The application of frequency-modulated continuous wave modulated thermoacoustic imaging in geological media

Abstract

A thermoacoustics imaging system is investigated in this paper to enhance conventional imaging modalities in geological subsurface situational awareness applications. While thermoacoustics imaging has traditionally been used in biological scenarios like breast cancer detection, this work aims to extend thermoacoustics imaging to geophysical applications by demonstrating that water-saturated sand can be distinguished from dry and oil-saturated sand based on their amplitude differences. This breakthrough enables the feasibility of monitoring water distribution in these media. Moreover, to compensate for the low conversion efficiency from electromagnetic power to thermoacoustics amplitude, the signal modulation method is used by applying the frequency-modulated continuous wave techniques. The experiment results show that the frequency-modulated continuous wave can enhance the signal-to-noise ratio while maintaining a similar resolution as the pulse-excited thermoacoustics wave. These findings pave the way for the future use of thermoacousticsimaging in subsurface sensing and imaging of fluid flow and transport in porous media.