Mechanism, theory and application research of a rotating electromagnetic energy harvester suitable for multi-directional excitation

Abstract

Energy harvesting in multi-directional excitation for human wearable devices is a challenge. A rotating electromagnetic energy harvester (REMEH) based on an eccentric rotor structure is proposed in this paper. Two poles of the magnets in the REMEH are alternately arranged in a ring. The electrical output characteristics of the energy harvester are analyzed through theoretical, numerical simulation and experimental testing methods based on the establishment of magnetic flux density models, the coil induced voltage, and the excitation direction of the eccentric rotor structure. Theoretical analysis and experimental results show that the design of the eccentric rotor structure is well adapted to multi-directional and irregular excitation. The circular staggered arrangement of the magnets effectively increases the output voltage and output power. The results show that the average output power increases slowly when the walking speed increases from 1 to 3 km h−1, and the average output power increases substantially when the walking speed increases from 3 to 5 km h−1. When the walking speed is 1 and 3 km h−1, the average output power is 0.439 and 0.638 mW, respectively. At a walking speed of 5 km h−1, the average output power increases rapidly to 1.68 mW, corresponding to a power density of 16.59 μW g−1. This high-performance energy harvester can provide effective power supply for wearable devices or low-powered sensors.

Characteristic Analysis, Simulation, and Experimental Comparison of Two Kinds of Circular Magnet Array in Energy Harvesting

“…where r 1 and r 2 are the inner radius and the outer radius of the circular magnet array, respectively, the gap between the magnet array and the coils is described as d m , z h is the width of the coils, and β(t) is the angular displacement between coil i and the magnet as shown in Figure 2. The induced voltage in coil i is caused by Faraday's law [30] and can be indicated as:…”

“…The induced voltages of the two coils have the same value and opposite directions at the same time. Two induced voltages tha are opposite in phase should be connected in series oppositely, thus enhancing the voltage by 2 times [30]. The induced voltage in the coil of the REMEH using the two-directional magnet array exhibits two different phases, as shown in Figure 14.…”