Double-core GMI current sensor

The design of a double-core giant magnetoimpedance (GMI) current sensor, which lowers the temperature influence and also improves linearity, is presented. The sensor consists of two ring cores made of 52 cm long CoFeSiBCr magnetoimpedance (MI) strips. In order to optimize the Ml characteristics, the ribbon was annealed at 390°C under axial field of 2400 kA/m. The sensor was driven by 1 MHz/5 mArms sinewave signal and the bias current I_b was 30 mA, corresponding to bias field of 80 A/m. Results show that the double-core sensor has smaller linearity error and temperature offset drift compared to single-core sensor. On the other hand, manufacturing of double core sensor is difficult, as suitable pair of magnetic cores with similar material properties should be selected, due to different magneto-impedance responses; hence the correction by detection electronics is usually needed.