航空电源产品金属机箱的电磁兼容性设计(上)

对航空电源系统中的电子产品来说,其金属机箱除了具有机械支撑和保护作用外,还应具有一定的屏蔽效能来提高电子产品的电磁兼容性.本文对航空电源产品金属机箱的电磁兼容性设计进行了分析研究,并以产品实际的电磁兼容性测试为例来说明金属机箱电磁兼容性设计对电子产品可靠性产生的重要意义,最后对金属机箱屏蔽效能测试的原理和方法进行了介绍.     

军用通信设备电磁兼容试验中的问题及对策分析

本文对军用通信设备电磁兼容性测试结果的失真问题进行了分析并提出了相应的解决建议.     

航空电源产品金属机的电磁兼容性设计(下)

对航空电源系统中的电子产品来说,其金属机箱除了具有机械支撑和保护作用外,还应具有一定的屏蔽效能来提高电子产品的电磁兼容性。文章对航空电源产品金属机箱的电磁兼容性设计进行了分析研究,并以产品实际的电磁兼容性测试为例来说明金属机箱电磁兼容性设计对电子产品可靠性产生的重要意义,最后对金属机箱屏蔽效能测试的原理和方法进行了介绍。     

一种车载通信系统电磁兼容性测试验证方法

为了提高车载系统的电磁兼容性,在设计阶段就需对其进行合理的电磁兼容设计,并且电磁兼容工作要贯穿该项目的全生命周期,因此需要采用恰当的方法对其实际的电磁兼容性进行系统的测试验证.提出了一种适用于车载通信系统的系统级电磁兼容性测试验证方法,通过对系统安全裕度、天线隔离度与驻波、通信射频兼容(含互扰、谐波和互调)、舱体屏蔽效能等项目的实际测试,实现对车载通信系统的系统级电磁兼容性的全面测试和验证.测试结果和获取的数据可以有效指导后续的电磁兼容加固和通信系统的使用.     

全自动平衡机系统中的EMC研究

介绍了全自动平衡机系统的组成及体系结构,并结合系统的运行环境、运行效果要求分析了系统的电磁兼容性,从电磁干扰三要素(干扰源、噪声耦合路径和敏感设备)着手,提出了保障系统电磁兼容性的若干手段.在此基础上进行了电磁兼容测试,给出了试验结果及结果分析.试验及实践结果表明,全自动平衡机系统达到了电磁兼容性要求.     

电磁兼容测试中的频谱仪饱和研究

随着电子设备的增加,系统的电磁兼容性(EMC)日益严峻,基于频谱仪的测试则是评价其电磁兼容性能的最直接手段,而在用频谱仪检测其电磁兼容性时,频谱仪的饱和问题较为突出.本文对实际测试中遇到的问题进行分析并给出解决方法,最后用实例进行验证.     

航空电源产品电磁兼容性测试的分析与研究

文章以某型飞机交流电源系统的电磁兼容性测试为例,介绍了航空电源产品电磁兼容性试验的测试方法,并对试验结果和电磁干扰控制措施进行了分析,提出了解决这些问题的建议.     

起重机电磁兼容性综述

随着起重机技术的发展,其电磁兼容性越来越受到重视,本文在介绍起重机电磁兼容性基本概念和重要性的基础上,对我国起重机电磁兼容性的研究现状进行分析,指出了起重机中常见的电磁干扰源及其产生原因,最后给出了抗电磁干扰措施在起重机上的应用,为起重机电磁兼容性设计和测试提供依据和参考。     

北斗卫星导航定位接收机电磁兼容性设计研究

介绍了北斗卫星接收机抗干扰的软硬件设计,分析了接收机抗干扰及电磁兼容性原理、算法以及约束规则,并对其抗干扰算法性能进行了仿真验证.     

