An object can have underwater acoustic privacy over a wide frequency range with a lightweight rubber and metal frame.
A submarine object can be hidden by an acoustic "cloak" so that neither sonar nor echolocating sea creatures can find it. Acoustic camouflage can blend an object into the background of water, similar to how camouflage clothing makes people disappear into their surroundings. While underwater acoustic cloaks have been demonstrated in the past, they typically only function in a small frequency range or are too large to be useful. At this point, a lightweight, broadband cloak made of a thin layer of material was demonstrated by Hao-Wen Dong of the Beijing Institute of Technology and his colleagues.
How Does Acoustic Privacy Happen?
The cloak provides acoustic privacy by preventing both the escape of the sound produced inside the concealed object and the reflection of sonar signals from the surface.
A 4 cm thick structure was created by Dong and colleagues combining an outer rubber layer and a “metamaterial” of porous aluminum to cover a steel plate. They adapted the interaction with underwater sound waves by optimizing the elastic properties of the metamaterial using a genetic algorithm. The metamaterial transforms longitudinal sound waves, which can travel very far underwater, into transverse sound waves that cannot propagate in water. These transverse waves are captured in the rubber layer, where they are absorbed and eliminate simultaneously transmitted and reflected waves.
To make sure the prototype cloak behaved as expected, the researchers built and tested it. In particular, it absorbed 80% of the energy of the incoming sound waves, while reducing the acoustic noise generated on the side of the steel plate by 100 times.
According to Dong, a similar concept could be used to increase the privacy of submarines or to protect the wildlife of motor boats from noise.
Source: physics.aps.org/articles/v16/s63
Günceleme: 28/04/2023 13:39