Youngsu Cha

A physics-based model of the electrical impedance of ionic polymer metal composites

In this paper, we analyze the chemoelectrical behavior of ionic polymer metal composites (IPMCs) in the small voltage range with a novel hypothesis on the charge dynamics in proximity of the electrodes. In particular, we homogenize the microscopic properties of the interfacial region through a so-called composite layer which extends between the polymer membrane and the metal electrode. This layer accounts for the dissimilar properties of its constituents by describing the charge distribution via two species of charge carriers, that is, electrons and mobile counterions. We model the charge dynamics in the IPMC by adapting the multiphysics formulation based on the Poisson-Nernst-Planck (PNP) framework, which is enriched through an additional term to capture the electron transport in the composite layer. Under the hypothesis of small voltage input, we use the linearized PNP model to derive an equivalent IPMC circuit model with lumped elements. The equivalent model comprises a resistor connected in series wit...

Energy harvesting from underwater base excitation of a piezoelectric composite beam

In this paper, we investigate energy harvesting from underwater base excitation of a piezoelectric composite beam. Four different geometric configurations are experimentally studied in which the beam is either fully submerged or is partially immersed, with an eighth, a quarter, or a half of its length vibrating underwater. The frequency and the amplitude of base excitation are systematically varied along with the shunting resistance to investigate the principles of piezoelectric energy harvesting from underwater vibrations. Results demonstrate that increasing the wet length produces a consistent reduction of the resonance frequency and the quality factor of underwater vibrations. On the other hand, the harvested power is found to generally decrease as the submersion length is increased. Experimental results are interpreted through a distributed piezohydroelastic model that accounts for added mass and nonlinear hydrodynamic damping effects. A reduced order modal model is further established to parametrically explore the system response across a variety of geometrical and physical parameters.

Energy harvesting from the tail beating of a carangiform swimmer using ionic polymer-metal composites.

In this paper, we study energy harvesting from the beating of a biomimetic fish tail using ionic polymer-metal composites. The design of the biomimetic tail is based on carangiform swimmers and is specifically inspired by the morphology of the heterocercal tail of thresher sharks. The tail is constituted of a soft silicone matrix molded in the form of the heterocercal tail and reinforced by a steel beam of rectangular cross section. We propose a modeling framework for the underwater vibration of the biomimetic tail, wherein the tail is assimilated to a cantilever beam with rectangular cross section and heterogeneous physical properties. We focus on base excitation in the form of a superimposed rotation about a fixed axis and we consider the regime of moderately large-amplitude vibrations. In this context, the effect of the encompassing fluid is described through a hydrodynamic function, which accounts for inertial, viscous and convective phenomena. The model is validated through experiments in which the base excitation is systematically varied and the motion of selected points on the biomimetic tail tracked in time. The feasibility of harvesting energy from an ionic polymer-metal composite attached to the vibrating structure is experimentally and theoretically assessed. The response of the transducer is described using a black-box model, where the voltage output is controlled by the rate of change of the mean curvature. Experiments are performed to elucidate the impact of the shunting resistance, the frequency of the base excitation and the placement of the ionic polymer-metal composite on energy harvesting from the considered biomimetic tail.

Energy harvesting from underwater torsional vibrations of a patterned ionic polymer metal composite

In this paper, we study underwater energy harvesting from torsional vibrations of an ionic polymer metal composite (IPMC) with patterned electrodes. We focus on harmonic base excitation of a centimeter-size IPMC, which is modeled as a slender beam with thin cross-section vibrating in a viscous fluid. Large-amplitude torsional vibrations are described using a complex hydrodynamic function, which accounts for added mass and nonlinear hydrodynamic damping from the surrounding fluid. A linear black box model is utilized to predict the IPMC electrical response as a function of the total twist angle. Model parameters are identified from in-air transient response, underwater steady-state vibrations, and electrical discharge experiments. The resulting electromechanical model allows for predicting energy harvesting from the IPMC as a function of the shunting resistance and the frequency and amplitude of the base excitation. Model results are validated against experimental findings that demonstrate power harvesting densities on the order of picowatts per millimeter cubed.

Energy exchange during slamming impact of an ionic polymer metal composite

In this letter, we study the response of an ionic polymer metal composite to impulsive loading due to impact on the free surface of a quiescent fluid. Experiments are performed in a miniature drop tower and time-resolved particle image velocimetry is used to illustrate the flow physics of the slamming impact. Images from these experiments are used to analyze the impulsive multimodal response of the ionic polymer metal composite, which is then used to estimate the energy transferred from the slamming impact. Reduced-order modeling of the fluid-structure interaction and electromechanical behavior are used to interpret the experimental findings.

