A Temperature-Insensitive AC Current Sensor Based on Two Opposite Bias Magnetic Circuits

An intensity-demodulated ac current sensor system based on two opposite bias magnetic circuits and two cascaded fiber Bragg gratings (FBGs), which can automatically compensate the ambient temperature, is proposed and demonstrated. Two giant magnetostrictive material (GMM) bars bonded, respectively, with two FBGs are placed in the two magnetic circuits. The magnetic fields with opposite directions are applied to the two GMM bars via the two magnetic circuits. When the current is simultaneously applied to the two GMM bars, one GMM bar will stretch and the other one will compress, leading to the opposite spectral responses of the two FBGs due to the strain variation. Moreover, the two FBGs have the same thermal responses. Therefore, optical intensity passing through the two cascaded FBGs varies monotonously with the measured current and has no relation to the environmental temperature. The experimental results show that our sensor has a linear response in the range of 0.6-159.8 A. The minimum ac current detected by the proposed sensor is 0.6 A.