Why EMP pulse destroy electronics?

[yungman]

Just like the tittle. I never understand why EMP destroy electronics. People talked about a nuclear explosion will destroy electronic that is on, not off. Why?

I just never understand this.

 

[es1]

I guess we have to agree on what exactly an EMP pulse is before answering, and once there is a clear definition I'll bet you'll have your answer as you know EM.

But if it is a varying magnetic and electric field then there should exist at least one field, given any coupling constant, that can generate a large enough current to damage an IC.

Say for example on an internal high impedance net without a high breakdown voltage. It should be not impossible to punch through a FET gate for example rendering the FET non functional.

I've seen plenty of designs where the reset net was high impedance with rats all over the place. This would be (and in one particular case I know of was) a good victim for EM. Blow out one FET such that it now has a strong pull down and the whole circuit can't work. (In the case I know of the IC was not damaged but the reset did fire at inopportune times.)

Is it practical to generate such a field? Guess it depends on how weak the net is and the coupling constant...

I don't think you need hollywood style sparks to render a circuit non-functional.

I guess you could start looking here:
http://en.wikipedia.org/wiki/Electromagnetic_pulse

 

[jedishrfu]

A magnetic field has a certian eneray stored in the field. If you were construct a magnetic field via coiled wire and electric current and then abruptly disconnected it, you'd see a spark jump across the switch. The collapsing magnetic field generates a current in the wires which jumps the gap causing the spark.

So a changing magnetic field would induce a current in electrical devices that might exceed their capacity to channel and thus burn out the circuit. Remember microcircuits can only handle so much current, the more current the higher the wire temperature and if its high enough the wire melts.

 

[yungman]

I really don't know anything other than watching the movie! That anything that is powered on at the time will be destroyed and anything that is not is ok! Do you mean this is Holly Wood's myth?

So a lot of the circuits that pass CE or UL test should survive because they do have transorbs and all to protect the circuits. I can see most circuits will render non function because of the EMP pulse, but a lot should be able to come back to live upon power down and power up again.

Maybe the military pcb should demand transorb arrays even in the internal bus and have a central power reset in every piece of equipment.

 

[phinds]

When an EMP takes out the power grid, it really won't matter if other devices COULD still work, because they won't have any power.

 

[yungman]

When an EMP takes out the power grid, it really won't matter if other devices COULD still work, because they won't have any power.

Why? What is so different about the power grid?

Still you can avoid the fighting jets, bombers and fighting vehicles from being toasted.

 

[nsaspook]

Why? What is so different about the power grid?

Still you can avoid the fighting jets, bombers and fighting vehicles from being toasted.

EMP for Mil-Spec equipment is not a problem. Everything critical built since the 1970s is hardened.
http://www.wbdg.org/ccb/FEDMIL/std188_125_1.pdf

 

[yungman]

That's music to my ears! So the movies are just sensationalized the whole thing?

 

[nsaspook]

That's music to my ears! So the movies are just sensationalized the whole thing?

No, I can actually spin bullets around the room to a target.

 

[Kholdstare]

Varying EM field produces current in a nearby conductor. The metals in the IC will act like small antenna and receive the signal from the field.
Let's see what can possibly go wrong in an modern IC.
The gate oxide dielectric may breakdown, The metallic interconnects may form discontinuity due to high current, even the field and isolation oxides may breakdown creating high parasitic. So I think all of these will occur together to bring down the IC.

 

[jim hardy]

completely out of my field. i claim ignorance on EMP.

but physics-wise it seems to me it'd take a substantial antenna to pick up much energy.

a 100 mile long power or telegraph line is one heck of antenna .

a 10mm IC pin is not
call me skeptical.

 

[yungman]

Varying EM field produces current in a nearby conductor. The metals in the IC will act like small antenna and receive the signal from the field.
Let's see what can possibly go wrong in an modern IC.
The gate oxide dielectric may breakdown, The metallic interconnects may form discontinuity due to high current, even the field and isolation oxides may breakdown creating high parasitic. So I think all of these will occur together to bring down the IC.

