Conformity Magazine - February 2009 - (Page 36)

This is not very critical for the proposed example, but in the next section we will show how it is important in saving CPU capacity when dealing with a real/complex enclosure design. Figure 7 illustrates the magnetic field distribution for two different frequency values. The field distribution remains confined inside the enclosure for the 500HHz considered frequency, but it starts to radiate thought the aperture located in the frontal panel of the box when the frequency is increased to 1GHz. The same simulation is also performed with the 3D full wave solver but based on the transmission line method (TLM) [10]. One of the main advantages of this numerical method is its strength for the EMC/EMI type of problems, due to the possibility of using compact models for small features like gaps, ventilation holes, honeycomb, and seams. In this way, it is not necessary to resolve (with a dense mesh) the small Conductivity (σ) [S/m] No loss 0.0001 0.0005 0.001 Table 1 Maximum deviation nominal value [dbuV/m] 5 4 5 10 Simulation time feature; an equivalent transmission line model can be used instead. In order to provide an idea on the approach used, Figure 8a illustrates ventilation holes and the corresponding equivalent circuit model. In particular for a thin panel, TEM transmission through a hole can be modelled by a shunt inductor. L is like a short at DC, but allows high frequency transmission. For a thick panel, the additional electric field inside the aperture can be modelled by a shunt capacitor. Figure 9 illustrates the comparison between the shielding effectiveness (SE) calculated by means of the two software applications. Good correlation is observed in the considered frequency range, but it is important to point out that the simulation only takes few seconds. This is due to the usage of the compact model for gap, which doesn’t have to be resolved by a fine mesh, which would cause a very small time step, a detrimental factor in a time domain simulation. 35 min 18 min 4 min 2 min a Figure 8: Ventilation holes and corresponding compact model. b a a b Figures 7a and 7b: Magnetic field on a cross section of the metallic enclosure: a) 500MHz; b) 1GHz 3 Conformity february 2009 b Figure 9: SE results, comparison between the two software applications

Table of Contents Feed for the Digital Edition of Conformity Magazine - February 2009

Conformity Magazine - February 2009 Contents Editor's Note FCC Clarifies Closed Captioning Requirements for DTV Receivers Commission Cracks Down (For the Fifth Time!) On Junk Fax Marketer FDA Requests Comments on Global Harmonization Documents Australia Now Requires Solar Panel Testing and Certification EU Drafting New Directive on Toy Safety EU Commission Revises Standards List for EMC, R&TTE Directives Additional Standards Published For the EU's Medical Devices Directive EU Commission Publishes Additional Standards for Directives on Active Implantable, In Vitro Medical Devices EMC For the Functional Safety of Automobiles ESD Open Forum The ILAC Arrangement: Facilitating Trade Efficient Methodology for the EMI Analysis of Optical Transceivers Including PCBs and/or Flex Circuits The EuP Directive - Implementation, Design Requirements and Issues Chambers, Shielding, and Accessories Buyer's Guide CPSIA Lead Requirements Apply to Existing Inventory, Says CPSC CPSC Clarifies Certifcation Requirements Other CPSC Actions in the News IEC Standards Update Product Reviews UL standards Update Telcordia Standards Update From Our "You Can't Make This Stuff Up" Department Looking Back: Items from Past Issues of Conformity Advertisers

Conformity Magazine - February 2009

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