Experimental evaluation of external and built-in stress in Galfenol rods

Magnetostrictive properties of Iron-Gallium alloys, such as the saturation of magnetic induction and magnetostriction can be derived from experimental measurements. It is known that, in order to exhibit the largest saturation magnetostriction, Galfenol requires the application of a suitable external compressive stress. In order to avoid a bulky system to provide such stress, a built-in stress could be added to the material through a technological process known as stress annealing. In this paper an experimental method to evaluate the stress applied to Galfenol rods is presented. Then, the method can be exploited either to evaluate the built-in stress or to develop a stress sensor. A concept device exploiting the method and its experimental characterization are presented.