US Military Developing Laser Plasma Speakers

It probably won’t surprise you to know that the US military is very interested in using lasers as weapons. Directed energy weapons such as lasers have many advantages over more traditional kinetic weaponry, not least of which the fact that you don’t need to cart around ammunition for them. But somewhat surprisingly, some of the most promising laser developments have been in the field of non-lethal weaponry. While the mental image of a laser is usually a destructive one, recent demonstrations by the Joint Non-Lethal Weapons Program show lasers can do more than blow holes your target.

As reported by [Patrick Tucker] of Defense One, a radical new laser-powered sonic weapon was shown off at the “Directed Energy to DC Exhibition”. The system uses two lasers: one to generate a ball of plasma when it hits the target, and another to modulate the plasma ball in open air. The result is a variation of the classic plasma speaker demonstration, where plasma is used as a a driver for a massless speaker.

Currently the system is capable of generating a deafening crack at the target area, with a measured intensity as high as 140 dB. That’s about as loud as fireworks or a shotgun going off at close distance, and in theory is enough to drive off whoever is unlucky enough to be targeted with the beam.

In time, the researchers hope to refine their secondary modulation laser to the point that they can play audio over the plasma. This would allow the beam to be used as a directed loud speaker of sorts, which could prove useful for defensive applications. Only the target would be able to hear the audio, which could be a recording telling them they were entering a secured area. A disembodied voice telling you to turn around sounds like a extremely effective non-violent deterrent to us. The voices in our head don’t have to tell us twice.

We recently looked at the possibility of targeted sonic weapons being used in Cuba, and of course, we’ve covered many plasma speakers on Hackaday over the years. Plasma speakers have always been more or less nothing more than a fun high voltage demonstration, so to see them potentially weaponized is a crossover episode we weren’t expecting.

[Thanks to Kenny for the tip]

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Semi-Automatic Rail Gun is a Laptop Killer

It’s huge, it’s unwieldy, and it takes 45 seconds to shoot all three rounds in its magazine. But it’s a legitimate semi-automatic railgun, and it’s pretty awesome.

Yes, it has its limits, but every new technology does, especially totally home-brew builds like this. The aptly named [NSA_listbot] has been putting a lot of work into his railgun, and this is but the most recent product of an iterative design cycle.

The principle is similar to other railguns we’ve featured before, which accelerate projectiles using rapidly pulsed electromagnets. The features list in the video below reads like a spec for a top-secret military project: field-augmented circular bore, 4.5kJ capacitor bank, and a custom Arduino Nano that’s hardened against the huge electromagnetic pulse (EMP) generated by the coils. But the interesting bits are in the mechanical design, which had to depart from standard firearms designs to handle the caseless 6 mm projectiles. The resulting receiver and magazines are entirely 3D printed. Although it packs a wallop, its cyclic rate of fire is painfully slow. We expect that’ll improve as battery and capacitor technology catches up, though.

Want to check out some more railgun builds? We’ve got them in spades — from one with $50,000 worth of caps to a wrist-mounted web-slinger.

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Propane-Powered Plasma Rifle

It may not be a “phased plasma rifle in the 40-watt range,” and it doesn’t even use plasma in the strict definition, but it’s pretty cool nonetheless. It’s a propane-powered bottle-launching rifle, and it looks like a lot of fun.

[NighthawkInLight] sure likes things that go pop, like his watermelon-wasting air-powered cannon and cheesy-poof pop gun. This one has a little more oomph to it, powered as it is by a propane torch. The principle is simple: fill a soda bottle with propane, ignite the gas, fun ensues. The details are a little more subtle, though, and allowances need to be made to keep back pressure from preventing the projectile from filling with fuel. [NighthawkInLight] overcomes this with some clever machining of the barrel. The final production version in the video below is needlessly but delightfully complex, with a wooden stock and a coil of clear vinyl tubing helical plasma accumulator before the barrel; the last bit is just for show, and we have to admit that it looks pretty good.

Unless you count the pro tip on using CPVC pipe to make custom fittings, this one is nothing but fun. But we don’t have a problem with that.

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Unlikely Cascade of Failures Leads to Microwave’s Demise

Surely a blown light bulb can’t kill a microwave oven, right? You might not expect it to, but that was indeed the root cause of a problem that [mikeselecticstuff] recently investigated; the cascade of failures is instructive to say the least.

