두 환경자계에서 탈자된 강자성체의 자기신호

Abstract

Demagnetization technique is used to reduce magnetic signal from a magnetic object and usually utilized in the navy. Demagnetization should apply magnetic field enough to saturate the object using a solenoid coil and reduce to 0[A/m] with a fine decrement. The earth magnetic field influence greatly demagnetization performance and need to be compensated with a horizontal(x) and a vertical(z) components of bias magnetic fields, which are generated from the solenoid coil and a z coil. The demagnetization of a ship-like ferromagnetic object was performed inside reinforced concrete building and outside the building. Magnetic signals were obtained using a magnetic field sensor having a resolution of 0.1[nT]. 1[m] long and 0.15[m] wide ferromagnetic object was made of a galvanized steel sheet. Background magnetic field signal was not uniform due to steel components such as steel bars inside reinforced concrete building. Each field strength in 3 directional magnetic fields was 22.8[A/m] in the south-north, 6.5[A/m] in the east-west and 29.4[A/m] in the upside-downside. Especially, there existed the difference of 4[A/m] in the upside-downside, whereas the field strength was the almost same magnitude as earth magnetic field in the measured place, which was 25.4[A/m], 0[A/m] and 30.2[A/m]. From the measured magnetic signals, the demagnetization should be performed in the place having a uniform background magnetic field.