Schlumberger-Doll Research, Cambridge, MA 02169, USA.
J Magn Reson. 2011 May;210(1):69-74. doi: 10.1016/j.jmr.2011.02.014. Epub 2011 Feb 17.
Nuclear magnetic resonance typically utilizes a tuned resonance circuit with impedance matching to transmit power and receive signal. The efficiency of such a tuned coil is often described in terms of the coil quality factor, Q. However, in field experiments such as in well-logging, the circuit Q can vary dramatically throughout the depth of the wellbore due to temperature or fluid salinity variations. Such variance can result in erroneous setting of NMR circuit parameters (tuning and matching) and subsequent errors in measurements. This paper investigates the use of a non-resonant transmitter to reduce the circuit sensitivity on Q and demonstrates that such circuits can be efficient in delivering power and current to the coil. We also describe a tuned receiver circuit whose resonant frequency can be controlled digitally. Experimental results show that a range of common NMR experiments can be performed with our circuits.
核磁共振通常利用调谐共振电路和阻抗匹配来传输功率和接收信号。这种调谐线圈的效率通常用线圈品质因数 Q 来描述。然而，在现场实验中，如测井中，由于温度或流体盐度的变化，电路 Q 会在井筒的整个深度内发生显著变化。这种变化会导致 NMR 电路参数（调谐和匹配）的错误设置，并导致后续测量出现错误。本文研究了使用非共振发射器来降低电路对 Q 的灵敏度，并证明这种电路可以有效地向线圈传输功率和电流。我们还描述了一个调谐接收器电路，其谐振频率可以数字控制。实验结果表明，我们的电路可以进行多种常见的 NMR 实验。
