Theoretical and experimental investigation of a quad-stable piezoelectric energy harvester using a locally demagnetized multi-pole magnet

Abstract

Existing research on piezoelectric energy harvesters (PEHs) has mainly relied on uniformly magnetized permanent magnets (PMs) to provide nonlinearity. Recently, it was reported that a locally demagnetized multi-pole permanent magnet (LDPM) may modulate the magnetic field locally without affecting its overall properties. This could lead to novel approaches for providing and tailoring nonlinearity in PEHs. In this study, we propose a quad-stable PEH composed of a cantilever beam and two PMs, one of which is uniformly magnetized and attached to the beam tip, while the other is a cylindrical LDPM fixed to the frame. The LDPM has four circular regions that are locally demagnetized, resulting in the appearance of different polarities on its surface. Additionally, we develop an equivalent physical model of the LDPM based on the magnetizing current method. By assuming that the LDPM has a piecewise uniform magnetization and neglecting its magnetic domain walls, the LDPM is represented by magnetizing current loops along its boundary and domain walls. Because the LDPM can be designed in advance, there are more parameters accessible for adjusting the system’s potential function, without making the system cumbersome or complex. The novel quad-stable PEH is studied both numerically and experimentally. The results indicate that the PEH with the LDPM outperforms the PEH with a normal magnet in the low-frequency range. Furthermore, in the PEH with the LDPM, the potential barrier is significantly decreased by 91.98% while the potential width is only decreased by 7.92% in comparison to the PEH with a normal magnet (which is bi-stable). This may provide a new method for optimizing PEHs.