Acoustic markers

摘要

An acoustic reflector is described comprising a shell around a core, in which portions of the shell are capable of transmitting acoustic waves incident on the shell into the core to be focused and reflected from an area of the shell located opposite to the area of incidence of the acoustic waves to provide a reflected acoustic signal output from the reflector. Incident acoustic radiation will be differentially reflected depending on the portion of the reflector on which the incident acoustic radiation impinges.