While the microwave that made its way to [mike]’s bench wasn’t exactly engineered to fail, it surely was not designed to succeed. We won’t spoil the surprise, but suffice it to say that his hopes for a quick repair after the owner reported a bang before it died were dashed by an arc across the interior light bulb that put a pulse of mains voltage in places it didn’t belong. That the cascade of failures killed the appliance is a testament to how designing to a price point limits how thoroughly devices can be tested before production runs in the millions are stuffed into containers for trips to overseas markets.

Even though [mike] made his best effort to adhere to the Repair Manifesto, the end result was a scrapped microwave. It wasn’t a total loss given the interesting parts inside, but a disappointment nonetheless unless it forces us to keep in mind edge-case failure modes in our designs.

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Custom Workstation Makes Plasma Cutting a Breeze

A plasma cutter is probably top of every metalworker’s short list of dream tools. From freehand curves to long straight cuts, nothing beats a plasma cutter for getting the creative juices flowing. Unfortunately, there’s also the jet of superheated metal blasting through the workpiece to deal with, which is the reason behind this shop-built plasma cutting workstation.

[Regalzack] looks like he had a couple of design goals in mind for his table. A solid work surface isn’t a great idea for plasma cutting, so he designed the top as a grid of replaceable steel slats. Underneath is a hopper to collect the slag, both for neatness and for fire safety. The table top and hopper live on a custom-built wheeled steel frame, and the lower shelf provides plenty of room for his Lincoln 375 plasma rig. With hooks for cables and a sturdy ground clamp tab, the whole thing is a nicely self-contained workstation. The video below shows the build and some of the fabrication techniques [Regalzack] used; we were especially taken by the clever way he cut the slots for the table slats.

Plasma is versatile stuff – you can use it to make music, cook a burger, or decorate wood. And it’s not too shabby for notching metal tubing either.

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Cooking With The Awesome Power Of Plasma!

There is something special about food that has been cooked in a grill, barbecue, or broiler. The charred surface brings both flavour and texture to the food, that other cooking methods fail to emulate. Of course, should you come from a part of the world in which the locals steam their hamburgers those are fighting words, but for [Robots Everywhere] the prospect of a flaccid patty cooked in a microwave oven was too much.

His solution? Broil the microwaved meat in double-quick time, using a plasma arc generated with a high voltage supply. The patty is placed in a grounded metal frying pan, and the high voltage probe is run over each side with accompanying plasma and sparks to lend that essential grilled exterior.

The power supply is a fairly simple affair, if a little hair-raising. A simple push-pull MOSFET oscillator drives a pair of flyback transformers whose secondaries are connected in series. It’s not the most efficient way to generate high voltages with a flyback transformer – the key is in the word “flyback” – but it generates enough juice for the job in hand.

It’s hardly the safest cooking method, and we’d be worried about contamination from whatever metal the electrode is made from. But it’s entertaining to watch, as you’ll be able to see from the video below the break.

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Little eBay Tesla Coil Gets an Upgrade

Like so many of the projects we feature, this one started with a cheap eBay module purchase. In this case, it was a little Tesla coil that made decent sized arcs but wasn’t quite good enough. The result was a super-sized solid state Tesla coil with better results and room to grow.

As [GreatScott!] discovered, the little eBay Tesla coil has a pretty neat design. The exciter is a Slayer circuit, a super simple one-transistor design. His reverse engineering revealed that the primary coil is simply a loop trace on the PCB under the secondary coil. Sadly, his attempt to replace the primary and reproduce the Slayer exciter resulted in anemic performance. What’s a hacker to do in that case except build a bigger coil? Much bigger — like “build your own winding jig” bigger. Twelve hundred secondary turns and an appropriately menacing-looking primary later, the results were — still anemic. It turns out the Slayer is just not up to the task. He turned to an inverter circuit that was previously used in a wireless energy transfer circuit, and we finally get to see a little of the Tesla coil magic. But wait! There’s more to come, as future videos will tweak the circuit and optimize the coil for better performance.

It’s no surprise that Tesla coils are a popular project around here, especially the musical kinds, from the tiny to the large. Music doesn’t seem to be on [GreatScott!]’s mind, though, and we’ll be watching with interest to see where he takes this build.

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