<論文>50cm長BIAXIAL型-CORE型FLUXGATE磁力計の製作

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Both resolution and sensitivity of a fluxgate magnetometer is theoretically expected to be improved if dimension ratio of its biaxial core is increased. Based on this theoretical expectation we manufctured a biaxial 6-81 Mo permalloy core with a dimension ratio of as high as l/d = 2.0 × 10^3, where length l = 500 mm, thickness h = 10 μm, width w = 5 mm, and d = 2 √ h・w/π. A drive current applied on the core with a 1-kHz frequency makes a 2-kHz pick-up current which is amplified and phase-detected. The output voltage from the phase detector stands for the magnetic field strength along the core axis. Geomagnetic field variations are recorded by this 50-cm biaxial magnetometer at the Onagawa Magnetic Observatory of Tohoku University and compared with those recorded simultaneously by another commercial biaxial magnetometer. It is concluded that this 50-cm biaxial one is very excellent magnetometer with resolution of 10^<-2> nT (100 times better than the commercial type) and with sensitivity of 10 mV/nT (〜100 times better).