15 November 2017
Porpoises twist laws of physics to aim their focused sonar beams
By Sam Wong
PORPOISES have the combination of acoustic controls built into their heads to thank for their ability to focus a directed beam of sonar on prey. The bone, air and tissues in their skulls behave like a metamaterial, a material designed to defy the normal laws of physics. These sea mammals can convert non-directional sound waves into a narrow laser of sound.
Like dolphins, porpoises use echolocation to detect prey under water up to 30 metres away. To do this, they emit high frequency clicks in a focused beam in front of their faces, controlling the direction of the beam without moving their heads. They can also widen the beam as they approach their target, helping them catch fish that try to escape.
https://www.newscientist.com/article/mg23631524-000-porpoises-twist-laws-of-physics-to-aim-their-focused-sonar-beams/
