Embodiments of the present disclosure relate to a vibration energy harvesting device for converting energy of targeted order oscillations in a rotor's angular speed into electrical energy. The vibration energy harvesting device comprising: at least one conductive coil and at least one permanent magnet. The vibration energy harvesting device comprises a carrier supporting one of: the at least one conductive coil, or the at least one permanent magnet. The carrier is configured to be mounted to, and thereby rotate at a same angular speed as, the rotor. The vibration energy harvesting device comprises a pendulum formed from an inertial mass suspended from the carrier such that the inertial mass can oscillate along a substantially tautochronic path which is tuned to the targeted order. The inertial mass comprises the other of: the at least one conductive coil, or the at least one permanent magnet. The relative motion between the at least one conductive coil and the at least one permanent magnet induces a voltage in the at least one conductive coil.