Material selection and design trends in magnetostrictive energy harvesters: a case study for IoT/wearable applications

Magnetostrictive energy harvesters (MEHs) are a promising option for powering wearable and Internet of Things systems because they offer good mechanical robustness, durability, and relatively high energy density. However, the field still faces important limitations, including multi-stage energy conversion, dependence on magnetic biasing, complex assemblies, and persistent trade-offs between power output, miniaturisation, and manufacturability. In addition, inconsistent performance reporting and limited system-level discussion make direct comparison and practical evaluation difficult. This paper presents a critical review of material selection and structural design in MEHs from a system-level perspective. It examines key materials, including Terfenol-D, Galfenol, Metglas, and Permendur, together with major device architectures such as cantilever beams, axial rods, and hybrid configurations. The review also discusses important constraints related to biasing, eddy-current loss, scaling, and integration, as well as recent advances in bandwidth enhancement, frequency up-conversion, and finite element method-based optimisation.