共查询到20条相似文献,搜索用时 64 毫秒
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Yiping Tang Xingguo Li Zhenfa Luo Guozhen Li 《Journal of Infrared, Millimeter and Terahertz Waves》1997,18(4):827-846
This paper researches mainly the radiation characteristics of the target and detecting techniques by superconducting detector in the submillimeter wave(SMMW) region. The calculation of transition wavelength(TW) between Planck and Rayleigh-Jeans is given out. The experiment of detecting different targets is finished by use of superconducting detector possessing high performances. Through the experiments in paper we can select and determine the wave bands of SMMW detecting and imaging system. The many novel theoretical analyses and experimental results are expressed in Figs and tables of the paper. Finally, a part of calculating results and experimental datum detected by a superconducting detector in SMMW regions are given in this paper. 相似文献
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Fujii M Sakamoto K Toda Y Negishi A Kanai H 《IEEE transactions on bio-medical engineering》1999,46(5):494-504
Undesirable temperature rise at the muscle-bone interface has been one of the major problems during ultrasound hyperthermia treatment. In this study, we examined by both computer calculation and phantom experiment the cause of this problem. Ultrasound penetrates a bone in two different waveforms, longitudinal and transversal. The transmission coefficient of these two waves vary greatly with the incident angle. From both theoretical and experimental results, the incident angle dependency of the interface heat was confirmed. When the incident angle is less than the critical angle of the longitudinal wave, the main cause of the temperature elevation is the absorption of the longitudinal wave in the bone. When the incident angle is larger than the critical angle of the longitudinal wave, the transversal wave becomes the major cause of the heat generation. At the incident angles larger than the critical angle of the transversal wave, no temperature rise is produced by the absorption of the ultrasound at the bone; the incident longitudinal wave, strengthened by the reflected wave, is absorbed in the muscle just in front of the bone. The heat generated in the muscle is transported to the interface so that the temperature of the interface and bone increases slightly. 相似文献
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A remote sensing technique based upon the measurement of three complex reflection coefficients is shown to facilitate the characterisation of a scattering surface, such as terrain, as a function of the polarisation of the incident wave. An experimental microwave scatterometer is described, together with experimental results from terrain which suggest that optimum scattering conditions may be produced when the incident wave has an appropriate characterstic polarisation. 相似文献
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《Microwave Theory and Techniques》1985,33(6):447-452
A theoretical and experimental study on the response of an E-field probe near a cylindrical model of the human body has been conducted. The body is simulated with a long cylindrical dielectric shell filled with saline water, and a single E-field probe oriented in various directions, or an orthogonal probe is heated near its surface. The model with the probe is illuminated by a TE or TM plane EM wave. The response of the probe was found to be strongly dependent on the probe location with respect to the direction of the incident EM wave, the probe separation from the model surface, the probe orientation and the polarization of the incident EM wave. The effect due to the dielectric shell on the probe response, with and without the presence of saline water, was carefully investigated. In all cases, the agreement between theory and experiment was found to be very good. 相似文献
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一种新的FDTD入射场设置方法 总被引:11,自引:1,他引:10
本文提出了一种新的入射场设置方法.采用一维FDTD算法来模拟入射波.所得结果与通常的入射场解析表达式的结果比较表明,采用一维FDTD算法引入的入射波在总场区分布均匀,在散射场区泄漏小. 相似文献
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本文主要介绍了采用超导约瑟夫森结实现的超导微波源的基本原理及实现方法。文中我们通过电路仿真得到了
输入为直流信号,输出为幅值可调的4.2GHz 微波信号,然后根据相应仿真参数绘制了芯片版图,并对实验室原有的自对
准剥离工艺进行了改进,完成了超导微波振荡器的制备,为将来利用超导材料实现具有实用价值的太赫兹源奠定了理论
以及实验研究基础。 相似文献
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Yassin G. Jung G. Dikovsky V. Barboy I. Kambara M. Cardwell D.A. Withington S. 《Microwave and Wireless Components Letters, IEEE》2001,11(10):413-415
It is well known that the boundary conditions of the electromagnetic fields on the surface of a superconductor are influenced by the field penetration into the material. In a series of recent publications, it has been suggested that this effect substantially influences the wave propagation in high-temperature superconducting waveguides, to the extent that the mode order becomes different than that predicted for perfect conductor waveguides. In this paper, we present experimental investigation of this effect. We show that the effect of superconductivity on the wave propagation in waveguides is very small for temperatures well below the transition temperature and away from cutoff. We also discuss the behavior of the waveguide near cutoff and very close to the transition temperature 相似文献
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以基于极化平面的波达角(Direction of Arrival,DOA)估计算法为基础,针对近地面天线受地面反射波影响从而极大地影响DOA估计的准确性问题,对如何去除地面反射波的影响进行深入研究.分别采用理想地面近似法、反射系数法和阵列抑制算法进行仿真试验,对比和分析这三种算法的优缺点,以及各自的适用性.理论分析和仿真试验表明:理想地面近似算法在实际地面参数与理想导电平面相近时,具有准确的计算结果,但在其他情况下计算结果与真实值误差很大;反射系数法通过地面的电导率σ、相对介电常数εr以及入射波的极角θ分别求出地面的水平反射系数和垂直反射系数,从而准确估算出来波方向,但由于该方法需要预先知道地面参数,故其应用场景受到了一定的限制;阵列抑制算法巧妙地利用地面反射波和直达波在相位延迟和入射角方面的关系,通过移相操作,生成抑制反射波的新数据,再对其进行处理,准确计算出DOA.通过比较分析可以得出,阵列抑制算法可用于任何类型的实际地面,且无需知道实际地面参数,同时该算法具有很好的准确性,因此其应用场景不受限制,具有很好的理论研究和实际应用价值. 相似文献
