Surface Magnetic-Field Enhancement Technology With a Double-Polarization Coil for Urban Hydrology Quantitative Survey

Electromagnetic geophysical methods are widely applied in urban shallow exploration, considering their convenience and noninvasiveness. As one of the emerging techniques, polarizing surface nuclear magnetic resonance (SNMR) shows significant potential for water-based target detections. However, problems involving weak signal response and strong noise interference are challenging to avoid. Therefore, numerous studies focused on suppressing the electromagnetic interference and improving the effective electromagnetic control accuracy to achieve high-precision shallow imaging. On this basis, we proposed a new magnetic-field enhancement technology that explored double-polarization coils, instead of the single loop, to improve the applications of polarizing SNMR. By controlling the current for double-polarization coils, the magnetic field, which is twice as strong as the single coil, could be provided. As a result, the sensitivities and signal responses for subsurface detection sensitive areas with the same power consumption were further enhanced. Considering the SNMR research, we also identified that this new configuration with double-polarization coil can effectively improve the resolution of the shallow depth because it compensates for the magnitude of the static magnetic field in the center. Based on the theoretical analysis, we developed the instrument and, for the first time, realized the accurate interpretation of the real ground soil in an urban environment, verifying the effectiveness of the proposed configuration and the reliability of the system.