低场核磁共振仪器振铃抑制新方法及其电路实现  

A New Method and Circuit of Ringing Suppression for Low-field NMR Instruments

作　　者：师光辉 肖立志[1,3] 廖广志 罗嗣慧[1,2] 侯学理 卢亚普 SHI Guanghui;XIAO Lizhi;LIAO Guangzhi;LUO Sihui;HOU Xueli;LU Yapu(State Key Laboratory of Petroleum Resources and Prospecting,China University of Petroleum,Beijing 102249,China;College of Geophysics,China University of Petroleum,Beijing 102249,China;Harvard SEAS-CUPB Joint Lab.on Petroleum Science,Cambridge,MA 02138,USA;China National Logging CO.LTD.,Xi’an 710077,China)

机构地区：[1]中国石油大学(北京),油气资源与工程国家重点实验室,北京102249 [2]中国石油大学(北京)地球物理学院,北京102249 [3]Harvard SEAS-CUPB Joint Lab.on Petroleum Science,Cambridge,MA 02138 [4]中国石油集团测井有限公司,陕西西安710077

出　　处：《波谱学杂志》2023年第1期68-78,共11页Chinese Journal of Magnetic Resonance

基　　金：中国博士后科学基金资助项目(2021M700172)。

摘　　要：加快天线残余能量释放以减弱天线振铃信号有利于缩短低场核磁共振仪器的回波间隔(TE),从而提高快弛豫组分的测量分辨率和信噪比(SNR).而天线Q值对能量的发射效率和泄放速度起着相反的作用.为此,我们首先设计了一种新型Q转换电路,在保证发射效率的同时,可以大大缩短能量泄放时间.在此基础上,应用了一种优化的脉冲序列以弥补传统相位交替对脉冲序列(PAPs)不能消除90脉冲振铃的缺陷,通过相位循环的方法进一步提高了信噪比.最后,在2 MHz岩心分析仪上测试了新型Q转换电路,当天线Q值降为发射期间的约1/5时,天线恢复时间由280.0μs降为18.2μs;而且,使用新型Q转换电路和优化的脉冲序列后,TE=60μs时,可以有效获得快弛豫组分的T2信号.Accelerating the release of the antenna residual energy to weaken the antenna ringing signal is beneficial to shorten the echo time(TE)of low-field nuclear magnetic resonance(NMR)instruments,thus improving the measurement resolution and signal-to-noise ratio(SNR)of fast relaxation components.The antenna Q value has an opposite effect on the energy emission efficiency and discharge speed.For this reason,we first designed a new Q-switch circuit,which can greatly shorten the energy discharge time while ensuring the transmission efficiency.On this basis,an optimized pulse sequence was applied to overcome the defect that traditional phase alternated pair stacking(PAPs)cannot eliminate 90°pulse ringing,and the SNR was further improved by the method of phase cycling.Finally,the new Q-switch circuit was tested on a 2 MHz core analyzer,the Q value of the antenna was reduced to about 1/5 of the transmit period,and the antenna recovery time was reduced from 280.0μs to 18.2μs.Moreover,with the new Q-switch circuit and optimized pulse sequence,the T2signal of the fast relaxation component can be effectively obtained when TE=60μs.

关 键 词：低场核磁共振(low-field NMR) Q转换 振铃 信噪比(SNR) 脉冲序列 

分 类 号：O482.53[理学—固体物理]