Newly developed cloak hides underwater objects from sonar

Newly developed cloak hides underwater objects from sonar: Fang's team designed a two-dimensional cylindrical cloak made of 16 concentric rings of acoustic circuits structured to guide sound waves. Each ring has a different index of refraction, meaning that sound waves vary their speed from the outer rings to the inner ones.
"Basically what you are looking at is an array of cavities that are connected by channels. The sound is going to propagate inside those channels, and the cavities are designed to slow the waves down," Fang said. "As you go further inside the rings, sound waves gain faster and faster speed."
Since speeding up requires energy, the sound waves instead propagate around the cloak's outer rings, guided by the channels in the circuits. The specially structured acoustic circuits actually bend the sound waves to wrap them around the outer layers of the cloak.