Spherical magnetic energy harvester with three orthogonal coils

We report a magnetic energy harvester able to convert vibrational energy into electrical power via a magnetic sphere moving in a spherical cavity. Via Faraday's law the rotating magnetic moment induces electromotive forces in three orthogonal coils. This configuration potentially improves the power harvesting efficiency by a factor of 3 over the previous state of the art with its uniaxial coil. Structures with cavity diameters between 8 and 12 mm and NdFeB spheres with diameters of 6 to 10 mm and surrounded by coils with 100 or 150 windings were tested. The structures were exposed to uniaxial vibrations from 8 to 30 Hz, as typical for human motion. The sphere motion was observed to transit from ordered motion at low vibration amplitudes to chaotic motion at high amplitudes, with a significant boost in harvested poster in the chaotic regime. Even small external magnetic fields influence the motion of the sphere and are capable of boosting or reducing the harvested power, depending on operating conditions.