Design Of AC Weak Magnetic Field Measurement System For Magnetic Nanoparticles

This thesis researches a AC weak magnetic field measurement system for magneticnanoparticles to measure the magnetization of the magnetic nanoparticles, whichcharacterizes the thermodynamic characteristics of magnetic nanoparticles by magneticmethods, and has a high temperature sensitivity.This thesis introduces the research back ground and significance of magneticnanoparticles, and understands the research status of magnetic nanoparticles. It is modeledthat the magnetization of the magnetic nanoparticles in the sinusoidal excitation. ACmagnetization model of Langevin function were discrete, and It is expanded thepolynomial measurement model by Taylor. Under weak magnetic excitation,magnetizationof the magnetic nanoparticles have a temperature sensitivity.It’s established that throughthe method of the odd harmonics of the measurement signal to design the experimentalsystem. This thesis describes the hardware systems of the experimental system. Helmholtzcoils are excited by the way of the amplifier to obtain excitation field. And it steadiescurrent through the feedback resistor to ensure the stability of the excitation field. We canobtain a large enough useful signal detection coils by study the amplifier circuit throughtwo differential circuits. It provides the basis for the later signal acquisition.More, usingthe Labview designs software par system. It’s elaborated that controlling the outputvoltage to ensure the stability of the feedback resistor by PID method.It describes thatusing a algorithm of digital phase-sensitive detection (DPSD) extracts a specific frequencysignal amplitude. It determines the parallel method to measure signal of each harmonicapproach. A specific measurement method is designed for each odd harmonics signals.The amplitude information of each of the odd harmonics of the desired signal can becollected by the system. the thesis processes data by matlab. Through the temperatureerror analysis,it determines that the theoretical model can be a good fit to the Langevinfunction. It proves that the data can characterize the thermodynamic characteristics ofmagnetic nanoparticles. And it determines the credibility of measuring the temperature ofthe magnetic nanoparticles.