**5. Discussion**

At present, there are various kinds of energy harvesters and some novel structures are selected for comparison and discussion. The main characteristics are shown in Table 1. In the structure of Reference [21], printed circuit board (PCB) coil is used to cut the magnetic field line of permanent magne<sup>t</sup> to generate electricity. It can harvest the energy of the human swing motion process but the energy it harvests is relatively low. In Reference [27], a new kind of vibration energy harvester which combines magnetostrictive material and piezoelectric material is used but it can only harvest single direction vibration and the power density provided in the paper only considers the volume of magnetoelectric laminate composites (MLCs). In Reference [11], the piezoelectric cantilever is excited by permanent magne<sup>t</sup> but it can only harvest the energy of rotation excitation and the harvesting energy power is low. Compared with the structures proposed in these papers, the harvester in the current paper used four permanent magnets to continuously excite the cantilever beams, which can produce continuous vibration with large amplitude. Four cantilever beams were used to harvest vibration energy in multiple directions. With the coupling of electromagnetic and piezoelectric, more vibration energy can be extracted when the appropriate interface circuit is selected.

**Table 1.** Comparison of several vibration energy collection structures.


1 The result is based on the information provided.