I understand EMP is strong, but as circuit shrink, circuit loops are getting smaller and smaller. Total flux is flux density times the area inside the loop. I just don't believe there are enough energy in the flux to burn something in circuit loops inside an IC.

The only loop that can cause enough energy are the interconnect between pc boards in the system. That's when transorbs come into play. By requirement, all I/O of the boards has to be protected by transorbs to pass CE test, that automatically protect the boards to a big extend.

 

[es1]

Not much science. But is does claim to show a 1MV EMP destroying a flying toy helicopter. It just kinda turns off.
Also he drives a car through and it kills the ignition.

Note: you don't need to burn out an IC to render it inoperable. just inject a small current into a weak node. a consumer electronics project typically has many such nodes.

http://www.youtube.com/watch?v=0odJKYTzXg8&feature=related

 

[Kholdstare]

I understand EMP is strong, but as circuit shrink, circuit loops are getting smaller and smaller. Total flux is flux density times the area inside the loop. I just don't believe there are enough energy in the flux to burn something in circuit loops inside an IC.

The only loop that can cause enough energy are the interconnect between pc boards in the system. That's when transorbs come into play. By requirement, all I/O of the boards has to be protected by transorbs to pass CE test, that automatically protect the boards to a big extend.

http://www.thespacereview.com/article/1549/2

The section "EMP effects upon IC-based devices" in this page may answer your question. Apparently EMP damages ICs which are already placed in PCB and turned on.

 

[es1]

A paper from the Air Force proposing a model for damage during EMP.
Page 6 provides a theory for why devices without power have high survivability.

http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA125976

 

[Mike_In_Plano]

I used to work in EMC, and this was an interesting topic that I never had to address in design or certification, but it was very interesting nonetheless.

Most of the movie stuff is bunk. For example, John Travolta inducing an EMP with an underground blast. That was almost as unbelievable as the people in the chamber getting far enough away in a few minutes...

As I'm given to understand, the effect happens when a nuclear event unleashes gamma rays above the atmosphere. Gamma rays are not particles, but rather extremely high energy photons.

When the gamma rays strike atoms in the atmosphere, they knock prodigious quantities of electrons free in a very short time. This somehow induces fields that may be as much as 25 kv / meter with a rise time down in the ns range.

I've never heard of the effect being created for mid and lower lever bursts.

As to how it gets to electronics, I suspect that it enters the packaging as most effects do - through the conductors, through an unshielded enclosure, or through poor attention to gasketing / seams in the enclosure. Subsequently, I suspect it destroys in a fashion similar to electrostatic discharge; it punches through gate oxide or physically damages the structure of fine structured devices (like RF amplifier transistors, low leakage devices, or ECL logic).

Now, electronics is generally designed with extremely fine structured components. This is to get more components out of less material, and to enhance performance / complexity for a given piece of material. The net result, is that modern active devices are extremely susceptible to ESD.

I suspect that very few bomb bursts would be required to totally destroy all civilian computing and communications throughout the developed world.

 

[es1]

I understand EMP is strong, but as circuit shrink, circuit loops are getting smaller and smaller. Total flux is flux density times the area inside the loop. I just don't believe there are enough energy in the flux to burn something in circuit loops inside an IC.

As circuits shrink, transistors also get much weaker and take much less J to damage. And you don't even need to fully damage it to make the internal digital gate not function properly.

Note in the car example shown on youtube the power windows and dash lights still worked. They're probably run by just a simple switches connected to the battery. It's probably the small weak transistors in some uC in the car that died.

And in the soviet experiments linked to by Kholdstare the old infrastructure survived.

 

[Mike_In_Plano]

Agreed,

The circuits are shrinking and take much much less energy to damage. The argument that circuit size leaves less loop area doesn't hold. Circuits have always been vulnerable at the interconnects. Simple current in, current out.

