Automatic flipping magnet type electromagnetic energy harvester

A new flipping magnet type electromagnetic energy harvester (EEH) suitable for scavenging energy from low frequency vibrations is presented in this Letter. The proposed EEH has a spherical permanent magnet (SPM), which is free to move inside a spherical bobbin that carries coils. Two cylindrical permanent magnets are employed to flip the SPM fast, even if the frequency of vibration source is low. This induces sufficient voltage in the coil to convert to dc and use. No such scheme has been reported so far and the existing EEHs give very low induced voltage for low frequency vibrations <5 Hz. Two versions of the new EEH prototypes, were built and tested. The peak-to-peak open circuit voltage of version-1 was 3.5 V and the power density was 445 μW/cm3 for a matched load of 52.5 ω at 3.5 Hz vibration. The power density of the version-2 harvester was 538.6 μW/cm3. One of the applications of the proposed EEH is to harvest energy from railway tracks, for powering trackside monitoring sensors. The prototype developed generated up to 2.44 mW for an emulated railway track vibration in the range of 4 Hz, which is a considerable improvement compared with the existing EEHs.