Shielded magnetic loops often don't work as well as unshielded loops! The shielding causes strong resonances that affect frequency response by tens of dB. The shields only appear to work to suppress e-fields if the e-fields are symmetric around the centerline of the loop, a condition that is met in the far field but not in most other uses. Also, the point of most e-field rejection on the probe is over the gap in the shield!!!
If you want to see how I arrived at the above from measurements (never seen this in a book) and analysis, read the paper and articles from my website linked below. https://emcesd.com/pdf/emc99-w.pdf My 1999 EMC Symposium paper. And these articles from my site. * June 2008, The Square Shielded Loop - Part 2, Parasitic Coupling<https://emcesd.com/tt2008/tt060208.htm> (Electric Field Shielding of Magnetic Loops is Not Always Effective!) * July 2008, The Square Shielded Loop - Part 3, Parasitic Coupling Between Unshielded Wire Loops<https://emcesd.com/tt2008/tt070508.htm> * August 2008, The Square Shielded Loop - Part 4, Coupling to a PCB<https://emcesd.com/tt2008/tt080108.htm> (From Shielded and Unshielded Magnetic Loops I tell attendees of my seminars a good way to get a free lunch from many EMC engineers is to ask them where on a shielded loop it is least sensitive to e-fields. Most do not realize it is right over the gap in the shield where the e-field is symmetric around the centerline of the loop. The explanation and supporting data is in the paper above. Worried about e-field coupling to unshielded loops? This very easy to measure in a few seconds, like 3 seconds, also covered above. For 90% of my measurements with loops unshielded one work best. I wish analysis like the above was widely covered in the literature. If you know of another source, please let me know. When I realized most of what I have been told about magnetic loops when I was younger was wrong, it motivated me to write the above articles and paper. Maybe I should combine all of the above into a new paper. Doug Smith Sent from my iPhone IPhone: 408-858-4528 Office: 702-570-6108 Email: [email protected] Website: http://dsmith.org - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to [email protected] All emc-pstc postings are archived and searchable on the web at: https://www.mail-archive.com/[email protected]/ Website: https://ewh.ieee.org/soc/pses/ Instructions: https://ewh.ieee.org/soc/pses/list.html (including how to unsubscribe) List rules: https://ewh.ieee.org/soc/pses/listrules.html For help, send mail to the list administrators: Mike Sherman at: [email protected] Rick Linford at: [email protected] For policy questions, send mail to: Jim Bacher: <[email protected]> _________________________________________________ To unsubscribe from the EMC-PSTC list, click the following link: https://listserv.ieee.org/cgi-bin/wa?SUBED1=EMC-PSTC&A=1
