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MineMan
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[*] posted on 14-2-2019 at 12:48
EMP and electric fields from explosives


Does anyone have any information on this? Appearently all chemical detonations realease EMPs... and current research is showing the VOD could be measured remotely. Here is an abstract from a paper:


Innovative Method to Approach Velocity of Detonation (VOD) by Measuring Electromagnetic Pulse (EMP) of Blast
M. Seo1, A. Torrance2, G. Cavanough3 and C. Johnson1; 1Nuclear and Mining Engineering, Missouri Science and Technology, Rolla, MO; 2Kilmorie Consulting, Cooks Hill, NSW, Australia and 3QMR Blasting Analysis, Pinjarra Hills, QLD, Australia
Velocity of detonation (VOD) is an important variable when evaluating the performance of mine blasts. Typically, for a VOD measurement, individual probes have to be loaded into each blast hole that requires a measurement, increasing the loading time and is not representative of the whole blast. Experimental studies of electromagnetic pulse (EMP) from the detonation of explosives charges show that electric and magnetic field signals are observed when chemical explosions occur in the air, at the ground surface, and underground. EMP has the potential to evaluate VOD of the whole blast without impeding the loading process. Due to a variety of physical causes which make the electromagnetic effects complex, measuring EMP of the detonation of explosive charge has not been fully studied yet. This paper presents experimental results of a study of EMP generation during the detonation of explosive charges in holes at quarry with various types of antennae. This study will help to determine the most suitable antennae for capturing EMP data from the field so that EMP data can be used to monitor blasting performance.
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VSEPR_VOID
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[*] posted on 14-2-2019 at 14:44


You can convert chemical energy from explosives into very large amounts of EM energy. This is how some EMP weapons work; using a shaped charge and super compressed thin copper conductor.



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MineMan
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[*] posted on 14-2-2019 at 18:46


I am well aware of that. But this is WITHOUT any magnets or copper wire!! It’s appearently intrinsic to detonation. I believe this has to do with the plasma generated.

Anyone have any information!?

[Edited on 15-2-2019 by MineMan]
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Vomaturge
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[*] posted on 14-2-2019 at 20:38


Found this a few years back. Focuses mostly on nuclear EMP's but in the second paragraph it references a journal article on chemically sourced emp. Couldn't get the whole article, but but here's the unhelpful abstract.

this 1998 Army report gives a literature review, which includes some results from the ieee article. Notably, their are reports of both weak, Mhz and GHz signals occurring during detonation, and also far later low frequency pulses.

Having skimmed over that report, I'm not really clear on why it happens. I would have expected the mechanism to be an expanding plume of reaction products interacting with the geomagnetic field, in a manner akin to what VSEPR is talking about, without any copper casings or electromagnets to optimize it. But one of the investigations (Gorshunov, L. M., et al, “EM Disturbances in Explosions,” translated, U.S. Library of Congress, ARD Rpt 68–88.) says that external electric and magnetic fields don't effect the formation of the pulse, which would seem to imply that it is produced by the actual reaction, not by interaction with the surroundings. I'm not seeing how generating a cloud of hot pressurized vapor would create any charge separation or magnetic field without needing some kind of 'seed' field. I may be confused, but I looks like there has been some investigation into these effects. I say effects in the plural because I think there is more than one process at work here.

[Edited on 15-2-2019 by Vomaturge]
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Herr Haber
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[*] posted on 15-2-2019 at 04:22


Explosives give off light and sound.

https://en.wikipedia.org/wiki/Electromagnetic_spectrum

Not just the kind of pulse that will fry electronics.
I've never heard of an explosion near electronics that would fry it and not obliterate it. At least not in the atmosphere.
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Sulaiman
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[*] posted on 15-2-2019 at 06:00


I think that any emp from chemical explosions must be either
. so miniscule that the 1000's of military radio operators never noticed it
. such common knowledge that no one has given any thought to it




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[*] posted on 16-2-2019 at 13:08


Thank you all for the replys, and sorry VSPER, for being short....! Vomaturge. That’s helpful. Yes, it seems to be small enough that it does not interfere with equipment, or else we would certainly hear reports. I suppose I am more interested in how we can use this information to remotely determine VOD and other explosive parameters. I want to say it has something to do with plasma generation... and a study done by los alamos investigated tuning the explosive properties through external electric/magnetic fields. So far, the internet has failed me on this one.

But for any civil projects. Using antennas to ensure all the charges went off would really be a leap into another generation. Currently it’s too messy to do with siesmic waves, and those will not relay VOD... only the P-wave velocity of the rock. And agian we could use these remote sensing techniques to figure out what explosives our foes (Russia/China) might be using, we ccould detect the VOD from far. It should would be valuable to know if thier current HEAT warhead uses Cl-20 or triazole or just HMX...
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[*] posted on 16-2-2019 at 19:07


I was curious what if any are the mechanism or proposed mechanisms that generate the EMP. In air explosions apparently its asymmetries in charge separation at the surface of the fireball produced by the explosion. Similar to the mechanism that generates nuclear EMP.

Below is a snippet from the note referenced in one of the previous posts.

