PZT ceramic particles/polyurethane composites formalism for mechanical energy harvesting Abdelkader Rjafallah, Abdelowahed Hajjaji, Fouad Belhora, Abdessamad El Ballouti, Samira Touhtouh, Daniel Guyomar and Yahia Boughaleb Eur. Phys. J. Appl. Phys., 89 3 (2020) 30901 Published online: 23 April 2020 DOI: 10.1051/epjap/2020190102