A power generator comprises a casing (110) that in use is deployed in an environment in which the casing is subjected to an excitation motion such as wave motion. A series of masses (101, 103a-c) is located within the casing, wherein at least a first mass is coupled to the casing by a first spring (102), each of the masses is coupled to at least one adjacent mass by a respective spring, and wherein the casing and the series of masses bring a motion of the power generator into resonance with the excitation motion. A plurality of electric machines each comprising a stator and a field source are each associated with a corresponding mass such that a relative motion of a mass and associated electric machine generates electrical power. A power takeoff circuit receives generated electrical power from the plurality of electric machines and outputs electrical power from the power generator.