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I got inspired by reading all about the Directed Energy Weapon programs.

What would happen if you could crank up this concept to eleven?

Please assume energy is not a problem. You have 'superbatteries' (please consider energy not relevant for this question).

They are powering a handheld microwave gun, about the size of an assault rifle. The power output should be several orders of magnitude higher than current DEW systems.

  • with energy out of the way, would this size be feasible for a really powerful gun?
  • Is it possible to focus microwaves into a rather narrow 'beam'?
  • With abundant energy, what is the effect of microwaves on human body, armored or naked, on tanks, buildings, etc.?
  • When maintenance / resources are not relevant, would this gun be really more useful than a modern assault rifle?

Edit after first answer:

  • I am looking for really advanced stuff (hence the sci-fi tag), not today's technology level
  • Is enough energy able to overcome the metal and water weakness (as in thucydides answer) of microwaves or is that just a physical limitation?
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  • $\begingroup$ "a rather narrow 'beam'?" microwave is a form of light, so it would be a laser in literally every way. $\endgroup$ – Mooing Duck Oct 7 '16 at 23:40
  • $\begingroup$ I don't know much, but I don't think microwaves would make good weapons, sitting right between radio and red light. You probably want the other end of the electromagnetic spectrum: ultraviolet, xray, and gamma rays. Now those are dangerous. $\endgroup$ – Mooing Duck Oct 7 '16 at 23:45
  • $\begingroup$ Also see: en.wikipedia.org/wiki/Directed-energy_weapon $\endgroup$ – Mooing Duck Oct 7 '16 at 23:51
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    $\begingroup$ Just want to point this out, microwaves tend to disperse quite rapidly if memory serves right. If you got a strong enough microwave dispersal, you probably would not get a beam but rather a giant wall of microwaves. Changes are, it would serve more as a flamethrower type thing than a laser gun. $\endgroup$ – The Great Duck Oct 8 '16 at 4:03
  • $\begingroup$ Hard to be sure but you might be asking about a portable maser (precursor to lasers). Not used much for weaponry, but have been superb for very long range communications. $\endgroup$ – user2338816 Oct 8 '16 at 4:12
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The US Army has the "Active Denial System", which is a truck mounted microwave projector that should serve to illustrate the effects such a weapon would have.

The ADS uses a large projector to send a beam of microwaves at 95 GHz at the target. This wavelength was chosen since the ADS is a non lethal system and the high frequency beam only penetrates @.04mm into the skin, while a conventional microwave beam (such as a microwave oven) can penetrate to a depth of 17mm. The effect is reported to "feeling like you have been set on fire" when volunteers are exposed to the beam, and the feeling reportedly ceases when you exit the beam. Crowd control and dispersal is the goal of this system and people fleeing the effects of the burning sensation would stampede the crowd away from the projector.

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The illustration demonstrates one of the issues with beam weapons of any sort (including lasers), the need for some sort of focusing optics to aim the beam at the target. Since microwaves are much longer than optical wavelengths used in laser weapons, the ADS has a correspondingly larger emitter. A hand held microwave weapon would have to have a large "dish" on the front in order to be effective, with obvious effects on soldier performance trying to move tactically with a large dish to project the microwave beam.

Microwaves are also affected by the atmosphere (like lasers as well), with the particular issue that microwave beams are easily absorbed by water (which is how microwave ovens work, after all). Rain, mist and even high humidity would affect the propagation of the beam. Finally, microwaves are absorbed or reflected by metal. Putting a spoon in a microwave oven demonstrates the effect when the emitter is close by, but metal mesh woven in the fabric of uniforms or even the proverbial "tin foil hat" will serve to protect the target from microwave beams.

Microwave weapons could have a place on the future battlefield, both as crowd control/crowd dispersal devices in urban environments and in COIN operations, and perhaps more importantly, as anti air devices to disable enemy drones and UAV's by interfering with the control signals.

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    $\begingroup$ The real hazard of using microwave weapons is that, sooner or later, somebody's going to show up on the battlefield with a corner reflector. $\endgroup$ – Mark Oct 7 '16 at 20:10
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    $\begingroup$ Someone showing up prepared for the ADS is demonstrating premeditated hostility; lethal response would soon follow. $\endgroup$ – Ghillie Dhu Oct 7 '16 at 22:33
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    $\begingroup$ Shooting at people wearing tin foil hats is a huge PSYOPS loss for your side....ROE's will have to be carefully thought out and easily interpreted by the soldiers in the field. $\endgroup$ – Thucydides Oct 7 '16 at 22:40
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I will focus on just one aspect of your question.

