Proceedings Article | 7 April 2009
KEYWORDS: Surface plasmons, Transducers, Stochastic processes, Energy harvesting, Signal attenuation, Analytical research, Feedback control, Systems modeling, Sensors, Bismuth
This paper presents recent analytical results pertaining to the optimization of power flow from vibratory energy
harvesting systems, using principles from optimal feedback control and network theory. Historically, much of the
research concerning such technologies has presumed that the vibratory energy source, from which power is to be
extracted, oscillates harmonically at a known frequency. In this case, the optimization of power extraction from
such sources by a resonant energy harvester can readily be accomplished through the use of classical impedance
matching techniques. However, in many applications, vibratory power sources exhibit dynamic behavior more
appropriately characterized by a stochastic process. In some cases, the power spectrum of this process may
exhibit a rather wide band. In such circumstances, impedance matching techniques cannot be used to optimize
power flow from the harvester, because the dynamic impedance they prescribe is always anticausal. This paper
presents several theoretical concepts, intended for broad application in the energy harvesting area, which can be
used to optimize power extracted from broadband sources. It is shown that in the broadband case, an optimal
causal impedance still exists which maximizes power generation, but in order to derive it, the dissipation in the
electrical system, as well as the mechanical system, must be taken into account in the system model. Levels of
power generation with this controller are compared to those of the anticausal optimal performance, as well as
to control design techniques that match the anticausal impedance at the resonant frequency. It is demonstrated
that such causal matching techniques can be significantly sub-optimal in broadband applications, especially when
electronic conversion is relatively efficient.
