A sensor assembly for detecting surfaces stresses and/or the microstructure state of a ferromagnetic workpiece, wherein at least one first base coil system having a first directional sensitivity is provided, at least one second base coil system having a second directional sensitivity is provided, and at least one third base coil system having a third direction and a third directional sensitivity is provided, and wherein at least the first base coil system and the second base coil system form a first differential angle and the second base coil system and the third base coil system form a second differential angle, and wherein the first base coil system, the second base coil system, and the third base coil system are arranged such that the mechanical surface stresses of the workpiece can be at least partially determined. A method for determining the mechanical surface stresses is also provided.