The Application of Fmcw Modulated Thermoacoustic Imaging in Geological Media

A TA (thermoacoustics) imaging system is investigated in this paper in order to enhance conventional imaging modalities in geological subsurface situational awareness applications. Previously, TA imaging has been mostly used in biological scenarios such as breast cancer detection. This work aims to extend the use of TA imaging to geophysical applications by showing that water-saturated sand can be distinguished from dry and oil-saturated sand based on the amplitude difference, which enables the feasibility of monitoring water distribution in these media. Moreover, in order to compensate for the low conversion efficiency from electromagnetic power to TA amplitude, the signal modulation method is used by applying the FMCW (frequency-modulated continuous wave) techniques. The experiment results show that FMCW can enhance the signal-to-noise ratio while keeping a similar resolution as pulse excited TA wave, thus paving the way towards its future use for subsurface sensing and imaging of fluid flow and transport in porous media.