<title>Magnetostrictive actuators compared to piezoelectric actuators</title>

Magnetostriction occurs in the most ferromagnetic materials and leads to many effect. The most useful one to refer to is the Joule effect. It is responsible for the expansion or the contraction of a rod subjected to a longitudinal static magnetic field. In a given material, this magnetostrian is quadratic and occurs always in the same direction whatever is the field direction. Giant Magnetostrictive Materials (GMM), especially Rare erath-iron discovered by AE Clark, feature magnetostrains which are two orders of magntitude larger than Nickel. Among them, bulk Tb_0.3Dy_0.7Fe_1.9, 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. In the 90s, bulk magnetostrictive composite materials have been developed for high frequency ultrasonic applications. More recently, high magnetostrains have also been obtained in rare earth-iron thin films.