Tunable double nonlinear design in the energy harvester to enhance energy harvesting Xiang Zhong, Buyi Wang, Yimin Wu, Rong Li, Mengchao Ma and Huaxia Deng Eur. Phys. J. Plus, 136 11 (2021) 1145 Published online: 15 November 2021 DOI: 10.1140/epjp/s13360-021-01967-y