Ultra Small and Thin Energy-Harvesting Device Based on Electromagnetic Induction

Energy harvesting devices (EHDs), which generate a small amount of electric power from energy sources in the environment, are expected to be power sources for Internet-of-Things (IoT) devices or wearable electronic devices to realize a high-grade sensor-network society. Many EHDs suitable for various applications have been reported so far and are being developed. In this study, we propose a novel EHD with an extremely small and thin structure. A potential application of the proposed EHD is its installation in the soles of shoes to generate electric power by the repeated loading and unloading of weight during walking to drive health-monitoring sensors. Such an application requires the EHD to be small and lightweight. We applied electromagnetic induction to the proposed EHD, although electromagnetic-induction based devices are generally considered difficult to be miniaturized. To our knowledge, the smallest electromagnetic EHD for application to shoes has a volume of 8.8 cm³ and thickness of 16 mm ; these dimensions are too large to allow embedding in a shoe sole. However, electromagnetic induction generates much lower voltage than power generators based on piezoelectric transducers and electrostatic induction, which are often used for small structures. Therefore, an electromagnetic generator can easily be used with an integrated circuit and electronic components, which are small but need to take into account electro-static discharge susceptibility. Based on this idea, we have developed a small electromagnetic generator with sufficient power generation capacity.