Study On Current Sensor Utilizing Giant Magneto-impedance Effect In Co-based Amorphous Ribbon Annealed By Pulse Current

Amorphous alloy as a new functional material with superior magnetic properties was developed in the mid-20th century. In 1992, people first found the giant magneto-impedance (GMI) effect in amorphous wires. Recently, many scholars in the world are researching on the GMI sensors actively. In this thesis, the theory and experiment of GMI effect were researched systematically. Based on the effect, a novel current sensor was developed utilizing amorphous ribbon. The main results are generalized as the followings:The preparative development of the amorphous alloy was introduced and the physical properties of amorphous alloy with different chemical constitutions were analyzed. Co-based amorphous alloy Co_66.5Fe₄ (SiB)₂₇M_2.5 was selected as sensor sensitive material. The expressions of orientation-related relative permeability in amorphous alloy ribbon under applied driving ac current flowing through the ferromagnetic materials and dc external magnetic field was derived by simultaneously solving the Maxwell's equations and the Landau-Lifshitz equation of motion and establishing the magnetic domain structure model. The calculation formula of mean relative permeability averaging over 90 orientation angle and the magneto-impedance are obtained. The influence factors of GMI effect were analyzed.The GMI effect dependence on pulse current annealing and driving current were studied. The experimental results show that the maximum GMI ratio increases continuously with frequency of ac driving sine-wave current up to 42.7% at 1MHz with amplitude of 10mA and then decrease with the increasing frequency.A novel non-contact type current sensor utilizing GMI effect in amorphous ribbon was developed. A high frequency signal generator and a power amplifier were designed to excit the amorphous alloy ribbon. Then the output voltage of amorphous ribbon sample was pre-processed with amplifier, peak detector circuit, low pass filter and precision differential circuit. The parameters of signal processing circuit are optimized and the linear region of GMI sensor was adjusted by bias current. The measurement results are analyzed: the accuracy of sensor is less than±0.81%FS with the measurement range±0.15A under the greenhouse, then by designing negative feedback to form a closed-loop system to improve the measurement range and the accuracy of sensor: The measurement accuracy is less than±0.62%FS with the linear range±0.9A.It can be used in the weak current measurement field.