三轴磁通门探头球型反馈线圈的设计方法研究

长周期大地电磁测量要求三轴磁通门传感器具有低的噪声水平及高稳定性，根据实际需求设计一个尺寸合适的球型反馈线圈可以有效提高反馈磁场的均匀性，进而降低磁通门传感器的噪声水平.本文首先分析了非均匀反馈磁场引入磁通门噪声的机理，然后根据毕奥-萨伐尔定律和矢量叠加原理，以等间距多个单匝线圈构成单轴绕组的形式，建立了球型反馈线圈轴线上的轴向磁场分布及磁场均匀度数学模型，在给定磁场均匀度和球型反馈线圈直径的条件下，运用控制变量法确定了球型反馈线圈的单匝线圈数量和间距等关键结构参数.我们把设计的结构参数代入球型空间磁场分布数学模型，验证了本设计方法的正确性.最后，按照设计的结构参数制作了基于球型反馈线圈磁通门探头的三轴磁通门传感器，通过与体积相近的基于亥姆霍兹型反馈线圈磁通门探头的三轴磁通门传感器对比测试噪声水平，结果表明球型反馈线圈磁通门探头能够使得三轴磁通门传感器具有更稳定和较低的噪声水平.

Design of a spherical feedback coil for the three-axis fluxgate probe

Long-period magnetotelluric measurement requires the three-axis fluxgate sensor have low noise level and high stability. According to this need, a spherical feedback coil with suitable size should be designed to effectively improve the uniformity of the feedback magnetic field, and thus the noise level of fluxgate sensor is reduced. To this end, the mechanism of introducing fluxgate noise caused by non-uniform feedback magnetic field is analyzed, and then, according to Bio-Savart's law and vector superposition principle, uniaxial windings are formed by equal-spacing single-turn coils. A mathematical model is established to describe axial magnetic field distribution and magnetic field uniformity on the axis of this spherical feedback coil. Under the condition of given magnetic field uniformity and spherical feedback coil diameter, the key structural parameters such as the number and spacing of the single turn coil of the spherical feedback coil are determined by using the control variable method. We introduce the structural parameters of the design into the mathematical model of magnetic field distribution in spherical space and verify the correctness of the design. Finally, the three-axis fluxgate sensor based on spherical feedback coil fluxgate probe is developed according to the designed structure parameters. Comparison with the Helmholtz feedback coil shows that this spherical feedback coil fluxgate probe can make the three-axis fluxgate sensor have more stable and lower noise level.