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Provided is the first experimental verification that a suitably designed textured surface can reflect a normally incident circularly polarised wave with the same sense. This is achieved by engineering the reflection phase of the orthogonal linearly polarised components of the incident wave by modifying the dimensions of the patches from which the textured surface is constructed such that they are 180deg out of phase with each other. It is shown that the axial ratio of an incident right-hand circularly polarised signal is 0.8 dB at 3.86 GHz and that the reflected signal is also right-hand circular. 相似文献
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Plane wave spectrum scattering analysis of near-field obstacle effects on directive antenna patterns
《Antennas and Propagation, IEEE Transactions on》1979,27(6):772-778
A plane wave spectrum scattering analysis of the effects of a near-zone obstacle on the pattern performance of a directive antenna is discussed. The free-space azimuth monopulse antenna is characterized by its sum and difference mode plane wave spectra, and a computed plane wave scattering dyad is used to characterize the scattering by a metallic right circular cylinder when it is excited by the incident antenna spectra. An efficient computer algorithm has been developed to compute the far-zone scattered and total fields for the antenna/cylinder system. Extensive experimental data have been obtained, and the patterns calculated using the present analysis are in agreement with the measured data. 相似文献
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Snell's law of reflection applies to a plane wave incident on an infinite surface. For finite surfaces the size of the surface, the angle of incidence, and the polarization of the incident wave all contribute to deviations from Snell's law. An eigenfunction expansion for the scattering pattern of a perfectly conducting strip and experimental bistatic scattering measurements of rectangular plates are used to verify the deviations. Physical optics calculations also predict these deviations and are used to provide a physical explanation for the deviations 相似文献
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Microwave reflectometry is a radar technique utilized by nuclear fusion diagnostics to evaluate the plasma electron density distribution (density profile) and its local fluctuations in experimental devices, e,g., tokamaks. It exploits the fact that an electromagnetic wave launched into the plasma is reflected at the layer where the refractive index vanishes. By mixing the incident and reflected waves, a phase-modulated reflectometric signal is produced. In O-mode broadband reflectometry, the density profile is determined by sweeping the frequency of the incident wave, estimating the phase-rate of the reflectometric signal and computing its Abel inversion integral. In this paper, a stochastic nonlinear filtering approach is adopted for the estimation problem. The joint phase and phase-rate dynamics is modeled as a vector Gauss-Markov process from which only the first component is observed. A suboptimal nonlinear filter tailored to the features of the problem under study is developed and tested by simulation and applied to real data. This estimator exhibits significant advantages over the extended Kalman-Bucy filter, which is used in this work as a benchmark 相似文献
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The relation between the surface impedance ZS(=RS?jXS) of superconductors and DC current I has been derived to determine the propagation constant of a superconducting microstrip line, and the relation between the phase delay ? of the superconducting microstrip line and DC current I is also presented. On the basis of these analytical results, a microwave phase shifter has been made by using YBCO superconducting thin film. In this paper, we describe the design principle of phase shifter, its fabrication, and present the experimental results. These measured values agree well with the theoretical curves. 相似文献
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This paper theoretically investigates a novel application of high-temperature superconductors where the superconductor serves as the active component in a microwave or millimeter traveling-wave amplifier. A guided electromagnetic wave interacts with a dc superconducting electron current to set up charge-density gradients within the superconducting electron "plasma." The electromagnetic wave gradually extracts energy from the superconducting electrons by traveling in phase synchronism with these charge gradients. The interaction mechanism is similar to that of a conventional traveling-wave tube amplifier or oscillator. We have modeled the wave behavior of superconducting electrons using the London equations and a two-fluid approach. Our model includes dissipation within the superconductor, and it shows that traveling-wave devices may be possible using high-quality thin-film superconductors in which dissipation is kept low. 相似文献
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Jean-Charles Bolomey 《电信纪事》1979,34(9-10):469-476
This paper is devoted to the determination of the power coupling factor between an arbitrary incident wave and the load of an antenna illuminated by this wave. The coupling factor is deduced, by means of reciprocity theorem, from the equivalent schema of the antenna. The power delivered to the load is expressed as a function of the spherical wave angular spectrum related to the incident wave and of the radiation characteristic of the antenna in emitting situation. The expression of the coupling factor is well suited for discussing the influence of various parameters and giving conditions for optimal coupling. 相似文献