| Traditional nuclear magnetic resonance instruments are bulky and difficult to move,which limit their application in the biomarkers point-of-care detection.This paper focus on designing and manufacturing a portable Halbach magnet structure,and developing key components including portable probes,duplexers and preamplifiers.Finally,a portable nuclear magnetic resonance instrument was assembled to detect the concentration of biomarkers rapidly and precisely.In this dissertation,human immunoglobulin G(IgG)was chosen as the experimental object to verify the reliability and accuracy of the portable nuclear magnetic resonance instrument.The specific achievements of this dissertation are as follows.(1)Design and manufacture of portable Halbach magnet.Based on the theory of Halbach magnet,a three-layer magnet structure was designed.The central magnet was composed of 16magnetic blocks made of Sm Co32 with a height of 120 mm,which can generate a static magnetic field of 1 T.In order to solve the problem of the inhomogeneity caused by the decrease of the end magnetic field strength,a novel structure composed of twenty magnetic strips made of N52 was added at both ends of the central magnet.The simulation results showed that the theoretical homogeneity can be increased by 25%to 60.4 ppm.In addition,an effective and reliable magnet installation solution was proposed to solve the effect of strong interaction force during the installation of the magnetic blocks.Finally,the assembled magnet had an outer diameter of 66 mm with a height of 132 mm,and the weight was only 2.02 kg.The actual average magnetic field strength was 0.999 T,and the actual magnetic field inhomogeneity was as high as 4434 ppm.(2)Passive shimming method of portable Halbach magnets.In order to counteract the influence of mechanical errors on the magnetic homogeneity during processing and assembly,based on integer linear programming algorithm and 3D printing manufacturing technology,a set of passive shimming schemes for miniature Halbach magnets was developed.According to the measurement of a magnetometer,this scheme can improve the magnetic homogeneity by93.3%to 299 ppm.Not only that,the full width at half maximum(FWHM)of the free induction decay(FID)signal results showed that the initial FWHM of the magnet can be up to 493 ppm,and the FWHM was decreased to 23 ppm after passive shimming.And after adding magnetic strips,the FWHM further decreased to 16 ppm.This result not only verified the superiority of the passive shimming scheme,but also laid the foundation for obtaining a high-quality signal from the portable nuclear magnetic resonance instrument developed in this dissertation.(3)Assembly and experimental research of portable nuclear magnetic resonance instrument.According to the requirements of signal transmission,a preamplifier based on BF998 dual-gate MOSFET and a miniature RF probe with integrated duplexer circuit and tuning and matching circuit were developed.Using the portable Halbach magnet and the commercial nuclear magnetic resonance spectrometer system,a portable nuclear magnetic resonance prototype was assembled.Based on the principle of immunology,100 nm streptavidin magnetic beads and biotinylated Anti-IgG protein were used to synthetic the immunomagnetic beads.According to the analysis of relaxation signals of different concentrations of IgG samples,the developed portable nuclear magnetic resonance prototype can achieve high sensitivity detection of IgG in the concentration range of 10~0-10~4 ng/m L.The transverse relaxation time of the mixed solution was linearly related to the concentration of IgG. |
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