The flexibility of amorphous Giant Magneto-Impedance (GMI) micro wires makes them easy to use in several magnetic field sensing applications, such as electrical current sensing, where they need to be deformed in order to be aligned with the measured field. The present paper deals with the bending impact, as a parameter of influence of the sensor, on the GMI effect in 100 µm Co-rich amorphous wires. Changes in the values of key parameters associated with the GMI effect have been investigated under bending stress. These parameters included the GMI ratio, the intrinsic sensitivity, and the offset at a given bias field. The experimental results have shown that bending the wire resulted in a reduction of GMI ratio and sensitivity. The bending also induced a net change in the offset for the considered bending curvature and the set of used excitation parameters (1 MHz, 1 mA). Furthermore, the field of the maximum impedance, which is generally related to the anisotropy field of the wire, was increased. The reversibility and the repeatability of the bending effect were also evaluated by applying repetitive bending stresses. The observations have actually shown that the behavior of the wire under the bending stress was roughly reversible and repetitive.

In this paper, the approach of using magnetic circuits in Giant Magneto-Impedance (GMI) current sensors is introduced for the first time in order to reduce the impact of magnetic disturbances on the sensor response. The studied current sensor had a toroidal structure. The GMI sensitive element circled the conductor carrying the measured current. The way to use a magnetic circuit in this configuration was established, and the rules of design and implementation were defined and validated by the simulation and by the measurements. The theoretical idea was to place the sensitive element on the surface of a magnetic circuit. However, in practical conditions, both simulation and measurement have demonstrated that a magnetic circuit must be placed at each side of the sensitive element if the idea is to prevent from the effect of the different types of magnetic disturbances.