EM Pulse

How do EM Pulses work? Apparently, they stop all kinds of machinery; cars, computers, phones, etc. But how?

Also, how would something llike this be deployed offensively?

Sorry, I’ve been living at the bottom of a mine shaft. What’s an EM pulse?

Electromagnetic pulse.

Generally, it’s a powerful electromagnetic wave that overloads the hardwired circuit boards of activated machinery. Nuclear explosions create a form of EM pulse.

Apparently, electronic equipment that isn’t poered up when the pulse occurs will not be affected. I’m not sure why, but my WAG is that the pulse merely intensifies an existing electron stream rather than instigating one where none exists.


stoli

Well, blessed is just about everyone with a vested interest in the status quo,
as far as I can tell.

“electronic eguipment that isn’t poered up”

Ahem, “powered”. Sorry.

As for offensive deployment, it is a difficult issue because EMP is omnidirectional, it cannot be focused. The nuclear device is the most feasible option that I know of. Hopefully soon someone who knows more will pop their head in. In the meantime, I’ll keep laying typos to give me an excuse to bump this up.


stoli

Well, blessed is just about everyone with a vested interest in the status quo,
as far as I can tell.

EM is short for Electo-Magnetic. An Electro-Magnetic Pulse is one of the things produced by a nuclear explosion, along with the heat and light normally associated with such things.

Now, one of the priciples of physics is that a changing magnetic field will induce an electric current in a wire, and a changing electric current in a magnetic field will cause a force to be exerted on the wire. This is how both electrical generators and electric motors work; in a generator wires are moved through a magnetic field (spun by being turned by a turbine) which causes an electrical current in the wires. In an electric motor, a changing current is put through the wires wrapped around a rotor inside of a magnet which causes the rotor to spin. (As a side note, a generator can also be used as a motor and a motor can be used as a generator.)

The magnetic pulse that is sent out by a nuclear blast has several effects. First, the magnetic pulse is very intense and very short; it rises and falls rapidly. The changing magnetic field would induce a current in any conductor in the area. Like the wiring in your house, the power lines along the street or even the circuits inside your computer. In many cases the current will be far more than the device is designed to handle, which will result in a lot of damaged and destroyed equipment.

In extreme cases, wires can literally be ripped from their mountings because of the force generated as well.

I have heard that a large nuclear device detonated high enough up in the air could destroy most computer and communication equipment in a city while producing very little actual blast damage. (We won’t discuss fallout here.)

Magnetic effects on wiring are real and something that utilities have to plan for. Induced current in long distance transmission lines caused by magnetic fluctuations (resulting from solar storms) have been known to burn out substations and generators. And that is a fairly weak fluctuation. The effects of a nuclear blast would be much worse.

Just something else to worry about…

“Sometimes I think the web is just a big plot to keep people like me away from normal society.” — Dilbert

Hi stolichnaya, near simulpost there. Actually, equipment that is turned off will be affected by the pulse. The magnetic field will still induce a current in the conductors. It will not be as bad (since presumably being turned off will mean that the circuit is open) but damage will occur. IC chips are particularly vunerable, since their conducting pathways are so thin and easy to damage.

“Sometimes I think the web is just a big plot to keep people like me away from normal society.” — Dilbert

Any electrical device is susceptible to damage by EMP whether it’s powered or not. The pulse is so powerful that any conductor becomes an antenna and absorbs a jolt of electricity, like a lightning strike, and fries all the unprotected parts.

Devices actually in operation at the time the pulse hits are particularly vulnerable because they will generally stop doing whatever it is they’re doing – controlling an airplane, maintaining a database, operating a communications channel. If they’re far enough away they’ll just reset and recover rather than melt but the interruption could have disastrous consequences.

Did I mention that it could also erase and/or scramble a lot of computer memories? Both RAM and magnetic media?

It’s a real problem. It’s kind of like all the Y2K disaster scenarios brought to life. Military hardware is generally designed to survive but most commercial products are not. No big deal if your cable goes out, but what about all the financial data in your banks computers?


“I used to think the brain was the most important organ in the body, until I realized who was telling me that.”
Emo Phillips

Thanks, guys. Man, I love this place.


stoli

Well, blessed is just about everyone with a vested interest in the status quo,
as far as I can tell.

I hate it when I type slow… ten minutes after reading this post and it’s already full of responses :frowning:

Well, I’m not going to waste my writing, so here’s my post anyway. To answer the OP, we might want to start with something a bit simpler. Take your common TV for example. Before cable was on the market, TVs worked liked radios, and received radio signals from TV broadcasting stations through their antennas. The term “radio waves” is just a fancy name for electromagnetic (EM) waves of a specific frequency, between 10 kilohertz and 100 gigahertz if I remember correctly. Anyway, EM waves will induce a small current in conductors that it passes through. When TV signals arrive at your TV’s antennas, they cause a small fluctuating current in the antenna, which the TV then reads and turns into pictures and sound.

