BALTIMORE — Metamaterials, among the most intricate and skillfully designed configurations of matter ever devised by science, could be improved with the help of Legos.

Famous for their use in cloaking devices, metamaterials are artificial structures that play unnatural tricks with light and sound and other vibrations. Scientists have investigated the use of such materials for soundproofing rooms or protecting buildings from the shaking of earthquakes, among other things. But to do their jobs, metamaterials must be properly designed and fabricated using precisely manufactured components. Testing ideas for new metamaterials is therefore time-consuming and expensive.
So Paolo Celli and colleagues at the University of Minnesota sought alternatives. They considered 3-D printing, Celli said March 15 at a meeting of the American Physical Society. But the printing process can be slow and the “ink” isn’t cheap, so they rejected that idea. “That’s when we thought, ‘Why don’t we use Lego bricks?’” he said. Legos are relatively cheap and can rapidly be rearranged into all sorts of configurations.

Celli and colleagues arranged Lego bricks on a base plate attached to a wooden frame and investigated how the arrangements influenced the way vibrations traveled through the plate. For some arrangements, certain vibration wavelengths could not be transmitted. Manipulation of the Legos allowed the scientists to determine what processes created the forbidden wavelength zones (known as bandgaps), providing valuable data for future designs of real metamaterials.

Further experiments showed how Lego arrangements could identify metamaterial architectures that might provide a shield for buildings at risk from earthquake waves. “We might be able to design a metamaterial shield that might block some frequencies that can be harmful to that structure,” Celli said.

Ahmed Elbanna, a materials researcher at the University of Illinois at Urbana-Champaign, called the work with Legos exciting and said in principle it could be applicable to designing metamaterials for some applications. He said he was “a little bit more skeptical” that it could result in useful earthquake protection.

Celli emphasized that the motivation behind the work was not solely to produce better metamaterials. “We’ve been looking for an agile and versatile experimental platform,” he said, “but we were also looking for something that people can relate to…. We think that this platform is probably very powerful” for promoting this branch of physics to a broader community.

Asked if he played with Legos as a child, Celli replied, “a lot.”

A year ago, researchers in two small submarines were exploring a seamount — an underwater, flat-topped mountain — off the Pacific coast of Panama when they noticed a dense cloud of sediment extending 4 to 10 meters above the seafloor. One of the submarines approached closer, and the scientists could soon see what was kicking up the cloud: thousands of small, red crabs that were swarming together like insects.

“The encounter was unexpected and mesmerizing,” Jesús Pineda of the Woods Hole Oceanographic Institution in Massachusetts and colleagues write in a paper published April 12 in Peer J.

The team decided to investigate further. They sent an autonomous underwater vehicle to pass over the swarm several times, capturing images and video of the crabs. At the densest points in the swarm, there were more than 70 crabs in a square meter of ocean bottom, and this occurred consistently in a water depth of 350 to 390 meters. The crabs, all 2.3 centimeters in carapace length and larger, were moving together in the same general direction. Some would jump and swim for about 10 centimeters or so before landing back in the pack.
Using one of the submarines, the researchers collected some crabs from the swarm. Back in the lab in Woods Hole, they used DNA barcoding to identify the species: Pleuroncodes planipes. This is the same species of crab that has sometimes washed up in mass stranding events on California beaches, which the team confirmed by comparing the DNA barcodes to those of crabs from a stranding event in La Jolla, Calif., in June 2015.

For reasons that scientists still don’t fully understand, seamounts are ecological hot spots where plankton get trapped and feed a wide array of fish and marine mammals higher up in the food web. Fishermen have figured out that they can take advantage of this, but scientists are just now getting into the game and exploring these sites. Because of this, less than one percent of the world’s seamounts have been checked out by researchers. That probably explains why no one had seen a crab swarm like this before on a seamount.
But this is not the first time crabs have been seen swarming. Scientists have previously documented large aggregations of king crabs, spider crabs, tanner crabs and lyre crabs on the seafloor. Such behavior may be linked to reproduction.

And then there are the red crabs of Christmas Island in the Indian Ocean, which swarm in the millions during the wet season, coming out of the forests and making a long trek to the beach for a massive mating party.