A vibrational energy harvesting device is disclosed, which comprises first and second assemblies mounted on a base at a distance one from the other. The first assembly comprises vibrational means adapted to stretch under a straining force, whereby the device exhibits monostable quartic nonlinearity. The first and second assemblies comprise respective magnetised means in opposite polarity to one another, so that the second assembly exerts a repulsive magnetic force upon the vibrational means, whereby the device exhibits bistability. Both the monostable quartic and bistable nonlinearities can be independently controlled. A method of harvesting energy with the vibrational energy harvesting device is also disclosed.