Metamaterials—materials engineered to have optical, thermal, or other specific properties naturally occurring substances don’t—can block, bend, and otherwise manipulate all sorts of waves: they can, at least in theory, twist light to render objects invisible, contort ultrasound waves to hide things from sonar, and disguise the telltale wake of a submarine. Now, in an arXiv paper, Australian and Korean researchers have suggested another wave-altering use for metamaterials: protecting buildings from earthquakes’ powerful seismic waves.
Artist’s rendering of an Australopithecus afarensis
When archaeologists hear whispers of humanity’s past, it’s through the painstaking work of piecing together a story from artifacts and fossilized remains: The actual calls, grunts, and other sounds made by our evolutionary ancestors didn’t fossilize. But working backward from clues in ancient skeletons, Dutch researcher Bart de Boer has built plastic models of an early hominin‘s vocal tract—and, by running air through the models, recreated the sounds our ancestors may have made millions of years ago.
Doctors already use concentrated sound waves to see through solid tissue and take a look inside the body, as with ultrasound scans. But in this week’s Proceedings of the National Academy of Sciences, Caltech scientists say they’ve developed a metamaterial that focuses sound to such a high concentration that it could go on the offensive, targeting cancers or kidney stones while leaving the surrounding tissues alone. Oh, and one other thing: The military could use it to make weapons.
“The beauty of this system is that it’s just a bunch of ball bearings that we control with weights,” said Chiara Daraio [Discovery News], a member of the research team. Caltech’s acoustic lens relies on the same principle as Newton’s cradle—that toy your high school science teacher probably kept on his or her desk with metal balls on strings that demonstrated the conservation of energy. In this design, 21 parallel chains each contain 21 bearings. When the team strikes one end, it starts a compression wave that carries through the system. But instead of having the last ball swing out like a pendulum and bring the momentum back into the system, like the toy does, the acoustic lens focuses all the energy at the end of the system onto one spot, just a few inches away from the metamaterial.
For everyone out there who’d like to hear a little less of their amorous neighbors, not to mention their kid badly playing the violin, there may be hope: Hong Kong scientists have devised a delightfully simple material made of latex and plastic that they say could one day reduce the racket at noisy places like airports. The paper appears in Applied Physics Letters.
Zhiyu Yang and colleagues devised a system of thin tiles that, when assembled into a large sheet, could cancel out noise in a huge range, including the bass frequencies that tend to breach the walls of our apartments and houses with ease. Each panel is just three millimeters thick, and less than half an inch wide, with the weighted plastic button in the middle. When sound waves hit the panel, the membrane and weighted buttons resonate at difference frequencies. “The inner part of the membrane vibrates in opposite phase to the outer region,” says Yang. That means the sound waves cancel each other out and no sound gets through [New Scientist]. Read More
Are you ready for some free fall?
Austrian daredevil Felix Baumgartner officially announced that sometime this year, he intends to jump from a balloon at a height of nearly 23 miles, breaking the 50-year-old world record for the highest parachute jump held by retired U.S. Air Force pilot Joe Kittinger. Kittinger is the Stratos mission’s capcom (short for capsule communicator), which means that he will be the voice in Baumgartner’s helmet. Kittinger’s advice to his successor: “Have fun, enjoy it, and tell us all about it when you get down” [Scientific American].
In several labs around the world, sound waves are doing things they’ve never done before. Teams working in England and the Ukraine have made a sonic laser, or “saser,” which operates in the terahertz range, with sound waves oscillating more than a trillion times per second. Meanwhile, in an Israeli lab, researchers say they’ve created the first ever sonic black hole that traps sound waves and won’t let them escape.
The saser uses packets of sonic vibrations called “phonons” much like a regular laser uses photons. Specifically, the acoustic laser device consists of a sonic beam traveling through a “superlattice” constructed of 50 sheets of material each only atoms thick that are alternately made of gallium arsenide and aluminium arsenide, two materials found in semiconductor [CNET]. The phonons bounce back and forth inside the lattice, which causes more phonons to be released and amplifies the overall signal. The result is the formation of an intense series of synchronised phonons inside the stack, which leaves the device as a narrow saser beam of high-frequency ultrasound [New Scientist].
At the moment the terahertz saser, described in a paper published in the journal Physical Review B, is mainly a neat trick, but it may find practical applications down the line, says lead researcher Tony Kent. “Fifty years ago many eminent scientists said that light amplification by the stimulated emission of radiation [lasers] was no more than a scientific curiosity,” says Kent, but lasers are now used for everything from digital storage and cancer treatment to weaponry [New Scientist]. Kent says the new saser technology could lead to breakthroughs in imaging for tiny, nanoscale objects.