This paper investigates the potential of designing a vibratory energy harvester which utilizes a ferrofluid sloshing
in a seismically excited tank to generate electric power. Mechanical vibrations change the orientational order of
the magnetic dipoles in the ferrofluid and create a varying magnetic flux which induces an electromotive force
in a coil wound around the tank, thereby generating an electric current according to Faraday's law. Several
experiments are performed on a cylindrical container of volume 5x10<sup>-5</sup> m<sup>3</sup> carrying a ferrofluid and subjected
to different base excitation levels. Initial results illustrate that the proposed device can be excited at one or
multiple modal frequencies depending on the container's size, can exhibit tunable characteristics by adjusting
the external magnetic field, and currently produces 28 mV of open-circuit voltage using a base excitation of
2.5 m/s<sup>2</sup> at a frequency of 5.5 Hz.
The purpose of this effort is to investigate the effect of bias conditions on the power harvested using magnetostrictive
materials. Towards that end, we first develop an analytical model to describe the dependence of the
constitutive parameters on the bias conditions. We validate this model experimentally and define a range for
its validity. We obtain a one-dimensional lumped-parameter model of the energy harvester and optimize it with
respect to the load resistance and frequency ratio. The optimal expressions are then used to study the effect of
bias conditions on the optimal values. We observe that the bias conditions significantly affect the antiresonance
frequency allowing for possible real time control to maximize the energy flow from the environment to the load.
Furthermore, it is observed that, in the range of bias conditions for which our model is valid, the harvested power
increases with magnetic bias and decreases with the prestress.