Magnetostrictive bilayers for multi-functional sensor families

The present paper summarizes the development of new types of soft magnetic materials which are highly sensitive to bending or temperature, respectively. They represent bilayer structures, the thickness ranging from a few micrometers up to about 300 μm. A thin magnetostrictive layer is combined with a non-magnetic counter layer which counter-balances mechanical stress. As a result, bending generates stress of constant sign within the magnetic layer, thus, strongly enhancing its change of permeability. The bending sensitivity can be adjusted by several design parameters like layer thickness and Young's modulus. Temperature sensitivity can be attained through different expansion coefficients. First sensor prototypes were focused on automotive fields like flow measurement and driver status monitoring. A second focus was monitoring of physiological quantities during sleep, or after accidents. A large variety of parameters can be detected by means of one and the same sensor concept, which represents the main attraction of the novel concept.