An energy harvesting device utilizing a monolithic, mesoscale, single-degree-of-freedom inertial based resonator in which the support structure, beam-spring, and proof mass are a single component without joints, bonds, or fasteners. Frequency tuning features include holes in the proof mass in which mass can be added to change the devices resonance frequency as well as levers which add curvature to the beam-spring system and adjust system stiffness. Robustness is increase by designing the resonator to exhibit nonlinear behavior such that its power density is maximized for low vibration amplitudes and minimized for high amplitudes. The device structural resonance modes are designed to be much higher than the resonators proof mass-spring resonance frequency. Electromechanical transducers are used to convert the resonators mechanical energy to electrical energy. Electrical circuitry is included to extract and condition the electrical charge.