共查询到17条相似文献,搜索用时 312 毫秒
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以带有返波结构的混响室为基础,研究了在复杂腔体内部返波结构的改变对场分布的影响效果。根据微波混沌理论分析了不规则腔内的场分布特征;结合统计电磁学,确立了在高功率微波短脉冲激励下的混响室中进行场均匀性和各向同性验证的指标;对复杂腔体中返波体的大小、数量及分布范围等因素进行了研究。数值模拟结果显示:凸起结构的尺寸越大,其对腔内电场的影响效果越为明显,尤其是腔内电场分布的统计均匀性和各向同性结果,都能得到很好的改善。同时凸起结构越多,分布的范围越广,腔内电场的统计均匀性和能流的统计均衡性就越好。 相似文献
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从本征模的角度阐明了频率搅拌技术的混响原理,并根据激励信号的频域特征,系统研究了频率搅拌方式下获取"实时均匀场"与"统计均匀场"的三种有效实现途径。选取线性扫频这一搅拌方式为主要研究对象,检验了混响室频率搅拌下的最低可用频率、场均匀性与统计特性三项主要技术指标。试验结果表明:线性扫频搅拌方式下,混响室的最低可用频域与机械搅拌方式基本一致;场均匀性满足IEC 61000-4-21标准规定的容差要求;场值波动规律符合理论分布模型。 相似文献
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使用微扰理论分析了腔体形变对谐振频率漂移的影响规律,从理论上论证了边界形变混响室的可行性,计算得到了边界形变参数对混响室空间电场均匀性的影响规律;采用了一种由柔性屏蔽布作为腔体材料、步进电机控制腔体表面形变的边界形变混响室设计方法,并对研制的几何尺寸为2.5 m×1.8 m×1.5 m的混响室的内部电场统计特性进行了试验测试。结果表明:混响室内部电场服从Rician分布,且随频率升高与理论模型的一致性变好;当形变幅度达到400 mm时,腔体内部电场扰动比大于20 dB,空间电场标准偏差小于3 dB,满足电磁兼容对混响室平台均匀性的限制要求。 相似文献
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从理论上分析了混响室采用频率搅拌的可行性,仿真计算和试验测量了频率搅拌混响室内部电场的均匀性和统计特性,探索了在屏蔽效能测试中的应用。研究结果表明:频率搅拌方法能够得到空间统计均匀的电场分布,电场直角分量的模值服从瑞利分布,并且频率越高电场的均匀性和统计特性越好。在频率搅拌混响室内部测试得到开缝小尺寸屏蔽体在1~10GHz频段的屏蔽效能约为15dB,与机械搅拌混响室测试结果基本一致。 相似文献
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利用柔性屏蔽材料不平整性使屏蔽腔内场环境易于满足各向同性、均匀分布、随机极化统计特征的特点,研究了三种不同柔性屏蔽材料搭建的模式搅拌混响室的可行性。在Z字形搅拌器的作用下通过测量得到低频场均匀性和高频归一化电场的概率密度函数,根据IEC 61000-4-21-2011标准和理想混响室模型验证了所搭建混响室的有效性。在此基础之上,通过实验测量分析了搅拌器转速、天线高度、天线位置对归一化电场概率密度函数(PDF)的影响,并利用所搭建混响室对加载开孔电大金属腔的电磁屏蔽效能进行了测试。研究结果表明利用柔性屏蔽材料搭建混响室具有较好的可行性。 相似文献
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I. N. Didenkulov A. I. Martyanov N. V. Pronchatov-Rubtsov 《Bulletin of the Russian Academy of Sciences: Physics》2016,80(10):1197-1202
Results from studying the interaction between gas bubbles and the field of a flow-through acoustic resonator, and the Raman scattering of acoustic waves by moving bubbles, are presented. The structure of the distribution of bubble concentration in the resonator is studied. It is shown that nonlinear scattering by moving bubbles can be used to image bubble objects. 相似文献
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An optimally arranged multiple-channel active-control system is known to be able to create a large quiet zone in free space for a stationary primary noise source. When the primary noise source moves, the active control of the noise becomes much more difficult, as the primary noise field changes with time in space. In this case, the controller of the control system must respond fast enough to compensate for the change; much research has been focused on this issue. In this paper, it is shown that a moving source also causes difficulties from an acoustical perspective. A moving source not only changes continuously the strengths and phases of the sound field in the space, but also changes the wavefront of the primary sound field continuously. It is known that the efficiency of active noise control is determined mainly by the wavefront matching between the primary and control fields. To keep the control system effective in the case of a moving source, the wavefront of the control field needs to change, in order to continuously match the primary-wavefront change. This paper shows that there are limitations to the control-wavefront change. An optimally pre-arranged, multiple-channel control system is not able to construct a matching wavefront when the primary source moves outside a certain range. In other words, the control system is still able to create a large quiet zone only when the primary source moves within a range around the central axis of the control system. Both the location and the size of the quiet zone change with the location of the primary source. 相似文献
