Re: Shielding Effectiveness - or when a dB is not a dB
I build them as needed. Nothing critical about that. Even unbalanced shielded loops are good for locating (say) coating process problems -- and you can throw them away without a qualm, later. Cortland == Original Message Follows Date: 01-Aug-00 06:57:16 MsgID: 1072-33989 ToID: 72146,373 From: d...@dsmith.org INTERNET:d...@dsmith.org Subj: Re: Shielding Effectiveness - or when a dB is not a dB Chrg: $0.00 Imp: Norm Sens: StdReceipt: NoParts: 1 List-Post: emc-pstc@listserv.ieee.org Date: Tue, 01 Aug 2000 06:58:47 -0700 From: Douglas C. Smith d...@dsmith.org Reply-To: d...@dsmith.org Subject: Re: Shielding Effectiveness - or when a dB is not a dB Hi Cortland, It is good to know that others are using the technique. I have seen many misapplications of shielding numbers in selection of a material. Do you buy or build your loops? Doug Cortland Richmond wrote: I have been using plane shielded loops for over 15 years. Small magnetic loops allow localizing defects to small areas and use of small samples. I don't claim objective figures, but by comparing the material under test to a known good shield (i.e.: galvanized iron sheet) and to air, one gets a good feel for the merit of the material in hand. Cortland == Original Message Follows Date: 31-Jul-00 20:53:05 MsgID: 1072-33864 ToID: 72146,373 From: Douglas C. Smith INTERNET:d...@dsmith.org Subj: Shielding Effectiveness - or when a dB is not a dB Chrg: $0.00 Imp: Norm Sens: StdReceipt: NoParts: 1 Date: Mon, 31 Jul 2000 20:53:52 -0700 From: Douglas C. Smith d...@dsmith.org Subject: Shielding Effectiveness - or when a dB is not a dB Reply-To: Douglas C. Smith d...@dsmith.org Hi All, Shielding effectiveness is normally measured using plane waves (relatively far from the source). This method of measurement for shielding effectivenes does not always correspond to the way a shielding material is used. It is especially true when shielding material is incorporated into small products, such as the new wave of wireless devices on the market. If you rely on shielding to keep different parts of a product from interfering with each other, correlation of specification to use is especially important. The August 2000 Technical Tidbit on http://www.dsmith.org (or http://emcesd.com) describes a simple method of shielding effectiveness measurement that can be easily done in the development laboratory. This measurement method can give a better measure of shielding effectiveness that industry standard measurement techniques when the shield is close to the source being shielded. Has anyone here who is into shielding used something like this method which uses magnetic field loops? Doug -- --- ___ _ Doug Smith \ / ) P.O. Box 1457 = Los Gatos, CA 95031-1457 _ / \ / \ _ TEL/FAX: 408-356-4186/358-3799 / /\ \ ] / /\ \ Mobile: 408-858-4528 | q-( ) | o |Email: d...@dsmith.org \ _ /]\ _ / Website: http://www.dsmith.org --- --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org == End of Original Message = --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org -- --- ___ _ Doug Smith \ / ) P.O. Box 1457 = Los Gatos, CA 95031-1457 _ / \ / \ _ TEL/FAX: 408-356-4186/358-3799 / /\ \ ] / /\ \ Mobile: 408-858-4528 | q-( ) | o |Email: d...@dsmith.org \ _ /]\ _ / Website: http://www.dsmith.org --- == End of Original Message
RE: Shielding Effectiveness - or when a dB is not a dB
I have successfully used small loops for performing shielding effectiveness measurements. They are ideal to locate weak spots or points in a seam or isolate the leakage from aperture areas. We then compared these readings to a final shielding effectiveness measurement for the entire chassis and found that on an empirical basis there was a reasonable correlation that the localized readings were typically always equal to or greater than the final measurement. Ed Nakauchi EMI/EMC Consultant Principal Scientist Instrument Specialties, Inc. -Original Message- From: owner-emc-p...@ieee.org [mailto:owner-emc-p...@ieee.org]On Behalf Of Douglas C. Smith Sent: Tuesday, August 01, 2000 4:54 AM To: emc-pstc; SI-LIST Subject: Shielding Effectiveness - or when a dB is not a dB Hi All, Shielding effectiveness is normally measured using plane waves (relatively far from the source). This method of measurement for shielding effectivenes does not always correspond to the way a shielding material is used. It is especially true when shielding material is incorporated into small products, such as the new wave of wireless devices on the market. If you rely on shielding to keep different parts of a product from interfering with each other, correlation of specification to use is especially important. The August 2000 Technical Tidbit on http://www.dsmith.org (or http://emcesd.com) describes a simple method of shielding effectiveness measurement that can be easily done in the development laboratory. This measurement method can give a better measure of shielding effectiveness that industry standard measurement techniques when the shield is close to the source being shielded. Has anyone here who is into shielding used something like this method which uses magnetic field loops? Doug -- --- ___ _ Doug Smith \ / ) P.O. Box 1457 = Los Gatos, CA 95031-1457 _ / \ / \ _ TEL/FAX: 408-356-4186/358-3799 / /\ \ ] / /\ \ Mobile: 408-858-4528 | q-( ) | o |Email: d...@dsmith.org \ _ /]\ _ / Website: http://www.dsmith.org --- --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
Re: Shielding Effectiveness - or when a dB is not a dB
I have been using plane shielded loops for over 15 years. Small magnetic loops allow localizing defects to small areas and use of small samples. I don't claim objective figures, but by comparing the material under test to a known good shield (i.e.: galvanized iron sheet) and to air, one gets a good feel for the merit of the material in hand. Cortland == Original Message Follows Date: 31-Jul-00 20:53:05 MsgID: 1072-33864 ToID: 72146,373 From: Douglas C. Smith INTERNET:d...@dsmith.org Subj: Shielding Effectiveness - or when a dB is not a dB Chrg: $0.00 Imp: Norm Sens: StdReceipt: NoParts: 1 List-Post: emc-pstc@listserv.ieee.org Date: Mon, 31 Jul 2000 20:53:52 -0700 From: Douglas C. Smith d...@dsmith.org Subject: Shielding Effectiveness - or when a dB is not a dB Reply-To: Douglas C. Smith d...@dsmith.org Hi All, Shielding effectiveness is normally measured using plane waves (relatively far from the source). This method of measurement for shielding effectivenes does not always correspond to the way a shielding material is used. It is especially true when shielding material is incorporated into small products, such as the new wave of wireless devices on the market. If you rely on shielding to keep different parts of a product from interfering with each other, correlation of specification to use is especially important. The August 2000 Technical Tidbit on http://www.dsmith.org (or http://emcesd.com) describes a simple method of shielding effectiveness measurement that can be easily done in the development laboratory. This measurement method can give a better measure of shielding effectiveness that industry standard measurement techniques when the shield is close to the source being shielded. Has anyone here who is into shielding used something like this method which uses magnetic field loops? Doug -- --- ___ _ Doug Smith \ / ) P.O. Box 1457 = Los Gatos, CA 95031-1457 _ / \ / \ _ TEL/FAX: 408-356-4186/358-3799 / /\ \ ] / /\ \ Mobile: 408-858-4528 | q-( ) | o |Email: d...@dsmith.org \ _ /]\ _ / Website: http://www.dsmith.org --- --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org == End of Original Message = --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. 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: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson:pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.org
