What the devil is an EMP and should you be afraid?


A discussion of electromagnetic pulse and how it can damage the electric grid and electronic equipment.

You may have heard of an EMP or electromagnetic pulse.  It is a phenomenon usually associated with a nuclear explosion.  An EMP is a very short term burst of electromagnetic energy that can actually disable or in some cases destroy nearby electric grids or electronic equipment.  It sounds like something out of a sci-fi or disaster movie, but it is also a real potential threat to us all.  And as it turns out, you can actually generate an EMP without a nuclear bomb.  That is a scary possibility but all too real.

EMPs also occur naturally.  A coronal mass ejection or CME from the sun produces the same effect as an EMP.  This event is a plasma discharge from the surface of the sun.  The plasma with all its charged particles travels at the speed of light toward the earth reaching us in about 8 minutes.  The plasma is a moving charge with an associated magnetic field that can induce huge voltages into any conductors causing massive current flow and related damage.  In the past, CME’s have caused outages in some electrical grids by burning out transformers.  Any closed loop circuit is a potential induction target.  Sensitive ICs are surely a major potential objective.  CMEs apparently occur all the time but thankfully most are weak when the get to the earth so cause no damage.  Every now and then a real whopper does some localized damage.

The real threat may be man-made EMP generators.  It is possible to build an EMP source with existing available electronic components.  It’s not the kind of parts you can buy at a Radio Shack or a Fry’s but you could order them online.  One possibility is a high power magnetron that could be powered up by a bank of high energy pulse capacitors that discharge rapidly producing a nanosecond of gigawatt microwave power.  Actual tests have shown that a generator like this can definitely disrupt radio communications and computers over a short range.  Severe damage to electronics can occur several thousand feet away from the source.  Even larger units can be built to extend the range and the damage.  You can actually buy an off-the-shelf 1.8 gigawatt EMP generator for $14,000 for “research” purposes.

The scary thing is that this is a terrorist weapon ready to happen.  Multiple EMP “bombs” could be detonated simultaneously around the country disrupting communications and perhaps even inflicting damage on part of the electrical grid.  EMPs have also been shown to set off explosions on gas pipelines or other flammable sources.  The EMP Commission says that the widely used Supervisory Control and Data Acquisition (SCADA) system is highly vulnerable to EMP and some minor incidents have been documented.  Such an EMP weapon is devastating to electrical and electronic equipment but it does not harm humans directly.

How do you protect against an EMP?  Shielding.  You put everything in a Faraday box to shield it from the pulse.  During the cold war, the military demanded that most electronics be shielded from EMP but over the years that requirement has been dropped for some equipment.  Such shielding is expensive and overly burdens electronic with extra weight and size.  No doubt some military gear is still EMP-protected.  No commercial or consumer devices are so shielded making them really vulnerable to attack.

I am not trying to make you paranoid but EMP is out there and a credible threat.  Lots has been written about it lately and you need to be aware of it.  One good source is a recent book by F. Michael Maloof titled A Nation Forsaken (www.wndbooks.com)Another related book is One Second After by William R. Forstchen.

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Blogs on topics such as wired and wireless networking.


Lou Frenzel

Lou Frenzel is the Communications Technology Editor for Electronic Design Magazine where he writes articles, columns, blogs, technology reports, and online material on the wireless, communications...
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