A thin coating of a rubbery material could make submarines more difficult to detect with sonar.
Sonar locates submarines by emitting sound at many different frequencies. Those sound waves reflect off the vessel as an echo which can then be detected by a receiver. But objects covered in materials that absorb sound are hard for sonar to spot.
at Xi鈥檃n Jiaotong University in China and his colleagues have now designed a new coating for masking submarines from sonar that, if fully manufactured, could be the thinnest yet to absorb a wide range of frequencies.
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The material is 32 millimetres thick and is made of strips of rubber that the researchers optimised with a machine learning algorithm. Some of the strips have a rectangular piece of lead running through them and others have pyramid-shaped air cavities. The algorithm determined that this was the best configuration for maximising the absorption of many different sound wave frequencies.
The team used a computer simulation to determine that if hit with the most common sonar frequencies, in the range between 1 and 10 kilohertz, this material would absorb them with around 95 per cent efficiency. In other words, the submarine鈥檚 echo would be faint and more likely to be missed or mixed up with some other underwater structure like a reef. Liang says that most similar stealth material designs do not work as well for as many frequencies, specifically underperforming for lower frequencies.
Adding a thin steel wall to the material could also make his team鈥檚 material work under 4.5 megapascals, the pressure experienced by submarines at depths over 450 meters, he says.
鈥淚f you can design any structure that naturally vibrates at a particular frequency, you can get a lot more sound absorption around that frequency than you can from traditional sound absorbers like foam,鈥� says at Duke University in North Carolina. Foam is commonly used to insulate buildings from sound and some types can be used in submarines as well.
Liang says that his team is currently working on developing a practical method for manufacturing their material.
Reference: Physical Review Applied,
