Improved energy harvesting from low frequency vibrations by resonance amplification at multiple frequencies

• We present a novel energy pumping based frequency up-conversion mechanism for effective energy harvesting from low frequency vibrations.
• It is for the first time that the high frequency resonator in a frequency up-conversion based harvester gets benefit from resonance amplification.
• The harvester shows resonance amplification at multiple frequencies and hence can be very effective in harvesting energy from multiple harmonics.
• The average power density of 183.34 μW/cm3 and volume figure of merit of 0.796% achieved at 10.3 Hz outperformed the efforts made to-date to harvest energy from low frequency vibrations.
• The method proposed can be easily adopted with other transduction mechanisms such as piezoelectric and electrostatic.

This paper reports on an electromagnetic vibration energy harvester that utilizes a novel method of energy pumping based frequency up-conversion to effectively harvest energy from a broad range of low frequency (<18 Hz) ambient vibrations. Energy from low frequency vibrations is absorbed by a low frequency bounded resonator and subsequently pumped, in the form of pulses, to a high frequency resonator. The mechanical energy of the high frequency resonator is then transferred to the electrical domain by electromagnetic induction. The test results proved that the energy pumping based mechanical frequency up-conversion gets benefit from the resonance amplification phenomenon at multiple frequencies corresponding to higher order of resonances. Resonance amplification at multiple frequencies can improve the efficiency of harvesting energy from broadband vibrations and from sources where energy is distributed in different harmonics. For a 1 g excitation at the third order resonance frequency of 10.3 Hz, the fabricated harvester generated a peak voltage of 7.92 V and RMS voltage of 3.88 V across an optimal load of 3 kΩ and delivered a peak power of 20.9 mW with an average power of 5.02 mW. The harvester is capable of working at as high acceleration as 1 g and produces a usable amount of power (26 μW) from as low acceleration as 50 mg.