Imagine a band playing indoors, but the neighbors cannot hear the music. However, if someone is talking outside, the musicians in the room can hear it. This kind of single-sided sound wall technology similar to a single mirror sounds a little unimaginable, but according to the US "Discovery" website reported on May 6, two Italian scientists are making this kind of sound operation technology closer to reality, and related research published In the newly published "Physical Review Letters" magazine.
The director of the Center for Nonlinear and Complex Systems at the University of Issubria, Italy, Julia Cassati, professor of physics, and the researcher of the Institute of Complex Systems of the Italian National Research Council, Stephen Laupre Inspired by the mechanism of transferring heat symmetrically, a new acoustic mechanism is proposed. They envisioned a metamaterial or a set of equipment with non-linear properties that could bend sound waves in unexpected ways (just like single-sided mirrors), so that sound can only be transmitted in one direction, blocking or shielding external sources The purpose of sound waves.
Kasati and Lepri have also proved mathematically that it is possible to make such metamaterials or equipment. Kasati said that compared with linearity, nonlinearity will make our world richer, and it will make us more likely. The single-sided mirror is an optical glass, which is totally reflective on one side, and cannot see the scene on the opposite side. It can only see the mirror image here like a mirror; on the other side, it is completely transparent glass, which can clearly see the opposite Scenery.
Kasati explained that, in theory, the single-sided mirror widely used by the police is not really a single-sided. The reason why it can produce a single-sided reflective effect is entirely because the two sides of the mirror are in different light environments. It must be completely dark on one side and bright on the other. Similar nonlinear acoustic materials will also enable sound to propagate in only one direction, while preventing incident sound waves.
In order to guide the sound waves, scientists propose to alternately lay linear and nonlinear material layers asymmetrically. Once constructed properly, when sound waves enter from one side, it must enter this metamaterial and then be redirected. Kasati explained that this is because the frequency of the sound wave has changed in two different directions.
The two physicists have proved mathematically that future scientists can build such an acoustic metamaterial. Leprey said that just like photonics, scientists had never expected that nonlinear photonics would appear, but now the development of nonlinear photonics is very good. He said that perhaps the manufacture of nonlinear acoustic materials may be a little harder, but many scientists are trying to make it a reality.
Stephen Kerm, associate professor of electronics and computer engineering at Duke University, said that it is possible to make this material. Once it is manufactured, it will have many practical uses. For example, someone may want to confine the sound in a room and not let it escape, but at the same time be able to hear outsiders talking.
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