A Non-Steady State NMR Effect Based Time-Varying Magnetic Field Measurement Method and Experimental Apparatus

Abstract

Accurate measuring magnetic induction intensity is important for some scientific research. In the paper, the conventional nuclear magnetic resonance (NMR) experiment under static magnetic field has been extended to longitudinal time-varying magnetic field (TVMF), and the time domain transient solution of the Bloch equations for spin nuclei exhibits the so-called non-steady state nuclear magnetic resonance (NSS-NMR) phenomenon. Based on the above effect and the precise gyromagnetic ratio of spin nucleus, a new magnetic field measurement method and corresponding experimental apparatus have been developed in longitudinal TVMF environment. The orthogonal dual-coil probe, radio frequency (RF) exciting and receiving hardware, key signal processing algorithms, host computer controlling and analysis software are deeply studied. In order to improve the signal-to-noise ratio of the NSS-NMR signal, the RF signal envelope shaping and the low-frequency pre-emphasis probe matching techniques are designed and verified by the invented circuit-field-nuclear multi-domain joint simulation subassembly (CFN-MDJS) which is integrated in the host computer software. Furthermore, the multi-tone RF excitation signal substituting the bandpass continuous spectrum signal for NSS-NMR experiment is also verified by the CFN-MDJS. The experimental results under longitudinal 50Hz TVMF environment has demonstrated the authentic existence of the NSS-NMR effect and simultaneously verified the effectiveness of the experimental scheme and signal processing algorithms proposed in the paper.INDEX TERMS time-varying magnetic field (TVMF), magnetic field measurement, non-steady state nuclear magnetic resonance (NSS-NMR), envelope shaping, low frequency pre-emphasis, circuit-fieldnuclear multi-domain joint simulation (CFN-MDJS).