Electromagnetic vibration energy harvester with ring magnets

This work investigates a one-dimensional electromagnetic vibration energy harvester (EMVEH) that uses magnetic interactions to convert ambient vibration into electrical energy. The prototype consists of four coaxial ring permanent magnets enclosed in a tube. Two of these are fixed at the ends of the tube while the two others are connected via a rod, resembling a dog-bone shape structure, to reduce the friction of the magnets with the inner walls of the tube. The ring magnets are placed so that same polarities are facing each other, resulting in a repulsive force that levitates the dog-bone structure. In this study the repulsive force between the ring magnets and the induced magnetic flux in a set of coils are derived by using a Fourier space approach and the shape function of the magnets. The derived functional expressions for the magnet-magnet and magnet-coil forces are validated by comparison with a finite element model. Then, an experimental prototype of a ring magnet EMVEH is tested and compared with a model evolving the state equations using the derived force expressions, and show that these agree. Finally, the output power of the experimental EMVEH is characterized and shown to be a strong function of the external driving amplitude.