浅层地面磁共振匀场预极化线圈多源探测阵列研究

Uniform-field multi-source detection array study of shallow surface nuclear magnetic resonance pre-polarization coils

地面磁共振(Surface Nuclear Magnetic Resonance,SNMR)技术是唯一能够实现地下水定性定量探测的地球物理方法,在水资源勘探、灾害水调查等领域有较好发展潜力.通过直流线圈发射预极化脉冲能够有效提升信号幅度,然而其布设配置及磁场均匀性直接影响激发及探测效果,探测阵列的配置方案少有讨论.针对上述问题,本文基于磁偶极子法构建了探测目标水体的均匀目标磁场方程,以线圈功耗为约束求解了规则的地面电流分布,在此基础上引入流函数法实现电流分布与线圈实际布设的等效转换,获取了匀场预极化线圈配置.分别构建方形及长方形分层目标水体模型求解匀场线圈配置进行验证,求解配置与常规方案相比磁场均匀性及分辨率有明显提升,证明了方案的有效性.结果表明:基于目标场法的配置求解方案与常规方案相比,可以根据不同探测目标获取针对性的匀场线圈布设方案并具有良好的探测分辨率和工程应用效率,能够弥补匀场预极化线圈配置设计空白.本文的研究成果,将为浅层多源预极化技术在复杂应用环境下的工程应用提供有力支撑.

Surface nuclear magnetic resonance(SNMR)technology is the only geophysical method that can realize the qualitative and quantitative detection of groundwater,and it has good development potential in the fields of water resources exploration and disaster water investigation.Pre-polarization pulses emitted by DC coils can effectively enhance the signal amplitude,but their layout configuration and magnetic field uniformity directly affect the excitation and detection effects,and the configuration of detection arrays hasrarely been discussed.In order to address the aforementioned issues,we constructed the uniform target magnetic field equations for detecting the target water body based on the magnetic dipole method.Furthermore,we solved the regular ground current distribution with the constraint of power consumption of the coil.In doing so,we introduced the flow function method to realize the equivalent conversion between the current distribution and the actual deployment of the coil.This resulted in the uniform field pre-polarization coil configuration.The uniform-field coil configurations are validated by constructing square and rectangular stratified target water models respectively.The magnetic field uniformity and resolution of the solved configurations are significantly improved compared with those of the conventional scheme,which proves the validity of the scheme.The results demonstrate that compared with the conventional scheme,the configuration solution based on the target field method can achieve a targeted uniform field coil layout scheme that is targeted to specific detection targets with high detection resolution and engineering application efficiency.This solution can also compensate for the design blank of the uniform field pre-polarization coil configuration.The findings of this study will provide compelling evidence to support the engineering application of shallow multi-source pre-polarization technology in complex application environments.