Well, once again, as a mental excercise for my wrinkled old cortex and working strictly from memory without external referencing, the way I understand it is thus:
1. Most of our control and computer circuitry nowadays is composed of large-scale integrated circuits, which are manufactured by vacuum deposition of masked-off layers of components. For example, a junction transistor can be manufactured by vacuum-depositing a layer of p-doped semiconductor, then a thin layer of n-doped semiconductor, then another layer of p-doped semiconductor, thus forming a PNP transistor. This is done on a microscopic scale, which is why some of our computer processing chips may contain literally millions of transistors as logical elements.
2. These logical elements must be connected to other circuit components such as tiny capacitors and tiny resistors, etc, and this is done by cleverly arranging vacuum deposition "masks" to the substrate and deposting other things on top of the first layers. For example, in the above PNP transistor, the top layer may be connected to other things by applying a layer of insulation with a hole in it right on top of the upper "P" layer, and then applying a layer of conducting material, which fills the hole and thus contacts the top "P" layer. This new top layer may now be connected to other components or to the outside world for taking output from that top "P' layer of that "layered" transistor. This forms a very simple "integrated circuit.
3. Multiply this process by many many layers, once again by applying cleverly-designed successive "masks" to the buildup of these layers, and you will have a complete set of circuitry capable of processing data --e.g., a computer processor chip.
4. The insulating layers which wer applied are very thin, since the thicker they are, the slower this new "integrated circuit" will work, and we are talking operating clock frequencies in the gigaHertz ranges. (When I started in electronics, 50 megaHertz was just about the edge of the observable universe, or at least that's the way I looked at it!)
5. SInce these insulating layers are so thin, it will not take a very high voltage to puncture them and ruin the circuit. Sometimes even only 10 volts can "pop" them.
6. This is the reason so much care is taken in assembling these circuits, for example, clipping the assembler's body to a ground circuit to dissipate any static charges on the assembler's body which might "pop" the insulation layers. Bear in mind that even slight movements, especially in a dry atmosphere, can build up thousands of volts. And they were shipped in "static bags."
7. Whle protective measure may be taken to prevent excessive voltages from appearing across these insulating layers (such as "layering in" protective diodes across the insulation layers), a really excesive voltage may destroy not only the layer, but the protective diodes themselves.
Bored yet?
8. Thus, for example, a lot of concern was generated as to how to protect the vast numbers of logical circuits aboard aircraft subject to lightning strokes ( a fairly common occurence) when the new composite skins of these aircraft began to be used. In "normal" metal-skinned aircraft, the strokes would usually just travel along the skin of the aircraft and that would be that, with rare damage to the electronic components. But with high-tech non-conducting skins, the only path was through the internal wiring of the avionics themselves, which would destroy all the computing equipment used nowadays.
(In this connection, I am told that one of the reasons the Russians kept using vacuum-tube ("valves" for the Brits among us) avionic equipment was to minimize the risk of damage from things like lightning.)
9. Obviously, static discharges are not the only things which can produce "higher-than-designed-for" voltages within these circuits. A good strong pulse of magnetism or a high-potential electric field can, too. And as much as the components themselves may be isolated or shielded from these things, inevitably, connections to the outside world must exist, which will conduct these pulses to the internal integrated circuits. Usually, these are called "antennas." :)
I even had a telephone anwering machine "smoked" by a not-very-close stroke on the power or telephone lines once, I could not tell which.
So, even if you can't (or won't ) call that a "demonstration" of vulnerability, I am sure that ll the effort involved in protecting the vital little "chips" inside our modern electronics is not wasted, and that somewhere there is a body of evidence to show that this kind of equipment has to be protected from both static and magnetic pulses. In this connection I suspect, without actually knowing, that there are also heating effects, besides the purely electronic effects, which can destroy all the delicate little insulating layers in integrated circuitry.
As far as "how" EMP or static protection is done, it can be by sheilding, where all the wiring to the critical circuits is surrounded by another conductor which is connected to ground, therby bypassing the excessive external voltages to ground. One example of this is the metal skin of an aircraft, another example is the braided conductor around microphone cables and your "cable TV" 75-ohm cables. This shielding is essentially nothing but a long, thin Faraday Cage which runs along the important wire. :)
It can also be done by providing alternate routes for the excessive voltages, as in the protective diodes I mentioned above. Most solid-state diodes have a "forward conduction" voltage, where they will not conduct in the normal direction until a certain voltage is reached, and this is usually 0.3 volts for germanium diods, and 0.6 or so volts for silicon diodes. Zener diodes, which will conduct in the "wrong" direction above a certain voltage, can also be used.
Ham operators usually have some kind of lightning protection for their antenna systems which consists of a "spark gap" connected between their feed-to-or-from-the-antenna transmission lines and a good earth ground. Thus, anything which exceeds the "normal" voltages on their transmission lines will jump that gap and be shunted to earth.
You will ocassionaly see what appear to be loose wires hanging down from high-tension electric power transmission lines. These are also "spark gap" protective devices, which will throw a spark to the neutral wire up there, performing the same function as the Ham's spark gap protectors.
The same techniques can be used for the micro-circuitry in electronic equipment, but it's just a matter of scale.
I welcome challenges and corrections to the above mental excercise.
Apologetically submitted, since I am working purely from memory,
Terry, 230RN
