Macro-fiber composite (MFC) piezoelectric materials have been applied to a number of problems requiring high actuation authority, ranging from morphing-wing aircraft to vibration control in flexible structures. Most recently we have employed such MFC structures in underwater bio-inspired locomotion employing large actuation levels. However, utilizing the converse piezoelectric effect to such a degree requires high electric field and strain levels, resulting in significant material and geometric nonlinearities, beyond low field nonlinearities typically encountered in energy harvesting and sensing. In this work, we explore the mathematical framework of an MFC bimorph cantilever under low to moderate excitation levels and compare the results to base excitation and actuation experiments. Further experiments are conducted for actuation experiments which result in high strain and electric field levels, and sources of higher order nonlinearities are proposed.
This work investigates the development and characterization of a bio-inspired swimmer actuated by Macro-Fiber Composite (MFC) piezoelectric laminates along with the required electronic hardware for untethered underwater operation. The main body of the swimmer is designed to imitate a trout-like streamlined geometry that has a 3Dprinted hard front enclosure and a soft tail portion. The focus is placed on the experimental characterization of the swimmer under various flow conditions and for various actuation frequencies. Straight swimming is explored in quiescent water, and further characterizations are performed in a water tunnel for different flow speeds.
The transformation of wind energy into low-power electricity using piezoelectric materials enables the possibility of powering wireless electronic components especially in high wind areas. This work thoroughly explores the effect of aspect ratio (length/width) on the performance of inverted flag-based piezoelectric energy harvesters. Wind tunnel experiments are conducted for a range of electrical loads to quantify the optimal power output. Conclusions are drawn regarding the overall dynamics of the multiphysics system for the design and optimization of this new class of scalable wind energy harvesters.
KEYWORDS: Microsoft Foundation Class Library, Composites, Capacitance, Statistical modeling, Velocity measurements, 3D modeling, Mathematical modeling, Amplifiers, Water, Robotics
For bio-inspired, fish-like robotic propulsion, the Macro-Fiber Composite (MFC) piezoelectric technology offers noiseless actuation with a balance between actuation force and velocity response. However, internal nonlinear- ities within the MFCs, such as piezoelectric softening, geometric hardening, inertial softening, and nonlinear dissipation, couple with the hydrodynamic loading on the structure from the surrounding fluid. In the present work, we explore nonlinear actuation of MFC cantilevers underwater and develop a mathematical framework for modeling and analysis. In vacuo resonant actuation experiments are conducted for a set of MFC cantilevers of varying length to width aspect ratios to validate the structural model in the absence of fluid loading. These MFC cantilevers are then subjected to underwater resonant actuation experiments, and model simulations are compared with nonlinear experimental frequency response functions. It is observed that semi-empirical hydro- dynamic loads obtained from quasilinear experiments have to be modified to account for amplitude dependent added mass, and additional nonlinear hydrodynamic effects might be present, yielding qualitative differences in the resulting underwater frequency respones curves with increased excitation amplitude.
We explore the potential of human-scale motion energy harvesting toward enabling self-powered
wearable electronic components to avoid the burden of battery replacement and charging in next-generation
wireless applications. The focus in this work is piezoelectric transduction for converting human motion into
electricity. Specifically, we explore three piezoelectric energy harvesting approaches experimentally and
numerically: (1) Direct base excitation of a cantilevered bimorph configuration without/with a tip mass; (2)
plucking of a bimorph cantilever using a flexible/nonlinear plectrum; and (3) direct force excitation of a
curved unimorph. In all cases, electromechanical models are developed and experimental validations are
also presented. Specifically a nonlinear plectrum model is implemented for the plucking energy harvester.
Average power outputs are on the order 10-100 uW and can easily exceed mW in certain cases via design
optimization.
This work aims to demonstrate the detrimental effect of fluid damping on the bandwidth of a flexible nonlinear energy harvester and thereby further enhance the performance by minimizing nonlinear damping. A vacuum setup has been introduced to conduct nonlinear base excitation experiments at different air pressure levels in an effort to control the quadratic (velocity-squared) damping coefficient. It is shown that reduced air pressure substantially enhances the frequency bandwidth for primary resonance excitation. The empirical electromechanical model is modified to express the fluid damping in terms of fluid pressure and validated experimentally for different excitation levels.
We explore the potential for bandwidth enhancement by merely exploiting the hardening nonlinearity of a flexible cantilever. To date, this cubic hardening behavior has been minor due to dissipative effects, especially fluid drag. The goal here is to minimize the fluid damping and thereby achieve the jump phenomenon. A vacuum setup that is compatible with the armature of a long-stroke shaker is employed. Experiments are conducted for a range of air pressure and base excitation levels. The overall nonlinear non-conservative elastodynamics of the cantilever is also modeled and experimentally validated by empirically accounting for fluid damping.
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