2.4 GHz is used to heat your food in the microwave. Pulses that increase the fluence by an order of magnitude or more could probably boil water for a microsecond inside the brain and cause some strange reactions.
What is unproven though, is how one would ever shrink the size of an electronic weapon like this.
Hopefully not bothering anyone with my wild speculation and incomplete physics knowledge here...
Could it be there is some way to target a location with multiple radio beams such that the damaging effect occurs at the point of interference? Maybe just constructive interference from multiple weaker beams? Something like this would need to be aimed precisely of course.
I was further led to thinking about the way you can generate sound at a distance from beams of ultrasound. [0] Either the fluid within the beam or an object struck by the beam acts as a demodulator. I don't really know if something like this could apply with radio.
The other thing that I thought of was the way microwave ovens excite water molecules specifically. Maybe there is some other wavelength or combination of them which excites other specific molecules or structures present in the brain?
> Could it be there is some way to target a location with multiple radio beams such that the damaging effect occurs at the point of interference? Maybe just constructive interference from multiple weaker beams? Something like this would need to be aimed precisely of course.
Yes, a phased array [1], which is likely what the GGP was referring to by "What is unproven though, is how one would ever shrink the size of an electronic weapon like this."
Advanced radars work by creating a concentrated beam of RF with constructive interference and scanning it across the sky, but the installations are huge. A smaller directed microwave weapon would be meters across, hard to hide, and noisy.
Source? I don't know of any plane that have a proper phased array - the only one I know of is the Airborne Phased Array Radar and that's still a WIP.
Note that just putting a couple of antennas close to each other to improve angular resolution on the radar isn't really a phased array in the sense that we're talking about.
Have you noticed how microwave cooking is not warming up the skin any faster than the insides? The wavelength is selected so that it penetrates and warms water molecules. It would cook your insides according to their water content.
Surface of the skin has less water than tissue inside, so you would feel pain beneath the skin.
MythBusters notwithstanding I have an RF burn on one of my fingers that was barely visible at the surface when it happened but which totally cooked the tissue up to about 6 millimeters inwards. It's a pretty weird spot, 2.5 mm across and even 35 years later it hasn't healed, the zone is simply dead to the touch even though the flesh has recovered. You can also still see exactly the shape of the original burn.
Note to self: pay attention when trimming HF transmitters about where you keep stray digits and where the locations of the tops of trimmers are relative to those digits.
The fact that reverse thermal gradients are often present in microwave thermal processing of materials is quite well known and can be replicated in food in your home microwave, precisely as nabla9 said, regardless of Mythbusters being able to produce a forward thermal gradient.
Microwaves attenuate as they penetrate a resistive or high-permittivity substance, because they deposit some of their energy as they pass through. In the limit of infinite depth, no radiation survives and there is no heating. Given a homogenous substance, the heating is always strongest at the surface, decaying exponentially (to a good approximation) as you go deeper.
However, heating is not the same thing as temperature. The surface of food in your microwave is exposed to room-temperature air and can therefore cool down by conducting its heat to that air. Food just under the surface can conduct its heat to the surface food, while deeper food cannot. It's easy to set up situations where this results in a reverse thermal gradient penetrating some distance into the food, or even all the way to the center. This is one of the most significant advantages of microwave heating in industrial material processing, because there are many cases where the normal thermal gradient produces cracking and microwave-induced reverse thermal gradients do not.
You can set up a forward thermal gradient with microwave heating by some combination of hot air, strong attenuation, short exposure times, shorter wavelengths, and great depth, although unless the air is actually hotter than the highest temperature reached within the food there will always be a reverse thermal gradient present at the surface, since the heat equation always produces a continuous temperature field at t ≠ 0. You may be able to get the reverse thermal gradient to be entirely outside the solid body if you work hard enough, but a much easier way is to only measure the temperature at intervals large enough that the entire reverse thermal gradient is smaller than the first interval. For example, if the thermal maximum is 8 mm under the skin, you could measure the temperature at the surface, 1 cm, 2 cm, 3 cm, 4 cm, and 5 cm.
The attenuation is dependent on the attenuating medium and on wavelength. As explained in https://en.wikipedia.org/wiki/Active_Denial_System the ADS uses 95-GHz radio waves with 0.4-mm penetration depth in human flesh, while your microwave oven used 2.4-GHz radio waves with 17-mm penetration depth in human flesh.
nabla9 has been downvoted for politely and straightforwardly, if briefly, explaining these perfectly correct and verifiable facts, facts which are central to the discussion. This makes it clear that the voting public at HN has extremely poor judgment and should not be permitted a vote on comments of decent people.
I'm not sure why my sibling is downvoted. See for example page E-17 of this manual
> When the radar transceiver is energized, it poses a microwave radiation hazard to personnel. The hazard distance for the Q-47 is much greater than the distance for the Q-37. The hazard distance for troops extends in front of the radar for 217 meters over the radars full 1600-mil area of scan. The radar also poses a hazard for electrically detonated explosives. Figure E-14 depicts the radar’s radiation hazard area.
I think your sibling is [dead]ed (not downvoted) because it is posted by a shadowbanned account (see their comment history of posting a lot of content-free flamebait: https://news.ycombinator.com/threads?id=JarlUlvi&next=166198...) and not enough people have vouched for the comment.
IIRC workers in front of radar antennas noticed chocolate bars melting in their pockets during WWII, and that observation inspired the development of microwave ovens. Not sure how long it took for people to realize that their internal organs were doing something similar to the chocolate bars...
