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基于等离子体反射特性的雷达诱饵技术研究 总被引:3,自引:0,他引:3
在研究等离子体与电磁波相互作用的基础上,得到了均匀非磁化等离子体对入射电磁波的反射系数,通过对反射特性的分析,讨论了等离子体用作雷达诱饵的有关问题. 相似文献
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正 自由电子激光器有可能产生从毫米波到可见光范围内的相干辐射,实现简单的电压连续调谐并能获得极高的输出功率。因此越来越引起人们的重视。它的工作机理可概述如下:当相对论电子束与入射的泵浦电磁波相互作用时,在电子束中激起纵向密度波并产生正向及反向的散射电磁波。我们仅考虑反向散射波,因为它经过两次多普勒频 相似文献
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本文讨论了不均匀磁化等离子体片对圆极化电磁波、异常模电磁波的吸收,计算了不同条件下衰减率.计算表明,当电磁波的频率接近电子碰撞频率时,磁等离子体对电磁波的吸收达到最大值.当入射电磁波的频率很低时,不均匀磁化等离子体中碰撞对雷达波的吸收非常小.当入射电磁波频率较高时,等离子体的碰撞对入射电磁波的衰减很有效.在磁场对电磁波衰减率的影响上,对右旋电磁波,磁场变大,衰减率曲线的峰值向较低的碰撞频率方向移动,且衰减率减小.而对左旋电磁波,磁场变大,衰减率曲线的峰值向高的碰撞频率方向移动,且衰减率也增大.同时,我们发现在一定条件下,磁场使电磁波的有效吸收带宽变宽.此时,等离子体对电磁波的吸收也最大.特别是当入射电磁波的频率较低时这一特性更显著. 相似文献
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应用相对论电磁粒子模拟程序,研究了线性极化强激光入射到无碰撞密度均匀等离子体时被加速的超热电子及电磁不稳定性机制。讨论了电磁不稳定性激发的自生磁场和超热电子热传导特性。 用Spitzer-Harm理论分析了电子热传导中能量的运输情况,观察到由激光的非等方加热引起的电子纵向加热现象。结果表明,不稳定性激发的强电磁场使电子束在1 μm的距离内沉积能量,同时对在激光有质动力推开电子时形成的电子热流产生抑制作用。 相似文献
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A novel infrared photodetector utilizing intersubband electron transitions and plasma wave excitation in a quantum well (QW)-the QW intersubband hot-electron phototransistor (IHEPT)-is proposed and evaluated. It is shown that the excitation of standing plasma waves in the QW base by incident modulated infrared radiation can result in resonant response of IHEPTs. The plasma resonance peaks of the linear responsivity of IHEPTs with a base contact spacing of about 1 μm correspond to the terahertz range of modulation (signal) frequencies. The resonant peaks of the responsivity can be tuned by the biasing voltage. The peak value of the IHEPT resonant responsivity can be of the order of the steady-state responsivity of standard QW intersubband infrared photodetectors, significantly exceeding the high-frequency performance of the latter. Relatively large values of the IHEPT resonant responsivity are associated with strong injected current stimulated by the plasma waves in the QW-base. Finally, it is shown that the nonlinear dependence of the injected current on the potential of the QW base results in the variation of the dc current with changing signal amplitude. The nonlinear response current as a function of the modulation frequency also exhibits resonant behavior with the peaks at the plasma resonance frequencies and can be used for the detection of the signal component envelope 相似文献
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A theoretical study of radiation of electromagnetic and electroacoustic waves in lossy compressible weakly ionized plasma has been made and its dependence on the ratio of source to plasma frequencies has been investigated. A linearized theory is used such that the isotropic electron plasma is regarded as a single fluid continuum. A thin linear resonant antenna is used as the source of radiation and the propagation constant on it is assumed to be the same as in free space. The propagation constant is taken to be complex in plasma for both electromagnetic and electroacoustic waves. Also the effect of electron neutral particle collision is taken into account wherever it is effective. It is shown that propagation is almost unaffected by plasma when source frequencies much higher than the plasma frequency are used. But the effect of plasma on radiation is found to be profound at frequencies smaller than the plasma frequency. General expressions of radiation resistance for both the electromagnetic and eloctroacoustic waves have been obtained and under these conditions the half-wave dipole is treated as a special case. The results deduced for these are found to be in agreement with those wherever obtained earlier. 相似文献
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Sh.E. Tsimring 《Journal of Infrared, Millimeter and Terahertz Waves》2001,22(10):1433-1468
The stability of the electron beams and maximum share of the electrons oscillatory energy, i.e. finally efficiency, power, and pulse duration of the gyrotron to a considerable extent depend on the velocity and the energy spread (VESP) of the HEB. The basic factors determining VESP in the helical beams are discussed. Among these factors static (initial velocities, cathode heterogeneities, space charge fields) and dynamic (negative mass and diochotron instabilities and a global instability connected with the capture of the electrons in the gyrotron adiabatic trap) factors are considered. Qualitative models of the excitation of the space charge oscillation as well the parasite electromagnetic radiation of the HEB are developed. Some experimental data of the investigation of the parasitic electromagnetic radiation spectrum in one gyrotron are discussed. The methods of the experimental investigation of the VESP are described. 相似文献
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S. N. SAMADDAR 《International Journal of Electronics》2013,100(3):279-299
The study of the radiation from a vertical magnetic dipole in mi inhomogeneous half space and also in inhomogeneous stratified media above a horizontal conducting infinite plane is considered. The formal expression for the Hertz potential, from which all the field components can be derived. is presented in the form of a contour integral. These formal results are employed for special cases using suitable profiles for relative dielectric constants so that the electromagnetic fields can be expressed in terms of known functions. The contour integral is evaluated asymptotically by saddle point method of integration in each of the examples using special profiles for ε(z). Possibilities of the existence of surface waves in appropriate configurations are also discussed. The results for homogeneous media are also extracted from those of the corresponding inhomogeneous media by taking appropriate limits. 相似文献
