I’ll fess up, this question is spurred by the new show Falling Skies.
Part of the premise is alien invasion, and one of their key attacks was to EMP pretty much everything.
So for the purposes of this question lets presume that whatever they use to generate their EMP, the end effect is in all ways the same as a nuclear EMP.
If I understand correctly, an EMP causes damage to electronics by creating voltage surges with the electronic components. To me that means that if I had my electronic doohickeys turned off, the EMP would have no effect, as there would be no live current running through the device to be surged?
By turned off, I mean completely off, presumably anything with a stand by mode would be affected.
That’s not it. Think about every wire in the device as a little antenna that can pick up the pulse. If it picks up a strong enough signal it can fry the transistors. In the days of the cold war, the Soviets had a big advantage because of their primitive electronic technology. It’s a lot harder to fry a vacuum tube that runs on 300 volts and handles larger currents, than a transistor that ran (in those days) on 5 volts with much smaller currents. Today’s transistors run on even smaller voltages.
Well let’s start with what an EMP is; A powerful burst of electromagnetic energy.
The thing about electricity and electromagnetic fields is that they’re related (as you may recall from your formative years’ education, or the X-Men cartoon whenever Storm tried to zap Magneto with a lightening bolt). When you run a current through a wire it gains a magnetic field, and when you move a magnetic field across a wire it induces a current.
This is the principle behind a generator (which basically spins a magnet around a coil of wire to produce a current) and an electromagnet (which runs a current through a coil of wire to create a magnetic field).
Any material which conducts electricity has free floating electrons within it which (to cut a long explaination short) carry the charge of a current (either by flowing or vibrating). An electromagnetic force moves them, thus creating a current (think of them as being pushed and pulled around by a magnet).
Basically, the EMP will induce the current in any wires in a device regardless of whether it’s switched on (they still conduct electricity either way), therefore leaving them switched off won’t help in the least. Furthermore EMPs will also wipe a computer’s HDD (but not SSDs) plus any cassette/VHS tapes and floppy disks (in the unlikely event you still use them), since they rely on a magnet to read and write data onto them.
Keeping a device switched off at the mains will protect it from a power surge coming from the mains and nothing else.
No idea. None of the characters have been shown to have one, so unless it is stated otherwise presumably they did
Thanks for the info bisected. I had got the idea it caused the existing current in a device to surge. I hadn’t put together the whole electromagnetic energy causing the current to flow.
Thanks.
On an aside then, I’ve heard of some military hardware being ‘EMP hardened’. Does that shield the electronics from the electromagnentic force in the first place? Or are the electronics manufactured to handle the potential current surge without frying?
It’s also worth adding, that it’s quite easy to protect a device from an EMP blast; you can build in surge protectors and use diodes to protect semiconductors and shield them with Faraday cages (which are basically just metal grids that have the current induced in them rather than the circuits).
I seriously doubt this.
EMP only couples well to relatively long wires (1m+). The magnetic field of an EMP at ground level would be insufficient to damage the data on magnetic media.
Here are some older and recent threads on the topic:
[POST=11781642]How much EMP shielding does military equipment has?[/POST]
[POST=13967041]Solar flares, EMP, and electronics damage[/POST]
[POST=13919909]how big is the “EMP cannon” for stopping cars?[/POST]
[POST=5931094]Question about Electromagnetic Pulses (EMP)[/POST]
It is important to understand that EMP is not just a burst of electromagnetic energy; it is a pulse of energy that are quasi-coherent; that is, the wave is in phase as if emitted from a giant free electron maser that is constructed out of the Earth’s magnetosphere. (I’m specifically referring to the E1 component of high altitude EMP, which is what is of concern with regard to damaging semiconductor electronics). EMP is in the radio frequency range and can deliver potentials of up to the 50 kV/m saturation range, after which the atmosphere will undergo dielectric breakdown, as with lightning. This pulse develops high potentials in semiconductors that causes them to physically breakdown, regardless of whether they are powered or connected to a power grid.
