The usual disclaimer about an unwillingness to debate anyone surnamed Maxwell in the field of electromagnetics...
I don't understand some of the statements and implications made in this exchange. 1) "ITO coating has a surface resistivity of 14Ohms/sq inch." First off, a nit, but per square inch is irrelevant, it is X Ohms per square. 2) "ITO coating has a surface resistivity of 14Ohms/sq inch." I think the resistivity would depend on the thickness of the deposited layer. A more correct statement would be, "ITO coating has a surface resistivity of 14Ohms/sq inch at a thickness of Y mils. 3) I am pretty sure ITO coatings are used as heaters for windshields/ windscreens. 14 Ohms per square is WAY more conductivity than necessary to dissipate static. I was warned that the conductive deposit Ford used a few years back on some passenger car models for instant windshield de-icing/ defogging would make a radar detector mounted behind the windshield useless. 4) Magnetic fields are by definition those whose field impedance is less than 377 Ohms. Basic Shelkunoff shielding theory says that the reflection portion of shielding is proportional to the mismatch between the wave impedance and the resistivity of the barrier. Clearly 14 Ohms per square is nowhere near as a good a mismatch as a metal enclosure, or a deposited metal coating on plastic, but it is not negligible if the impinging wave is close to far field in nature. > From: "Chris Maxwell" <[email protected]> > Date: Thu, 16 Sep 2004 08:41:38 -0400 > To: "Barker, Neil" <[email protected]>, "Price, Andrew P \(UK Basildon\)" > <[email protected]>, "Emc-Pstc \(E-mail\)" <[email protected]> > Subject: RE: Germanium & ITO Window shielding effectiveness > > I agree with Andy. > > ITO coating has a surface resistivity of 14Ohms/sq inch. You could probably > get just as much surface resistivity from a coating of dust :-) > > ITO coatings are good at dissipating static; but I think that they are pretty > much useless for shielding. > > I shudder to think of how naïve we were back in 1995 when this whole EMC (CE > marking) kick began. We had one product with a window about 2" x 2". We had > the window ITO coated. We spaced mounting screws every 1/2" around its edge > and then used conductive RTV between the edge and the Aluminum panel into > which it mounted. We took a $2 window assembly and turned it into a $50 > window assembly. (we did this on the advice of someone we trusted) I looked > into it a little while later and found the above facts regarding the surface > resistivity of the ITO coating. We would have done just as much good by > flushing money down the toilet. > > I would recommend a window with a fine, high mu wire (monel?) mesh shield. > Tecknit and Chomerics make some shielded windows like this. > > Best regards, > > Chris Maxwell > > -----Original Message----- > From: [email protected] > [mailto:[email protected]] On Behalf Of Barker, Neil > Sent: Thursday, September 16, 2004 3:44 AM > To: 'Price, Andrew P (UK Basildon)'; Emc-Pstc (E-mail) > Subject: RE: Germanium & ITO Window shielding effectiveness > > Andy, > > While I have no objective evidence on this subject, I would not expect > either of these to be particularly effective against magnetic fields as they > are both thin films of fairly high resistivity. I suspect that it could be > one of our products behind these windows, so is there any way that we can > help? > > Best regards, > > Neil R. Barker C.Eng. MIEE FSEE MIEEE > Manager > Compliance Engineering > e2v technologies (uk) ltd > 106 Waterhouse Lane > Chelmsford > Essex > CM1 2QU > UK > > Tel: +44 (0)1245 453616 > Fax: +44 (0)1245 453410 > e-mail: [email protected] > Web: http://www.e2v.com > > > -----Original Message----- > From: Price, Andrew P (UK Basildon) > [mailto:[email protected]] > Sent: 16 September 2004 08:21 > To: Emc-Pstc (E-mail) > Subject: Germanium & ITO Window shielding effectiveness > > > Hello group. > > Can anyone help with finding information on shielding effectiveness of > Germanium and ITO coated windows against magnetic fields? > > Regards > Andy > > Andrew Price > Principal Development Engineer (EMC Specialist) > BAE SYSTEMS Avionics > A125 > Christopher Martin Road > Basildon, Essex > SS14 3EL > > tel: +44 (0) 1268 883308 > email: [email protected] > > > ******************************************************************** > This email and any attachments are confidential to the intended > recipient and may also be privileged. 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