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A wild shrimp inspires a robot claw that shoots plasma



The Pistol shrimp, also known as the snapping shrimp, is a peculiar contradiction. With only a few centimeters in length, he has a proportionally large claw and another, which engages with such a force that the resulting shock wave beats their prey cold. When the two parts of the claw come together, bubbles form, which quickly collapse and shoot out a plasma ball, which in turn produces a flash of light and temperatures of 8,000 degrees Fahrenheit. That's right – an underwater creature that fits into the palm of your hand can destroy a shot of incredibly hot bubbles at the touch of a claw.

Now scientists are learning to use this impressive power themselves. Today, researchers in the journal Science Advances detail how they modeled a robotic claw on the pistol shrimp plasma cannon to create their own plasma. That could find a series of underwater operations if the scientists have refined their version of one of the strangest inventions of evolution.

When all pistol shrimps have a plasma hammer, the whole world looks like a nail. It uses its claw to hunt safely, but also to communicate with short snaps that measure an insane 21

0 decibels. (A real pistol shot produces around 150 decibels.) Some species even use the plasma blasts to carve reef pieces. The result is a seabed that is so loud that it can disturb sonar.

Mechanical engineer David Staack of Texas A & M thought versatility could be of benefit to people. His team started bringing some live pistol shrimps. Like other arthropods, these animals shed regularly and discard their exoskeletons as they grow. These exoskeletons gave Staack a nice cast of the claw, which he then scanned to create a detailed 3D model. He sent him to Shapeways, the commercial 3D printing service, and received a plastic version of the Pistol Shrimp Plasma Pistol.

This allowed Staack to experiment with the unique structure of the limb. The upper half of the claw, which is retained and locked by the shrimp, comprises a "piston" which beats into a "socket" in the lower half of the claw. This creates a fast-moving jet of water that creates bubbles that are also referred to as cavitation in this situation.

"That reminded us of a mousetrap," he says. "So we've done some experiments, flooding some mousetraps, just to see how fast the little arm turns when you trigger it. We took up this idea of ​​the mousetrap to close the claw. "

In Staack's version of the claw, its upper half rotates quickly on a spring-loaded rod, producing enough force to knock the piston into the pan. This action generates a jet of water at high velocity, which in turn creates a cavitation bubble that is initially low in pressure and relatively large. But then it starts to collapse.

"The water penetrates, pushes in and pushes in and you get very high pressures and temperatures," he adds. In fact, the temperatures are so high that they create a light-emitting plasma that can be seen when the shrimp snatch their own claws. "When it tries to push out the water again, it sends out a shockwave." So the crustacean proposes its prey in the wild.

Shockwaves due to the robot claw snapping into place.

David Staack

The incredibly strong snap closure creates a cavitation bubble that collapses and emits light.

David Staack

In the lab, researchers used high-speed cameras to observe the stream of water emanating from their claw. They also displayed the resulting shockwaves and captured the flash of light as the plasma formed.

The shrimp has no monopoly on the production of underwater plasma. People weld under water with plasma, known as plasma welding, which generates strong heat. And with lasers, researchers can also generate plasma in water. The problem is, these funds are inefficient. The use of the claw to generate plasma is ten times more efficient than the previously studied methods, according to Staack. However, it will require more development on a scale.

It may well be even more efficient, as the researchers do not have to follow the biology of pistol shrimp faithfully. In fact, Staack realized that they could reduce the size of the upper bit of the claw. In the actual shrimp it is bulbous, because it holds the muscles that are required for the operation of the penis. However, this robotics version is not limited by this biology.

"The repetition of the animal's process is the first step," says Stanford University biologist Rachel Crane, who helped develop Ninjabot, a device that replicates the attack of the mantis shrimp, which similarly generates cavitation bubbles , "Then you can look at it and find out, yes, I do not need a huge muscle and I can cut that part out. Then you can develop a better system.

The researchers may even want to look for ways to optimize the system. Hundreds of pistol types snap into the sea with their own customized claw. This and even individuals within of a species vary in their morphology.

"The substrate for evolution, the only reason we grab prawns from all these different varieties today, is due to individual variations," says Duke biologist Sheila Patek, who studies the mantis shrimp strike. However, while researchers can optimize their claw robot themselves, they may also be inspired by the inherent variety of pistol shrimp to play with claw morphologies other than those originally printed in 3D.

This variety may someday be a result of gun-prawn-inspired device in a number of areas. One approach would be to use claws generated plasmas to drill through rocks, as does the crustacean in the wild to make a home in a reef. Or you can use the system for water purification by breaking down water into its components, creating a peroxide. "These peroxides can then attack organic contaminants in the water," says Staack. "When you think about cleaning municipal water or cleaning wastewater, efficiency becomes very important."

And so the pistol shrimp still finds a few nails.


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