Low-Grade Heat Energy Harvesting System Based on the Shape Memory Effect and Hybrid Triboelectric-Electromagnetic Nanogenerator

Low-grade heat energy is a kind of widely existing energy, due to the limitation of the collection technology, most of the energy is wasted. It would be vital to harvesting this kind of energy by effective acquisition techniques. With the shape memory effect of Shape memory alloy (SMA), a low-grade heat energy harvesting system based on the hybrid triboelectric-electromagnetic nanogenerator is proposed. A ring SMA is embedded in two round wheels, in which the high-temperature wheel (HTW) is immersed in the low-grade heat source. The ring can only rotate around the wheels due to the shackles of wheels when the SMA in the HTW is heated and straightened out. The working principle of deformation and rotation of the SMA at transformation temperatures is studied and analyzed with three aspects, including infrared detection, temperature simulation, and force analysis. Moreover, a soft-contact freestanding rotation triboelectric nanogenerator and electromagnetic generators are designed at both sides of the low-temperature wheel to generate high voltage and high current, respectively. Benefiting from the power of nearly 4.3 mW of the system, some small electrical devices, and a self-powered wireless sensor network are successfully powered. Considering the excellent output performance of the system, the system is expected to be a reliable and effective device for large-scale low-grade heat energy harvesting in the future.