EMP question.

Thread Starter

quaser

Joined Sep 22, 2012
7
Hello!!

I wanted to know if an emp can distrupt a simple flashlight (incandescent or led... if there might be a difference, please elaborate) at about 10 feet away.

Will it only flicker the bulb or will it simply not make it work?

What will be the physics behind it?.... will it affect the battery source or will it affect the filament inside? what will happen in case of led light?

Do let me know abt the feasibility of this thought...

{Inspiration:- After watching ocean's 11 emp scene... i just couldn't digest the idea of the lights going out... i mean what about the standby generator.}

P.S:- A simple schematic for the "Torch Take-down Device" will be appreciated. Since RavenPhoenix mentioned about lighting a bulb... I thought it can even distrupt it.
 

bountyhunter

Joined Sep 7, 2009
2,512
I know it can't hurt an old style incandescent bulb flashlight.

The new LED type probably would be damaged by an EMP. Most semiconductor devices are vulnerable to it.
 

DerStrom8

Joined Feb 20, 2011
2,390
I know it can't hurt an old style incandescent bulb flashlight.

The new LED type probably would be damaged by an EMP. Most semiconductor devices are vulnerable to it.
Mostly MOSFET-based devices are vulnerable to EMPs, due to the thin layer of insulation between the gate and the doped silicon. A surge of voltage/current will melt the insulation, thus causing it to not work. Most ICs use microscopic MOSFETs, so they too are vulnerable. Bountyhunter, you are correct--an EMP will not do a thing to an incandescent light bulb flashlight. But it probably won't affect an LED flashlight either unless it uses a driver circuit with a FET or IC.
 

ErnieM

Joined Apr 24, 2011
8,377
Raise your hand if you know "Ocean's Eleven" is a work of fiction and thus not bound by the laws of physics.

Of course, if you choose to believe you can turn off all the lights in even a small city with a small box of glowing green liquid then there is no way you're listening to me now anyway.
 

bountyhunter

Joined Sep 7, 2009
2,512
Interesting:

EMP pulses are short, in the order of 100 billionths of a second, dropping to half amplitude within 200 billionths of a second, but there is low frequency energy that lasts up to 1000 seconds.

Also consider that the typical reflector opening size of an inch or so.
A wavelength at this diameter would be 1.18 GHz. Energy below this frequency would be greatly attenuated.

There are two major modes for EMP to get into equipment:
-Front Door Coupling occurs typically when power from a electromagnetic weapon is coupled into an antenna associated with radar or communications equipment. The antenna subsystem is designed to couple power in and out of the equipment, and thus provides an efficient path for the power flow from the electromagnetic weapon to enter the equipment and cause damage.

-Back Door Coupling occurs when the electromagnetic field from a weapon produces large transient currents (termed spikes, when produced by a low frequency weapon ) or electrical standing waves (when produced by a HPM weapon) on fixed electrical wiring and cables interconnecting equipment, or providing connections to mains power or the telephone network . Equipment connected to exposed cables or wiring will experience either high voltage transient spikes or standing waves which can damage power supplies and communications interfaces if these are not hardened. Moreover, should the transient penetrate into the equipment, damage can be done to other devices inside.

Notice how both modes for a significant amount of the pulse to get in, are mainly antennas and wiring.


There is one very specialized version of the EMP bomb, called a HPM, but they only have a small area of effect:

HPM weapons operating in the centimetric and millimetric bands offer an additional coupling mechanism. This is the ability to directly couple into equipment through ventilation holes, gaps between panels and poorly shielded interfaces. Under these conditions, any aperture into the equipment behaves much like a slot in a microwave cavity, allowing microwave radiation to directly excite or enter the cavity.

An example is that of a 10 GW 5 GHz HPM device illuminating a footprint of 400 to 500 metres diameter, from a distance of several hundred metres. This will result in field strengths of several kiloVolts per metre within the device footprint, in turn capable of producing voltages of hundreds of volts to kiloVolts on exposed wires or cables.

Now, how long is a flashlight like an HDS? 4 inches? So this will attenuate the voltage to 10th the voltage at 1 meter.

Anyone have the spectrum plot of what a large area EMP pulse weapon produces?

I know that in the case of a nuclear detonation, an electromagnetic pulse consists of a continuous frequency spectrum. Most of the energy is distributed throughout the lower frequencies between 3 Hz and 30 kHz. As such, most metal LED flashlights would be rather safe. There is a weaker initial spike at the first time of arrival from 1 to about 300 MHz caused by gamma radiation. Following that, there is energy from 1 to 100KHz which lasts a total of about 1 millionth of a second. Then there is a bunch of low frequency activity, that mainly threatens long power lines, data lines, and antenna cables, that goes on for up to 1000 seconds.

Also, realize the strength of the pulse drops with the distance from the detonation. For more info on this look here:
http://electromagneticpulse.quickseek.com/


In the case of a EMP bomb at altitude, typically, the field strength on the ground drops to 300 volts per meter at only 3 miles from the burst, at ground level.

Did you know that the effect of a altitude EMP burst, once you get away from "ground zero", on the ground follows a boomerang shape, and the peak field is in the V of the boomerang, which is always pointed south? And it is very weak to the North. This is due to the earth's magnetic field.

More detailed info here:
http://www.usace.army.mil/publicatio...10-3-2/c-2.pdf
 

Thread Starter

quaser

Joined Sep 22, 2012
7
Ok.. I guess if i want to visualize it... during an emp, the incandescent flashlight might flicker , but will still function after the emp has stopped.. am I right?
 

praondevou

Joined Jul 9, 2011
2,942
This is all theory. Anyone can prove that no incandescent light bulb flashlight under no circumstances can be affected by any EMP? I don't think so.
What if wires/metal parts inside the flashlight have just the wrong length?

The exact power and frequency distrubution of an EMP can hardly be predicted, right?

@Quaser: You will have to try it out ;)
 

bountyhunter

Joined Sep 7, 2009
2,512
This is all theory. Anyone can prove that no incandescent light bulb flashlight under no circumstances can be affected by any EMP? I don't think so.
What if wires/metal parts inside the flashlight have just the wrong length?
It doesn't matter. The energy in an EMP pulse is microscopic, the only way it can damage anything is if there is an antenna which can capture a signal and create a voltage high enough to do harm to the device. Semiconductors can be easily damaged by pulses of very low energy content, which is why they always warn about careful ESD handling because walking across a carpet can pick up enough energy to easily kill an IC. The reason an IC can be harmed is because it looks like a high impedance and the tiny energy discharge can create sufficient voltage to break down the internal structure of the device.

An incandescent lamp has no high impedance anything in it: it is literally a bunch of wire and a battery. Even the bulb itself is a piece of wire. There is just nothing there which is sensitive to any kind of low energy HV discharge.

And for the record: I do not think an incan light would "flicker" from an EMP because there is nowhere near enough energy to make the filament glow.
 
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