EXPERIMENTAL STUDY ON LOW NOISE SENSOR FOR FLUXGATE MAGNETOMETER

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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.