A centrifugal softening impact energy harvester with the bistability using flextensional transducers for low rotational speeds

This paper presents a centrifugal softening impact energy harvester with the bistability using flextensional transducers. The bistability is firstly demonstrated to further enhance the advantages of the centrifugal softening effect in improving the impact energy output at low rotational speeds. In the harvester, two flextensional transducers are impacted by a centrifugal softening driving beam, which is experiencing the magnetic repulsive force at the same time. The flextensional transducers are adopted for their high electromechanical coupling coefficient and robustness under the large impact force. A theoretical model is built and validated by experiments. Experimental results show that the bistable harvester can generate higher energy output than the non-linear monostable and linear harvesters at the rotational speed ranging from 60 rpm to 360 rpm and a certain clearance of 1.07 mm. Its maximum instantaneous power and RMS voltage at 60 rpm are respectively increased by 323.1% and 184.3% compared with the non-linear monostable one, and 899.9% and 304.2% compared with the linear one. Such significant improvement cannot be achieved by changing the clearance in the linear harvester while it can be achieved by adding the bistability. Therefore, our proposed method facilitates the effective energy harvesting from widely-distributed low-speed rotations.