Conformity Magazine - February 2009 - (Page 33)

methodology, electric (E) and magnetic (H) fields are calculated on a plane defined at 300mils above the PCB (see Figure 2a). Figure 2b illustrates the E fields evaluated at two different frequencies, 0.5GHz and 1GHz. The equivalent source (also defined as compact model) is then used [7] in order to calculate the E/H fields at the same frequencies. As already mentioned, the compact source is based on the “equivalence theorem.” Let us assume a closed surface S which divides a region (1) containing sources from a source-free region (2), as illustrated in Figure 3. The EM field outside of S can be replaced by a distribution of electric and magnetic current densities (Js, Ms) over the surface S, and the compact source captures the spatial variation and frequency dependency of PCB emissions. In particular, the time domain waveform is synthesized based on the frequency content provided in the near field scan data, as depicted in the same Figure 3. Results for the PCB described in Figure 2 are illustrated in Figures 4a and 4b, and good agreement for the color map plots of both E and H fields can be observed. It is important to point out that the simulation of the compact model takes only a few seconds, since the details of the PCB have already been simulated, and they are somehow captured by the E/H field value in the region occupied by the PCB. Furthermore, the novelty of this approach is the ability to directly obtain a broadband response from the compact model. This means that multiple frequencies can be analyzed all in once, thereby strongly reducing the computational effort. The same compact mode is used to study the EMC of a simple metallic enclosure [1]. A view of this enclosure is shown in Figure 5. It is a 300mm x 300mm x 120mm box with a thin slot (100mm x 5 mm) on the front panel. On the top of the box is mounted a cover, and the previous calculated current distribution is located inside. The thickness of the metal walls (modelled in first approximation as perfect electric conductor (PEC) material) is t = 2 mm. Due to the relatively small frequency range, the EMC analysis has been performed in the first stage by using a three dimensional (3D) EM simulator [8] based on the finite integration technique (FIT) [9], and it uses a similar principle (equivalence theorem) to study the EMI performance of a device in time domain. However, only one reference frequency can be chosen for the compact model (which still contains the informations of a broadband E/H fields). Therefore, multiple simulations are necessary to cover a broadband frequency range, and consequent interpolation among the different calculated samples can be performed. Due to the highly resonant behavior of the box, simulation time is sped up by distributing a very small value of loss throughout the solution space by artificially assigning a conductivity (σ=0.0001 S/m) to the free space cells of the calculation domain. It is important to verify how big the impact of this assumption is on the calculated radiated emissions. In order to quantify the effect of the fictitious loss assigned to the free space of Figure 3: Equivalence theorem february 2009 Conformity 33 http://www.spira-emi.com http://www.spira-emi.com

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

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.