Shahrokh Daijavad

Radiation and scattering from structures involving finite-size dielectric regions

A full-wave approach is presented for calculating the scattered fields produced by structures that involve finite-size dielectric regions. The dielectric is first approximated by an array of interlocking thin-wall sections; the electric field boundary conditions are then applied through the use of appropriate surface impedances. Rooftop basis functions, chosen to represent the surface current, are appropriately placed on the thin-wall sections in such a way as to accurately represent the polarization current while preventing fictitious charge within the dielectric. Rooftop currents are also used to represent the current on any conductor that may be present. The matrix elements are calculated, depending upon the distance between the source and field locations, through a scheme that employs Taylor series expansions and point source approximations. The technique is applied to scattering from dielectric cubes and composite dielectric-conductor structures, and to radiation from microstrip structures. Numerical convergence and agreement with the literature are demonstrated. >

Workload and network-optimized computing systems

This paper describes a recent system-level trend toward the use of massive on-chip parallelism combined with efficient hardware accelerators and integrated networking to enable new classes of applications and computing-systems functionality. This system transition is driven by semiconductor physics and emerging network-application requirements. In contrast to general-purpose approaches, workload and network-optimized computing provides significant cost, performance, and power advantages relative to historical frequency-scaling approaches in a serial computational model. We highlight the advantages of on-chip network optimization that enables efficient computation and new services at the network edge of the data center. Software and application development challenges are presented, and a service-oriented architecture application example is shown that characterizes the power and performance advantages for these systems. We also discuss a roadmap for next-generation systems that proportionally scale with future networking bandwidth growth rates and employ 3-D chip integration methods for design flexibility and modularity.

A team collaboration space supporting capture and access of virtual meetings

In this paper, we address the design issues of a collaborative workspace system, called TeamSpace, that supports geographically distributed teams by managing shared work processes and maintaining shared artifacts in a project. TeamSpace attempts to integrate both synchronous and asynchronous types of team interaction into a task-oriented environment. Since meetings are an integral part of teamwork, our current work focuses on supporting virtual meetings as part of a larger collaborative work process. We present an initial TeamSpace prototype that supports asynchronous meeting management seamlessly integrated with capture and access of synchronous distributed meetings. The captured synchronous data is integrated with other related information in TeamSpace, enabling users to efficiently gain knowledge of both current and past team activities.

Collaborative customer services using synchronous Web browser sharing

For complicated transactions and inexptienced users, se~-smite may not be *cimL b addition, for marketing and sales, there maybe no substitute fm a good salesperson. Thus, there is tiue in combining ~chronous am to products and services OVHthe Web with Wchronous, human assistance v’hen needd h ord~ to pr~ vide better service to customas, increase d=, and ~erentiate their Webbased services tiom the repetition, a numbs of businesses are starting to fiTlore means of integrating Eve customs service into their Web sites.

Integrating Meeting Capture within a Collaborative Team Environment

Meeting capture has been a common subject of research in the ubiquitous computing community for the past decade. However, the majority of the research has focused on technologies to support the capture but not enough on the motivation for accessing the captured record and the impact on everyday work practices based on extended authentic use of a working capture and access system. Our long-term research agenda is to build capture services for distributed workgroups that provide appropriate motivation and further understand how access of captured meetings impacts work practices. To do this, we have developed a testbed for meeting capture as part of a larger distributed work system called TeamSpace. In this paper, we discuss the requirements for meeting capture within TeamSpace, describe the initial prototype developed, and report on initial usage.

Calculation of multi-port parameters of electronic packages using a general purpose electromagnetics code

A powerful code developed by the authors to solve radiation and scattering problems from arbitrary 3D dielectric-conductor structures is modified to provide the terminal characteristics of arbitrary package structures. By incorporating a general de-embedding procedure to eliminate end effects, Y- and S-parameters can be obtained for 3D transmission-line structures; other parameters such as the C and L matrices can also be obtained. Results for microstrip twin-tee and mesh-plane structures are presented and compared with results already in the literature.<<ETX>>

Modeling common-mode radiation of 3D structures

Common-mode radiation, which is often the predominant contributor to the overall radiation from circuit boards and electronic hardware, has in the past been difficult to calculate. Since the return paths for common-mode currents are not obvious, all parasitic circuit elements must be properly taken into account. The authors calculate the radiation, which includes both differential and common-mode components, from arbitrarily shaped 3-D conductor-dielectric composite structures using a full-wave approach. Excellent agreement between measured and calculated results is demonstrated. Further, a great deal of insight into the mechanism for generation of common-mode current, and hence radiation, is obtained. >

On the effectiveness of decoupling capacitors in reducing EM radiation from PCBs

The effectiveness of using decoupling capacitors (decaps) between power and ground planes in a typical PC or workstation printed circuit board (PCB) is studied from an electromagnetic-compatibility (EMC) point of view. By examining the radiation from the board, the effects of the total number of decaps, the placement of decaps, and lead inductances are investigated. The novelty of the present studies is that they focus directly on electromagnetic radiation as opposed to the more traditional investigation of decaps by only examining their equivalent impedances.<<ETX>>

A fast method for computing radiation from printed circuit boards

An alternative approach for computing radiation from a multilayer circuit board is presented. Compared to a full-wave electromagnetic approach, this method is much faster and requires less storage space for data. Computational efficiency is the key attribute of the approach. It allows solutions, previously unobtainable, to complex and realistic structures, such as those arising from typical product designs. The radiation is calculated using a transmission line model to find the amplitude and spatial distribution of currents in printed circuit traces. The far field is computed using the Greens function of a current element just above, or inside, a thin dielectric sheet. Two examples are considered: (1) a comparison of results in the frequency domain obtained by using the method described here with those of a full-wave electromagnetic approach based on the method of moments; and (2) a comparison of simulation results with real semianechoic chamber measurements.<<ETX>>

Methodology for evaluating practical EMI design guidelines using EM analysis programs

Most companies oflering products that mus t pass FCC or’ other regulatory agency specifications have compiled EMI design guidelines which are practiced b y their engineers. I n this paper, we take one such practical E M I design guideline and, through extensive use of a state-of-the-art electromagnetic analysis code, investigate its range of applicability, and show its lamitations. The emphasis is placed on the methodology, rather than the guideline itself, so that a framework is established under which other EMI design guidelines can be similarly “revisited”.