The ability to focus a microwave depends on the size of the "lens" (reflector) compared to the wavelength. If you intend to use the wave to "cook the enemy", you will want to use a frequency of a few cm (the shorter the wavelength, the more local the damage will be to the surface). But the problem is that you will need a very large dish to get a sufficiently focused beam. The angle (in radians) of spread of the beam is a result of diffraction, and roughly given by

$$\alpha = 1.22\frac{\lambda}{d}$$

where $\lambda$ is the wavelength and $d$ is the diameter. So if you want to focus the beam to a point the size of a head (20 cm) at a distance of 100 m, for a wavelength of 3 cm (10 GHz) you would need a diameter of 6 meters. Not really "hand held" any more. Make the wavelength shorter, and you will have less ability to penetrate (you would take off the skin, but not kill).

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  • $\begingroup$ Now you have me curious about the other end of the spectrum. How hard would it be to focus XRay weapons? $\endgroup$ – Mooing Duck Oct 7 '16 at 23:44
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    $\begingroup$ @MooingDuck there is a thing called an X-ray optic that works OK with soft X-rays - used for some astronomy applications. It uses very low (glancing) angle incidence, concentric structures. The problem with X-rays is that the refractive index of matter is very close to 1.000 for them, so no good refractive lens exists; and the wavelength is too short for reflection except at glancing angles. So - pretty hard. $\endgroup$ – Floris Oct 7 '16 at 23:49
  • $\begingroup$ Of course, the atmosphere is also opaque to X-rays as well. $\endgroup$ – Thucydides Oct 8 '16 at 1:44
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The military is looking into a hand held MW weapon in the near future.

"While larger devices will be mounted on ground or air vehicles, some smaller devices will be hand held.(79)"[1]

 

"The real question is what all these technological developments mean for future warfare. To try to answer this question as completely as possible, we will look at a future scenario in the 2020-2030 timeframe."[1]

 

"Finally, the size of microwave weapons will depend upon the target, delivery application, and desired effects, and thus microwave weapons are well suited for covert military operations. It is conceivable that “hand-held” missions could employ a system that weighs less than ten pounds."[2]

References:

[1] Geis, John P. (2003, April). Directed Energy Weapons On Battlefield: A New Vision For 2025. Retrieved (2018, Oct. 4). dtic[mil]. Available from: http://www.dtic.mil/dtic/tr/fulltext/u2/a463429.pdf

[2] Walling, Eileen M., High Power Microwaves; Strategic and Operational Implications for Warfare, Center for Strategy and Technology Occasional Paper 11, Maxwell AFB, AL, p. 7. Available from: https://pdfs.semanticscholar.org/f579/e74e39dbe7ac33a952c8c3c2382426e93f13.pdf

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You could not use a conventional focused microwave beam because you'd need a very large antenna dish to do that. Granted, you could imagine a nanotech dish deploying very quickly when shooting - sort of a large umbrella opening. But that's unwieldy.

You would need very advanced metamaterial technology to build a linear, room-temperature MASER amplifier in the shape of a barrel. Once you have that, you also need very efficient transducers and very powerful supercapacitors (you can do with current technology but you need a handle like a battery drill and God's own heat exchangers, or large parts of the device would melt or catch fire).

Finally you're left with Flash Gordon's ray gun: a pencil-thick MASER beam that will cook anything in its path, unless protected by a conductive shielding. Given that there'll be Joule energy transfer, the shielding can't be just aluminum foil, you need something like copper (or even better, silver) mesh chain mail.

In practical terms it's not very much better than a bullet gun, and in several ways, it's worse, except perhaps somewhere you can't risk perforation damages or splinter ricocheting:

  • the weapon is line-of-sight, very much like a bullet gun.
  • no traces are left except on the victim - no powder smears, gases, spent cases or anything - and the noise is probably reduced. Unless the MASER bolt triggers some kind of sonic boom, not unlike the thunder from a lightning discharge.
  • it can only shoot a few shots before you need a fresh battery (magazine).
  • the range is limited. Not affected by wind and droop; but fog, rain and heat haze might be an issue.
  • shielding is much easier than against a solid bullet

On the other hand, time to target is negligible, so you could have some kind of friend-or-foe autotargeting system and actually make it work.

Also, shape recognition could allow "impossible" shots - just wave the gun in the general direction of the target, and, provided it ever gets aligned, even for a millisecond, the gun could successfully shoot the victim through an eye. Defensive shields could feature wide-spectrum face simulations to thwart this approach, though.

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