| Transient temperature is a topic gotten much attention due to the ability to characterize the process of material properties.In the field of biomedicine,microelectronics and others,transient temperature changes often occur inside the non-transparent media.Limited by the measurement speed and depth,there is a lack of available measurement method at present.Magnetic nanoparticles sensor has been considered as an effective semi-intrusive(noninvasive)thermometer with the potential to solve the problems in internal temperature measurement.Therefore,based on the magnetic temperature sensitivity of magnetic nanoparticles,this dissertation studies the transient temperature measurement method which is suitable for the internal of non-transparent object,which provides feasible solutions for the monitoring and control of dynamic temperature in vivo in tumor magnetic hyperthermia and the observation of the ultrafast heat process.Firstly,this dissertation has made a theoretical study on the dynamic magnetization of magnetic nanoparticles for the improvement of the transient response performance of magnetic nanometer thermometer.Using high-frequency magnetic field to excite magnetic nanoparticles can not only expand the applicable magnetic field frequency range of the magnetic nanothermometer,but also improve the transient response performance.This dissertation derives the magnetization response with significant relaxation effect of magnetic nanoparticles in the high frequency magnetic field,analyzes the relationship among the applied field,the temperature and the magnetic response based on the Shliomis’s relaxation equation.In addition,considering that the temperature dependence relaxation process is not a simple Brownian relaxation,this dissertation studies the coupling of Neel relaxation and Brownian relaxation under different applied magnetic fields through establishing magnetic thermal dynamic stochastic motion model of magnetic nanoparticles.The simulation results show that the two relaxation processes are coupled with each other and there will be anomalous phenomena under thestrong alternating magnetic field,which provides a theoretical basis for the correction of relaxation model.In order to simulate the tumor magnetic hyperthermia environment and realize the corresponding temperature measurement,this dissertation constructs a set of hardware and software system,which mainly includes high frequency alternating magnetic field generating device,magnetic measuring device and software module.Base on this,due to the high harmonic distortion of the high-power alternating magnetic field will lead to the invalid of the magnetic nanoparticles temperature sensing model,this dissertation proposes a temperature estimation method which uses neural network to fit the nonlinear model among the harmonics of applied field,harmonics of magnetic nanoparticles response and temperature,and then inverts the transient temperature by measuring the harmonics.The experimental results of test tube show that the mean error of temperature measurement is 0.41 K with the standard deviation of 2.08 K.Base on this proposed method,this dissertation controls the temperature of magnetic fluid in the magnetic heating process using the results measured by magnetic nanothermometer.The experimental results show that the temperature fluctuation range is 0.40 K within ten minutes after stabilization,which preliminarily verifies the feasibility of temperature feedback control by magnetic nanothermometer in magnetic hyperthermiaand lays the foundation for the next step in vitro experiment.Consider further improving the transient response of the magnetic nanothermometer to meet the needs of ultrafast thermal process observations,this dissertation analyzes the rate of magnetic-thermal response and proposes a time-resolved temperature measurement method based on magnetization temperature characteristics of magnetic nanoparticles.According to the temperature measurement model,the corresponding temperature measurement device has been built.A transient thermal process is generated by pulsed laser and corresponding measurement can by carried out by this device.The experimental results verify the feasibility of the method above,and the temporal resolution can reach 14.4 ns. |
