Preliminary Study On Miniature NMR Instrument

With the introduction and application of digital instrument technology and computer technology and the continuous progress of electronic technology, modern nuclear magnetic resonance (NMR) instruments tends to develop the miniature NMR instrument with better system performance and more functions. However, the perfect balance of miniaturization with performance and functions is not only specific issues in engineering, but also the hot topics of instruments technologies. The purpose of this study is to explore the paths of developing miniature NMR instruments with fully functions.This dissertation mainly studies the relevant technologies and methodologies on miniature NMR instrument, further explores their characteristics and concrete applying conditions. Then, some hardware design works are carried out for "0.5T MRI system for joints".Firstly, it includes two works that the studies on the related techniques of digital transmitters. One work is the summary about the characteristics of these technologies and their applicability. The other is the discussion on the correlations of different technologies and the possibility of transformation between them. Based on the studies, a design scheme of quadrature direct up-conversion transmitter based on AD9857is proposed for the miniature NMR instrument. This scheme not only can be applied to the design of digital transmitter in "0.5T MRI system for joints" project, but also can be extended to a superheterodyne digital transmitter with adding mixing and filter.Secondly, an analysis on the original definition of band-pass sampling reveals the importance of avoiding overlapping spectrum for signal recovery. Based on the conclusion, a new study has been done on the band-pass sampling in different perspectives. And the practical expression of sampling rate was deduced and validated in band-pass sampling. Furthermore, in view of specialty of frequency transformation in band-pass sampling, an assumption has also been demonstrated and validated that baseband signal can be demodulated by band-pass sampling and digital low-pass filter directly.Finally, some conclusions are reached by studying about the technologies of digital receiver. Some technologies and methods are chosen, which apply to digital receiver for miniature NMR instrument. And the effects are made clear on decimate and interpolation. Moreover, in order to meet actual requirements, various functional units were designed in detail. Then, a hardware design has been finished, which was a direct sampling digital quadrature receiver in "0.5T MRI system for joints".