系统电磁兼容性问题预测实例

系统电磁兼容性预测不仅在方案阶段需要,在工程阶段仍然重要,是进行合理电磁兼容性设计,争取时间、减 少费用的有效手段。系统电磁兼容性预测可以使用专业软件进行仿真计算、分析,在特殊情下也可以采用工程简化方法 计算、分析,还可以用工程经验进行分析评估。在电磁兼容性预测计算、分析中,仿真软件一般考虑全面,简化方法计 算相对快捷,建立简化且与实际接近的干扰源模型、传输特性模型以及敏感度域值模型是计算、分析准确程度的关键。 本例中是用简化方法对实际系统电磁兼容性问题解决提供了理论依据,并进行了仿真和试验验证,结论一致。说明,除 了用专业仿真软件进行预测计算,用工程简化方法计算也会常常遇到;实际电磁兼容工作中系统预测是重要的并且不一 定非常复杂,供参考     

A treatment of impurity diffusion in oxidizing ambients

The linear diffusion equation may be transformed to a moving reference frame which corresponds to a linear-parabolic or experimental oxide growth law. The resulting partial differential equation is separable and may be Laplace transformed. If the semiconductor is initially uniformly doped and semi-infinite, solutions in the Laplace transform domain are expressible as parabolic cylinder functions. Integration constants for constant interface concentration or deposition diffusions as well as leaching boundary conditions may be determined.A space-time solution for the deposition problem is derived. Leaching from a uniformly doped substrate is treated in some detail. Residue techniques are used to develop analytic expressions for the dominant solution term, which is compared to published results. The complete solution may be obtained by using approximate analytic inversion, which requires numerical computations. Results are compared with data from existing theories, which are special cases of the present model.     

Thermal effects in n-channel enhancement MOSFET's operated at cryogenic temperatures

Thermal effects in n-channel enhancement-mode MOSFET's operated at cryogenic temperatures are discussed. Device heating is identified as the cause of drain current transients and the origin of this phenomenon is considered. Experimental results are presented in which thermal effects are studied as functions of temperature for various gate and drain biases. Drain current is found to be a monitor of device temperature, From an understanding of the thermal behavior of devices, the channel electron mobility can be examined as a function of temperature and gate bias. The observed thermal effects are explained in terms of material and device properties. The implications for future low-temperature CMOS VLSI development are discussed.     

A SPICE model for multiconductor transmission lines excited by anincident electromagnetic field

This paper describes a SPICE model that may be used for predicting the time-domain or frequency-domain voltages and currents induced at the terminations of a multiconductor transmission line (MTL) by an incident electromagnetic held. Explicit results for the entries in the SPICE circuit model are obtained for an incident uniform plane wave that may represent sources such as radio and television transmitters, radars, lightning, etc. The result relies on the transformation of the MTL equations into uncoupled modal lines by similarity transformations. The entries in the similarity transformations are provided for lossless lines. The model is implemented using controlled sources to implement the modal transformations and delay lines to implement the modal lines. If the model is implemented as a SPICE subcircuit model, the time-domain form of the incident field can be implemented as a source external to that subcircuit model so that changes in the line responses due to changes In the incident field waveform can be simulated without changing the subcircuit model. In order to avoid negative line delays, the result is restricted to incident waves having components of the propagation vector in the positive direction along the line. This restriction can be removed by simply reversing the line. The paramount advantages of the model are that both time-domain and frequency-domain results can be easily obtained with the existing SPICE code, and nonlinear loads, such as transistors and digital devices, as well as dynamic loads, such as inductors and capacitors, may be easily incorporated using the existing elements in the SPICE code. Predicted results for MTL's using the method are compared to those of the time-domain to frequency-domain transformation and finite difference-time-domain (FDTD) methods     

Lasing wavelength changes due to degradation in buriedheterostructure distributed Bragg reflector lasers

Changes in the wavelength and lamp characteristics due to the degradation of distributed Bragg reflector (DBR) lasers are investigated and the lasers are confirmed to be reliable enough for application as the light sources in WDM systems. The change in wavelength characteristics is due to degradation of the DBR or phase control region and the change in lamp characteristics is due to the degradation of active region. These changes in the characteristics are caused by diminished recombination carrier lifetime. The wavelength stability is strongly correlated with the injected current density. The lamp characteristics is confirmed to be almost as stable as in conventional Fabry-Perot lasers. The applicability of DBR lasers as the light source for wavelength division multiplexing (WDM) systems is demonstrated for actual-use conditions     

Nonlinear systems analysis with non-Gaussian white stimuli; General basis functionals and kernels (Corresp.)

