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After nearly two decades of war against technologically unsophisticated foes, the Army Research Lab is reorienting to counter China and Russia.
The Army Research Lab is turning more of its attention to fighting land wars against far more technologically sophisticated adversaries than it has in the past several decades. In the coming months, the Lab will fund new programs related to highly (but not fully) autonomous drones and robots that can withstand adversary electronic warfare operations. The Lab will also fund new efforts to develop battlefield communications and sensing networks that perform well against foes with advanced electronic warfare capabilities, according to Philip Perconti, who became the director of the Lab in June.
After nearly two decades of war against determined but technologically unsophisticated foes in the Middle East, U.S. Army tech has, in some ways, fallen behind that of competing states, according to a May report from the Center for Strategic and International Studies on U.S. Army modernization.
For instance, Russia has invested heavily in anti-access / area denial technologies meant to keep U.S. forces out of certain areas. "There are regions in Donbass where no electromagnetic communications—including radio, cell phone, and television—work," says the CSIS report. "Electronic warfare is the single largest killer of Ukrainian systems by jamming either the controller or GPS signals."
Source: DefenseOne.com
(Score: 3, Informative) by c0lo on Monday July 24 2017, @12:56PM (5 children)
Optimal? If suboptimal is still effective enough and cheap, one may want to escape the law of diminishing returns
Explosively pumped EMP - helical type [wikipedia.org]
But Ok. let's see about frequency tuning.
Suppose you have a coil with a single turn, in which a 10-100kA current flows, coil with a diameter of 5cm (around 2 inches) - think a slinky explosively formed as a a single turn coil.
What do you think happens when you section that circle (easy to achieve by putting a cutting notch at the end of the tube)? To my mind, that segment will act as a half-wavelength dipole, in the 30 cm wavelength (15 cm at half length) - that's 1GHz. Suppose now that you cut that single turn into 2 pieces - on equal length: 2GHz radiated frequency; if you cut it in unequal fragments, you get to tune the dipole to different frequencies.
Now, let's see what the "pulse" factor brings.
Suppose the initial multi-turn coil is 30 cm in length. Suppose that you "explosively pump" the EMP with the easiest explosive you can get you hands on - ANFO [wikipedia.org], high speed explosive - 3,200 m/s velocity. At this speed, 30 cm coil will be compressed down in a single turn in 10usec. The cited says 20% efficiency transformation between explosive energy=>current (that is magnetic field). I'll assume 0.5kg of ANFO - with a specific energy of 3MJ/kg [dynonobel.com]. So you have 20%*3e6J/10e-6s/2 = 3e10W.
The problem of computing a Fourier spectrum of a pulse raising in 10usec and decaying in, say, 2-3 times longer is left an an exercise to the reader (if you take a gaussian, the fourier transform is also a gaussian). Due to the short raise rime, it is expected that high frequency components will be present with significant enough coefficients.
With a total power of 3e10W and assuming a distribution of power over the frequency spectrum proportional with the Fourier coefficient, one has a hunch that the microwave component will transport enough power at a distance of 200-300m to fry a receiver prepared to deal with signals in the 0.1W (you will need a Fourier coefficient as low as 10e-6 to fall under 1W of power).
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 2) by BsAtHome on Monday July 24 2017, @01:12PM (4 children)
The major problem is that it is predominantly a "magnetic pulse". That means there is quite a lot of energy that goes lost because the EM fields are not coupled nicely at the right frequencies. It is true that, ahem, quite a bit of energy will be released, and, many receivers will be fried. However, considering (semi-)military grade means a lot of energy has to be directed at the target at a rather narrow band. You will need a nicely coupled EM field for optimal effect (i.e. better absorption by the target). Converting the magnetic pulse into a narrow-band EM field can be done (use a resonator cavity that survives the blast) and it would make the device ever so more devastating for nearby receivers.
(Score: 2) by c0lo on Monday July 24 2017, @01:49PM (3 children)
What's wrong with dipoles oscillating at high currents for tuning the frequency post initial raise pulse?
Segment the single turn coil at the "exit" of the exploding tube in lengths of appropriate values.
Yes, further tuning will increase the efficiency, but will drive the "solution" outside low-tech domain.
See vircators [wikipedia.org]; maybe of special geometries [radioeng.cz]
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 2) by BsAtHome on Monday July 24 2017, @02:38PM (2 children)
Nothing is wrong with a dipole. But, it has a problem not being able to convert the wide-band energy to small-band efficiently.
The "special" geometries are actually relatively easy to make. They basic idea is that you have a (virtual) cavity which gets pumped. It is all about using the right materials and especially the right sizes. You could make one with kitchen stuff.
I do agree with you that "low-tech" is the quick-and-dirty way. That said, with just some small thoughts you can do much better and broader destruction.
And, for my home-tests, I'd rather not have to blow up my kitchen every time I test a device ;-)
(Score: 2) by c0lo on Monday July 24 2017, @09:28PM
:)
That was an exercise of engineering thinking.
By no means an advice on how to build a low-tech EMP, much less a suggestion that anyone should build one.
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 2) by bob_super on Monday July 24 2017, @10:56PM
> And, for my home-tests, I'd rather not have to blow up my kitchen every time I test a device ;-)
An anonymous tipster only known as Kim J recommends building various self-propelled aerial devices so that you can safely discard experiments into the nearest sea.