Table 18.1 shows the figures of merit for vibrating energy harvesters with different types of working mechanisms and materials, including magnetoelectric, electrostatic, piezoelectric, magnetoelectric sensor based, magnetostrictive, and high-permeability material-based devices. Among all these different mechanisms, the wide bandwidth energy harvester based on the magnetic coupling between the high-|x material and the bias field of the hard magnets, generates a relatively high power density and a wide working bandwidth. The metallic high-permeability single-layer beam has advantages from the material point of view as well. First of all, it is mechanically more robust compared with most of the piezoelectric materials or glue bonded multilayer materials. Second, it does not have possible problems of degraded performance over the lifetime of the device.