It is often suggested that devices can be protected by placing them in a conductive faraday cage, or providing adequate grounding. This is based on a lack of understanding of how faraday cages work, which is distributing a static charge around the exterior such that no net charge can exist in the interior. However, faraday cages do not provide much protection against moving electric charges or electromagnetic radiation and provide no protection against induced magnetic fields. Grounding will help conduct a pulse to earth, preventing arcing, but will not prevent a semiconductor device from developing large potentials within the circuit array, which is what causes damage. The only way to protect electronics from the effects of EMP is to physically isolate them from the environment (remove all antenna-like structures and place them behind a large mass of material that will absorb the pulse) or make them robust enough to endure the effects of the pulse. The latter is why vacuum tube and thermionic diode electronics can survive EMP with only minor disruption, while low power solid state electronics, and especially integrated circuits, get completely fritzed; the potential range of the induced pulse is similar to what tube electronics see in operation, while it is several orders of magnitude greater than unisolated semiconductor electronics can endure.
This is not correct. EMP will not damage magnetic media or (in general) distort the data encoded within. EMP will damage the electronics that drive the read head and do all of the encoding, but the information on the drive itself should be intact unless it was corrupted by a failure of the head during the pulse, or a magnetic field is induced as a secondary effect, say in the motor. However, the permanent rare earth magnets in the drive head are much more powerful than anything the motor coils could induce. Solid state devices, on the other hand, can be corrupted by a large pulse, although they’ll more likely be rendered completely inoperative. The Pioneer 10 and 11 and Voyager probes recorded data on magnetic tape not dissimilar to commercial high grade metallic tape, and despite suffering the equivalent of repeated EMP much greater than terrestrial electronics would experience, resulting in numerous anomalies but no loss or recorded data. Galileo also experienced both radiation and pulse damage which even adversely impacted the robust quartz oscillator (which is basically its main timekeeping and sequencing device) but did not experience any loss of data from its magnetic hard drive.
Quite accurate, your response jogged my memory regarding protection of sensitive electronics in military equipment during the cold war.
Where mu-metal and other shielding was installed in equipment, conductive gaskets had to be maintained on that equipment and shorting plugs used for connectors.
There were highly specific instructions on how to run wires, both inside of a unit and to/from the unit.
On an alert, all electrical equipment was to be disconnected, shorting plugs installed and wait for the weapon to detonate.
One thing you mentioned was the high altitude burst, but there were low altitude bursts that could be highly destructive over a small area. Newer EMP weapons exist, but are still classified, hence not subject to discussion.
But, as with the E1 component, the other components are similar in nature, regarding geomagnetic field lines, save for the localized weapons, who generate their limited effects as a primary, rather than “riding” on the Earth’s geomagnetic field.
The wire acts as an antenna, that I get, but not knowing much about antennae: does a wire forming a circle, or some sort of completed circuit, suffer differently to a normal straight bit of wire?
Both, usually. The device will usually be enclosed in metal to form a Faraday cage. Electronics inside the device will often have larger footprint transistors and such so that they can survive a larger surge going through them, and protective devices like metal oxide varistors may be installed to clamp any induced voltage to a safe level, and other similar things may be done.
EMP hardened locations (like military data centers) will have even more done to them. The building steel will often be connected to ground, which helps to form a natural cage around whatever you are trying to protect. In addition to Faraday cages, you will also see things like ring grounds and halo grounds being used. The idea behind these is that you surround whatever you want to protect with a metal ring. When an EMP strikes, the energy from the EMP goes into inducing currents in this ring, which are then shunted harmlessly into the building’s ground system. This leaves significantly less energy left over to induce currents into devices that you want to protect.
There wasn’t much information on ring grounds and halo grounds on the web the last time I searched. There is some information on Ufer grounds if you want to google that.
