<p>This paper investigates vibration-based electromagnetic energy harvesting in an excited Duffing oscillator coupled to a RLC circuit with a van der Pol component. The electromechanical coupling mechanism between the van der Pol resonant circuit and the mechanical structure is achieved by the permanent interaction of the magnet and the coil. The modulation equations of vibration and output voltage responses are obtained using the averaging method and analytical approximate solutions of the periodic responses are derived. Using a second-step perturbation method on the slow flow, approximate quasiperiodic solutions of the response and the corresponding output voltage are obtained. Energy harvesting performance of the harvester is examined in the presence of the van der Pol resonant circuit and compared with the case where only a linear resonant circuit is considered. The effect of different parameters of the harvester on the output voltage is analyzed in the periodic and quasiperiodic regimes. The advantage of using a van der Pol resonant circuit to scavenge energy is demonstrated in both regimes. It is revealed that energy can be harvested efficiently from periodic or quasiperiodic vibrations depending on the choice of the system parameters. Numerical simulations are performed to support the analytical results.</p>