Weston, I will change the simulation to allow a common mode signal. In the present simulation there is no way to introduce a common-mode signal; the shield is floating and there is no reference point to develop a common-mode signal against.
However, in a real application there is a shielded enclosure at one or both ends of the cable. I can drive a common-mode signal referenced to an enclosure (in this case I will use a infinite ground). I believe that the shield voltage will be equal to the common-mode voltage of the T-line. Therefore there will be a common-mode voltage between the shield and the enclosure (infinite plane), which leads to common-mode current, which leads to EM radiation. Dave Cuthbert From: Beal, Weston [mailto:[email protected]] Sent: Monday, September 19, 2005 10:57 AM To: drcuthbert; [email protected]; [email protected] Cc: [email protected] Subject: RE: cable shield simulation Dave, This looks like a good experiment. I think the key that most engineers have tried to reinforce is the differential signal. Since you ran this experiment in a simulation, the signal was somewhat ideal and the radiation is as expected. Can you run the same simulation with a small amount of common-mode current, maybe 5%, to simulate the non-ideal circuits of reality? Regards, Weston From: [email protected] [mailto:[email protected]] On Behalf Of [email protected] Sent: Monday, September 19, 2005 9:05 AM To: [email protected]; [email protected] Cc: [email protected] Subject: cable shield simulation For what it's worth I ran a NEC-2 model of a differential transmission line under these conditions: 1) free space 2) covered with a mesh shield open at each end 3) covered with a mesh shield closed at each end The radiation under condition 2 is the same as condition 3. The radiation in condition 2 and condition 3 is 13dB below condition 1. >From this I infer that closing the ends makes no difference, as several here have stated. I can improve the model in various ways but I will wait for more input from all of you. NEC-2 Model: 7.0" differential line spaced 0.1" 7.5" mesh shield Mesh shield: Six sides 0.5" diameter 0.5" distance between "rings" Dave Cuthbert Micron Technology - 2005 IEEE Symposium on Product Safety Engineering 3-4 October Schaumburg, IL http://www.ieee-pses.org/symposium 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/listserv/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: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc - 2005 IEEE Symposium on Product Safety Engineering 3-4 October Schaumburg, IL http://www.ieee-pses.org/symposium 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/listserv/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: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
