Preliminary Study Of NMR Under Time-varying Longitudinal Magnetic Field

In recent years, high magnetic field environment, which provides a new platform forscientific research, has been widely studied and applied. So, the calibration of magneticfield has been paid more and more attention. Currently, most of the high magnetic fieldsare generated by pulse method, with some characteristics of large range of magnetic fieldchanges, short duration, large non-uniformity,and high difficulty of calibration. Due to theadvantage of big measurement range and high precision, scholars have started to payattention to Nuclear Magnetic Resonance (NMR). The subject use "UWB_NMR" methodto measure high magnetic field, which does not emphasize the arrival time of magneticfield, and can depicts laws of time-varying magnetic field. It has a greater innovation inexperimental methods and research of Physical mechanism.This paper, which based on the basic theory and analysis method for conventionalpulse NMR, theoretically analyzes the change rule of magnetic moment for NMR undertime-varying longitudinal magnetic field. After the analysis and author, this paperproposes that this NMR is different from conventional pulse NMR in several aspects, suchas nutation angle variation and macroscopic magnetic moment variation.To inspect the physical mechanism proposed in NMR under time-varyinglongitudinal magnetic field, the subject builds the experimental platform with the core ofdouble coil probe system, and proposes the electronics system for it, which containes ofthree components: unit of broadband RF signal generation, unit of broadband RF signaltransmission and NMR signals reception acquisition, unit of data processing. This paperintroduced the parameter calculation and selection of each components of theexperimental platform, such as double coil probe winding and impedance matching.Combined with the signal analysis for NMR under time-varying longitudinalmagnetic field, this paper introduced experimental steps under low-field, and analyzesthe results of pulse NMR experiment from the envelope, spectrum and statisticalproperties, etc. Finally, this paper proposed some experimentally improvement, hoping tohave good experimental resultsin in future.