Passive underwater acoustic markers using Bragg backscattering.

This letter demonstrates the feasibility of a passive underwater acoustic marker technology (or "AcoustiCode") for use in underwater navigation. An AcoustiCode tag is a planar surface with machined periodic patterns capable of producing Bragg backscattering beampatterns with engineered spatial and frequency variations, thus having a unique three-dimensional acoustic signature over a selected frequency band. Hence, these AcoustiCodes enable three-dimensional navigation and information signaling in a totally passive manner for existing high-frequency SONAR systems (potentially mounted on autonomous underwater vehicles), which naturally operate in a narrow frequency band and can also be used over significantly longer ranges compared to optically-based systems.