US Patent 10978038 Invisible sound barrier

An invisible sound barrier includes a periodic array of spaced apart, columnar unit cells. Each unit cell includes a pair of joined, and inverted, columnar Helmholtz resonators, having neck portions that point in opposite directions. Each of the Helmholtz resonators can be formed of a sound absorbing material and coated with a light reflective material causing light to reflect around the resonators, thereby conferring invisibility. Each of the Helmholtz resonators can alternatively be formed of a light reflecting material, and positioned in between vertical mirrors, with a transparent material filling space between the resonators and the vertical mirrors.