MAHRU-M: A mobile humanoid robot platform based on a dual-network control system and coordinated task execution

This paper introduces a mobile humanoid robot platform able to execute various services for humans in their everyday environments. For service in more intelligent and varied environments, the control system of a robot must operate efficiently to ensure a coordinated robot system. We enhanced the efficiency of the control system by developing a dual-network control system. The network system consists of two communication protocols: high-speed IEEE 1394, and a highly stable Controller Area Network (CAN). A service framework is also introduced for the coordinated task execution by a humanoid robot. To execute given tasks, various sub-systems of the robot were coordinated effectively by this system. Performance assessments of the presented framework and the proposed control system are experimentally conducted. MAHRU-M, as a platform for a mobile humanoid robot, recognizes the designated object. The objects pose is calculated by performing model-based object tracking using a particle filter with back projection-based sampling. A unique approach is used to solve the human-like arm inverse kinematics, allowing the control system to generate smooth trajectories for each joint of the humanoid robot. A mean-shift algorithm using bilateral filtering is also used for real-time and robust object tracking. The results of the experiment show that a robot can execute its services efficiently in human workspaces such as an office or a home.

Flexible Piezoelectric Energy Harvesting from Mouse Click Motions

In this paper, we study energy harvesting from the mouse click motions of a robot finger and a human index finger using a piezoelectric material. The feasibility of energy harvesting from mouse click motions is experimentally and theoretically assessed. The fingers wear a glove with a pocket for including the piezoelectric material. We model the energy harvesting system through the inverse kinematic framework of parallel joints in a finger and the electromechanical coupling equations of the piezoelectric material. The model is validated through energy harvesting experiments in the robot and human fingers with the systematically varying load resistance. We find that energy harvesting is maximized at the matched load resistance to the impedance of the piezoelectric material, and the harvested energy level is tens of nJ.

Energy harvesting from fluid-induced buckling of ionic polymer metal composites:

In this article, we assess the feasibility of energy harvesting from mechanical buckling of ionic polymer metal composites induced by a steady fluid flow. Specifically, we consider an underwater energy harvester composed of a paddle wheel, a slider-crank mechanism, and two ionic polymer metal composites clamped at both their ends. To enhance electromechanical transduction, the electrodes of the ionic polymer metal composites are split into three parts via a selective platinum deposition process. The system is installed in a water tunnel and experiments are performed to elucidate the influence of both the flow speed and the shunting resistance on energy harvesting. To provide a theoretical interpretation of the experimental results, the classical post-buckling theory of inextensible elastic beams is adapted to predict mechanical deformations and a lumped-circuit model is utilized to estimate the harvested power.

Fabrication and buckling analysis of ionic polymer metal composite pipes

In this paper, we study buckling of ionic polymer metal composite (IPMC) pipes under uniaxial compression. A novel methodology to fabricate shell-like IPMCs is developed by combining hot pressing and chemical reduction. In the compression tests, IPMC pipes of varying thickness are clamped at their ends through custom-made fixtures and both short-circuit current and deformation are recorded as a function of the applied load. Experimental results are interpreted using classical findings on the buckling of thin shells and finite element simulations. Our results demonstrate that IPMC buckling can be accurately sensed through the short-circuit current, which is nearly zero during the loading phase, before suddenly increasing at the onset of the elastic instability. The buckling patterns of the samples are largely non-axisymmetric with a number of lobes appearing along the axial and circumferential directions of the IPMC pipes.

A particle image velocimetry study of the flow physics generated by a thin lamina oscillating in a viscous fluid

In this paper, we study the flow physics produced by a thin rigid lamina oscillating in an otherwise quiescent viscous fluid. Particle image velocimetry (PIV) is used to extract the flow kinematics, which is, in turn, utilized to reconstruct the pressure distribution around the lamina through the integration of Navier-Stokes equations. The hydrodynamic loading experienced by the lamina is ultimately estimated from PIV data to investigate added mass and fluid damping phenomena. Experiments are conducted for varying Reynolds and Keulegan-Carpenter numbers to elucidate the relative weight of inertial, convective, and viscous phenomena on the resulting flow physics. In agreement with prior numerical studies, experimental results demonstrate that increasing the Reynolds and the Keulegan-Carpenter numbers results into the formation of coherent structures that are shed at the edges of the lamina and advected by the flow. This phenomenon is associated with nonlinearities in the hydrodynamic loading, whereby fluid...