[SI-LIST] Re: emi shielding
The mechanism for reflection is that em fields incident on a surface induce currents to flow such that the flow of current opposes the field which caused it. The material must have enough absorption and homogeneity (i.e., limited apertures) such that the induced currents remain on the side of the material where they were induced and do not re-radiate. That is the function of absorption and aperture control above 30 MHz. -- >From: "Wani, Vijay (V)" >To: "'ghery.pet...@intel.com'" , "'emc-p...@majordomo.ieee.org'" , "'si-l...@freelists.org'" >Subject: RE: [SI-LIST] Re: emi shielding >Date: Fri, Nov 9, 2001, 11:52 AM > > > all:thanks for your time and response. > > I understand the frequency range we worry about (30MHz - 2GHz), any metal > (or metallized plastic) would be overkill and effect of apertures will be > mostly determing factor for shielding effectiveness. > but, the shielding mechanism of conductive metals (or metallized plastics) > is mostly reflective rather than absorbtion. > > if we have a meterial with absorbtion shielding mechanism (in 30 MHz-2GHz > frequency range), is there any advantage? i would guess, that will reduce > antenna effect in the system. would appreciate any thoughts. > > vijay wani > Dow Chemical > > -Original Message- > From: Pettit, Ghery [mailto:ghery.pet...@intel.com] > Sent: Friday, November 09, 2001 12:14 PM > To: 'Wani, Vijay (V)'; 'emc-p...@majordomo.ieee.org'; > 'si-l...@freelists.org' > Subject: [SI-LIST] Re: emi shielding > > > Vijay, > > The relative proportions are a function of frequency and the relative > conductivity and relative permittivity of the material. > > The attached file is from a MathCAD 7.0 model that I put together a while > back. The equations came from a Technit design guide published about 20 > years ago. > > You will note that in the frequency range that we usually worry about almost > any metal you might use is overkill. It is the apertures that create the > problems. The example in the document is copper. > > I hope this helps. > > Ghery Pettit, NCE > > > > -Original Message- > From: Wani, Vijay (V) [mailto:vw...@dow.com] > Sent: Friday, November 09, 2001 7:36 AM > To: 'emc-p...@majordomo.ieee.org'; 'si-l...@freelists.org' > Subject: emi shielding > > > > hello: > > as we know, threre are two main component of shielding effectiveness. > (Absorbtion and Reflection). is there any way to find out.. what percentage > of overall shielding is due to absorbtion / reflection for a given material? > > thank you in advance. > > Vijay Wani > Dow Chemical > > --- > 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: > majord...@ieee.org > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Michael Garretson:pstc_ad...@garretson.org > Dave Healddavehe...@mediaone.net > > For policy questions, send mail to: > Richard Nute: ri...@ieee.org > Jim Bacher: j.bac...@ieee.org > > All emc-pstc postings are archived and searchable on the web at: > No longer online until our new server is brought online and the old > messages are imported into the new server. > > > > > -- > To unsubscribe from si-list: > si-list-requ...@freelists.org with 'unsubscribe' in the Subject field > > or to administer your membership from a web page, go to: > http://www.freelists.org/webpage/si-list > > For help: > si-list-requ...@freelists.org with 'help' in the Subject field > > List archives are viewable at: > http://www.freelists.org/archives/si-list > or at our remote archives: > http://groups.yahoo.com/group/si-list/messages > Old (prior to June 6, 2001) list archives are viewable at: >http://www.qsl.net/wb6tpu > > > --- > 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: > majord...@ieee.org > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Michael Garretson:pst
RE: [SI-LIST] Re: emi shielding
all:thanks for your time and response. I understand the frequency range we worry about (30MHz - 2GHz), any metal (or metallized plastic) would be overkill and effect of apertures will be mostly determing factor for shielding effectiveness. but, the shielding mechanism of conductive metals (or metallized plastics) is mostly reflective rather than absorbtion. if we have a meterial with absorbtion shielding mechanism (in 30 MHz-2GHz frequency range), is there any advantage? i would guess, that will reduce antenna effect in the system. would appreciate any thoughts. vijay wani Dow Chemical -Original Message- From: Pettit, Ghery [mailto:ghery.pet...@intel.com] Sent: Friday, November 09, 2001 12:14 PM To: 'Wani, Vijay (V)'; 'emc-p...@majordomo.ieee.org'; 'si-l...@freelists.org' Subject: [SI-LIST] Re: emi shielding Vijay, The relative proportions are a function of frequency and the relative conductivity and relative permittivity of the material. The attached file is from a MathCAD 7.0 model that I put together a while back. The equations came from a Technit design guide published about 20 years ago. You will note that in the frequency range that we usually worry about almost any metal you might use is overkill. It is the apertures that create the problems. The example in the document is copper. I hope this helps. Ghery Pettit, NCE -Original Message- From: Wani, Vijay (V) [mailto:vw...@dow.com] Sent: Friday, November 09, 2001 7:36 AM To: 'emc-p...@majordomo.ieee.org'; 'si-l...@freelists.org' Subject: emi shielding hello: as we know, threre are two main component of shielding effectiveness. (Absorbtion and Reflection). is there any way to find out.. what percentage of overall shielding is due to absorbtion / reflection for a given material? thank you in advance. Vijay Wani Dow Chemical --- 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server. -- To unsubscribe from si-list: si-list-requ...@freelists.org with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: http://www.freelists.org/webpage/si-list For help: si-list-requ...@freelists.org with 'help' in the Subject field List archives are viewable at: http://www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu --- 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
[SI-LIST] Re: emi shielding
Vijay, The relative proportions are a function of frequency and the relative conductivity and relative permittivity of the material. The attached file is from a MathCAD 7.0 model that I put together a while back. The equations came from a Technit design guide published about 20 years ago. You will note that in the frequency range that we usually worry about almost any metal you might use is overkill. It is the apertures that create the problems. The example in the document is copper. I hope this helps. Ghery Pettit, NCE -Original Message- From: Wani, Vijay (V) [mailto:vw...@dow.com] Sent: Friday, November 09, 2001 7:36 AM To: 'emc-p...@majordomo.ieee.org'; 'si-l...@freelists.org' Subject: emi shielding hello: as we know, threre are two main component of shielding effectiveness. (Absorbtion and Reflection). is there any way to find out.. what percentage of overall shielding is due to absorbtion / reflection for a given material? thank you in advance. Vijay Wani Dow Chemical --- 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server. -- To unsubscribe from si-list: si-list-requ...@freelists.org with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: http://www.freelists.org/webpage/si-list For help: si-list-requ...@freelists.org with 'help' in the Subject field List archives are viewable at: http://www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu
[SI-LIST] Re: emi shielding
Vijay, Check out FloEMC, http://www.floemc.com/. You can have the software determine this by integrating the losses in the material, whether they are resistive or dielectric to find the absorption. Jeff Walden -- To unsubscribe from si-list: si-list-requ...@freelists.org with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: http://www.freelists.org/webpage/si-list For help: si-list-requ...@freelists.org with 'help' in the Subject field List archives are viewable at: http://www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu
