Conformity Magazine - November 2007 - (Page 49)

Limitations of Traditional EMC Simulation Practices There’s nothing new about the idea of mathematically simulating electromagnetic interactions by providing a 3D solution of Maxwell’s equations. However, in EMC applications, important detail such as narrow gaps, air-vent apertures, wires and thin conductive coatings are a challenge to model, because their dimensions are typically orders of magnitudes smaller than the overall enclosure dimensions. The disparity in dimensions causes a large number of cells in the mesh and increased computer run times. Furthermore, EMC analysis requires solving the system over a very wide frequency range, typically from a few KHz to many GHz. The transmission line matrix method (TLM) performs the field solution in the time domain using a broadband impulsive excitation, yielding data over the entire band in a single simulation run. In TLM, critical detail can be represented by compact models which enable the physical geometry to be replaced by an equivalent electrical model. This ensures that the effect of the detail is included in the simulation, without requiring extensive computer memory and run-time. Typical system-level EMC applications include: designing enclosures to ensure maximum shielding effectiveness; assessing the EMC ramifications of component location within an enclosure; computing cabling coupling both internal and external to the system; and examining the effects of radiation from the cables. EMC simulation can identify the specific mechanisms driving unwanted electromagnetic transmissions through chassis and subsystems, such as cavity resonances, radiation through holes, slots, seams, vents and other chassis openings, conducted emissions through cables, coupling to and from heat sinks and other components, and unintentional wave guides inherent to optical components, displays, LEDs, and other chassis mounted components. Analyzing Thermal and EMC Design Issues Concurrently However, up to now, EMC simulation has been used relatively infrequently and mostly in the later stages of design to diagnose and identify solutions for problems identified during compliance testing. Forward-looking companies are realizing that a different approach will reap significant benefits, by applying EMC simulation early in the design cycle. The rest of this article will show how a step-by-step approach can be applied to thermal and EMC design, using a 2U server as an example. Parallels between the thermal and EMC simulation process will be highlighted. An important aspect of this approach is that it begins with a very coarse model of the system that is used to identify the most critical aspects of the design and moves progressively to more detailed analysis of the critical areas. Developing an EMC Budget The new approach starts by determining an EMC budget used to set a goal for the shielding effectiveness required for the enclosure. This is analogous to the creation of a thermal budget. Depending on the application area, this budget Figure 2: The EMC budget estimates emissions from internal components and provides margin of error protection, typically between 10 and 30 dB. The shielding effectiveness (SE) required is usually plotted against frequency and compared to the SE of the enclosure as determined by physical testing. Black horizontal line shows the required shielding effectiveness (the budget). Red horizontal line shows the actual effectiveness of the shields. NOVEMBER 2007 CONfORMity 49 http://www.captorcorp.com http://www.captorcorp.com

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Conformity - November 2007 Contents Editor’s Note Commission Sets Date, Terms for 700 MHz Auction FCC Reaffirms Roaming Obligations Commission Moves to Improve USF Management FCC Proposes Fines for Violations of E911 Handset Requirements Commission Levies $1 Million Plus Fines for Unsolicited Fax Advertisements GR-3150 - Lithium Battery Certification Levels Based on Criteria for General Product, Safety, and Performance, Part 2 ESD Open Forum Machinery Field Evaluation for the United States Validation, Verification, and Immunity Testing Techniques for EMC for Functional Safety Thermal/EMC Simulation Addresses New Mechanical Design Challenges Product Safety Equipment Buyer’s Guide FCC Releases Report on Telephone Numbering Resource Utilization Canada Still Has PCS Spectrum to Assign Updated Standards List for the EU’s Medical Devices Directive Updated Standards List for EU Directive on Active Implantable Medical Devices Call for Papers for the 2008 EOS/ESD Symposium Announced Mobile Phone Use in Hospitals May Be Dangerous CPSC Actions in the News IEC Standards Update UL Standards Update Telcordia Standards Update From Our “You Can’t Make This Stuff Up” Department Product Reviews Looking Back: Items from Past Issues of Conformity Upcoming Events Advertisers

Conformity Magazine - November 2007

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