Design And Implementation Of Hardware System For Miniaturized NMR Spectrometer

Nuclear magnetic resonance(NMR)technology plays an important role in the field of oil exploration,and it provides more information about the richness of the formation information than any other single logging method.The NMR spectrometer is the basis of the NMR logging tool,but the traditional NMR spectrometer system is large in size and heavy in weight,and can only be installed in a relatively fixed experimental environment,which is difficult to meet the needs of real-time on-site detection.Therefore,the miniaturized spectrometer has always been one of the research hotspots in the field of nuclear magnetic resonance.This thesis is devoted to the research of miniaturization of the hardware system of NMR spectrometer.A set of miniaturization hardware system of NMR spectrometer has been completed.The test results of transmitting and receiving links of hardware system show that the hardware system of miniaturized spectrometer designed and manufactured in this thesis meets the basical design requirements.In this thesis,the main work and achievements are as follows:(1)The hardware system of miniaturized spectrometer is designed and completed,including the control console with FPGA core board as the core control unit,dual DDS structure with ADC and DDS chip as the core,pulse transmitting circuit with adjustable amplitude,frequency,phase and action time,signal receiving circuit of down-conversion echo based on IF sampling and communication interface circuit.(2)A microprobe for the detection of trace liquid samples was designed and fabricated.The probe is tuned and impedance matched by vector network analyzer,and the S parameters of the probe in static magnetic field are tested.The applicability of the probe in NMR spectroscopy experiment is verified.(3)A Halbach array structure consisting of NdFeB permanent magnet materials was fabricated to provide the static magnetic field required for the NMR spectrometer system test.The finite element simulation software COMSOL was used to simulate the structure.The influence of the non-uniformity of the central magnetic field of the Halbach array caused by the demagnetization effect and assembly error on the NMR spectroscopy experiment was studied,which laid a foundation for the passive shimming method.(4)A passive shimming structure of Halbach array based on mechanical regulation is designed and fabricated.By adjusting the position of the magnet elements of the Halbach array,the structure can change the contribution of each magnet element to the central magnetic field and compensate for the magnetic field inhomogeneity caused by demagnetization effect and assembly error.The simulation results show that the uniformity of magnetic field in the 5 mm DSV range of Halbach array center can reach 150 ppm by the passive shimming structure based on mechanical regulation.(5)The electronic circuit of the miniaturized spectrometer is tested by imitate pulse sequence transmitting and echo signal receiving,and the performance of communication interface circuit,transmitting link and receiving link is tested.The test results show that the hardware system of miniaturized spectrometer has met the design requirements.