EXPERIMENTAL STUDY ON LOW NOISE SENSOR FOR FLUXGATE MAGNETOMETER

磁通门磁力仪在地球、空间和行星观测卫星的研究中被经常使用。近年来，各种实验都要求具有较高的灵敏度、分辨率和最小的传感器噪声电平，这是决定磁场测量分辨率的关键。从美国进口的传感器磁芯已经在卫星上使用，但还需要开发一种国产的低噪声磁芯。但到目前为止，噪声特性还没有表现出来。日本现有的每一个传感器核心都进行了测试。特别是对日本核和美国核的噪声水平和灵敏度进行了比较。实验参数为驱动电流、频率、传感器尺寸和温度。结果表明：(1)最佳低噪声高灵敏度传感器的驱动频率为8 kHz，驱动磁幅为10。(2)噪声水平与使用的坡莫合金的长度成反比，灵敏度与磁芯直径的三次方成正比。它们与坡莫合金的缠绕层数无关。岩心直径与磁导率差成正比，决定了传感器的灵敏度。(3)近室温时温度梯度为0.2 nT/度，与岩心尺寸和长度无关。从-20度到+70度的宽频带内，日本岩心的噪声电平变化比美国岩心的大。据推测，美国筒管的热膨胀系数接近坡莫合金，因此美国芯的张力和应力都很小。(4)结果表明，直径27 mm的15圈坡莫合金日本芯的噪声水平比美国芯低，灵敏度也比美国芯好。

Fluxgate magnetometer has been very often used in research on satellites for Earth, space and planetary observations. Recently, every experiment is required high sensitivity resolution and minimization of sensor noise-level that are to decide resolution detecting the magnetic field. Import sensor cores from USA have been used on satellites but a homemade low noise-level core should be developed. But the noise characteristics have not shown till now.Every sensor core that exists in Japan have been tested. Especially, Japanese core and US core was compared for their noise-level and sensitivity. The experimental parameters are drive current, frequency, sensor size and temperature. And also a small tri-axial sensor and a residual magnetic moment measurement system for satellite instruments have developed.The following results were obtained.(1) The optimum low noise and high sensitive sensor is 8 KHz for drive frequency and 10 Oersted for drive magnetic amplitude.(2) Noise-level is inverse proportional to the length of used permalloy and sensitivity is proportional to the cubic of core diameter. They are independent on the number of winding layer of permalloy. The diameter of core is also proportional to the differential permeability and it decides sensor sensitivity.(3) Temperature gradient is 0.2 nT/degree in Centigrade for near room temperature and it is independent on core size and permally. The change of noise-level for wide band between from -20 to +70 degrees shows large for Japanese core compare with US core. It is guessed that the coefficient of heat expansion of US bobbin is near to that of permalloy, so tension and stress are small for US core.(4) As a result, the Japanese core of 27mm in diameter with 15 turns of permalloy is less the noise-level and also better the sensitivity than those of US core.