7 ms·

The Active Denial System, listed on your link, causes pain by heating water in the skin. What is the proposed system for getting microwaves past the skin into

The Active Denial System, listed on your link, causes pain by heating water in the skin. What is the proposed system for getting microwaves past the skin into the brain without creating the same effect as the ADS?

bmicraft 6y ago
Using longer wavelengths should do exactly that.
- vermilingua 6y ago
  But do longer wavelengths act on water in the same way as microwave?
  - fzzzy 6y ago
    They act on systems of distributed induction and capacitance which are resonant to that longer wavelength.
- truth_ 6y ago
  Or longer frequency i.e. shorter wavelength?
- shawnz 6y ago
  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?
  - fouric 6y ago
    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.
- Jenda_ 6y ago
  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.
nabla9 6y ago
Using the same frequency range as your home microwave does.
- jeltz 6y ago
  Which would be very painful when it heats the skin.
  - nabla9 6y ago
    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.
    - ben_w 6y ago
      MythBusters tested that, the outsides (of food) heat up first.
      - kragen 6y ago
        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 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.
smolder 6y ago
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? [0] https://en.m.wikipedia.org/wiki/Sound_from_ultrasound https://en.m.wikipedia.org/wiki/Sound_from_ultrasound
- akiselev 6y ago
  > 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. [1] https://en.wikipedia.org/wiki/Phased_array https://en.wikipedia.org/wiki/Phased_array
  - na85 6y ago
    I have dinner plates that are larger than the phased array under the nose cone/radome of the C-130 Hercules or the 737. Phased arrays can be very small.
    - akiselev 6y ago
      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.

bmicraft 6y ago

Using longer wavelengths should do exactly that.

vermilingua 6y ago
But do longer wavelengths act on water in the same way as microwave?
- fzzzy 6y ago
  They act on systems of distributed induction and capacitance which are resonant to that longer wavelength.
truth_ 6y ago
Or longer frequency i.e. shorter wavelength?
shawnz 6y ago
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?
- fouric 6y ago
  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.
Jenda_ 6y ago
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.

nabla9 6y ago

Using the same frequency range as your home microwave does.

jeltz 6y ago
Which would be very painful when it heats the skin.
- nabla9 6y ago
  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.
  - ben_w 6y ago
    MythBusters tested that, the outsides (of food) heat up first.
    - kragen 6y ago
      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 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.

smolder 6y ago

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? [0] https://en.m.wikipedia.org/wiki/Sound_from_ultrasound https://en.m.wikipedia.org/wiki/Sound_from_ultrasound

akiselev 6y ago
> 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. [1] https://en.wikipedia.org/wiki/Phased_array https://en.wikipedia.org/wiki/Phased_array
- na85 6y ago
  I have dinner plates that are larger than the phased array under the nose cone/radome of the C-130 Hercules or the 737. Phased arrays can be very small.
  - akiselev 6y ago
    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.