Design Of Ac Susceptibility Measurement System For Temperature Detection

This thesis aims to design a temperature measurement system, which is made from magnetic nanoparticle and is under sine ac magnetic field excitation. Through the measurement of the ac susceptibility of the magnetic nanoparticle, this system measures its relaxation time, and further the temperature of the magnetic nanoparticle sample through the relation between the relaxation time and the temperature is measured. This system provides new ideas for non-contact temperature measurement of magnetic nanoparticle, and it promoting the development of magnetic nanoparticle in bio-medical fields such as biological detection and hyperthermia.Firstly, this thesis introduced the research background of magnetic nanoparticle, its value for biomedical research especially in the field of hyperthermia treatment for cancer, correlational research status in this field, and its magnetic properties including the magnetic susceptibility and the relaxation time. Through the research on the relationship among the ac susceptibility, the relaxation time and the temperature, this thesis explored the possibility of a new method for con-contact temperature measurement.Then the theoretical approach for measuring ac susceptibility was obtained and the relationship between susceptibility and temperature measurement was established by physically modeling ac susceptibility of magnetic nanoparticle and analyzing both real and imaginary parts of ac susceptibility. After that, this thesis introduced the hardware structure design of this weak magnetic field measurement system, i.e. after passing through the power amplifier, the signal source actuates the excitation coil and generate exciting magnetic; and the pick-up coil in magnetic field generate induces electromotive force after it detects the responding magnetic field generated by magnetic nanoparticle sample; the induced electromotive force is brought into PC through DAQ Card, and then data acquiring and analyzing is accomplished. In the following, the thesis introduced the software design of the system, primarily the part written by Lab VIEW language. Specifically, it introduced how to keep the stability of exciting magnetic field by controlling out-put signal source through PID algorithm module; as well, it introduced how to acquire magnetic induction signal through the application of DPSD in weak signal extraction; also, it introduced how to read and process data timely through the application of TDMS data storage and processing methods. In the end, this thesis described the experiment process and introduced the treatment of experiment results, i.e. fetching the temperature information in both the real and imaginary parts by measuring as susceptibility of different samples; and then matching them. It was been found that the results are consistent with the model. Hence, the feasibility of this new method is been proved.