A simple finite-difference frequency-domain (FDFD) algorithm for analysis of switching noise in printed circuit boards and packages

Simultaneous switching noise (SSN) compromises the integrity of the power distribution structure on multilayer printed circuit boards (PCB). Several methods have been used to investigate SSN. These methods ranged from simple lumped circuit models to full-wave (dynamic) three-dimensional Maxwell equations simulators. In this work, we present an efficient and simple finite-difference frequency-domain (FDFD) based algorithm that can simulate, with high accuracy, the capacity of a PCB board to introduce SSN. The FDFD code developed here also allows for simulation of real-world decoupling capacitors that are typically used to mitigate SSN effects at sub 1 GHz frequencies. Furthermore, the algorithm is capable of including lumped circuit elements having user-specified complex impedance. Numerical results are presented for several test boards and packages, with and without decoupling capacitors. Validation of the FDFD code is demonstrated through comparison with other algorithms and laboratory measurements.     

用最佳终端匹配策略降低电磁辐射的干扰

为使产品达到EMI辐射标准，往往需要给系统增添一些复杂的滤波器、屏蔽密封材料和其他一些昂贵的元器件。由于电磁相互作用的本质相当复杂，因而确定EMI辐射究竟是从什么地方泄漏出去的非常困难，所以降低EMI辐射常常被认为是“魔术”，因此我们常盲目地使用一些单凭经验的解决办法。然而那些单凭经验的解决办法是根据以前的技术发展起来的，不一定适用于当今的设计实践。不添加任何元器件往往不可能降低系统的辐射干扰，但如果仔细分析系统内部某些值得注意的信号，就可以减少需要添加的元器件，从而降低系统的制造成本。     

Adaptive absorbing boundary conditions in finite-difference timedomain applications for EMC simulations

A special adaptation of the Liao's (1984) absorbing boundary condition (ABC) is presented to optimize the solution of a class of EMI/EMC problems when using the finite-difference time domain (FDTD) method. The Liao ABC is constructed on a per-cell basis to accommodate the most likely direction of incidence on the mesh terminating boundary. Numerical results are presented to demonstrate the validity of the formulation and the improvements over traditional ABC applications     

Analysis of power/ground-plane EMI decoupling performance using thepartial-element equivalent circuit technique

The design of printed circuit (PC) boards with decoupling capacitors has been the subject of debate and different opinions for many years. The design and electrical impact of the capacitors has been difficult to separate from all other electrical interactions occurring on a conventional PC board populated with integrated circuits. This work demonstrates how the partial-element equivalent circuit (PEEC) modeling technique can be used to accurately predict the performance of various decoupling design strategies. Computer modeling using the PEEC approach is very flexible due to the ease of mixing physical geometries with a large number of circuit elements. Also, the compute time for such practical mixed EM and circuit problems are relatively short. Using this technique, the usual iteration between a number of different designs of test boards can be avoided. We show that the change of the voltage across the PC board, or the voltage gradient, can be used as an effective tool for the improvement of the decoupling efficiency     

Technological and scientific landscape of laser cladding process in 2007

In the last 30 years, public and private organizations involvement in laser cladding R&D activities is increasing. These activities are mainly conducted in universities, public research institutes and technical centres of private companies worldwide. This study shows a bibliometric analysis of the patents and scientific publications in the laser cladding field for the period ranging from 1985 to 2007. This seeks to identify the activity and trends in its environment for strategic purposes. All the laser cladding processes and all the substrates (steel, aluminium and superalloys) used for coating, repairing and 3D fabrication were taken into account. At first, the world patent production was analysed in terms of volume (580 patent families found since 1985), frequency and applications. Then, the same strategy was applied to the scientific publications for a total volume of 588 targeted papers. Using bibliometric techniques, an analysis and mapping of the information was performed to highlight the temporal, geographical and institutional aspects of R&D activities. The patented applications were also classified in order to identify opportunities. This study shows the evolution of the scientific and technological environments of the laser cladding technology and can help public or private organizations to generate new ideas, gain awareness of emerging trends and validate the relevance of projects.     

Feature selective validation (FSV) for validation of computational electromagnetics (CEM). part II- assessment of FSV performance

The feature selective validation (FSV) method has been proposed as a technique to allow the objective, quantified, comparison of data for inter alia validation of computational electromagnetics. In the companion paper "Feature selective validation for validation of computational electromagnetics. Part I-The FSV method," the method was outlined in some detail. This paper addresses two specific issues related to the implementation of the FSV method, namely "how well does it produce results that agree with visual assessment?" and "what benefit can it provide in a practical validation environment?" The first of these questions is addressed by comparing the FSV output to the results of an extensive survey of EMC engineers from several countries. The second is approached via a case study analysis.     

Thermally accelerated life testing of single mode, double-heterostructure, AlGaAs laser diodes operated pulsed at 50mW peak power

Single spatial mode, double-heterostructure, channel-substrate-planar AlGaAs laser diodes have been life tested under thermally accelerated conditions to characterize the reliability of the diodes in a digital, optical communication system intended for space application. The diodes were operated pulsed under constant drive current conditions at 50 mW peak power, 25 ns pulse width, and 1 percent duty cycle in a dry, inert environment at ambient test temperatures at 40,55, and 70°C. Diode performance parameters as related to the space application, such as pulsewidth, peak power, wavelength spectrum, spatial mode, and threshold current, were periodically monitored. Tests have continued for over 14 000 h. The test results for all diodes with failure defined by power degradation alone is compared to the test results for single mode diodes with failure defined by power degradation, wavelength shift and spatial mode changes. It is found that the life test results are substantially equivalent but differ from earlier published reports for laser diodes operated CW. An activation energy of about 0.39 eV is deduced with a predicted median life of about5 times 10^{4}h at 20 °C. These values are somewhat lower than those found for diodes operated CW and are attributed to the use of single mode laser diodes here. It is concluded that thermally accelerated life testing for single spatial mode laser diodes must incorporate a means to separate bulk material, current, and optical density induced degradation effects. A test scheme is proposed.