You may expect a small improvement because the overlap forms a weak capacitor, which will short circuit some high frequency currents across the gap.
I really can't fathom a guess at how much improvement. It would be an interesting mathematical experiment to model the capacitance of the seam. Chris Maxwell | Design Engineer - Instruments Group email [email protected] | dir +1 315 266 5128 | fax +1 315 797 8024 NetTest | 6 Rhoads Drive, Utica, NY 13502 | USA web www.nettest.com | tel +1 315 797 4449 | > -----Original Message----- > From: [email protected] [SMTP:[email protected]] On Behalf Of Jeff Chambers > Sent: Monday, November 17, 2003 10:22 AM > To: [email protected] > Subject: Leakage at Enclosure Seams > > > I have been asked to comment on what improvement might be expected in > changing the design of an equipment lid from: > > A flat lid sat on the edges of the box, where the gaps between fasteners can > be modelled as a simple aperture, where the attenuation decreases linearly > with log(f) to zero at a half wavelength. > > To: > A stepped lid, with the lid sat on the edges, and with the projection > extending below the inner edge of the box.This removes the 'line of sight' > gap into the enclosure. Does this improve the attenuation? Intuitively it > should, but if the leakage occurs because of the interruption in shielding > conductivity and hence current flow at the seam, it won't. > > Does anybody have any references to analyses of the above, or comments, > please? > > (No emi gaskets are used btw). > > Thanks, Jeff Chambers > > ---------------------------------------------------------- > Dr Jeff Chambers > Westbay Technology Ltd > Main St > Baycliff > Ulverston > Cumbria LA12 9RN > England > Tel: 01229 869 108 > Fax: 01229 869 108 > http://www.westbay.ndirect.co.uk > > > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Ron Pickard: [email protected] > Dave Heald: [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > Jim Bacher: [email protected] > > Archive is being moved, we will announce when it is back on-line. > All emc-pstc postings are archived and searchable on the web at: > http://www.ieeecommunities.org/emc-pstc This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
