The main goal of work presented in this manuscript was to design and build energy harvesters optimized for maximum electric power output, utilizing flexible piezoelectric cantilever beam structures available on the commercial market. The devices were constructed to simultaneously harvest magnetic field and vibration energies present in vicinity of current-carrying conductors, such as those used in power lines. Gradient-free Nelder-Mead optimization algorithm was used to find geometries that maximized the power output from the harvesters, tuning them to 60-Hz electric frequency of the AC current flowing in the energized line. The harvesters' electric load was also adjusted to assure the optimal energy transfer. The findings were then used to build harvesters. The optimization process allowed to achieve power densities up to 35.6 mW/cm(3) from the constructed scavengers.