As one who fought in the die size reduction wars, I became intimately familiar with the smaller chips hanging up where the larger ones didn't. Back then, few people understood how to deal with the issue. Surprisingly, McDonald's Restaurants published one of the better papers regarding the matter.

 

[Kholdstare]

McDonald's restaurant ?
How is it related with EMP ? microwave oven ?

 

[Mike_In_Plano]

In the late eighties, you could fall back on military documents, Guru's that gave obtuse answers, or the hard fought knowledge of the fast food restaurant world. With RS232 and RS485 cables being dropped in every other month to automate the burger delivery process, they learned that arcing contacts in fryers, fans switching on/off, or poorly thought wiring would play havoc with so many of their systems that worked great in the lab.
So, they did the smart thing and researched the causes and migrations.
In an age when the military was suggesting such things as the "chattering relay" test, this actually proved helpful.
Dan White and consultants were also useful as was Henry Ott.

 

[Mike_In_Plano]

In the late eighties, you could fall back on military documents, Guru's that gave obtuse answers, or the hard fought knowledge of the fast food restaurant world. With RS232 and RS485 cables being dropped in every other month to automate the burger delivery process, they learned that arcing contacts in fryers, fans switching on/off, or poorly thought wiring would play havoc with so many of their systems that worked great in the lab.
So, they did the smart thing and researched the causes and migrations.
In an age when the military was suggesting such things as the "chattering relay" test, this actually proved helpful.
Dan White and consultants were also useful as was Henry Ott.

 

[nsaspook]

I understand EMP is strong, but as circuit shrink, circuit loops are getting smaller and smaller. Total flux is flux density times the area inside the loop. I just don't believe there are enough energy in the flux to burn something in circuit loops inside an IC.

http://www.futurescience.com/emp/E1-E2-E3.html

These 2 MEV gamma rays will normally produce an E1 pulse near ground level at moderately high latitudes that peaks at about 50,000 volts per meter. This is a peak power density of 6.6 megawatts per square meter.

The process of the gamma rays knocking electrons out of the atoms in the mid-stratosphere causes this region of the atmosphere to become an electrical conductor due to ionization, a process which blocks the production of further electromagnetic signals and causes the field strength to saturate at about 50,000 volts per meter. The strength of the E1 pulse depends upon the number and intensity of the gamma rays produced by the weapon and upon the rapidity of the gamma ray burst from the weapon. The strength of the E1 pulse is also somewhat dependent upon the altitude of the detonation.

http://www.futurescience.com/emp/RR00092.pdf

 

[jim hardy]

great links, nsa...

very enlightening.

thank you !

 

[Bassalisk]

Myth it isn't for sure. I don't have advanced EM knowledge but I do believe that EMP(strong enough) would fry all circuits.

https://www.youtube.com/watch?v=0odJKYTzXg8&feature=related

at 01:30 you will see what you want.

 

[yungman]

http://www.futurescience.com/emp/E1-E2-E3.html



http://www.futurescience.com/emp/RR00092.pdf

Thanks for this detail article. This make a lot more sense.

I really never buy into just a simple EM wave inducing high voltage that burn the ICs. This talk about the secondary effect of extreme high electric field.

 

[yungman]

In the late eighties, you could fall back on military documents, Guru's that gave obtuse answers, or the hard fought knowledge of the fast food restaurant world. With RS232 and RS485 cables being dropped in every other month to automate the burger delivery process, they learned that arcing contacts in fryers, fans switching on/off, or poorly thought wiring would play havoc with so many of their systems that worked great in the lab.
So, they did the smart thing and researched the causes and migrations.
In an age when the military was suggesting such things as the "chattering relay" test, this actually proved helpful.
Dan White and consultants were also useful as was Henry Ott.

