Anybody remember Plasmagnetic Levitation by Hovertech? It was supposed to be a levitation technology that used a UV laser to ionize the air underneath the vehicle and then an alternating magnetic field to repel this cold plasma downward, imparting an upward force to the vehicle.* The same technique is used in "mass driver" devices some hobbyists have built, where a capacitor bank is dumped through a pancake coil, launching a hard drive platter or similar object placed against the coil into the air. The theory is apparently that the magnetic field induces a current in the conductive medium (plasma or hard drive platter), which then generates its own magnetic field, opposing the applied one. These opposing magnetic fields result in repulsion. It seems to me that this is just like electromagnetic braking but with the roles and action reversed.
My idea here is to use that repulsion to repel incoming bullets. I'm imagining a shield similar in shape, size, and probably material to the ones used currently by SWAT teams (so it's still usable to block any bullets it fails to repel, or in case it stops working) with embedded coil(s) and capacitor bank(s). It also has a pulse doppler radar module built in —these are cheap (tens of dollars) now. When the radar detects an incoming bullet (by how it dopples the radar return), it waits for it to get close enough (by radar pulse time of flight) and then fires the repeller. Hopefully, this results in the bullets dropping to the ground in front of it. I don't expect it to be strong enough or aimable enough to usefully throw the bullets back at the shooter, but maybe if it was mounted on a robot arm or similar (or could control the user's muscles) this could be attempted.
The expected advantages over a passive shield that absorbs bullets' kinetic energy with its material are: - Doesn't wear out as seriously. (The capacitors will wear out, but they can be replaceable. With a regular shield, it might wear out in one spot while still being fine elsewhere, but at least with some types I expect you have to replace the whole thing.) - Slows the bullets more gradually, reducing the peak force applied to the user's hand and arm, reducing fatigue, or to the stand if used stationarily, reducing the risk of toppling and/or enabling the stand to be lighter. - Stops the bullets without deforming them, enabling easier forensics on them. - Might (conceivably but I don't know if even theoretically) be able to recover energy from the bullets to recharge its battery. - Might be lighter, and can more easily be transparent or even open in the middle, if you're willing to forgo some passive protection.
It could also conceivably be built into body armor, vehicle armor, building armor, etc.
N/A [probably around 2006–2007]
*That was how I understood it, anyway. But PL apparently evolved from their earlier ferrofluid levitation technology, which used a hollow cylinder of ferrofluid contained by a magnetic field to contain a column of pressurized air that supported the vehicle's weight. So maybe PL was supposed to work that way too, just with plasma replacing ferrofluid.-- notexactly, Mar 18 2019 Gunfire-activated electromagnet By [Voice]. The idea that prompted me to post this idea after so many years [notexactly, Mar 18 2019] Electromagnetic Reactive Armor By [paru]. I found it while browsing the armor category and thought it might have been the same idea, but it's not. [notexactly, Mar 18 2019] Myth: Busted http://www.discover...tic-deflect-bullet/Not happening with a small electromagnet. [James Newton, Mar 21 2019] Physics be damned!-- James Newton, Mar 21 2019 I think a shield is generally considerably larger than a wristwatch. Also, I'm imagining the bullets approaching the shield head-on, whereas with the watch, it sounds from the description that they might be flying past it—I can't watch the video right now.-- notexactly, Mar 24 2019 I could be wrong but an electromagnet capable of either magnetically or dia-magnetically repelling a bullet in flight would be powerful enough to either pull the iron from your blood and amalgam from your fillings or pop you like a grape as the water tried to exit your relatively stationary body.
Like I said, I could be wrong, but I don't think so... you're going to need a small nuclear power plant to generate that much electricity and I don't think you'd want to be around when the capacitor discharges that much power.
The bullet might miss you... but you'd literally be toast.-- 2 fries shy of a happy meal, Mar 24 2019 I have doubts that this could possibly work, but hereis an alternative:
Fast computers and cameras calculate the bullet's trajectory; only those bullets likely to reach a target are singled out for EM efffects.
Bullets, or perhaps miniature whiffle balls,or expandable trees (pointy end first) are then fired at the other bullets, striking them and changing their trajectory to something less likely to hit the target.
I think this is obvious enough to have been researched previously.-- beanangel, Mar 24 2019 random, halfbakery