The Wiener-Lee-Schetzen scheme of using Gaussian white noise to test a nonlinear dynamical system is extended in two ways. 1) An arbitrary non-Ganssian white noise stationary signal can be used as the test stimulus. 2) An arbitrary function of this stimulus can then be used as the analyzing function for cross correlating with the response to obtain the kernels characterizing the system. Closed form expressions are given for the generalized orthogonal basis functions. The generalized kernels are expanded in terms of Volterra kernels and Wiener kernels. The expansion coefficients are closely related to the cumulants of the stimulus probability distribution. These results are applied to the special case of a Gaussian stimulus and a three-level analysis function. For this case a detailed analysis is Lade of the magnitude of the deviation of the kernels obtained with the ternary truncation as compared to the Wiener kernels obtained by cross correlating with the same Gaussian as was used for the stimulus. The deviations are found to be quite small.     

The semiconductor waveguide facet reflectivity problem

The problem of the facet reflectivity of a semiconductor slab waveguide is reexamined as an extension of Ikegami's original approach that includes radiation-like modes. Using a guide-within-a-guide geometry, the radiation-like modes are included as modes bound to a thick air-cladding guide that contains the core profile of interest. In this model, the coupling from the fundamental model to radiation modes can be analyzed using a relatively simple analysis. The cross-coupling to the radiation modes for the simple double heterostructure waveguide is considered in detail and is shown to be important only for a large core-cladding index differences and for strong model confinement that results in a true facet loss. The conditions for this are the same as for low threshold lasers so that the loss sets a maximum limit on the equivalent internal quantum efficiency. A separate 1D finite-element numerical mode matching program, which treats evanescent and propagating radiation modes, is used as a comparison. The two methods of accounting for radiation modes are shown to be in good agreement. Modern graded core cases are treated as general examples. Specific quantum well laser structures taken from the literature, including II-VI and III-V structures spanning wavelengths from 0.5 μm to 10.0 μm, are also considered     

水浴条件下YAG倍频激光切割Si片的实验研究

用Nd:YAG固体倍频激光器在水中对Si片进行微刻蚀比在空气中产生的飞溅物少。对两种条件下的刻蚀速率、刻槽表面形貌进行了比较。实验结果得到最窄的刻缝宽度小于50μm,表面不平整度小于5μm,为工业用激光切割Si片提供了更好的工艺。     

Measurement Techniques for Planar High-Frequency Circuits (Short Paper)

Planar bismuth bolometers can be used as measuring elements in planar millimeter-wave circuits. These devices are easy to fabricate and calibrate; moreover, their responsivity is thought to be nearly independent of frequency throughout the millimeter-wave regime. Furthermore, they are inherently linear detectors over as much as seven orders of magnitude. Noise-equivalent powers of 2x 10/sup-10/ W/Hz/sup 1/2/ can be attained. The high sensitivity of these devices makes them suitable for use in probes. Techniques for measurement of current and reflection coefficient are proposed. Trial measurements, using simulation at 1 GHz, are described.     

Optimal Design of Nearfield Wideband Beamformers Robust Against Errors in Microphone Array Characteristics

Nearfield wideband beamformers for microphone arrays have wide applications, such as hands-free telephony, hearing aids, and speech input devices to computers. The existing design approaches for nearfield wideband beamformers are highly sensitive to errors in microphone array characteristics, i.e., microphone gain, phase, and position errors, as well as sound speed errors. In this paper, a robust design approach for nearfield wideband beamformers for microphone arrays is proposed. The robust nearfield wideband beamformers are designed based on the minimax criterion with the worst case performance optimization. The design problems can be formulated as second-order cone programming and be solved efficiently using the well-established polynomial time interior-point methods. Several interesting properties of the robust nearfield wideband beamformers are derived. Numerical examples are given to demonstrate the efficacy of the proposed beamformers in the presence of errors in microphone array characteristics.     

光纤传感器在机械设备检测中的应用

阐述了光纤传感器在国内外桥梁检测及其他领域中的应用状况,并论述了光纤传感器在诸多重要领域中可发挥的独特优势.此外,还对光纤传感器的基本组成、原理、分类及工作特点进行了介绍.由于在大型机械设备的检测中,不能破坏检测对象,因而重点介绍了光纤传感器在大型机械设备检测中的应用.根据光纤传感器的诸多特点及在桥梁检测中的应用,光纤传感器能够满足机械设备的检测要求,实现对机械设备的无损检测.