I threatened to write a 19" rack box design procedure, and now I have done it. I have documented the lay-out and the DFMA. The one thing I am not sure about is EMI/RFI shielding. I am Googling it.
Can anybody recommend a good book or article on EMI/RFI shielding of enclosures?
i seem to recall seeing copper wire mesh screen being used at the EMP site near Sandia Labs. It’s been 40+ years since i saw it, so memory has faded.
Short of that, refer to:
and
good luck!
It’s… complicated. I have been shown the tip of the iceberg, and seen what lies beneath it… but enough of that metaphor.
Shielding is its own system working in parallel with the system of equipment being installed in the enclosure, and becomes part of the enclosure itself. It depends on the sensitivity of the victim(s) and the noisiness of the source(s). When it is a serious design issue, it usually goes beyond just having braids around wire bundles and an extra busbar, to be effective. You’ll have to know or make assumptions about the sources and victims that will be at play, before you can be sure you are making the right provisions within the enclosure.
Sorry I can’t be immediately useful, and instead just pose more questions back to you. I think the answer will be different, depending on what the enclosure does and where it is mounted.
Do you know what equipment is being mounted inside the enclosure?
Do you know where the enclosure will be mounted, and the RF environment it will be exposed to?
Will the enclosure house sensitive equipment and be mounted in a noisy RF environment? Or will the enclosure house noisy EM equipment and be mounted near sensitive equipment?
Sparweb,
In general, EMI/RFI shielded enclosures must grounded, so the enclosures must be conductive. Forget anodize finishes on your aluminium panels. You need conversion coatings.
Another issue, and the one I am curious about, is holes in the enclosure, for cooling or whatever. These must be smaller than the EMI/RFI wavelengths. This also affects screwed joints between sheet metal and/or machined parts.
If you aren’t able to consider the system, environment or the installation, then all you can do is come up with an enclosure design. You’ll kind of be in the dark as to what’s good enough - that’s determined by the installation, not the enclosure. It will be like designing the perfect car, when you don’t know if it’s for a Sunday driver or a Formula 1 driver.
Let me know if this helps.
InterferenceTechMag_Design_Considerations_Large_Aperture_Effects.pdf (220.1 KB)