Omnidirectional passive acoustic identification tags for underwater navigation.

A class of passive acoustic identification (AID) tags with curved symmetry for underwater navigation is presented. These AID tags are composed of radially stratified shells designed to backscatter a unique specular reflection pattern independent of the incidence orientation in a monostatic configuration, thus acting as acoustic bar-codes. The AID tag's response can be uniquely engineered by selecting the thicknesses and material properties of the individual constitutive shells. Furthermore, in the high-frequency regime, the specular component of the AID tag's response can be simply predicted numerically assuming horizontally stratified layers. This approach is demonstrated using scaled experiments with an AID tag constructed from 3D printed hemispherical shells.