Research On Multilayer Halbach Permanent Magnet For Human Finger Blood Glucose Noninvasive NMR Monitoring

Blood glucose noninvasive NMR detection has the advantages of non-invasive,rapidity and accuracy,which has received widespread concern from scholars both at home and abroad.Magnet is an indispensable module to nuclear magnetic resonance(NMR)system.The magnetic field strength and uniformity in its interest region will directly affect the NMR signal.However,commonly used NMR magnets are too bulky and expensive,restricting the development and promotion of NMR technology for blood glucose noninvasive detection.Therefore,the purpose of this dissertation is to develop a NMR magnet device for noninvasive glucose monitoring.Firstly,based on the theory of magnetic circuit design and finite element method(FEM),a magnet structure is designed with strong strength,homogeneity in small size.And the geometric parameters of magnet are optimized.Then the detection probe is developed and the NMR experimental platform is established.Finally,the application experiments are researched,testing glucose solution and human finger.The results show that the developed magnet structure can be effectively applied to blood glucose noninvasive NMR detection.Major results are as follows:(1)Based on the theory of magnetic circuit design and magnetostatic field finite element analysis method,the performance of various types of magnetic circuits is analyzed and a multilayer Halbach circular magnet structure is designed,applying to human finger blood glucose noninvasive NMR detection.The field inhomogeneity caused by the end effect of Halbach magnet is mainly solved.The radial adjustment method is innovatively proposed to optimize the structure and shim the field.The magnetic field in the cylindrical region(020 X 20mm)of the structure center is calculated,whose final strength achieves up to 447mT and homogeneity is 4.46 x 102 ppm,even within 50ppm in 010 x 10 mm.The structure assembly process of the multilayer Halbach magnet is researched and completed.The finished multilayer magnet assembly has a size of(?)180mm X 107.2mm with a hollow(cross section 40mm×40mm)in the center,whose weight is only 7.4kg(5.3kg magnet material and 2.1kg aluminum).(2)Combining the developed magnet and solenoid NMR probe with commercial electronic control system,the experiment platform is established.The exploration and application NMR experiments for blood glucose noninvasive monitoring are carried out.The experiment results verify that the developed multilayer Halbach magnet structure can be effectively applied to blood glucose noninvasive NMR detection.By detecting the free induction decay(FID)signal of the deionized water,the field uniformity of the magnet device is verified through experiment method.NMR CPMG decay signals of five different samples are measured and the results demonstrate that transverse relaxation times conincide with commercial device.Aiming at the application target for human blood glucose noninvasive detetion,the experiment for testing glucose solution concentration is carried out.The experimental results illustrate that the transverse relaxation time reduces linearly with the increase of solution concentration,which prove that NMR method is feasible to detect small concentration variation.Eventually,by monitoring and analyzing the NMR signals before and after dinner through human finger,experimental results are found perfectly consistent with conventional method,which demonstrate that the variation of glucose concentration before and after dinner can be effectively monitored by the experiment platform developed in this dissertation.