According to scientists from the University of Illinois, they managed to create a special coating that in the future could make submarines completely invisible to sonars and other sonar devices operating on ultrasound.
The coating consists of 16 concentric rings, which form acoustic circuits capable of picking up sound with a frequency of 40 to 80 kilohertz and "conducting" it along the acoustic circuits, forcing it to actually bend around the object. Note that military sonars used on modern submarines generate a signal with a frequency of 1 to 500 kilohertz, but scientists are confident that in the future they will be able to modify the material.
During the experiment, the researchers covered objects of different densities and materials with a new material, and then lowered them into a pool of water. An ultrasonic emitter was placed on one side of the pool, and recording equipment on the other. During the experiment, the sensors did not detect any objects in the pool.
Scientists also believe that the new coating can be used to suppress noise emitted by the movement of a submarine. In particular, the new material will help fight cavitation - the formation of small hollow bubbles in water when an object moves at high speed.
