Structure Design Of Portable NMR Main Magnet System And RF Coil

As a precise,rapid and nondestructive measurement technology,nuclear magnetic resonance has been widely used in materials science,structural biology,medicine and other disciplines.However,the disadvantages of NMR system,such as heavy equipment,large volume,high cost and limited detection location,make the measurement technology not effectively popularized in daily life.In order to further develop the technology and make the magnetic resonance system have the advantages of small size,low cost and can be used for field testing,the portable magnetic resonance main magnet system has become a new direction of the development of nuclear magnetic resonance.In view of the shortcomings of the current portable nuclear magnetic resonance main magnet system,this topic takes coal powder as the detection object,and designs a Halbach array type main magnet system based on the design requirements by determining the array cross section,the number of magnetic blocks,the inner and outer radius of the magnetic ring,the height of the magnetic ring,the number of magnetic ring layers and the distance between the magnetic rings.The main magnet system has the advantages of high field intensity,small size,low cost and can be used for field testing.In view of the uniform passing difference caused by the end effect,this topic to the main magnet system to put forward one by one to adjust the magnetic block height,step by step optimization scheme,and introduces the quality factor Q is used to characterize the magnetic block unit height change on the evenness of hoisting capacity,make the uniformity increased by 95.15 %.Finally,the RF coil and RF probe matching the main magnet system are designed by optimizing the SNR of the coil.This paper provides reference for the follow-up research of portable magnetic resonance main magnet system.The main contents of this paper are as follows:1.In this paper,based on the finite element simulation analysis method,around the design requirements and determine the structural parameters,the final design of a main magnet system with 9 layers of magnetic rings,the size of the system is ? 240 × 138 mm,the size of the through hole in the middle is ? 60 × 138 mm,the size of the working area is ? 20 × 20 mm.The magnetic field intensity is 1029 m T,and the overall uniformity is 8612 ppm.2.In order to solve the end effect caused by the low height of the main magnet system,a scheme was proposed to adjust the height of the magnetic block pair by pair and optimize it step by step,and the quality factor Q was introduced to represent the improvement ability of the uniformity of the magnetic block unit height change.Finally,the optimized system size is ?240 × 141.8 mm,the magnetic field intensity is 1.09 T,and the overall uniformity is 418 ppm.After optimization,the uniformity is improved by 95.15 %,the magnetic field intensity is increased by nearly 6 %,but the optimized structure consumes 13.38 % more magnetic materials.3.In view of the problem that the system performance is greatly affected by the material properties,the material properties of the system are analyzed in this study.The results show that the uniformity is less affected when the material properties errors are symmetrically distributed.Therefore,the material should be selected strictly on the same magnetic material.Aiming at the problem that the system performance is greatly affected by the operating temperature,this study analyzes the operating temperature characteristics of the system,and the results show that the magnetic field intensity decreases linearly with the increase of the operating temperature.4.The RF coil and RF probe matching the main magnet system are designed.The type and material of the RF coil are determined,and the coil structure parameters are calculated by optimizing the relative SNR of the coil,and the concrete structure of the solenoid coil and the RF probe is finally designed.