I was not involve in this particular research so I am not going say one way or the other. I did spent a few months on the Land Warrior soldier communication and weapon system. We had continuous burning of Firewire and USB interface when soldier rolling on the ground. It turned out to be momentary disconnect of the Vcc or the GND contacts of the connecting cables. We actually capture the contact breaking for very short time of one or two nS. Yes we capture on the scope of a mechanical contact bounced at nS speed! The capacitance of the cable zap the input. I just don't quite remember the exact process of burning of the interface ICs...just old age! I solve the problem by putting transorbs to protect the Firewire and USB link. It has nothing to do with arc, high voltage. It was just a capacitance of the cable that is capable to dump enough energy to burn the input. It has absolutely nothing to do with loops or electric field or arcing.

 

[yungman]

Another question, any ferromagnetic material like steel will block EM wave. Does this block the EMP pulse and components? If so, electronics in cars are surrounded by steel shell, why is the electronics affected?

 

[sandy.bridge]

Perhaps the entirety of the electrical circuit is not shielded? For example, gaps. Moreover, I recall reading somewhere that EMP can affect devices with antennae, which would include vehicles.

 

[Kholdstare]

Any "conductive" material will block EM wave, not ferromagnetic material. Its because the electric field cannot sustain inside the conductor. Thus EM wave decays to 1/e at the skin depth inside conductor. Ferromagnetic material will just block magnetic field.

In RF sense, in a particular frequency a material can either be dielectric or conductive and it depends on the EM wave's frequency. Thus mica a dielectric for low freq EM wave becomes conductor for high freq EM waves. Look at the link below for seawater and metallic mirror reference.
http://farside.ph.utexas.edu/teaching/315/Waves/node49.html

I guess the frequency of EMP was so high that the skin depth of those metals were not sufficient to block it.

 

[cmb]

The main effect is induced currents onto wiring harnesses (incidental antenna) that then feeds into circuitry, which, other than the obvious direct feed of current, may include effects such as a 'ground bounce' on a scale that causes the whole working potential of a circuit to deviate so far from its surroundings that other forms of damage may occur.

I'm not aware that direct irradiation of ICs is of much concern, comparatively. Fast suppression circuitry in the form of both very fast TVS components and then active circuits to switch everything off are usually sufficient to achieve the desired hardness, for any 'realistic' scenario.

The use of non-silicon parts also helps. I do not have a reference for you, but as far as I understood it was not unknown for the whole of a plane's main flight controls to be executed in miniature thermionic valves, rather than silicon.

It is worth noting how 'EMP' differs from 'EMC'. In EMC you may see a very high current level at a particular frequency (carrier wave, or some form of pulse or amplitude modulation on the CW). This is a 'susceptibility' and may or may not be 'damaging'. Whereas, an EMP is a wide-band pulse, usually a single intense pulse that carries a large spectrum of EM energy with it. It is the sum total of EM energy that makes EMP destructive, rather than some particular frequency-dependent susceptibility.

But, further, there is a class of weaponry called 'electromagnetic weapons' whose aim is to generate EM energy that can be targeted at some combatant weapons platform. I don't expect to find many citations for such a subject, but I imagine that these would cover both wide and narrow band devices.

As part of normal EMC qualification testing for aircraft systems (civilian and military), components are subjected to induced and injected currents and voltages so as to simulate lightning strike pulses, which, I imagine, would go some way to cover an EMP scenario.

 

[yungman]

Any "conductive" material will block EM wave, not ferromagnetic material. Its because the electric field cannot sustain inside the conductor. Thus EM wave decays to 1/e at the skin depth inside conductor. Ferromagnetic material will just block magnetic field.

In RF sense, in a particular frequency a material can either be dielectric or conductive and it depends on the EM wave's frequency. Thus mica a dielectric for low freq EM wave becomes conductor for high freq EM waves. Look at the link below for seawater and metallic mirror reference.
http://farside.ph.utexas.edu/teaching/315/Waves/node49.html

I guess the frequency of EMP was so high that the skin depth of those metals were not sufficient to block it.

