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Design Decisions: What Designers Need to Know About EMI Shielding

Comparison of EMI wavelengths to recognizable objects.
Comparison of EMI wavelengths to recognizable objects.

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Greg M. Jung
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Thermal Management
Greg M. Jung   12/25/2012 3:40:46 PM
I agree that sometimes a completely enclosed metal box must be used. In these cases, more expensive heat pipes and heat sinks can also be used for thermal management.

Cabe Atwell
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Re: More valuable info is necessary...
Cabe Atwell   12/7/2012 6:20:16 PM
Almost everything the military and NASA designs is in a metal enclosure afterward. It is fairly common practice to do so, I have found. I place a lot of my more sensitive projects inside a metal box routinely. So often the 60hz at the wall has been an issue with my testing, it was a necessity after.


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Re: More valuable info is necessary...
gamzoom   12/6/2012 11:14:29 AM
              Sizing Honeycomb EMI Shielding  - Broader implications.

This is a new concept for me and I can't help think about the wider implication of extending the principles to portable items and weatherproof vehicles.

In aircraft and outdoor portable units a small bore honeycomb would be vulnerable to water ingress due to capillary action. Exhaust blown air would help remove damp and condensation moisture but any air intake would be vulnerable. There would also be the issue of corrosion in residual trapped water in untreated copper or aluminum honeycomb. This could set some minimum diameter guideline.

The other out-door issue common to aircraft owners, is the minimum diameter of openings that resist the entry of insects. At certain time of the year insects find tubular openings that they can enter. They make silky nests for their larvae to grow in and can obstruct critical airflow. The maximum diameter seems to be about 0.125", which must be too small for a wasp's whiskers and head.  

In common households, and maybe some industrial environments, there is the problem of dust accumulation. Think of the PC CPU cooling fins that get clogged with dust (and fine cat hair if you are a pet lover). Again with input airflow, smaller orifices attract more significant obstruction over time.

So there seems to be some mechanical Max/Min guidelines to consider in a non-sterile existence.

I wonder what has been the experience of the Laser printer manufacturers with their honeycomb blocks. This maybe synthetic, thermally and electrically non-conductive material though. Would plated plastic work?


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More valuable info is necessary...
Amclaussen   12/5/2012 3:44:49 PM
Although the short article invites to see this matters in more detail, a little more info would be appreciated...

Like: Comparing between std. aluminum vs. copper enclosures, can we use thicker aluminum wall enclosures, or using a copper layer or sheet under the aluminum box acomplish a better result? Then, how thick?...  Are there any thumb rules regarding ventilation hole sizes/pitch and area, size of the perforated section? Location of perforated areas? and so on.  Amclaussen.

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