The metamaterial,
shown here, is made of paper and aluminum -- but its structure
allows it to
manipulate acoustic waves in several ways. Photo credit: Chen Shen.
(December 16, 2015) Researchers
from North Carolina State University and Duke University have developed a
metamaterial made of paper and aluminum that can manipulate acoustic waves to
more than double the resolution of acoustic imaging, focus acoustic waves, and
control the angles at which sound passes through the metamaterial. Acoustic
imaging tools are used in both medical diagnostics and in testing the
structural integrity of everything from airplanes to bridges.
“This metamaterial is something that we’ve known is
theoretically possible, but no one had actually made it before,” says Yun Jing,
an assistant professor of mechanical and aerospace engineering at NC State and
corresponding author of a paper describing the work.
Metamaterials are simply materials that have been engineered
to exhibit properties that are not found in nature. In this case, the
structural design of the metamaterial gives it qualities that make it a
“hyperbolic” metamaterial. This means that it interacts with acoustic waves in
two different ways. From one direction, the metamaterial exhibits a positive
density and interacts with acoustic waves normally – just like air. But from a
perpendicular direction, the metamaterial exhibits a negative density in terms
of how it interacts with sound. This effectively makes acoustic waves bend at
angles that are the exact opposite of what basic physics would tell you to expect.
The practical effect of this is that the metamaterial has
some very useful applications.