of nanomaterials in near atmospheric pressures is developed. The developed environmental cell is a side-entry type with built-in specimen-heating element and micropressure gauge. The relationship between the cell condition and the quality of the transmission electron microscopic (TEM) image and the diffraction pattern was examined experimentally and theoretically. By using the cell consisting of two electron-transparent silicon nitride thin films as the window material, the gas pressure inside the environmental cell is continuously controlled from 10(-5)?Pa to the atmospheric pressure in a high-vacuum TEM specimen chamber. TEM image resolutions of 0.23 and 0.31?nm were obtained using 15-nm-thick silicon nitride film windows with the pressure inside the cell being around 5?×?10(-5) and 1?×?10(4)?Pa, respectively. 相似文献
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The finite-difference time-domain (FDTD) method is applied to study the performance of E-plane sectoral horn antennas designed for broad-band applications. These antennas (proposed for 6-18 GHz phased arrays) have a large bandwidth, and they are easily array integrated. These antennas have a highly complicated geometry that is modeled using a polygonal approximation in the curved boundaries. Perfect matched layers (PMLs) combined with first-order absorbing boundaries are employed to simulate the free-space environment in the FDTD mesh 相似文献
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