Experimental validation of an impact off-resonance energy harvesterG. Martinez-Ayuso, M.I. Friswell, H. Haddad Khodaparast and S. AdhikariEur. Phys. J. Special Topics, 228 7 (2019) 1635-1646DOI: https://doi.org/10.1140/epjst/e2019-800155-0