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Mini Inside-Out Nuclear Magnetic Resonance Sensor Design for Soil Moisture Measurements

机译：用于土壤水分测量的微型内外核磁共振传感器设计

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The improvement of water management in agriculture by exactly detecting moisture parameters of soil is crucial. To investigate this problem, a mini inside-out nuclear magnetic resonance sensor (NMR) was proposed to measure moisture parameters of model soils. This sensor combines three cylindrical magnets that are magnetized in the axial direction and three arc spiral coils of the same size in series. We calculated and optimized the magnet structure by equivalent magnetization to current density. By adjusting the radius and height between the cylinders, a circumferential symmetric constant gradient field (2.28 T/m) was obtained. The NMR sensor was set at 2.424 MHz to measure the water content of sandy soil with small particle diameter and silica sand with large particle diameter. The complete decaying, an NMR signal was analyzed through inverse Laplace transformation and averaged on a T2 space. According to the results, moisture content of the sample is positively correlated with the integral area of T2 spectrum peak (Apeak); T2 of the water in small pores is shorter than that in large pores, because the movement of water molecules are limited by the inner wall of the pores. In the same volume, water in large pore sample is more than that in small pore sample, so Apeak of silica sand is larger than Apeak of sandy soil. Therefore, the sensor is capable of detecting moisture both content and pore size of the sample. This mini sensor (4.0 cm in diameter and 10 cm in length) is portable, and the lowest measurable humidity is 0.38%. Thus, this sensor will allow easy soil moisture measurements on-field in the future.
机译：通过精确检测土壤的水分参数来改善农业用水管理至关重要。为了研究这个问题，提出了一种微型的由内而外的核磁共振传感器（NMR）来测量模型土壤的水分参数。该传感器将轴向磁化的三个圆柱状磁体和三个相同大小的弧形螺旋线圈串联在一起。我们通过等效于电流密度的磁化强度来计算和优化磁体结构。通过调节圆柱体之间的半径和高度，可获得周向对称的恒定梯度场（2.28 T / m）。 NMR传感器设置为2.424 MHz，以测量粒径较小的沙质土壤和粒径较大的硅砂的含水量。通过逆拉普拉斯变换分析完全衰减的NMR信号，并在T2空间上求平均值。根据结果​​，样品的水分含量与T2谱峰的积分面积（Apeak）正相关；小孔中的水的T2短于大孔中的水，因为水分子的运动受孔的内壁限制。在相同体积下，大孔隙样品中的水分要大于小孔隙样品中的水分，因此硅砂的Apeak大于沙质土壤的Apeak。因此，该传感器能够检测样品中的水分和孔径。这款微型传感器（直径4.0厘米，长度10厘米）是便携式的，可测量的最低湿度为0.38％。因此，该传感器将允许将来在现场轻松进行土壤湿度测量。

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