Controlling the phase response of a phased array system

摘要

Phased array techniques, based on interference of diffuse photon density waves, have been demonstrated to be a sensitive method of detecting and localizing objects embedded in heavily scattering media. They have also been used as a sensitive method of detecting functional changes in the brain. Previous experiments using anti-phase sources have shown that the phase response to the scan of an object through the medium is π radians regardless of object size. This provides information about the position of an object but none about the size. In this paper we demonstrate that controlling the relative phase between the sources enables different phase gradients to be set within the medium. The consequence of this is that the phase response is dependent on the size of an object whilst still maintaining the localization information. Furthermore, it is demonstrated that the phase response can be turned to be most sensitive to the object size under investigation. The effect of source separation on the system response is also investigated. It is demonstrated that there is an optimum source separation to produce the maximum signal to noise ratio. Sources positioned close together provide too much destructive interference whereas sources well separated do not provide enough interference.