  Luneburg lens is a gradient index lens that focuses the incoming wave on the
opposite side of the lens without aberration. We developed a two-dimensional
acoustic Luneburg lens by changing the refractive index of the medium in the
lens. It has a cylindrical shape and is composed of 701 aluminum columns with
various radii of less than 1cm. It focuses the incoming sound wave on the edge
of the opposite side of the lens without aberration as well in the frequency
range of 1,000 - 3,200Hz. It increases the amplitude of the incoming sound wave
by 3 - 4 times, and the amplification corresponds to the sound level difference
of 10 - 15dB. The ability of the acoustic Luneburg lens as sonar was checked by
VU meters in the air. Acoustic Luneburg lens has a simple structure and easy to
build. It could be a strong candidate of a next generation of sonar.