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At high frequencies, e.g., Q- and W-bands, it is advantageous to make the axial length of loop-gap resonators (LGRs) at least as long as a free-space wavelength. The opposite scaling of capacitance and inductance with LGR length suggests that the length of an LGR can be increased without limit, with the axial radio frequency (rf) field profiles and resonance frequency independent of length. This scaling is accurate for resonator dimensions much less than one free-space wavelength. When the resonator length approaches one-tenth of a free-space wavelength, the rf field uniformity degrades. From one-tenth to one free-space wavelength, computer simulations and experimental measurements show that the axial magnetic field energy density profile is peaked in the center of the LGR, gradually decreases from 25 to 50% at a distance one radius from the end, and rapidly there-after. The nonuniformity is of two types. One type, in the vicinity of one radius of the end, is caused by the flaring of the field as it curves from the central loop to the end region, into the larger return loop(s). The other type, in the central part of the resonator, is caused by impedance mismatch at the ends of the LGR. The LGR may be viewed as a strongly reentrant (ridge) waveguide nearly open at both ends and supporting a standing wave. A transmission line model relates the central nonuniformity to the fringing capacitance and inductance at the ends of the resonator. This nonuniformity can be eliminated in several ways including modifying the ends of the LGR by adding a small metal bridge or a dielectric ring. These uniformity trimming elements increase the fringing capacitance and/or decrease the fringing inductance. With trimmed ends, LGRs can be made many free-space wavelengths long. The maximum resonator length is determined by the proximity in frequency of the fundamental LGR mode to the next highest frequency mode as well as the quality factor. Results of this theory are compared and conformed with finite-element simulations. This theory connects the uniform LGR with the uniform field cavity resonators previously introduced by this laboratory. 相似文献
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A. D. Lapin 《Acoustical Physics》2000,46(4):491-493
The sound field generated by a point source of volume velocity in a room with a Helmholtz resonator is determined. The shift produced by the resonator in the natural frequencies of the room is calculated. 相似文献
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He G Petryakov S Samouilov A Chzhan M Kuppusamy P Zweier JL 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2001,149(2):218-227
EPR spectroscopy has been applied to measure free radicals in vivo; however, respiratory, cardiac, and other movements of living animals are a major source of noise and spectral distortion. Sample motions result in changes in resonator frequency, Q, and coupling. These instabilities limit the applications that can be performed and the quality of data that can be obtained. Therefore, it is of great importance to develop resonators with automatic tuning and automatic coupling capability. We report the development of automatic tuning and automatic coupling provisions for a 750-MHz transversely oriented electric field reentrant resonator using two electronically tunable high Q hyperabrupt varactor diodes and feedback loops. In both moving phantoms and living mice, these automatic coupling control and automatic tuning control provisions resulted in an 8- to 10-fold increase in signal-to-noise ratio. 相似文献
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《中国光学快报(英文版)》2015,(11)
We report experimental progress in weakening the frequency difference lock-in phenomenon in a Y-shaped cavity dual-frequency laser. A cube coil pair is chosen to provide a uniform magnetic field for tunability and uniformity of magnetic field strength. When the transverse magnetic field intensity is 9 m T, the frequency difference lock-in phenomenon is evidently weakened and the frequency difference can be continuously tuned in the range of0.12 MHz to 1.15 GHz. Moreover, the relationship between the minimal frequency difference and magnetic field intensity are investigated and discussed. Then a Y-shaped cavity dual-frequency laser is expected to be utilized as an optimum light source for heterodyne interferometric sensing and precise laser measurement. 相似文献
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Akio Yoshizawa 《Optical and Quantum Electronics》1995,27(2):127-131
A simple system for producing a step-like optical frequency sweep is proposed and demonstrated using a distributed Bragg reflector laser as a light source and a Fabry-Perot resonator as a frequency discriminator. Such a step-like sweep is realized by changing the injection current continuously. 相似文献