Research on Metrology Techniques for Strong Magnetic Fields Using the Magnetic Flux Modulation Method
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摘要: 恒稳强磁场在科学研究、生物医疗和材料科学等领域发挥着举足轻重的作用。针对超强磁场难以测量和溯源等问题,采用基于磁通调制原理的强磁场测量方法研制了高稳定强磁场测量装置,通过开发信号调理电路,利用锁相原理获得最佳信噪比,最终获得与被测强磁场磁感应强度相对应的感应电动势值。采用标准磁场对测量装置的线圈常数标定后,该线圈常数可作为传递标准,实现超强磁场的测量和校准。对1~7 T范围内超导强磁场开展测试和比对,并对测量装置及线圈常数进行了详细的不确定度分析评估,结果表明,1~7 T磁场测量的偏差优于0.083%,测量装置引入的相对不确定度达到3×10−4,这对于超强磁场的测量有重要的参考意义。Abstract: Stable, strong magnetic fields are instrumental in scientific research, biomedicine, and material science. Addressing the challenges in measuring and tracing super-strong magnetic fields, we introduce a measurement method derived from the magnetic flux modulation principle, leading to the development of a highly stable magnetic field measuring instrument. By employing a refined signal conditioning circuit and harnessing the phase-locking principle to achieve optimal signal-to-noise ratio, we deduce the induced electromotive force corresponding to the magnetic induction intensity of the inspected strong magnetic field. Calibration of the instrument's coil constant with a standard magnetic field allows the constant to serve as a transfer standard, facilitating ultra-strong magnetic field measurements and calibrations. We examined superconducting strong magnetic fields within the 1-7 T range, providing an in-depth analysis and evaluation of the measuring device and coil constant. Our findings highlight that the measurement bias for the 1-7 T magnetic field is better than 0.083%. The relative uncertainty introduced by our instrument is up to 3×10−4, marking a significant advancement for ultra-strong magnetic field measurements.
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Key words:
- metrology /
- strong magnetic field /
- magnetic flux modulation /
- coil /
- lock-in amplifier /
- uncertainty
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表 1 分压电阻阻值与分压比
Table 1. Resistance and ratio of voltage divider
/Ω 固定电阻R1 可调电阻R2 分压比(R1+R2)/R2 100012.139 11110.266 10.00178 5262.647 20.00415 3447.737 30.00806 2563.864 40.00838 2040.865 50.00478 1694.988 60.00464 1448.980 70.02243 表 2 测量装置对磁场影响
Table 2. Impact of measurement device on magnetic field
磁体 装置放入磁体 装置取出 磁感应强度/T 2.0039095 2.0039888 2.0039093 表 3 2 T标准磁场磁感应强度
Table 3. Magnetic induction intensity of 2 T standard magnetic field
磁感应强度/T 2.0036780 2.0036787 2.0036787 2.0036767 2.0036760 2.0036775 2.0036782 2.0036769 2.0036761 2.0036762 平均值/T 2.0036773 分散性 5.29×10−7 表 4 感应电动势值
Table 4. Induced electromotive force values
感应电动势值/mV 79.372 79.293 79.552 79.495 79.524 79.439 79.540 79.582 79.366 79.544 79.413 79.378 79.331 79.357 79.620 79.532 79.536 79.482 79.386 79.355 平均值/mV 79.455 平均值相对标准差 2.71×10−4 表 5 磁场测量结果
Table 5. Magnetic field measurement results
测量
组数核磁共振仪
标准值/T原始的电动势
(幅值)/V磁感应强度
计算值/T相对误
差/%1 0.9963256 1.11865 0.99715 0.083 2 2.0040518 2.24709 2.00304 -0.051 3 3.0031943 3.36687 3.00121 -0.066 4 4.0026359 4.48698 3.99967 -0.074 5 4.9941496 5.59935 4.99123 -0.059 6 5.9943002 6.72875 5.99797 0.061 7 6.9960330 7.85282 6.99996 0.056 表 6 分压电阻的不确定度汇总表
Table 6. Uncertainty components summary for voltage divider resistance
电阻阻
值/Ω分散性引入不
确定度uA/Ω数字万用表引入
的不确定度uB/Ω合成不确
定度uR/Ω相对不确
定度/uRrel100000 0.054 0.462 0.465 4.65×10−6 11111 0.106 0.051 0.118 1.06×10−5 5263 0.050 0.026 0.056 1.07×10−5 3448 0.037 0.018 0.041 1.20×10−5 2568 0.021 0.014 0.025 9.86×10−6 2041 0.019 0.012 0.023 1.11×10−5 1695 0.002 0.008 0.008 4.62×10−6 1449 0.003 0.007 0.007 4.93×10−6 表 7 分压比例的不确定度汇总表
Table 7. Uncertainty components summary for voltage divider ratio
分压
比例
(n:1)电阻R1引入的
不确定度uR1rel电阻R2引入的
不确定度uR2rel分压比不
确定度uαrel10 4.65×10−6 1.06×10−5 1.16×10−5 20 1.07×10−5 1.17×10−5 30 1.20×10−5 1.29×10−5 40 9.86×10−6 1.09×10−5 50 1.11×10−5 1.20×10−5 60 4.62×10−6 6.56×10−6 70 4.93×10−6 6.78×10−6 表 8 线圈常数的不确定度分量汇总表
Table 8. Uncertainty component summary for coil constant
不确定度来源 符号 评定方法 标准不确定度 测量分散性 uErel A 2.71×10−4 标准磁场 uBrel B 6×10−5 电阻分压比 uαrel B 1.17×10−5 表 9 指零仪的不确定度分量汇总表
Table 9. Uncertainty component summary for null meter
不确定度来源 评定方法 标准不确定度/mV uV1 读数分散性 A 0.096 uV2 分辨率不足 B 0.003 uV3 非线性 B 0.01 表 10 测量装置的不确定度分量汇总表
Table 10. Uncertainty component summary for measuring device
不确定度来源 符号 评定方法 相对标准不确定度 分压网络 uαrel A, B 1.29×10−5 线圈常数 uNSrel A, B 2.78×10−4 指零仪 uVrel A, B 8.63×10−5 探头剩磁对磁场的畸变 u1rel B 2.29×10−5 温度变化 uCrel B 5.8×10−5 合成标准不确定度 urel 3×10−4 -
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