An ultra-low-frequency, broadband and multi-stable tri-hybrid energy harvester for enabling the next-generation sustainable power

This work presents a highly miniaturized, ultra-low-frequency, multi-stable and tri-hybrid portable energy harvester to harness structural and biomechanical vibration energy efficiently. This energy harvester is developed by using a novel multi-stability-based frequency up-converted approach, in which two new configurations of magneto-multi-stable oscillators are closely integrated. Hence, the displacement stroke of low-frequency vibration and the mechanical energy transfer process can almost completely overlap, and consequently magnify the power output and power density under low-frequency broadband vibration sources. By hybridizing two impact-driven piezoelectric generators, an array-type electromagnetic generator, a sliding-mode triboelectric nanogenerator and a contact-separation triboelectric nanogenerator in a highly compact design arrangement, more electric power can be generated from a single mechanical motion, which can successfully enhance the output performance. A fabricated prototype of the present design is tested using shaker excitations and body-induced motions. Under the shaker test, the prototype works well at a wide bandwidth of 1–11 Hz under 1 g (=9.8 m s⁻²) and generates a maximum output power of 85.9 mW across the optimum resistance loads, corresponding to the normalized power density of 3.70mW cm^-3g^-2 at 3 Hz under 1 g. During the human activity motions (i.e., walking, slow running, and handshaking), the prototype also shows good performance under different wearable positions of the human body and can power up 20 thermohygrometers and 296 commercial light-emitting diodes continuously. The present energy harvester is a promising application to enable as a sustainable power source for wearable/portable electronics and wireless monitoring systems.