"The emission n of electromagnetic pulses from
chemical explosions was demonstrated almost 30 years
ago (Ref. 1-3)J. An explosion near the earth produces
a vertical electric dipole moment that varies on a
millisecond time scale (Ref. 4-10). It is thought to
be the result of charge separation at the explosion products/air interface and the asymmetry produced by
reflection of the shock from the earth (Ref. 11).
The frequency of this signal is consistent with the
time scale of the hydrodynamic development of the
fireball.
Higher frequency signals in the VHF and UHF
bands have also been observed (Ref. 12). Some of
these have been associated with the fragmentation of
the metal cases enclosing explosives. Others have
attributed electric signals to piezo-electric effects
in dielectrics (Ref. 13)."
Attachment: expemp.pdf (1.4MB)
This file has been downloaded 58 times




i am wg48 but not on my usual pc hence the temp handle.
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Vomaturge
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[*] posted on 16-2-2019 at 23:30


Thanks for uploading that, wg! Very interesting. What really struck me was that most of the signals were emitted at a time (12 to 100 microseconds, even milliseconds for some signals) when most or all of the charge was consumed. Of course, there could still be other earlier signals which would be more informative about the actual reaction rate.

I'm still confused how the expansion of a hot cloud of gas or the breakup of a metal case could generate a radio signal. It is well known that heating a gas can cause electrons to separate from atoms, but I always thought the electrons and positive ions would be more or less evenly dispersed, like the atoms and shared electrons inside a metal. I can understand how it would be different during a pulse of gamma rays, since gamma rays can have masses/energies greater than the rest mass/energy of an electron, and might transfer considerable momentum (that is, assuming photon's momentum is proportional to energy, and is transferred to electrons- I'm no Einstein when it comes to this stuff) If the gamma rays were coming from a source distant from the material being irradiated, then there could be a surge of electrons all moving away from the gamma source.

But with electrons inside the fireball of an HE, the electrons and positive ions should be all moving away from the burst point together. The individual charged particles may be moving around randomly due to their high temperature, but that should at most create blackbody radiation (mostly visible, UV, and near IR, as Herr Haber duly noted). all the electric fields are pointing in different directions, and you won't get a net voltage of the type an antenna could pick up. On a macroscopic scale, we don't have any moving charges, but rather merely an expanding electrical conductor. One of the few ways I can see this making an electromagnetic field are like this:

P_20190216_232933-360x640-144x256.jpg - 8kB

Prior to burst, the charge is surrounded by an external magnetic field (grey). When it is initiated, the cloud of conductive vapor, and/or the conductive case, expands and pushes against surrounding magnetic flux. It gets a circular current (red) induced in it, generating a secondary magnetic field (green) which opposes the passage of the ambient field. This effectively reduces the strength of the ambient field passing through the fireball, and forces it to increase within the immediate surroundings. This change in the ambient magnetic field would induce a pulse of current in other, stationary, nearby conductors (orange).

A similar process would involve the fireball shorting part of an ambient electric field, changing its intensity in much the same way. But neither of these can explain the fact that UHF signals are emitted, rather than a gradual change in voltage. Nor can the explain the component of the signal which stays the same even in an artificially enhanced electric or magnetic field. Perhaps the piezoelectric effect, or thermionic emissions from heated fragments, or something entirely different is responsible for those signals.
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[*] posted on 17-2-2019 at 02:37


On the a-priori assumption that a miniscule quantity of anti-matter may be produced during a significant explosion, it is possible that graded lengths (length corresponding to well defined and unique wavelengths/frequencies for remote identification) of crystaline 2(5)6 dilithium 2(:)l diallosilicate 1:9:1 heptoferranide, one crystal embedded per explosive package, would work, but I could not find a source or a practical synth.



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MineMan
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[*] posted on 17-2-2019 at 12:54


Sulaiman, could you expand on your point?

We and Vom. The article I referenced is regards to ANFO charges underground... so no fireball there....
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[*] posted on 17-2-2019 at 14:09


It's a Star Trek reference, probably commenting on excessive technobabble in my previous post. Buried charges may not form a visible "fireball", but they will still form a hot mass of gas,and it will still have to expand in order to fracture rock.

There must be some other 'early' signals, as in, not delayed by 100μsec, or they wouldn't be trying to measure VOD with it. A composition with 3 km/sec VOD burns 30 cm in 100μsec.
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[*] posted on 18-2-2019 at 02:05


Quote: Originally posted by Vomaturge  
... probably commenting on excessive technobabble in my previous post.
:D sorry, I could not resist the temptation :D

@MineMan "The article I referenced is regards to ANFO charges underground..."
If underground then there may be significant piezo-electrically generated signals due to shockwave compression of rocks ?




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[*] posted on 26-2-2019 at 18:51


All,

I was able to obtain a copy of the paper. It seems as if the industry and the authors are really still uncertain about the cause of the EMP. But they speculate is occurs due to molecular collisions at high tempatures behind the shock zone... the two most responsible molecules being N2+ and O2+

The EMP can be modeled by a changing charge quadrupole decaying in amplitude 1/r^4...

They were able to pick up VODs using antenna and oscilloscope as you probably could have guessed. They did not compare thier results with standard VOD test... which is upsetting. They tested a stick of emulsion but the VOD they reported seemed too low.
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