Dynamics and Control of Energy Harvesting Device

Energy harvesting from the environment has the potential to produce low cost power for portable electronics to homes. This thesis investigates energy harvesting from human motion, air flow, and the sun using model-based design and experimental testing of devices tailored for specific energy harvesting modalities. Specifically, this thesis develops piezoelectric energy harvesters for wearables and heating ventilation and air conditioning (HVAC) ducts and tracking solar energy harvesters using shape memory alloy (SMA) actuators.;Piezoelectric energy harvesters typically perform poorly in the low frequency, low amplitude, and intermittent excitation environment of human movement associated with wearables. A piezoelectric compliant mechanism (PCM) energy harvester is designed, modeled, and analyzed that consists of a piezoelectric unimorph clamped at the base and attached to a compliant mechanism at the tip. The compliantmechanism has two flexures that amplify the tip displacement to produce large motion of a proof mass and a low frequency first mode with an efficient (nearly quadratic) shape. The compliant mechanism is fabricated as a separate, relatively rigid frame with flexure hinges, simplifying the fabrication process and surrounding and protecting the piezoelectric unimorph. Comparing the time domain performance based on realistic wrist acceleration data, the PCM produces 6 times more average power than a benchmark proof mass cantilever with the same unimorph area and natural frequency. Experiments with a fabricated PCM energy harvester prototype show that the compliant hinge stiffness can be carefully tuned to enforce a quadratic boundary condition, approaching the theoretical high power output and mode shape efficiency.;The bridge structure of the PCM also introduces an axial tensioning nonlinearity that self-limits the response to large amplitude impacts, improving the robustness of the device. A nonlinear model of the PCM energy harvester under large base excitation is derived to determine the maximum power that can be generated by the device. Experiments show that the compliant mechanism introduces a stiffening effect and a much wider bandwidth than the proof mass cantilever design. The PCM outperforms the cantilever in both average power and power-strain sensitivity at high accelerations due to the PCM axial stretching effect and its more uniform strain distribution.;Piezoelectric energy harvesters can also be used to scavenge energy for unattended sensors in HVAC ducts. An aeroelastic energy harvester using a pinnedpinned beam is designed, modeled, and analyzed. Nonlinear Euler-Bernoulli beam theory, a linear piezoelectric constitutive law, and nonlinear pressure dynamics are used to obtain the desired model. Compared with the traditional cantilever beam used by previous researchers, the pinned-pinned beam has a higher frequency limit cycle and more efficient mode shape, which ensure higher power output at the same strain level. The pinned-pinned boundary condition also self-limits the response amplitude, limiting strain in the piezoelectric beam and premature failure. Simulation results show that the pinned-pinned beam can harvest at least 4 times more average power than a cantilever beam with the same maximum strain.;Wrist-worn devices often use a magnet on a spinning rotor to interact with a magnet on a piezoelectric cantilever, transferring energy from the rotor to the cantilever. Electrical energy can then be harvested from the cyclically strained piezoelectric material as the vibration transient decays. From the viewpoint of designing the rotor system, it is desirable to model these complex orthogonal interactions by an equivalent damping. The equivalent damping of orthogonal magnetic interactions can be calculated using a simplified model. A magnet connected to an inertia that is moving along one axis can interact with another magnet connected to an inertia that is initially at rest and constrained to move along an orthogonal axis. This orthogonal interaction results in a decreased speed and loss of energy for the moving mass and an increased speed and gain of energy for the initially-stationary mass. The damping predictions are compared with simulation results from an energy harvester consisting of a rotating proof mass that interacts orthogonally with a petal arrangement of piezoelectric bimorph beams. (Abstract shortened by ProQuest.).