Nonlinear piezoelectric devices for broadband air-flow energy harvesting Y. Bai, Z. Havránek, P. Tofel, C. Meggs, H. Hughes and T.W. Button Eur. Phys. J. Special Topics, 224 14-15 (2015) 2675-2685 Published online: 20 November 2015 DOI: 10.1140/epjst/e2015-02582-8