MadSci Network: Physics

Re: Does an electromagnetic pulse destroy inactive electric circuits?

Date: Wed Aug 2 21:11:09 2000
Posted By: Karl Kolbus, Staff, Data processing, Mequon Consulting Corp.
Area of science: Physics
ID: 965188591.Ph

Hello Peter,

You are the first person I have talked to from New Zealand. Welcome to the 
Mad Scientist network!

Shortly after nuclear testing began, it was found that some of the 
instrumentation used to monitor the tests malfunctioned. Careful 
examination revealed that the electronic circuits were destroyed, and the 
hunt for the culprit was begun. It didn't take them long at all to 
discover that the EMP was doing it. Because the explosion occurs so 
rapidly, on the order of a few billionths of a second, the gamma radiation 
in the form of electrons, forms a very intense and concentrated pulse of 
electromagnetic energy.

To answer your question, it doesn't matter if the circuit is active or 
not. Consider a simple tarnsistor radio. Even if you remove the batteries 
from it, many internal connections remain. The base of a transistor may 
have a biasing resistor connecting it to ground, and the emitter, through 
other resistor/capacitor networks, may also be connected to ground. The 
same applies to the collector. Elements of a circuit share many common 
paths, albeit through passive components, but the fact remains that they 
are complete circuits - even without the battery. Therefore, any voltage 
induced into the wiring or the components themselves, can and will destroy 
the circuits.

On one of the recent space missions, an expirement was attempted which 
involved trailing a very long, very thin wire from the orbiting 
spacecraft. They were trying to see if the Electromotive Force (EMF) 
induced into the wire by the weak magnetic field of the Earth, could be 
used to power on-board instrumentation, or at least help charge the 
batteries. Unfortunately, the tether broke, and the experiment was never 
completed; but the theory was sound. If a weak magnetic field can produce 
energy in a long wire, think of what an extremely strong field would do in 
a short wire, such as wire traces on a computer circuit board, or even the 
electric power transmission lines coming into your home. It truly boggles 
the mind! 

Something you might find interesting: After the EMP was discovered and 
sicentists and others started thinking about how it could affect worldwide 
communications, they came upon a plan whereby data, voice or otherwise, 
could be routed around an area affected by the EMP. Packets of data could 
be sent thru different routes of the system and, in theory, at least one 
path would remain unaffected and the data would get through. I think you 
know what resulted. Yup, the Internet! It was originally a joint 
University/Military project, and ended up being what it is today.

Thanks for the question, and if you need any more info, please contact me 
directly at:

Your not-so-mad scientist,

Karl Kolbus       

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