  We present the design, architecture and detailed performance of a
three-dimensional (3D) underwater acoustic carpet cloak (UACC). The proposed
system of the 3D UACC is an octahedral pyramid which is composed of periodical
steel strips. This underwater acoustic device, placed over the target to hide,
is able to manipulate the scattered wavefront to mimic a reflecting plane. The
effectiveness of the prototype is experimentally demonstrated in an anechoic
tank. The measured acoustic pressure distributions show that the 3D UACC can
work in all directions in a wide frequency range. This experimental
verification of 3D device paves the way for guidelines on future practical
applications.
