Reducing the environmental impact and cost of ultra-low frequency vibrational energy harvesters based on magnetic levitation

• Design of ultra low frequency levitation vibration harvesters based on ferrite magnets. • A 2.8 Hz resonant frequency prototype is analyzed and tested. • The proposed device has reduced cost and environmental impact. Vibration energy harvesting is a technology that can harvest energy from environmental vibrations to power sensors and actuators, replacing batteries and avoiding extensive wiring in remote applications such as wireless sensor networks or infrastructure monitoring. Commercial devices successfully operate at low frequency, but some challenges remain to be solved. On one hand, the advantages over batteries depend on the actual environmental impact and cost of the harvester itself, both features hindered by the use of rare earth magnets. On the other hand, operation under ultra-low frequency vibrations is problematic even for laboratory prototypes. In this work, one-degree-of-freedom magnetic levitation-based energy harvesters are analyzed for ultra-low frequency vertical vibrations. Strategies for decreasing the resonant frequency and replacing rare earths for ferrite magnets are discussed. A prototype incorporating ferrite magnets is built and tested, achieving a resonant frequency of 2.8 Hz (the lowest for a portable harvester of this kind). In addition, different housing materials are compared to reduce friction and reliability, introducing 3D-printed resin housings as a promising alternative. The obtained results are compared with those of previously reported devices published in the literature in terms of environmental impact and cost, including LCAs (life cycle assessment) of the permanent magnets used in the prototypes, concluding that ferrite magnets can be successfully implemented in this kind of devices. The use of ferrites instead of NdFeB reduces the environmental impact of the fixed magnet by at least 20 %, and decreases its cost by 50 %.