Research On Magnetic Field Generating Device In Magnetic Nanometer Thermometer

The magnetic naonparticles thermometer is an novel temperature measurement system different from the traditional thermometers,which measures the temperature based on the magnetization response of magnetic nanoparticles induced by excited magnetic fields and has good application prospects in the treatment of tumor(such as,magnetic nanoparticles hyperthermia and targeted drugs).However,the magnetic nanoparticles thermometer is to be assessed in practical application because of the temperature accuracy to be improved.Consequently,the thesis focus on the AC susceptibility model of magnetic nanoparticles,the design of a high-precision magnetic field generator system,and the thermal management of the magnetic field generator system with low-temperature drift,improving the temperature accuracy of magnetic nanoparticles thermometer.(1)The AC susceptibility model of magnetic nanoparticles is studied.The dynamic magnetization of magnetic nanoparticles can be described based on the Fokker-Planck model.We analyzed the difference in AC susceptibility between the Fokker-Planck model and the Debye model.The phenomenological model of AC susceptibility is proposed based on analysis results,avoiding the linear model errors of Debye model in large excited magnetic fields.The simulation and experiment results show that the proposed phenomenological model can accurately describe the AC susceptibility.The temperature can be estimated in the high-frequency magnetic field via the temperature model constructed based on the proposed phenomenological model of AC susceptibility,and the simulated temperature error is less than 0.012 K.Moreover,we investigated the dependence of temperature error on the uniformity of the AC magnetic field,which is that the uniformity of the AC magnetic field needs to be less than 0.01% for the temperature accuracy of 0.1 K.(2)An improved structric of Helmholtz coil is proposed to avoid the temperature error of magnetic nanoparticles thermometer caused by the uniformity of magnetic field generator.We simulated the uniformity of excited magnetic field based on the position and size of the Helmholtz coil.The simulation results show that the proposed structric of Helmholtz coil can enlarge twice the uniform area of magnetic field compared to that of the normal structric.It is expected to provide a solution for the high-precision magnetic field generator in magnetic nanoparticles thermometer.(3)To solve the problem of coil heating affecting temperature drift of alternating magnetic field,a design method of low-temperature drift coil was proposed,and the coil heating mechanism was analyzed from thermal model and simulation experiment.The characteristic parameters of the coil will be changed by the heating of coil,resulting in the fluctuation of magnetic field.Therefore,we proposed three solutions for the low-temperature drift magnetic field generator,reducing the temperature coefficient of coil impedance by the multi-strand wires and materials with a smaller temperature coefficient of resistance,and compensateing the coil resistance temperature drift by connecting a negative temperature coefficient resistor in series with voltage correction table.The low-temperature drift magnetic field generator is expected to provide a solution for the technical problem of magnetic nanothermometers exceeding 0.1K accuracy.