I will agree with Brent completely on this. Prior to retiring I've had chambers built both ways. Carbon loaded pyramidal foam absorbers are big. The chamber I had built for Tandem Computers in 1989 had cones that were 8 feet tip to base. The chambers I had built for Intel Corporation back in 1995/6 used hybrid absorbers. Ferrite tiles for the lower end of the spectrum, cones at the higher end. Like Brent, I haven't seen pure cones used in years. They require a larger envelope for the chamber and add cost to the project. If you are retrofitting and existing chamber the hybrid approach becomes all the more critical.
I can't speak to the potential for migration of the fire retardant salts in cones, but from what I remember hearing decades ago a fire in absorbers is not something that you want to experience, so a fire suppression system is imperative. Ghery S. Pettit Pettit EMC Consulting LLC [email protected] <mailto:[email protected]> From: Brent DeWitt <[email protected]> Sent: Tuesday, March 16, 2021 4:46 AM To: [email protected] Subject: Re: [PSES] RF absorber for EMC room Yes, but..... To be effective down to 30 MHz, "classic" carbon loaded, tapered foam absorbers need to be huge, on the order of 2 meters high. That eats a lot of internal chamber volume. I'm also not sure if anyone makes them currently. Also, do _not_ buy old (10 year +), used absorbers! They still work fine as absorbers, but tend to lose there self-extinguishing capability due to the migration of the retardant salts used in the manufacturing process for that purpose. Urethane fires are not something you want to experience. Respectfully, Brent DeWitt iRobot Bedford, MA On 3/16/2021 5:13 AM, McBurney, Ian wrote: A question for the EMC experts. Is there an alternative rf absorber to ferrite tiles that works between 30MHz to 1GHz? I am thinking of the pyramidal type absorber. This is for research for partially lining a pre compliance radiated rf emission EMC room. Many thanks in advance. Ian McBurney Lead Compliance Engineer. Allen & Heath Ltd. Kernick Industrial Estate, Penryn, Cornwall. UK. TR10 9LU. Tel: 01326 370121 Email: [email protected] <mailto:[email protected]> Allen & Heath Ltd is a registered business in England and Wales, Company number: 4163451. Any views expressed in this email are those of the individual and not necessarily those of the company. - ---------------------------------------------------------------- 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] <mailto:[email protected]> > All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) <http://www.ieee-pses.org/list.html> List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected] <mailto:[email protected]> > Mike Cantwell <[email protected] <mailto:[email protected]> > For policy questions, send mail to: Jim Bacher <[email protected] <mailto:[email protected]> > David Heald <[email protected] <mailto:[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] <mailto:[email protected]> > All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) <http://www.ieee-pses.org/list.html> List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected] <mailto:[email protected]> > Mike Cantwell <[email protected] <mailto:[email protected]> > For policy questions, send mail to: Jim Bacher <[email protected] <mailto:[email protected]> > David Heald <[email protected] <mailto:[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.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) 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]>
