Practical use of GMI effect to make a current sensor (Invited talk)

International audienceGiant Magneto-Impedance (GMI) is a large change of the high frequency impedance of somesoft magnetic materials when they are subjected to an external magnetic field. This effect can beused to realizemagnetic sensors based on the impedance measurement of the sensitiveelement.Despite the great advantages of the GMI such as the high sensitivity, the potential ofminiaturization as well as the large bandwidth, there is still only a few concrete or industrialachievements of these sensors.One of the key features of these GMI sensors is their ability to measure both DC and ACmagnetic fields by the same sensitive element. This feature is of great value for a large palette ofapplications like the contactless current measurement(based on the measurement of the magneticfield produced by the measured current [1]).For this application, the mechanical flexibility ofsome GMI elements (like amorphous wires) is also another key andvery useful feature forrealizing toroidal flexible sensors (the sensing element forms a loop around the conductor ofinterest). Such flexible sensors are needed in many industrial environments where rigid toroidalstructures of the current sensor are not convenient.This paperpresents an overview of a full attempt of design andrealization of a quasi-industrialGMI-based currentsensor. The sensor combines DC/AC measurements in a same flexiblesensitive element. The paper addresses several practical problems encountered in a realmeasurement environment. In this context, main attention is paid to the impact of the influencequantities that largely condition the implementation strategies and solutions of the sensor. For theintended industrialapplication,these influence quantitiesfirstly include the operating temperature[2]. Its impact on the intrinsic sensor response is addressed in a quasi-industrial temperaturerange. Secondly, bending stress on the sensitive element is another involved influence parameterin the toroidal and flexible structure. This constraint effect is also characterized [3] - [4]. Finally,the third considered influence parameter is the effect of magnetic disturbances such as theeccentricity of the conductor of interest and the impact of the surrounding magnetic fields (earthfield or fields produced by others conductors in close proximity to the sensor). Differentstrategies of implementation and solutions, taking into account the impact of influenceparameters, are proposed and compared. A sensor prototype is realized and its performances aregiven and discussed