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Mitigation of radiated EMI from SD Card slot?

Mitigation of radiated EMI from SD Card slot?

Mitigation of radiated EMI from SD Card slot?

(OP)
Anyone have suggestions for physical design of slot that have proven successful in reducing EMI? Assuming that a small grounded door is not an option.
We have experimented with slotted metal fascia plates and with metallized plastic fascia plates that recess the SD Card into a throat. Neither proved hugely successful.

Anything that was tried and worked to mitigate emissions would be helpful.
Thanks, NigelT

"You will master any feeling of inadequacy you may be having"
....from my fortune cookie @ the buffet!

RE: Mitigation of radiated EMI from SD Card slot?

Find the radiation source within the box, and shield that.

Yeah, I know it's not easy.

As for mods associated only with the SD slot, all I can think of is a metal box extending inward from the fascia, surrounding the card for much of its length, possibly flanged and bonded to the fascia.

A simple slot in a flat metal faceplate constitutes a 'slot antenna', basically a dipole of approximately the slot length, and should be a pretty good radiator. I don't know offhand it there's a way to degrade a slot antenna; maybe a different shape?



Mike Halloran
Pembroke Pines, FL, USA

RE: Mitigation of radiated EMI from SD Card slot?

Not knowing your exact application, rather than 'sealing' the SD slot against EMI emissions/susceptibilities, could you instead use a metalized SD card to 'plug' the hole created for the SD slot? My thought is that the metal encased SD card (standard form factor - provided by Samsung) should have more than enough surface area in contact with your SD slot to provide an adequate bonding path such that inserting the metal card into the slot works to effectively 'plug' your chassis. You would only have to make sure that the rails onto which the SD card inserts are metal and tied to your chassis ground.

I haven't proven out this idea, simply because the metal door would have been my first suggestion (or a metal flap that can snap down in front of the slot when not in use).

RE: Mitigation of radiated EMI from SD Card slot?

(OP)
Thanks for suggestions, all.
I will check out the metal SD Cards though they look a little like St Steel appliances - "dressed up". They have, I think a plastic frame exposed around the edge but it's hard to see in pictures. And, of course we can't control what brand of card our customers may use.
When we tried the plastic fascia plate with metallized internal paint we actually found the emissions were boosted locally at the card opening. Also several card brands are themselves significant emitters.

"You will master any feeling of inadequacy you may be having"
....from my fortune cookie @ the buffet!

RE: Mitigation of radiated EMI from SD Card slot?

Have you considered running the interface slower, or is that even a possibility? Lower operating frequency would drastically lower the emissions, since the wavelengths will increase in addition to the spreading of the power over time.

TTFN
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RE: Mitigation of radiated EMI from SD Card slot?

Quote:

When we tried the plastic fascia plate with metallized internal paint we actually found the emissions were boosted locally at the card opening.

It's called a slot antenna.
They can be very effective. ... as you now know.

IRStuff's idea is most likely to be effective, since you have already excluded a door as a solution.



Mike Halloran
Pembroke Pines, FL, USA

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