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研制一种新型低场核磁共振孔隙介质分析仪,通过对不同直径岩样的实际测量,可以快速提供含流体孔隙介质的T2分布,T1分布,T1-T2和D-T2二维分布等重要信息,证实了仪器的合理性,有效性,及便捷性。采用Hal-bach磁体和可变尺寸开槽法拉第屏蔽螺线管天线,方便了样品制备和探测效率。低成本线性功率放大器的输出功率可达250 W,能够满足线圈激励要求,并降低成本。有源场效应管组成的隔离电路工作频率较宽,具有通用性。射频三极管组成的负反馈放大电路作为前置放大电路的第一级保证接收回路的低噪声设计,三极管集电极电流由运放为核心的虚拟电流源,使电路设计简化。DSP和FPGA作为主控电路的运算和逻辑控制单元,使回波信号提取和脉冲序列时序生成更灵活。
A new type of low-field nuclear magnetic resonance porous media analyzer is developed. By measuring the different diameter rock samples, important information such as T2 distribution, T1 distribution, two-dimensional distribution of T1-T2 and D-T2 can be quickly provided , Confirmed the instrument rationality, effectiveness, and convenience. The Hal-bach magnet and variable-size slotted Faraday shielded solenoid antennas facilitate sample preparation and probing efficiency. Low-cost linear power amplifier output power up to 250 W, to meet the coil excitation requirements, and reduce costs. Active field effect transistor composed of a wide range of isolation circuit frequency, with versatility. As the first stage of the preamplifier circuit, the negative feedback amplifier circuit composed of RF transistors ensures the low noise design of the receiver circuit. The transistor collector current is the virtual current source with the op amp as the core, which simplifies the circuit design. DSP and FPGA as the main control circuit operation and logic control unit, the echo signal extraction and pulse sequence timing generation more flexible.