Regarding the snippet below from Mr. Maxwell. There is no question and no argument that transitioning from milli- or micro-ohms per square to 14 Ohms per square will cause aperture or seam leakage and a degradation of shielding effectiveness (SE) relative to a contiguous low impedance shield. I was simply saying that 14 Ohms per square will preserve some enclosure SE, it is not completely useless. We are saying the same thing, but like the optimist and the pessimist viewing the glass whose volume is 50% occupied, we see it as either half full or half empty... Which view is more useful depends on how much enclosure SE is necessary for a given design, and how close the ITO gets the designer to his goal.
> From: "Chris Maxwell" <[email protected]> > Date: Fri, 17 Sep 2004 09:10:36 -0400 > To: "John Woodgate" <[email protected]>, <[email protected]> > Subject: RE: Germanium & ITO Window shielding effectiveness > > Will ITO provide some shielding? Sure 14 ohms/square will provide an > impedance mismatch with air. You'll get some reflection of plane waves. > But think about some of the other requirements of good shielding. A > well shielded enclosure needs to treat seams and aperatures so that they > won't radiate according to Babinet's principle. For instance, consider > a metal enclosure with an ITO coated window. As surface currents flow > on the enclosure, they will encounter the window. Most of the current > will flow around the window, since the conductivity of the metal is > orders of magnitude below the ITO. When the current flows around the > window, you have charge acceleration (it changes direction)...which > yields radiation. This is why I said ITO isn't so great for shielding. > It provides some, but not much. 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: Ron Pickard: [email protected] Dave Heald: [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
