The present disclosure describes a vibration energy harvester with increased output power density. The vibration energy harvester has two magnetic solenoids, each with cores that include multiple layers of high permeability materials. The two magnetic solenoids are fixed at two sides of a movably supported hard magnetic core, such as a magnet pair with anti-parallel magnetization, which produces a spatially inhomogeneous bias magnetic field for switching the flux inside the solenoids during vibration of the magnetic core. An output voltage of 2.52 V and a power density 20.84 mW/cm3 at 42 Hz, with a half peak working bandwidth of 6 Hz.