An EM pulse is just like a radio wave, except it’s a lot stronger, hence the word “pulse”. It’s also not restricted to a specific frequency range like radio waves, so a flash of light can technically be called an EM pulse just as much as a surge of X-rays. Now when an EM pulse comes along and passes through a TV’s antenna, it will induce a much larger than usual current, which basically fries all the circuits connected to the antenna, and effectively kills your TV, perhaps permanently.

So to get back to your original question, how do EM pulses stop machinery, cars, computers, phones, and etc.? Well, all of these things have electronic circuits within them. These circuits act like tiny antennas, and when an EM pulse passes through them, a large current will arise on the circuits and wreak havoc. This means that if an EM pulse is strong enough, your TV will still be dead even if it didn’t have an antenna, because the circuits within are susceptible to EM pulses.

As has been mentioned in earlier post (grrr…), EM pulses are usually associated with the detonation of a nuclear bomb. In recent years however, EM pulse weapons have been slowly developing under the banner of smart weapons. There are actually a few working models on the market, but they are still quite expensive. One which I have seen before is a car mounted EM pulse canon (sounds neat, eh?) that has just enough power to fry the circuits of another car within a few hundred feet (can’t remember the exact range), and it can actually be aimed. Aside from the price of the equipment itself, I suppose EM pulse canons won’t be all that popular due to the possibilities of collateral damage. Bring one up to Wall Street and you can probably cause a economic disaster all by yourself…

Why don’t EMPs hurt vacuum tubes? Or is this a misconception? I have an old tube amplifier (an Ampeg Super Echo Twin, if you’re curious), and when I bought it, a friend of mine said, “It has a really warm tone, and it’ll work even after a nuclear warm.” I knew exactly what he meant (we both assumed there would be plenty of fuel and generators post-apocalype!), but I don’t know how I knew. So what’s the deal?

How do you harden solid-state gear against EMP? Big metal shields? Lead masks so Superman can’t see through? Put all your machines on rubber mats?

There was an apocryphal story about Soviet aircraft being less susceptible to EMP because of their old-fashioned vacuum tube technology. It may have been true, but vacuum tubes are susceptible to damage in the same way other electronics are but in general they are built of beefier (i.e., larger) components–wires instead of little traces of copper on a circuit board or tiny regions of silicon. I’m not an EE but I presume they can stand a larger current pulse without damage.

And your guesses on shielding solid state components are pretty much on the money. Metal shielding, careful grounding, large pathways in the circuit. The idea is to dissipate or divert the pulse before it can reach the sensitive circuits.

I’ve heard rumors that some missiles were built with fluidic controls, wich are not susceptible to EMP.

Well, I’ve been waiting for the best opportunity to send a post for the last few days, and damned if I don’t think this is the one.

The Master on EM pulses

Having said that…

taking out a little sparkler and a flag with the number “500” on it

Wheeeeee!!! 500 posts for me!!!

Thenk yew.


All I wanna do is to thank you, even though I don’t know who you are…

Having read the link - I thought I was the only one trying to think of a way to knock out those car stereos.

Seriously, I wonder if a small, directional EM pulse (if technology is developed for this) might have the effect of stopping someone’s heart. I wouldn’t want to do that.

Or start hearts that have stopped. Just aim and “Clear!”

One reason that valves may survive EMP better than solid state components is that they operate on higher voltages commonly 400v or more,solid state stuff,especially IT use voltages typically less than 5V.

When a charge is induced the voltage will rise up to a point where it will find a way to equalisation or until the charging force is no longer present and the higher insulation requirements of valves mean that this force will probably have passed before their limit is reached also valves take a relatively long time to warm up before they become effective conductors.

One major problem in building construction is the requirement to predicting the effect of lightening strikes not just by discharging the current safely but also the EMP effect which could cause serious disruption to critical building services such as alarms sytems, lift controllers, IT systems etc.

Serious damage can also occur in high voltage switchgear when fault conditions occur not just from massive heating effects on conductors but from the sheer mechanical force exerted by the associated magnetic fields,again a good example of EMP.

I have a friend who works at a switchgear manufactures where they test stuff to maximum possible fault conditions-it’s amazing seeing the films of thick solid bars being twisted by EMP forces.

You could build youself a big Faraday cage if you’re the paranoid type that would keep EMP at bay.

JONF,
Plenty of missiles are built using hydraulics because you can use the thrust from the motor to compress oil filled sacs(accumulators) to produce the pressure .EMP is not the main reason why its done.
Its just very light compared to the alternatives and when you think about the G’s involved it is robust too.

By the way,the oil once it has been used does not return to the system it’s vented out of the missile body so it’s most often used on short range weapons .