First three-dimensional sound cloaking

Science News : Most cloaking devices attempt to prevent sound or light waves from reflecting by redirecting the waves around the cloaked object. José Sánchez-Dehesa of the Polytechnic Institute of Valencia in Spain and his colleagues have taken a different approach and created a cloak that uses the same principle as noise-canceling headphones. They created a design of 60 rings of varying sizes that form a cage-like structure around a sphere and used a 3D printer to make the rings. The rings are shaped and placed in such a way that the reflected sound waves interfere with each other, resulting in no detectable reflected sound wave. The researchers tested the cloak by hanging the caged sphere in an anechoic chamber and shooting it with sound waves. For most frequencies, sensors were able to detect reflections, but at 8.55 kHz, they detected nothing. While a very small step forward in sound cloaking, this is the first time that an object has been hidden in three dimensions. Future applications could range from reducing public noise pollution to creating stealthier submarines.