The purpose of this work is to model a magnetic field sensor based on magneto-electric effect. The magneto-electric effect is obtained by the combination of piezoelectric and magnetostrictive constituents in a multilayer. A non linear constitutive law of magnetostriction is developed in order to define the magnetostrictive coefficients of the magnetostrictive constituent under static magnetic field loading. A harmonic finite element calculation is then performed to study the response of the sensor. Indeed the magneto-electric coefficents of thesse devices are enhanced when a harmonic magnetic field is superimposed to the static field to measure.