核磁共振接收线圈谐振优化分析与标定

地面核磁共振接收机接收的核磁共振信号的初始振幅直接决定其反演的含水量大小。目前的核磁共振找水仪采用由线圈和配谐电容等组成的LC谐振回路接收核磁共振信号,该谐振接收回路对接收线圈感应的核磁共振信号存在选频放大效应,忽略该效应会造成初始振幅回推时产生较大误差。本文在对谐振接收回路建立精确电气模型的基础上,分析并计算了谐振接收回路各元件参数对选频放大效应的影响,并对100 m边长线圈谐振接收回路选频放大效应进行了标定,经过校正后初始振幅最大值由1 560 n V降至305 n V,与法国仪器基本一致。验证了野外施工谐振接收模型及模型计算的正确性,为地下水害的直接探测提供了仪器稳定性保障。

Resonance receivinig circuit analysis and parameters demarcating of NMR equipment

The signal amplitude of NMR receiver receives the ground for underground water directly determines the inversion water content. The LC resonance receiving circuit made up of receiving coil and chime capacitor is used in the equipment. The resonance circuit attaches an effect of frequency selection and amplification on the NMR signal. Serious error will occur if this effect is ignored. In the paper, the accurate electric model is established and the resonance circuit parameters that will influence the frequency selection and amplification effect is calculated and analyzed. With the demarcated parameters of receiving coil with 100 m side length, after correcting the initial maximum amplitude falls from 1 560 nV to 305 nV, consistent with the French instruments. Verify the correctness of the construction field resonance model and model calculations reception, providing stability guarantee for direct detection of groundwater harm instrument.