Magnetostrictive Actuators Compared to Piezoelectric Actuators

Magnetostriction occurs in the most ferromagnetic materials and leads to many effects [1,2]. The most useful one to refer to is the Joule effect. It is responsible for the expansion (positive magnetostriction) or the contraction (negative) of a rod subjected to a longitudinal static magnetic field. In a given material, this magnetostrain is quadratic and occurs always in the same direction whatever is the field direction. Giant Magnetostrictive Materials (GMM), especially Rare earth-iron discovered by A.E.Clark [3], feature magnetostrains which are two orders of magnitude larger than Nickel. Among them, bulk Tb0.3Dy0.7Fe1.9, called Terfenol-D, presents the best compromise between a large magnetostrain and a low magnetic field, at room temperature. Positive magnetostrains of 1000 to 2000 ppm obtained with fields of 50 to 200 kA/m are reported for bulk materials [3,4]. In the 90s, bulk magnetostrictive composite materials have been developed for high frequency ultrasonic applications [5]. More recently, high magnetostrains (in the range of 500 to 1000ppm) have also been obtained in rare earth-iron thin films [6].