排序方式: 共有15条查询结果,搜索用时 62 毫秒
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为了实现对散射介质的非接触测量,有效地提高灵敏度,提出了光学低相干干涉测量方法.采用光纤型迈克尔逊干涉结构,增加了扫描延迟线和光学外差探测电路,实现了具有光程分辨能力的干涉测量.以脂肪乳剂Intralipid为样本,通过稀释和加入染色剂的方法改变其散射和吸收特性.通过对溶液内反射信号的干涉测量和曲线拟合,研究了光程相关的干涉光信号与物质浓度的依赖关系.实验对象为散射和吸收特性相对稳定的脂肪乳剂和印度墨水混合物,其中Intralipid乳剂浓度在4%~16%之间,印度墨水浓度在0~1%之间.拟合方法引用了广义惠更斯菲涅耳(EHF)模型的解析表达式,拟合相关系数在0.98以上.实验结果与积分球测量结果进行了比较,初步验证了理论方法的可行性. 相似文献
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This paper reports line-of-sight propagation measurements performed at 37.2GHz between two terminals in an empty room in order to investigate the spatialand temporal fadings in terms of antenna directivity and human motion,respectively. The empirical data base consists of recordings of CW envelopefading waveforms with a fixed transmitter and either moving or stationaryreceiver. The reported results include amplitude fading distributions,propagation loss gradients, level crossing rates and fade durationsstatistics. These results can be used in the modeling, design reliableoperation of local multi-point communication systems. 相似文献
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介绍了卫星和地面站天线越来越需要高性能的双频段波纹喇叭馈源,给出了额Ka/EHF双频段波纹喇叭的结构组成,详细地给出了该波纹喇叭各段的设计公式和波纹喇叭槽参数,利用Champ仿真软件仿真计算了该波纹喇叭2个频段的反射损耗和归一化辐射功率方向图,并且在微波暗室测出了该波纹喇叭反射损耗和归一化辐射功率方向图。测试结果和仿真计算结果吻合良好,因此,证实了该波纹喇叭设计的正确性。 相似文献
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针对传统分波器影响高频方向图的问题,提出了一种新型的Ka/EHF频段分波器设计方法。与传统分波器相比,该分波器具有低损耗、低驻波、高频段隔离的优点,其通过使用皱褶波纹滤波器和sin^2曲线过渡,实现了Ka、EHF频段信号的低损耗分离,分布式参数综合设计的波纹滤波器对高频信号产生了极佳短路面,sin^2函数曲线过渡较好地抑制了高次模。设计、加工和测试了样机,接收频段的回波损耗小于-22 dB,发射频段的回波损耗小于-25.2 dB,仿真结果与测试结果基本吻合,验证了方法的正确性和有效性。 相似文献
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This paper provides estimates of the frequency of occurrence, duration and probability of satellite EHF communication outages due to attenuation by rain. These can be used to determine optimum frequencies, power levels and the need for space diversity of terminals or other alternatives to maintain reliable communications. Ten years of 1 min rain rates at each of 12 U.S. cities were used in conjunction with an attenuation model to quantify communication outages at locations representing a variety of climatic regimes. Analyses of the 1 min rain rates and outage estimates at 10, 30 and 45 GHz for elevation angles of 10°, 30°, 50° and 70° are presented. 相似文献
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Simone Caramel Stagnaro Sergio Pyatakovich Felix A. Yakunchenko T.I. Makkonen K.F. Moryleva O.N. 《红外与毫米波学报》2014,33(1):1-18
The effects of background millimeter radiations (BMR) in patients with coronary artery disease (CAD), hypertension and in subjects with Inherited real risk of CAD, were investigated through invariant statistic measures, typical of nonlinear dynamics analysis of biological systems. The experimental evidences show that BMR ameliorate the nonlinear complexity in biosystems, recognized sign of physiological behavior, by increasing both the rate of unpredictability of heart rate variability (HRV) in patients with metabolic syndrome and the fractal dimension of coronary microvessel oscillations in subjects with pre-metabolic syndrome, healing their genetic alteration and CAD Inherited real risk. 相似文献
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Sanjeev Kumar Raghuwanshi Nimish Kumar Srivastava Akash Srivastava 《International Journal of Electronics》2013,100(10):1689-1699
Microwave photonics is a prominent field in which photonic technologies are used to empower and extend the functionalities of microwave system which is a very tough exercise to fulfil directly in microwave domain. A photonic technique to generate a high chirp rate arbitrary microwave waveform using dual-drive LiNbO3 has been put forward and demonstrated experimentally in this paper. Nowadays in order to increase the Range-Doppler resolution of radar, the chirp microwave waveform is widely used. The Mach-Zehnder modulator (MZM) performs the intensity modulation techniques which can operate on the principle of electro-optic effect. In this paper, the authors used a very simple and straightforward method of producing chirped arbitrary millimetre waveform by change in phase at the two arms of dual-drive LiNbO3 MZM. The generated waveform has the 3 dB bandwidth of 12.6 GHz which exists in extremely high-frequency band applicable in high-frequency microwave radio relay, microwave remote sensing, radar range resolution and millimetre wave scanner. The proposed design is simpler, cost-effective and compact than the previously proposed model of chirped waveform generation using MZM and fibre Bragg grating. 相似文献
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《Journal of Materials Processing Technology》2014,214(4):865-875
Electrically driven rapid vaporization of thin conductors is known to produce short-duration pressure pulses of high magnitude. This impulse can be used for applications such as high strain rate forming, shearing, collision welding, and springback calibration. Mechanical impulse was developed from aluminum foils of various thicknesses, which were vaporized using a capacitor bank discharge with a maximum charging voltage of 8.6 kV. Peak current was delivered on the order of 100 kA with rise times of about 12 μs. In this work, polyurethane was used as a medium to transfer pressure from the aluminum foil vaporization zone to the workpiece. Fundamental experiments, where AA 3003-H14 aluminum alloy was formed into perforated plates, show that for a given foil thickness, a limit existed over which supplying higher electrical energy from a given capacitor bank did not necessarily result in higher pressure. The magnitude of generated pressure was proportional to the excess Joule heat deposited into the foil before it burst. Although the polyurethane layer helped spread the pressure pulse over a larger area, the resulting pressure distribution remained heterogeneous. Practical applications, such as forming into cavities and embossing into shallow dies, were possible with this method. Sheets of 0.508 mm thick commercially pure titanium were nearly fully formed into a cellphone case die using a hybrid process that combined a quasistatic pre-forming step with a vaporizing foil forming step. Sheets of 0.508 mm thick AA 2024-T3 aluminum alloy were embossed into a die with features of varying depths. Aluminum foils with straight and curved active sections were used as actuators. The curved-section foils resulted in higher conformation of the workpiece to the die in the center region, while the straight-section foils produced better conformity to the die features on the ends. 相似文献