The higher the frequency, the thinner the conductor metal needed to shield the EM wave as the skin depth is very small. Steel skin of cars are both ferromagnetic and good conductor. The skin depth is very small meaning the EM wave will be attenuated and not passing through. I understand the exposed harness will be affected, but if the military machines are designed to have a total shield, then it should protect the electronics inside. Transorbs can be very very fast, the SMD packaging enable the design to rid of most of the parasitic inductance.

Also if the communication link is designed to be slower speed, you can afford to put bigger transorbs or more in parallel. Seems like there is always a way to protect electronics from EMP.

My understanding is cars use the popular CAN bus which is slow like snail, you can triple transorbs and won't affect the communications.

face it, majority of the pcbs are badly design with bad EMC practice. They pass emission test by back door approach of some copper tape etc. They don't stand a chance on any significant EM susceptibility. If boards are well designed and with transorbs protection, there got to be a way to protect the circuit.

 

[jim hardy]

Will the fast (E1 and E2) part of EMP have a direction to it, like a flux field? maybe generally down, perpendicular to Earth's magnetic field?

so if a fellow wanted to EMP-harden his personal vehicle a good start might be to shield the wiring harness? Especially around the back of the hood where there's a space for windshield wipers to sleep, and a big harness just beneath?

i think i'll keep my '83 Ford Ranger diesel - only electronics in it is the radio.

 

[yungman]

i think i'll keep my '83 Ford Ranger diesel - only electronics in it is the radio.

 

[cmb]

i think i'll keep my '83 Ford Ranger diesel - only electronics in it is the radio.

Presuming you're saying it is a fully mechanical system, I suspect you'll still find there are several weak components in there, such as alternator electronics and fuel lifter pump and control. Does it have a manual knob you pull and hold, to turn the engine off? If not, there is an electronic solenoid too. How much of the instrument panel is electronic?

I've had a few ancient Merc diesels that mostly fitted the bill of 'EMP proof', even with pure mechanical dashboard parts (ever had an oil leak from your dashboard? The oil pressure gauge had a direct capillary from the engine that could, therefore, leak oil!) but still a few circuits. Actually, I think the most EMP proof was an ageing American Plymouth with manual carbs, spark gap distributor (nothing to go wrong there) fully hydraulic gearbox [your Ranger probably has an electronic auto box?] and 'best' (read; most ancient) of all - a solenoid based voltage regulator, from the days when you needed a set of feeler gauges to set the points in the voltage regulator! I don't suppose there's many folks left that remember setting their regulator points!

 

[jim hardy]

I don't suppose there's many folks left that remember setting their regulator points!

you and i are among the few I'm sure... airgap and spring tension too.

re Ranger:
instruments are the old Ford heated wire type from 1930's, they'll be okay.

but you're right there's an electric valve that must close to run, it dumps fuel pressure.
but injector pump is an old fashioned mechanical one. Should stand tall after "The Big One".

that particular model is still sought after, for the little engine is an industrial Perkins design that's known for lasting nearly forever. there's an active community of enthusiasts still driving them.

ahh nostalgia...

 

[Antiphon]

A gap is as good as a wire antenna or coupling. A car has so many gaps it might as well not have the hood on at all for EMP purposes.

As for how it blows up electronics, it's mostly overvoltage on semiconductor devices.

The EMP fields my devices are tested to are 50kV/meter. If you have any kind of antenna (deliberate or incidental) in a field like that, you need special circuits to protect the ICs inside. It's exactly the same damage mechanism as a carpet (static) shock only much larger in area.

Vacuum tube electronics are the most robust without special protection. I have a collection of around 150 triodes and pentodes "just in case."

 

[gorgon53]

50kV/meter? Will there be anyone left to care about what what happened to electronics?

 

[Antiphon]

I don't thinks that's a lethal field- unless maybe you're perched on the edge of the grand canyon in your Hoveround electric wheelchair. The EMP might fry just the joystick controls but not the motor drive...