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《Microwave Theory and Techniques》1971,19(11):882-883
The problems of electromagnetic waves in moving isotropic or uniaxial mediums have been dealt with by numerous authors. Chawla and Unz considered the fields in a moving anisotropic plasma, and Chen and Cheng analyzed waves in an isotropic plasma in a moving dielectric medium. In this note we consider electromagnetic fields in a moving anisotropic medium and propose the network formulation of electromagnetic fields in the moving medium in the radial cylindrical coordinate. The method is an extension of the transmission line representation of electron beams on infinite magnetic fields. We can apply these results to the cases of any magnetic field intensity and, further, solve the complex problems for a stationary anisotropic plasma by a similar method. 相似文献
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The radiation characteristics of a line source of magnetic current are studied for the case in which the source is situated in a half-space of isotropic, compressible plasma which is bounded on one side by a perfectly conducting, rigid plane screen. In addition to the electromagnetic and plasma space waves, the line source excites a boundary wave. This boundary wave is a coupled wave. It has associated with it both a magnetic field component and the pressure term. This is in contrast to the space waves which can be decomposed into an electromagnetic (EM) mode with no pressure term and a plasma (P) mode with no magnetic field associated with it. The characteristics of this boundary wave are evaluated. The boundary wave propagates for all frequencies and the power carried by the boundary wave becomes smaller as the frequency is increased. 相似文献
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The problem of a magnetic line source in a ground plane coated with a warm plasma slab is investigated. Consideration is given to electromagnetic and plasma waves in the slab and to the coupling at the boundaries between these waves and the free-space fields. An integral expression for the radiation field is obtained and is evaluated by the method of steepest descent. The resulting radiation patterns display interesting effects due to electron pressure near the electron plasma frequency, and these are discussed with the help of the transmission line analog to the problem. The surface-wave poles are located and discussed using this same analog. 相似文献
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You-Lin Geng Xin-Bao Wu Le-Wei Li Bo-Ran Guan 《Antennas and Propagation, IEEE Transactions on》2005,53(12):3982-3989
Electromagnetic scattering by an inhomogeneous plasma anisotropic sphere is formulated and obtained, where the inhomogeneous plasma anisotropic sphere is divided into (s-1) homogeneous anisotropic spherical layers. The electromagnetic fields in the inner spherical multilayers and outer free space of the inhomogeneous plasma anisotropic spherical structure can be expanded in terms of the spherical vector wave functions in plasma anisotropic medium and in isotropic medium, respectively. By applying the continuous boundary conditions of electromagnetic fields on the spherical interfaces of the (s-1)-layered homogeneous anisotropic plasma medium, the unknown expansion coefficients of fields in the multilayered plasma spherical structure are obtained, and then the electromagnetic field distributions are calculated. Numerical results for the very general inhomogeneous plasma dielectric material sphere are given and the data in a special case are obtained using the present method and the method of moments accelerated with the conjugate-gradient fast-Fourier-transform approach and compared to each other to verify the correctness and applicability of the present analysis. 相似文献
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The propagation of a transient electromagnetic field through a cold, isotropic, lossless, inhomogeneous plasma is considered. The electron density of the plasma decreases exponentially in the direction of propagation. For incident transient signals whose Laplace transforms are regular at infinity and whose only singularities are poles, the transient electric field propagated through the plasma can be expressed as a sum of exponential waves at discrete complex frequencies. The characteristic frequencies of the inhomogeneous plasma are related to the zeros of the modified Bessel function of the first kind of fixed argument and variable order. When the Laplace transform of the incident signal is not well-behaved at infinity, approximate methods may be used to evaluate the transient electric field. The propagation of a step sine wave and of a quasi-monochromatic Gaussian pulse are considered. It is found that for plasmas characteristic of reentry boundary layers, the effect of the plasma layer on dispersion is very small. The principal effect of the layer is to attenuate a signal propagated through it. 相似文献