https://phys.org/news/2018-07-hybrid-device-harvests-mechanical-magnetic.html

Over the past several years, energy harvesting has become an increasingly attractive option for replacing the batteries that are used in low-power devices. Whereas batteries have a limited lifetime and must be replaced or recharged on a regular basis, energy-harvesting devices can ideally operate autonomously for much longer periods of time.

One of the greatest challenges facing energy harvesters is generating enough power for practical applications. One way to increase the output power is to harvest more than one type of energy. For example, although there are a variety of devices that harvest either mechanical energy or magnetic energy, very few devices can harvest both, despite the fact that ambient mechanical and magnetic energy often appear together in industrial settings, such as near rotating electrical machines.