**6. Conclusions**

In this paper, a new structure of piezoelectric electromagnetic coupling up-conversion multi-directional vibration energy harvester is proposed. Four piezoelectric electromagnetic coupling piezoelectric cantilever beams are installed on the axis of base along the circumferential direction. The permanent magne<sup>t</sup> on the beam is placed on the free end of the cantilever beam as a mass block. Four coils for collecting energy are arranged on the base under the permanent magnets on the cantilever beams. Four permanent magnets arranged on the rotating mass block continuously excite the cantilever beams. The piezoelectric cantilever is induced to vibrate at its natural frequency by the interaction between the magne<sup>t</sup> on cantilever and the magnets on the rotating mass block. With the coupling of electromagnetic and piezoelectric, more vibration energy can be extracted when the appropriate interface circuit is selected.

**Author Contributions:** Conceptualization, G.S.; methodology, G.S. and J.C.; software, J.C. and M.S.; validation, H.X., Y.Y. and Y.X.; formal analysis, G.S. and H.X.; investigation, G.S. and J.C.; resources, G.S. and Y.X.; data curation, X.W.; writing—original draft preparation, G.S. and J.C.; writing—review and editing, G.S.; visualization, M.S.; supervision, Y.P.; project administration, G.S.; funding acquisition, G.S., Y.Y., H.X. and Y.X. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research is supported by the National Natural Science Foundation of China under Grant U1709218, Grant 61971389, Grant 61801253 and Grant 61601429, the Natural Science Foundation of Zhejiang Province Grant LZ20F010006 and Grant LY20F010003 and the Natural Science Foundation of Ningbo Grant 2018A610091,2019A610113.

**Conflicts of Interest:** The authors declare no conflict of interest.