Yeah this is why I usually get better results a 70% or so setting rather than 100% as it gives the heat a chance to spread a bit better than nuking at full power.
> Have you noticed how microwave cooking is not warming up the skin any faster than the insides?
No. Microwave hot pockets are famous for coming out boiling on the outside, cold on the inside (if you don't let it sit for a couple minutes to equalize).
How would that achieve what the other poster is saying, which is to heat the insides more than the surface? Wouldn't that just heat both the insides and the surface more evenly?
Even if this was the case - the insides and surface of the human body have rather different characteristics, with the inside being more sensitive to, well, just about everything than the surface.
Longer wavelengths require huge antennas to concentrate the energy at a distance. It would be probably very difficult to perform this attack. I also think that such energy density with relatively low frequency (~3 GHz) would disturb operation of computers, phones and other electronics, so it would be pretty suspicious.
Microwave transmitters are not that big. 4 kW generator or 100 kW pulse generator fits into a suitcase.
What you need is a horn antenna that directs the beam from the distance, across the street for example. It's also possible to have multiple horns around the target. Only in the intersection of the beams the radiation reaches dangerous levels.
Horn antennas have radiation pattern tens of degrees wide, so it's difficult to target one room across the street. I'm not sure intersecting a few of them helps, maybe by a factor of two or so.
Back of the envelope math: per Wikipedia: "The gain of horn antennas ranges up to 25 dBi, with 10 - 20 dBi being typical." Let's say you are transmitting 4 kW with a 20 dBi horn, thus having 400 kW EIRP. At a distance of 15 meters, the energy spreads across a sphere of 4PI15^2 = 2800 m^2, for an energy density 140 W/m^2. So yes, this indeed exceeds health limits (in .cz: 50 W/m^2 for workers, 10 W/m^2 for civilians) and is kind a lot.
On the other hand, having a 400 kW EIRP source anywhere nearby should be immediately obvious to a NSA or probably anyone with almost any radio receiver, the interference would be terrible.
> On the other hand, having a 400 kW EIRP source anywhere nearby should be immediately obvious to a NSA or probably anyone with almost any radio receiver, the interference would be terrible.
This was exactly my thinking, somebody in the local area surely would have noticed this thing was turned on. You're not going to dump 400kW of energy without screwing with something.
> So yes, this indeed exceeds health limits (in .cz: 50 W/m^2 for workers, 10 W/m^2 for civilians) and is kind a lot.
Is that an enormous difference? It's three times health limits - but how long would you need to hold it there to get health problems? My guess is quite a while to fry your noodle?
Advanced problem: how do you avoid accidentally killing someone while targeting this?
You're just talking about shooting "at" someone's head, you're talking about positioning their head in 3D space and shooting so precisely (through potentially layers of brick, metal brick ties, lath etc.) that you hit only inside their head and don't leave any marks or burns on the skin.
We don't have the technology to reliably do this today at range.
Use radar for targeting. WiFi has been used to see peoples bodies through walls, 10GHz has been used in radars, the same beam that destroys can be used to image the target. You may not even need to do imaging, just look for resonance or increased energy absorption to indicate the beam is on target.
Beamforming is a solved problem, using the interference of multiple antennas' energy to resonate at exactly the right location for maximum strength. Why do you think this technology isn't reliable?
Because you are trying to hit a 15cm by 15cm sphere in 3D space that you cannot see.
That it could maybe be done under ideal conditions doesn't explain how you do it when the target is mobile (but let's be generous and say you assume they're in bed), and you need to accurately visualize where they are through an unspecified amount of intermediate interfering elements (people's bedrooms aren't glass boxes).
Foil wall insulation would disrupt an attempt at microwave beamforming - so how is targeting being achieved so precisely as to be undetectable and cause no other environmental effects?
That's not the point: it's the "undetectable" part that's the problem.
You could definitely point a bunch of microwave equipment at someone's room and cause some damage, that's not in question - but to somehow cause a bunch of neurological problems, but not leave thermal burns, or heat up jewellery, or fry electronics?
And this isn't a "with todays tech" issue either. This is all being proposed as being totally possible with 90s-era technology. The sheer amount of wireless tech innovation and availability since then has been enormous - what feels possible today is ignoring that in the 90s a cellphone looked like a brick with an antenna on it. Solid-state microwave elements weren't COTS parts you bought from China in bulk.
We're talking about doing a lot of very difficult to do things, with equipment and power outputs which would require substantial draw from either residential electricity supply systems, or banks of lead-acid batteries (no lithium ion in that age either - so you have a transport and weight problem).
The more disperse you propose the signal is, the less plausible it gets too - at some point your number of field teams and the size of the equipment is going up and up and up and all of this is happening within line-of-sight (or near enough) of a target - microwaves don't penetrate multiple buildings.
Do you have any sources regarding the effect of pulses, e.g. in animal studies? Most materials I have found are dealing with average/CW power. (I work with weather radars, so I was doing some research recently to find out what I should do to not die)
IIRC The pressure inside the eyeball is relatively high, and the fluid that is inside is very viscous - more like a gel. This could mitigate the effects.
I think it is the other way round. I saw this discussed for microwave from mobile phones, so no movement of fluids makes excessive heat more dangerous.
https://en.m.wikipedia.org/wiki/Directed-energy_weapon
2.4 GHz is used to heat your food in the microwave. Pulses that increase the fluence by an order of magnitude or more could probably boil water for a microsecond inside the brain and cause some strange reactions.
What is unproven though, is how one would ever shrink the size of an electronic weapon like this.