The use of solid cavities around electromagnetic sources has been recently reported as a mechanism to provide enhanced images at microwave frequencies. These cavities are used as measurement randomizers; and they compress the wave fields at the physical layer. As a result of this compression, the amount of information collected by the sensing array through the different excited modes inside the resonant cavity is increased when compared to that obtained by no-cavity approaches. In this work, a two-dimensional cavity, having multiple openings, is used to perform such a compression for ultrasound imaging. Moreover, compressive sensing techniques are used for sparse signal retrieval with a limited number of operating transceivers. As a proof-of-concept of this theoretical investigation, two point-like targets located in a uniform background medium are imaged in the presence and the absence of the cavity. In addition, an analysis of the sensing capacity and the shape of the point spread function is also carried out for the aforementioned cases. The cavity is designed to have the maximum sensing capacity given different materials and opening sizes. It is demonstrated that the use of a cavity, whether it is made of plastic or metal, can significantly enhance the sensing capacity and the point spread function of a focused beam. The imaging performance is also improved in terms cross-range resolution when compared to the no-cavity case.

Accurate predictions of fluid flow, mass transport, and reaction rates critically impact the efficiency and reliability of subsurface exploration and sustainable use of subsurface resources. Quantitative dynamical sensing and imaging can play a pivotal role in the ability to make such predictions. Geophysical thermoacoustic technology has the potential to provide the aforementioned capabilities, since it builds upon the principle that electromagnetic and mechanical wave fields can be coupled through a thermodynamic process. In this letter, we present laboratory experiments featuring the efficacy of thermoacoustic imaging in the monitoring of preferential flow of water in porous media. Our laboratory experimental equipment can be readily packaged in a form factor that fits in a borehole, and the use of multiple acoustic transducers—which can be combined with volumetric coding techniques—has the potential to provide quasi‐real‐time imaging (0.5 Hz video rate) of regions in close proximity (a few meters) of an open field well.

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.

Accurate predictions of fluid flow, mass transport, and reaction rates critically impact the efficiency and reliability of subsurface exploration and sustainable use of subsurface resources. Quantitative dynamical sensing and imaging can play a pivotal role in the ability to make such predictions. Geophysical thermoacoustic technology has the potential to provide the aforementioned capabilities since it builds upon the principle that electromagnetic and mechanical wave fields can be coupled through a thermodynamic process. In this letter, we present laboratory experiments featuring the efficacy of thermoacustic imaging in the monitoring of preferential flow of water in porous media. Our laboratory experimental equipment can be readily packaged in a form factor that fits in a borehole, and the use of multiple acoustic transducers—which can be combined with volumetric coding techniques—has the potential to provide quasi-real-time imaging (0.5 Hertz video rate) of regions in close proximity (a few meters) of an open field well.

Accurate monitoring of temperature variations in fluid flow through porous media is important for numerous geophysical, environmental, and chemical processes. Traditional temperature measurement techniques often suffer from limitations such as invasiveness, restricted spatial coverage, or limited capability for real-time subsurface sensing. Thermoacoustic (TA) methods provide a promising alternative by combining electromagnetic excitation with acoustic detection to enable non-contact subsurface monitoring. In this work, thermoacoustic measurements were conducted over a temperature range of 20–60 °C using a water-saturated sand porous medium, and a multiphysics simulation framework incorporating rock physics models, temperature-dependent material properties, acoustic dispersion, and attenuation calibration was developed to reproduce the experimental observations. A clear relationship between temperature and TA signal amplitude was observed, and strong agreement was achieved between the experimentally measured and simulated thermoacoustic responses after applying the proposed calibration procedures. The results demonstrate the feasibility of using thermoacoustic signals to monitor bulk temperature variations in porous media and establish a foundation for future development of spatially resolved thermoacoustic temperature imaging methods.

The process of two-phase fluid displacement in the porous medium is still poorly understood partly due to the absence of effective reconstruction methods featured in a 3D real-time fashion. This manuscript proposes the application of thermoacoustics (TA) imaging, an emerging real-time imaging technique, to reconstruct the dynamic surfactant-enhanced imbibition process into the oil-saturated sand. It is both theoretically and experimentally demonstrated that a significant TA contrast exists between the water-saturated sand and oil-saturated sand under the same microwave power. In the experiment, a U-shaped infiltration path is embedded 20mm underneath the oil-saturated sand as the ground truth profile of the water flow. A calibration process is conducted to account for the amplitude attenuation and velocity dispersion effects of the TA wave in the sand, and a two-layered medium sensing matrix is built for the inversion process. The reconstructed images match well with the infiltration path, which makes it feasible to monitor the subsurface 3D water-oil displacement in non-transparent porous sand in a real-time fashion.