The Method And Experimental Researches Of Measuring Time-varying Magnetic Field Based On Broadband Nuclear Magnetic Resonance

The environment of the high magnetic fields is a new platform for physics, chemistry, lifesciences, and other disciplines to explore uncharted territory; it can also help scientific researchersto find innovative approaches in experiment. Accurate calibration of pulsed high magnetic fields isnot only the scientific research needs but also will be helpful to the development of precisemeasurement technique. Wide dynamic range, short duration and spatial non-uniformity make ithard to calibrate the magnetic field’s variation with time. Magnetic fields measurement based onNMR has the advantages of wide range of measurement, high precision, which is to be betterchoice for scholars.The conventional pulsed nuclear magnetic resonance (NMR) technology is limited to measureconstant longitudinal magnetic fields or pulsed longitudinal magnetic fields at some givenmoments, however, this project based on ultra wide band nuclear magnetic resonance principle(UWB-NMR) investigates a new kind of precise measurement of high magnetic fields. In otherwords, wide band RF fields are used to drive the samples to emerge the NMR phenomenon so thatwe can avoid field-frequency chain link appeared in the conventional measurement and we candescribe the time-varying law of magnetic fields in the same time. There exist some innovations inthe physical mechanism, experimental method design and signal processing technique in thisproject.This thesis first analyzes the relaxation process of nucleus, and then solves the Bloch equationin the time-varying longitudinal magnetic fields, finally we derivate the variation and detectionform of induced electromotive fore, which can confirm the correctness of measurement used inthis paper.Based on the above theoretical basis, electronics system with the orthogonal dual coil probeand advanced signal processing skills as core are built, in which an experimental platform with thefunctions of broadband RF signal generation, low distortion emission, non-steady NMR signalreceiving and collecting in large dynamic range under the low pulsed magnetic field is set up andwe utilize this platform to conduct some experiments with single frequency, discrete multi-toneand UWB pulse in low field. Afterward we use an adaptive interference cancellation algorithm toprocess the result and deduce backward to get magnetic fields variation characteristics in the timedomain. In the end, relative improvements are proposed. looking forward better experiment result.