Electromagnetic-triboeletric hybridized generator based on magnetic levitation for scavenging biomechanical energy

The popularity of various portable electronics and biological health monitoring devices, such as pedometers, pulse oximeters, mobile telephones, wearable watches, has greatly changed our lifestyles and brought significant convenience to us. Energy harvesting has been a key technology for the self-powered mobile terminals, because there are many defects such as limited lifetime, large size, low energy density and environmentally unfriendly feature for the traditional chemical batteries. Lots of devices used for the energy harvesting of the human movement have been reported. However, some problems such as poor efficiency, low output power and low sensitivity need further studying. In this work, we demonstrate a novel magnetically levitated electromagnetic-triboelectric generator. The device size is φ4.8 cm×2.4 cm, and its weight is 80 g. The device uses the magnetically levitation structure as the core components, and the structure contains four magnets to form a magnetic array, in which three cylindrical magnets are placed around a bigger magnet. And two coils with polyvinyl-acetal enameled copper wires of 70 μm areplaced at the top and bottom of the device, respectively. Then two silica gel thin films with inverted tetrahedron patterned on the surface are integrated inside the structure. Then, we analyze the motion feature with the Maxwell simulation software, and discuss output characteristics of the two energy harvest units theoretically. The device possesses a high sensitivity, wide frequency response and high output performance. The dynamic response characteristics are analyzed in this paper.The frequency response range of the device is from 2 Hz to 20 Hz. The wider frequency response means that it can harvest more energy from complicated external environment. Furthermore, we analyze the output signal at low frequency, which has more than one wave crest after an environment perturbation. The triboelectric units can deliver peak output voltages of 70 V and 71 V, respectively, and the electromagnetic units each can deliver a peak output voltage of 10 V. In addition, the triboelectric units can produce peak output powers of 0.12 mW and 0.13 mW, respectively, under a loading resistance of 10 MΩ, while the electromagnetic units produce peak output powers of 36 mW and 38 mW, respectively, under a loading resistance of 1 kΩ. We discuss the energy output and energy conversion efficiency of the device, which are 750.89 μJ and 18%, respectively. Then we use the hybridized generator to charge a capacitor of 33 μF, the output voltage of which can reach 8 V in 2 seconds. Furthermore, the hybridized generator can power a pedometer continuously, which can work steadily and display movement data. This work has a significant step toward human mechanical energy harvesting and potential application in self-powered wearable devices.