Anecdotal story; my brother built a sailboat with a carbon fiber hull and deck. Two issues came up, ESD that would knock you out of the boat; and the radios would not work below the deck. They worked fine on deck. ps. screaming fast sailboat too. He also had a magnetic problem many years later in a professional setting. The AC mains power vault, transformers and distribution to the building was adjacent to the computer room. The monitors jiggled with the 60 Hz field. He asked me about it and I remarked that either move the computer room or add several sheets of cheap steel to the wall between. I don't know what he did since I didn't follow it - free advice to family, ya know how it goes. MRI's have a safety concern with distance of magnetic material such as oxygen tanks since they have had a couple of severe incidents where the patient and his tank occupied the same space when the MRI was turned on. Shielding Teslas vs milli or micro teslas can be an exercise in futility?? So far as I know, shields either reflect or absorb. One will certainly heat up and the other will likely heat up to some degree in the process. And the uni-direction shields may stay in the realm of science fiction for quite some time yet. - Bill In the event of a national emergency, click on the following links to provide directions to your duly elected mis-representative.
http://www.usa.gov/Contact/Elected.shtml or... https://writerep.house.gov/writerep/welcome.shtml http://www.senate.gov/general/contact_information/senators_cfm.cfm ________________________________ From: Robert Johnson <[email protected]> To: [email protected] Cc: emc-pstc <[email protected]> Sent: Tue, December 29, 2009 10:54:17 PM Subject: Re: shielding both DC and AC fields in medical implants Not unusual, but mu-metal (http://en.wikipedia.org/wiki/Mu-metal) comes to mind. Bob Johnson Doug Smith wrote: I have a related question to my first one below to refine my first question. Does anyone here know of an existing (probably medical) product that uses unusual shielding techniques to avoid immunity problems when exposed to high amplitude DC and AC magnetic fields such as in MRI tests. By unusual, I mean things like non-metallic shields or exotic materials we do not normally use. In many medical tests, most shielding materials are not usable because of eddy current heating or disruption of the field used in the test. I am looking for material in existing products that does not heat up in strong fields and does not disrupt the field itself much outside of the shield. A reference to a supplier of such materials would good. I am not even sure if this is possible, especially the lack of disruption of the field outside of the shielded circuit/apparatus (any academics out there want to weigh in on this?). An academic question might be: Can one shield a circuit or apparatus to a very strong magnetic field (DC and/or time varying) without significantly affecting the field outside of the shielded part? Doesn't seem possible to me. Doug Doug Smith wrote: I have a question (as opposed to the usual article post). Can anyone point me to some resources online concerning shielding methods applied to medical implants that shield both high amplitude DC as well as AC magnetic fields such as found in MRI machines. I have been searching around Google finding only standard EMI shield solutions. References to currently existing produces would be great. 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: [email protected] \ _ / ] \ _ / Website: http://www.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 http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher <[email protected]> David Heald <[email protected]> - 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 http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher <[email protected]> David Heald <[email protected]> - 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 http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher <[email protected]> David Heald <[email protected]>
