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• The proposed device contains magnetic coupling and vortex-induced vibrations. • The structural parameters of vibrating column affect the efficiency. • The magnetic repulsion system is suitable for low-speed water flow environment. • The magnetic attractive system is suitable for high-speed water flow environment. The rapid development of the fifth-generation mobile networks (5G) and the Internet of Things (IoT) is inseparable from a large number of miniature, low-cost, and low-power sensors and actuators. To solve the problem of self-powered underwater wireless sensor nodes (WSNs), this paper proposes a magnetically coupled piezoelectric energy harvester (MPEH) based on fluid-induced vibration (FIV) to achieve high-efficiency performance in low-velocity water environments. The results show that compared with the non-magnetic PEH, the initial vibration velocity, velocity bandwidth, and maximum output voltage of the magnetic attraction coupling piezoelectric energy harvester (MAPEH) are increased by 18.42%, 41.38%, and 5.79% respectively. Besides, it is also shown that the vertical distance between the magnets, the diameter, and the mass of the vibrating column have a significant effect on the vibration characteristics, water velocity bandwidth, and performance of the magnetic repulsion coupled piezoelectric energy harvester (MRPEH). The initial vibration velocity of the MRPEH is reduced by 42.1%, and when the water speed is 0.2 m/s, its output voltage is 12.21 times that of the classical configuration. This proposed structure can provide a reference for the optimization of underwater FIV-based PEH, and also lay a foundation for further interconnection of underwater self-powered sensors. [ABSTRACT FROM AUTHOR]

• When the flow rate is high, the change of the L and H has a great influence on the of the PEH array. • The single-row parallel-arranged array (PEH-2P and PEH-3P) can improve the system's initial vibration velocity and half-frequency bandwidth. • The single-row series-arranged array (PEH-2S and PEH-3S) can increase the maximum energy harvesting power. • The energy harvesting capacity of nine-vibrators square array is 102.4% higher than the reference value, and the initial vibration velocity is 25.95% lower than the reference value. This paper mainly uses simulation and experimental methods to analyze the output characteristics of different piezoelectric energy harvester (PEH) arrays based on flow-induced vibration, which is mainly used in low-velocity water in a natural environment. Each PEH consists of a piezoelectric beam and an interference cylinder. The PEH arrays presented in this paper include the double-vibrators parallel array (PEH-2P), double-vibrators serial array (PEH-2S), three-vibrators parallel array (PEH-3P), three-vibrators serial array (PEH-3S), and nine-vibrators square array (PEH-9). Prototypes of the different PEH arrays are fabricated and experiments are conducted to explore the energy harvesting capacity, the maximum energy harvesting power, initial vibration velocity and half-power bandwidth of the different PEH arrays. The experimental results demonstrated that the PEH-2P and the PEH-3P can improve the system's initial vibration velocity and half-power bandwidth, but the maximum energy harvesting power of the PEH array is relatively not good. The PEH-2S and the PEH-3S can increase the maximum energy harvesting power of the PEH array, but the initial vibration velocity and half-power bandwidth of the PEH array are relatively not good. The average value of energy harvesting capacity of the PEH-9 is the largest, which is 102.4% higher than the reference value, and the initial vibration velocity of the PEH-9 is the lowest, which is 25.95% lower than the reference value. This work provides a comprehensive experimental guideline for further designing an efficient PEH array used in the low-speed water environment. [ABSTRACT FROM AUTHOR]