As a result of the documented performance limitations of conventional linear piezoelectric energy harvesters, researchers have focused their efforts towards device designs that can better capture broadband energy. The approaches used can be classified into three categories: frequency tuning, multi-modal energy harvesting, and nonlinear energy harvesting<sup>1</sup>. Of the nonlinear harvesting approaches studied, bistable energy harvesters have been shown to have the most robust performance when subjected to broadband harmonic & stochastic excitation<sup>2-4</sup>. A conventional method for developing a nonlinear bistable restoring force is through use of magnetic repulsion. In these studies, a common theme of high-energy orbit breakdown occurs during a frequency upsweep. The issue at hand is the inability of the device inertial forces to overcome the potential energy barrier (separatrix) inherent to a bistable potential energy. This paper proposes the use of a high-permeability electromagnet for adaptively controlling the bistable magnetic repulsion force to expand the frequency bandwidth for high-energy harmonic oscillations. Numerical simulations of the nonlinear oscillator are used to study the system response under varying parameters of separation distance and electromagnetic coil current. An analytical model of the magnetic moment of an electromagnet is developed for use in studying the force interaction between repulsing magnets and to determine the parametric space that generates buckling loads in a cantilever bimorph energy harvester.
New developments in novel energy harvesting schemes for structural health monitoring sensor networks have progressed in parallel with advancements in low-power electronic devices and components. Energy harvesting from galvanic corrosion is one such scheme that has shown to be a viable solution for powering sensing platforms for marine infrastructure. However, with this particular energy harvesting scheme, the power output is current limited as a result of a high terminal resistance that increases with time. In addition, the output voltage is non-stationary, and is a function of several environmental parameters and the applied resistive load. Variability in the power source requires a robust conditioning circuit design to produce a regulated power supply to the sensing and computing electronics. This paper experimentally investigates the non-stationary power characteristics of a galvanic corrosion energy harvester; and uncertainty quantification (UQ) is performed on the measured power characteristics for two experimental specimens subject to resistive load sweeps. The effects on designing a low-power sensor node are considered, and the uncertainty characteristics are applied to a low-power boost converter by means of a Monte Carlo simulation. Lastly, the total energy harvester capacity (measured in mA-Hr) is approximated from the data and is compared to a conventional battery.
Sensing systems play a lead role in the structural health monitoring (SHM) paradigm by performing actuation, data
acquisition, and communication in order to enable the implementation of a health monitoring strategy. In many
applications power provision is limited by the use of a battery as their power capacity often fails to exceed the intended
long-term sensing requirements of the host structure. Energy harvesting has emerged as a potential powering solution to
provide autonomous functionality to sensing systems.
Galvanic corrosion as a form of energy harvesting has proved to be a viable source for operating simple low-power
sensing and computing platforms for marine structures. The power characteristics of the energy harvester define a unique
design problem for the sensor node power electronics, as the output voltage and current are extremely limited. This
initiative considers the design of a sensor node that makes use of high-efficiency switching converters and low-power
microprocessors to reduce the power demands on the energy harvester. In addition, the power electronics features a low
duty-cycle control circuit to isolate the energy harvester from the sensing electronics for more efficient operation. A
sensing proof-of-concept is conducted by means of temperature measurement.
The U.S. Department of Energy (DOE) proposes to meet 20% of the nation's energy needs through wind power by
the year 2030. To accomplish this goal, the industry will need to produce larger (>100m diameter) turbines to
increase efficiency and maximize energy production. It will be imperative to instrument the large composite
structures with onboard sensing to provide structural health monitoring capabilities to understand the global
response and integrity of these systems as they age. A critical component in the deployment of such a system will be
a robust power source that can operate for the lifespan of the wind turbine. In this paper we consider the use of
discrete, localized power sources that derive energy from the ambient (solar, thermal) or operational (kinetic)
environment. This approach will rely on a multi-source configuration that scavenges energy from photovoltaic and
piezoelectric transducers. Each harvester is first characterized individually in the laboratory and then they are
combined through a multi-source power conditioner that is designed to combine the output of each harvester in
series to power a small wireless sensor node that has active-sensing capabilities. The advantages/disadvantages of
each approach are discussed, along with the proposed design for a field ready energy harvester that will be deployed
on a small-scale 19.8m diameter wind turbine.
Structural health monitoring consists of an integrated paradigm of sensing, data interrogation, and statistical modeling
that results in a strategy to assess the performance of a structure. Sensor networks play a central role in this paradigm, as
such networks typically perform much of the actuation, data acquisition, information management, and even local
computing necessary to enable the overall implementation of the strategy, increasingly in a wireless mode. In many
applications power provision can become a limiting factor, as the conventional strategy for wireless networks is a
battery. However, batteries require replacement, as their useful shelf lives often do not exceed the intended service of
their host structures.
Energy harvesting has emerged as a class of potential network powering solutions whereby one form of energy available
on the structure is harvested and converted to useful electrical energy. The objective of this work is to investigate the
harvesting of energy from galvanic corrosion that typically occurs naturally in many structures. Specifically, this study
considers corrosion between magnesium and graphite rods embedded in a concrete structure immersed in seawater. The
energy was evaluated by connecting a .1F capacitor and measuring the voltage charge over finite time intervals during
the corrosion process. A carbon fiber admixture was introduced to the concrete host to improve electrical conductivity,
and the power increase was calculated from voltage measurements. The investigation concludes that the voltage levels
achieved may be naturally integrated with a booster circuit to provide CMOS voltage levels suitable for sensor network
powering in some applications.