My knowledge is limited in this area, but try contacting Tech-Etch, Plymouth MA - USA http://www.tech-etch.com They supply (manufacturer?) honeycome filter panels. Hope this helps.
-----Original Message----- From: [email protected] [mailto:[email protected]] Sent: Friday, October 20, 2000 9:31 AM To: Paolo Roncone; [email protected] Subject: Re:Holes, waveguides and honeycombs forwarding for [email protected] ____________________Reply Separator____________________ Subject: Holes, waveguides and honeycombs Author: Paolo Roncone <[email protected]> List-Post: [email protected] Date: 10/20/00 12:03 PM Group, We are working on a couple of designs of telecom gear contained in metal s.u.b.-racks and we have to meet emission limits up to 40 GHz. I need some advice on the workings of waveguides below cut-off and honeycombs, because we have to include ventilation openings without possibly degrading the shielding effectiveness. First, I made an inquiry on textbook formulas for circular and rectangular waveguide cut-off frequencies. I was happy to find consistency among three different sources (I found the same formulas although rearranged in different fashions). From Ott's "Noise reduction techniques in electronic systems" I found: fc = [6.9/d] GHz for circular waveguides fc = [5.9/l] GHz for rectangular waveguides where fc = cutoff frequency d = diameter of circular section (inches) l = longer side of rectangular section (inches) Now my question is: what about honeycomb panels ? Can I use the same formulas for honeycombs ? Here the single cells are neither circular nor rectangular. Can I still apply these formulas with good accuracy ? If not, anyone knows of other formulas that apply in this case? As for attenuation (shielding effectivenes) of one single waveguide opening, if the frequency is well below cutoff , this is proportional to the ratio of length/diameter of the waveguide. The recommended ratio is 2:1 to 4:1 in order to get good attenuation. Now, I just found a formula for attenuation of honeycomb panels as function of frequency, length-to-width ratio of each cell and also number of cells: S [dB] = 20log(fc/f) + 27.3(t/W) - 10log(n) (f < fc/10) where: S [dB] = Shielding Effectiveness in dB fc = cutoff frequency of waveguide f = frequency t = cell length (or thickness) W = cell section width n = number of cells in honeycomb panel I have no problems with the first two terms in the above equation. As for the third term, that means that increasing the number of cells (n) in the honeycomb panel degrades the shielding effectiveness of the panel (ex. 1000 cells means 30 dBs lost). Before finding this formula I had a feeling that due to the skin-effect each honeycomb cell could be treated as a single cell. So far I wasn't able to find other formulas for honeycomb panels. So I'd like to have some feedback on this. I hope to get some useful directions. Thank you in advance, Paolo Roncone Cisco Photonics, Italy ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: [email protected] Michael Garretson: [email protected] For policy questions, send mail to: Richard Nute: [email protected] ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: [email protected] Michael Garretson: [email protected] For policy questions, send mail to: Richard Nute: [email protected]
