h a l f b a k e r yExpensive, difficult, slightly dangerous, not particularly effective... I'm on a roll.
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This device, mounted on a backpack, would use radar to detect bullets and shock waves therefrom. A computer would analyze trajectories. Bullets not directly bound for the user would be ignored. For anything over half a second away an audible alarm may let the user move enough to save himself. For anything
temporally closer intense direct nerve simulation could be used instead, causing the user's muscles to contract, altering the physical position of the user and hopefully saving his life.
A more sophisticated version could also try to move the user in one direction or another such that incoming bullets aimed at something vital would at least hit something less vital.
US 2013/0021195
https://patents.goo.../US20130021195A1/en
[xaviergisz, Dec 11 2020]
Doppler effect
https://en.wikipedi...wiki/Doppler_effect
Determines frequency shift depending on relative velocity. [8th of 7, Dec 11 2020]
And just in case you cannot ...
No_20Pain_2c_20No_20Drain_20Body_20Armor
[normzone, Dec 11 2020]
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// radar ... half a second // |
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For a 5.56mm round, the velocity is about 900m/s. |
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For a half-second warning, your radar needs to detect a target with a frontal area of about 25mm^2, but an ogival form which will not return much of an echo, because of its angles - at a range of 400 - 500m. |
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There will be a lot of ground clutter, so significant processing power will be needed. |
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So you're going to need extraordinary amounts of millimetric microwave energy, and don't forget that the echo is 1/X^4 ... so a highly sensitive receiver. |
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To be useful, the detection field needs to be radially isotropic; multiple phased-array emitters on the headgear ? Compensated for tilt ? |
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How long do you need to track it for to get a hit/no-hit determination ? Assume that a human is a 1m x 2m target ... at 500m that represents about 7 minutes of arc. Though "a miss is as good as a mile", exquisite accuracy will be needed to determine if the path of the projectile will intersect that 2m2 sweet spot - how many plot points, at what accuracy, will be needed ? |
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If your human target is moving, in the erratic pseudo-random way that humans usually do, then that adds to the fun. |
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Let us know when you're ready to test; we promise to keep the change lever at "R" ... |
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I can dodge bullets some of the time, if they're
thrown at me quite gently |
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You won't object if we determine an exact quantitative value for "quite gently" by experimental means ? |
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//thrown at me quite gently// Easier to dodge them if they are just placed on the ground. |
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H-how did you do that Neo? |
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Well, you place the bullet on the ground, and then you very carefully walk around it without touching it. |
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//radar to detect bullets and shock waves// |
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The shock wave is no good to you at all. Most bullets will
pass through you before the shock wave is detectable,
that's the thing about supersonic speed. Even subsonic
bullets are close enough to the speed of sound they'd
leave you with no time to react. |
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//There will be a lot of ground clutter,// |
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The thing about bullets, their main distinguishing feature,
is they zip around at high speed. The bullets you're
interested are moving toward you, so a prime application
for looking at the Doppler shift. A big advantage of that is
that you don't need to switch between transmit and
receive. You can transmit and receive simultaneously,
which should help somewhat with the time resolution. |
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You could theoretically use the Doppler shift to
determine the hit likelyhood. If the bullet is headed right
for you, it's Doppler shift will be in the highest range for
that type of ammunition. AND the Doppler shift will only
fall off because the round is losing velocity. If the round
is missing, the Doppler shift will fall because of speed and
angle change. |
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//extraordinary amounts of millimetric microwave
energy,// That should discourage people getting close in
the first place. |
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Well clearly what you need to do is to look at the bullet, and
if it is .0002% slightly blue-shifted, then you should worry
about dodging. |
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You dropped a few zeros, [RayfordSteele]. Here you go. 0000000 0000000 0000 |
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// theoretically use the Doppler shift to determine the hit likelyhood. // |
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Theoretically, yes; but ... |
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If the projectile is likely to be a hit, then it's coming "straight on", and the physical form is going to mean that it scatters energy sideways rather than forwards - so the closer to a hit, the lower the return energy. |
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As to angle, the nearer to a hit the smaller the angular change. If the angular change is large, fair enough, it's going to fly by; but to discriminate between a very near miss, and (at best) a nasty flesh wound will be very difficult. |
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And yes, shock waves. So obviously irrelevant that we didn't think it worth mentioning. |
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//You dropped a few zeros.// |
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No, I didn't. 3e8 m/s is 428,571 times as fast as a 700 m/s
bullet. If the bullet is flying towards you, then the wave is
compressed by that 700 m/s, or 1/428,571, which is 2.3E-6,
or 2.3E-4%, or 0.00023%. |
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Percent faster is not the same as percent blueshifted. |
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The speed of light is approximately 3.0E8 m/s. 600 m/s is .000 002, or .0002%, of the speed of light. |
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Inscribe the word 'WORK' on the tip of the bullets. Some
people will AMAZE you with their dodging abilities. |
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^^Quite; and as V<<C, the approximation applies. On this occasion, [RayfordSteele] is entirely correct. It had to happen eventually. |
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I was mistaken, and I'll be mistaken again. |
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Not if you're mistaken about the bullet missing you... |
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// It had to happen eventually. // |
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That's just the Blue Whale effect... |
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Unlike me. I'm always correct, but no-one believes me. It's an Alan Davis - Cassandra type situation. |
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// I'm always correct, but no-one believes me. // |
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Yes, it's tough, isn't it ? We share your pain, Brother ... |
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Don't worry, I believe you. (See what I did there? Mwa ha ha ha! <Dons black cape, twirls moustaches, fetches small round bomb>) |
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<Proffers much larger round bomb clearly labelled BOMB in white block capitals, with disconcertingly short length of fuse./> |
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"The boy's a fool, Moriarty." |
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Thinks: Yet another week where Blunebintle gets dedded by the Dreaded Dynamite ... |
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And with just a jot of math, more of my enemies have turned
on each other. My work here is complete. |
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