Cylindrical acoustic Luneburg lens

We developed a two-dimensional acoustic Luneburg lens by changing the density of the medium inside the lens. The lens has a cylindrical shape and composes of about seven hundred aluminum columns with various radii of less than 2cm. It has 15 layers and the diameter of the lens is 60cm. The lens focuses the incoming acoustic waves on the edge of the opposite side of the lens as well in the frequency range of 1, 500Hz ~ 2, 500Hz. It increases the acoustic pressure of the incoming wave by 3 ~ 5 times.