Research On Key Technologies Of Temperature Measurement Using Magnetic Nanoparticles And Its Application

The temperature of magnetic nanoparticles is measured by utilizing the temperature sensitive properties of magnetic nanoparticles and the nonlinear characteristics of the magnetization curve of magnetic nanoparticles. The temperature information is extracted from the magnetizationharmonic amplitudes under AC magnetic field excitation. Magnetic nanoparticles temperature measurement, as a novel non-contact temperature measuring method, provides a new solution for the temperature measurement in special environment. We successfully developed the magnetic nanothermometer in2014, applied it in the high-power LED junction and phosphors temperature measurement and provided the experimental basis for the debate "The junction temperature is or not the highest in the high-power LED". The measurement accuracy is0.1K and the measurement time is1s.The principle of the temperature measurement in the magnetic nanoparticle thermometer is to use the magnetic nanoparticles with the properties of temperature sensitivity and the nonlinear characteristics of the magnetization curve, which obey the Langevin paramagnetic function. However, Langevin function does not have an analytical solution. The model of the nanoparticles’temperature solved from the magnetization amplitudes of different harmonics expressed as discrete Langevin function under AC magnetic field excitationis proposed. The corresponding optimization scheme is proposed to improve the precision of the magnetic naoparticle thermometer in this thesis through simulation experiments on temperature measurement model and the parameters in the model. The optimum excitating magnetic field strength is from100to200Guass, the excitating frequency is below1kHz, the mean particle size is from10to12nm, the deviation of the particle distribution is smaller than0.15nm. According to the difference between magnetic nano-solid powder and magnetic properties of nano-colloid solution, the unique thermodynamic behavior phenomenon of the conversion between polymer and monomer of nano-colloid solutionis also studied. The frequency of the excitation magnetic field is found to be one of the important factors affecting the conversion between polymer and monomer. The classical Langevin function is modified according to the characteristics of magnetic nano-colloidal solution so that the theoretical basis for the application of magnetic nano-colloidal solution in temperature measurements is provided, which extends the application fields of magnetic nanoparticles (solid/liquid).Then the precision of the magnetic nano-thermometer, especially the system error and anti-noise performance of the system is studied in this thesis. In terms of the system error, the signal transfer path is observed as the research object and the error sources introduced during the signal flow through the system are analyzed. Through mathematical modeling and simulation, significant error sources are found and then the optimal signal transfer path with the minimum errors is found by analyzing the changes of the significant error sources. The theoretical foundation for the high precision magnetic nano-thermometer system design is established in this way. In terms of the anti-noise performance, the harmonic noise, frequency noise, Gaussian noise, sampling rate and sampling period are analyzed so that a design index for improving the accuracy of temperature measurement of magnetic nanoparticles is established as well. The ratio of the signal-to noise (SNR) should be higher than80dB when the measurement error of the magnetic naothermometer is below0.1K.In addition, the stability of the magnetic nano-thermometersystem is analyzed. The important factors that affect the system stability, namely the non-linear drift caused by Helmholtz coil and the power amplifier heating problems, are found through lots of experimental analysis. The working environment with a constant temperature should be provided for the Helmholtz coils. The Helmholtz coils are suggested to be soaked in the silicone oil using the circulation cooling system for keeping the temperature stable. The digital feedback preprocessing technology is proposed in this thesis to achieve the nonlinear compensation of power amplifier so that the problem of the long-term stability of the magnetic nano-thermometer system is solved.After the discussion on the measurement precision and stability of the magnetic nano-thermometer system, the magnetic nano-thermometer system with high measurement precision is introduced in this thesis. The THD parameters generated in the AC excitation magnetic field should be less than0.01%so that the magnetic field volatility is below0.01%. The requirement is far higher than the national measurement standard for AC magnetic field. In the harmonic signal detecting device, the eliminating AC bias is lower than80dB by three-stage method.At the end of this thesis, the successful application of the magnetic nano-thermometerin high power LED junction temperature measurement is discussed. In addition, the measured temperature data through the magnetic nanothermometer directly show that the LED junction temperature layer is less than the fluorescent layer, which provide the experimental basis for the dabate "The long-standing debate of whether the junction temperature of LED layer is the highest temperature layer".