I suspect there are two effects that are maybe the one and the same and look different to me. I have noticed the same changes in shielding effectiveness with a solid metal cover when moving it closer and further >from a source. I attributed it to the capacitive coupling and subsequent current flow. At the frequencies involved, there was not much going through the cover being many skin depths thick. Better seam termination around the edges and added known contact points at several places away from the edges cured variation, and the emissions. With a mesh there is now a surface that current can flow on that is outside of the general mesh shielding. There is a IEEE paper from many years ago about the SE of coax braid/mesh, I think the vaiables were pitch and coverage, and the conclusion, if I remember correctly, was that the current on the shield preferred to flow on each wire of braid, instead of crossing over at each junction of wire crossings to stay on the inside. The braid contact points, wire to wire, were higher resistance than just a wire sureface.
- Bill --- Derek Walton <[email protected]> wrote: > Hi All, > > in testing a product with a mesh cover I've shown > that moving the cover > further from and closer to the source affects > shielding effectiveness. > While I knew this in principal, can anyone point me > in the direction of > formula that predict the SE of a welded wire mesh, > with 1/4" grid made > from 0.025" wire. I'm curious to know what happens > to SE between 30 MHz > and 200 MHz as the radiating source gets closer to > the mesh. > > Thanks, > > Derek Walton > L F Research > > - > > This message is from the IEEE Product Safety > Engineering Society > emc-pstc discussion list. Website: > http://www.ieee-pses.org/ > > To post a message to the list, send your e-mail to > [email protected] > > Instructions: > http://listserv.ieee.org/request/user-guide.html > > List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > > Scott Douglas [email protected] > Mike Cantwell [email protected] > > For policy questions, send mail to: > > Jim Bacher: [email protected] > David Heald: [email protected] > > All emc-pstc postings are archived and searchable on > the web at: > > http://www.ieeecommunities.org/emc-pstc > - Bill You can say what you want about the South, but you never hear of anyone retiring and moving North!!! _________________________________ __________________________________________________ Be a better friend, newshound, and know-it-all with Yahoo! Mobile. Try it now. http://mobile.yahoo.com/;_ylt=Ahu06i62sR8HDtDypao8Wcj9tAcJ - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Jim Bacher: [email protected] David Heald: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
