DEVELOPMENT OF A LOW-FREQUENCY HARVESTER BASED ON A ROPE-DRIVEN ROTOR WITH ROTATION SPEED UP-REGULATION FUNCTION

Harvesting the ubiquitous low-frequency mechanical energy for power generation can reduce the number of expired batteries, achieve self-sustained sensors, and cut down the costs for deploying and maintaining the sensor networks. However, the conventional vibrational energy harvesters (VEHs) perform poorly in exploiting low-frequency mechanical energy due to the mismatch between the excitation frequency and the working frequency of the conventional VEHs. To effectively harvest the low-frequency mechanical energy from the surrounding environment, we report herein a rope-driven electromagnetic harvester with a magnetic gear for enhancing the rotation speed and then improving the output power. By transforming low-frequency vibrations to bi-directional rotation via a rope-driven shaft and then converting the bi-directional rotation of the shaft to uni-directional rotation of a driven wheel with enhanced speeds through a stiffness-variable plectrum and a magnetic gear, the proposed motion-transmission system can achieve high-speed rotation under low-frequency vibrations. Based on the motion-transmission system, an electromagnetic energy harvester was designed and fabricated by embedding magnets into the driven wheel and arranging coils in the proximity of the wheels. A theoretical model for the proposed harvester was developed and then validated by experimental test. When excited at 2 Hz with an amplitude of 40 mm, the maximum output power of the proposed harvester reaches 7.82 mW with the aid of the magnetic gear with a transmission ration of 10:4, corresponding to 143% improvement as compared with that of the harvester without the magnetic gear (3.22 mW). Under the same excitation condition, the proposed harvester can increase the voltage of a 220 μF capacitor from 0 V to 1.5 V in 1.2 s via a standard rectifier to convert its alternating current (AC) output into direct current (DC) output. In addition, the proposed harvester can provide 0.35 mW electric power under low-frequency and irregular vibration excitation. Therefore, the proposed design may be a feasible strategy for developing high-performance low-frequency energy harvesters.