Research Of Using The Reference Coil To Improve SNR Of Advanced Detector By MRS

With the rapid development of China’s economy and society, the exploitation andutilization of underground resources is increasing, tunnels and other undergroundconstruction projects become increasingly important to the national economy. Thework of caring tunnel water advanced exploration is an important scientific andengineering problem. This work can prevent tunnels from water inrush and protectpersonnel and property safety. Magnetic Resonance Sounding (MRS) technology isthe only way to directly detect groundwater and calibrate water content in geophysicalmethods at this moment. Nuclear magnetic resonance detection method hashigh-resolution, efficiency, informative and uniqueness explanation, etc. MRS plays avery important role in the research of tunnel water advanced detection. The methoduses paramagnetic of hydrogen nuclei in water to cause the magnetic resonanceeffects of hydrogen nuclei in the detection space’s water occurs. When the excitationfield disappears, hydrogen nuclei will radiate the electromagnetic field of Larmorfrequency. Using a received coil to pick up the induced electromotive force signal,after data processing and interpretation of the inversion can get hydro geologicalparameters in the detection space. Because of the power line harmonic interference inthe tunnels is very strong; the effectiveness of traditional filtering methods is limited.This paper is a research of solving the interference problem of JLMRS-Ⅱ typeinstrument which is independent developed by Jilin University’s MRS project team,using the reference coil method to suppress power line harmonic. A first subtractinglater collection signal receiving system is designed in this paper, according to thespace environment of tunnels. The distance of reference coil away from the detectioncoil is theoretically calculated and actually verified. An adjustment program ofnon-normal resonance receiving coil is presented to solve the signal phase shift errorof primary coil of the primary coil and the reference coil. The hardware design andsoftware design of signal receiving system by coil reference is completed. The basicfunctional test and field measurement of the system is conducted. Here are the main contents of this paper.1. A brief description of the significance in the application of tunnel water advanceddetection by MRS technology. The world’s development of MRS technology isintroduced.2. The principle of MRS detection of groundwater is analyzed and illustrated. Theworking principle of JLMRS-Ⅱ advanced nuclear magnetic resonance detector andproblems of the instrument encountered in tunnel detection is described.3. The basic principle of the reference coil method’s immunity is described and thescheme selection is made. The distance of reference coil away from the detection coilis theoretically calculated and actually verified. The system’s architecture is designed.4. An adjustment program of non-normal resonance receiving coil is proposed.Complete the design of signal adjustment circuit, subtraction circuit, amplitudedetection circuit and controllable amplifier, and design the system control softwarebased on STM32.5. Verify the basic functionality of the receiving system based on the referencesignal coils meet the design requirements after pilot testing. Prove this system caneffectively improve the signal to noise ratio of NMR tunnel water detection’s signalby field measurement.