David Pugal

An explicit physics-based model of ionic polymer-metal composite actuators

The Poisson-Nernst-Planck system of equations is used to simulate the charge dynamics due to ionic current and resulting time-dependent displacement of ionic polymer-metal composite (IPMC) materials. Measured data show that currents through the polymer of IPMC cause potential gradients on the electrodes. Existing physics based models of IPMC do not explicitly consider how this affects the charge formation near the electrodes and resulting actuation of IPMC. We have developed an explicit physics based model that couples the currents in the polymer to the electric current in the continuous electrodes of IPMC. The coupling is based on the Ramo-Shockley theorem. The circular dependency concept is used to explain how the dependency between the ionic current and the potential drop in the electrodes is calculated and how they affect each other. Simulations were carried out using the finite element method. Calculated potential gradients, electric currents, and tip displacement of IPMC were validated against exper...

An IPMC-enabled bio-inspired bending/twisting fin for underwater applications

This paper discusses the design, fabrication, and characterization of an ionic polymer?metal composite (IPMC) actuator-based bio-inspired active fin capable of bending and twisting motion. It is pointed out that IPMC strip actuators are used in the simple cantilever configuration to create simple bending (flapping-like) motion for propulsion in underwater autonomous systems. However, the resulting motion is a simple 1D bending and performance is rather limited. To enable more complex deformation, such as the flapping (pitch and heaving) motion of real pectoral and caudal fish fins, a new approach which involves molding or integrating IPMC actuators into a soft boot material to create an active control surface (called a ?fin?) is presented. The fin can be used to realize complex deformation depending on the orientation and placement of the actuators. In contrast to previously created IPMCs with patterned electrodes for the same purpose, the proposed design avoids (1)?the more expensive process of electroless plating platinum all throughout the surface of the actuator and (2)?the need for specially patterning the electrodes. Therefore, standard shaped IPMC actuators such as those with rectangular dimensions with varying thicknesses can be used. One unique advantage of the proposed structural design is that custom shaped fins and control surfaces can be easily created without special materials processing. The molding process is cost effective and does not require functionalizing or ?activating? the boot material similar to creating IPMCs. For a prototype fin (90?mm wide ? 60?mm long ? 1.5?mm thick), the measured maximum tip displacement was approximately 44?mm and the twist angle of the fin exceeded 10?. Lift and drag measurements in water where the prototype fin with an airfoil profile was dragged through water at a velocity of 21?cm?s?1 showed that the lift and drag forces can be affected by controlling the IPMCs embedded into the fin structure. These results suggest that such IPMC-enabled fin designs can be used for developing active propeller blades or control surfaces on underwater vehicles.

Electromechanically driven variable-focus lens based on transparent dielectric elastomer

Dielectric elastomers with low elastic stiffness and high dielectric constant are smart materials that produce large strains (up to 300%) and belong to the group of electroactive polymers. Dielectric elastomer actuators are made from films of dielectric elastomers coated on both sides with compliant electrode material. Poly(3,4-ethylenedioxythiophene) (PEDOT), which is known as a transparent conducting polymer, has been widely used as an interfacial layer or polymer electrode in polymer electronic devices. In this study, we propose the transparent dielectric elastomer as a material of actuator driving variable-focus lens system using PEDOT as a transparent electrode. The variable-focus lens module has light transmittance up to 70% and maximum displacement up to 450. When voltage is applied to the fabricated lens module, optical focal length is changed. We anticipate our research to be a starting point for new model of variable-focus lens system. This system could find applications in portable devices, such as digital cameras, camcorder, and cell phones.

Monolithic IPMC Fins for Propulsion and Maneuvering in Bioinspired Underwater Robotics

Emerging bioinspired underwater systems, such as autonomous ocean mapping and surveillance vehicles, that maneuver through their environment by mimicking the swimming motion of aquatic animals, can benefit from soft monolithic actuators and control surfaces capable of undergoing complex deformations. Herein, an electrically driven ionic polymer-metal composite (IPMC) artificial muscle with uniquely patterned electrodes for creating complex deformations is presented. The surface electrode pattern on the IPMC is created using a simple surface machining process. By selectively activating specific regions of the IPMC, bending, twisting, flapping, and other bioinspired locomotive behavior can be achieved. For instance, the bending and twisting response of an example 50 mm × 25 mm × 0.5 mm patterned IPMC actuator is characterized to determine its range of motion, output force and torque, as well as its effectiveness as a fish-fin-like propulsor. The experimental results show that the twisting angle exceeds 8 °; the blocking tip force and torque can be as high as 16.5 mN (at 3 V) and 0.83 N·mm (at 4 V), respectively (driven at 0.05 Hz); and an average thrust force of approximately 0.4 mN (driven by 4-V sinusoidal input at 1 Hz) can be generated. These newly developed IPMC fins can be exploited to create novel and efficient propulsors for next-generation underwater robotic vehicles. An example bioinspired robotic fish is presented which exploits the capabilities of the patterned IPMCs for propulsion and maneuvering, where an average maximum swimming speed of approximately 28 mm/s is reported.

Nanothorn electrodes for ionic polymer-metal composite artificial muscles

Ionic polymer-metal composites (IPMCs) have recently received tremendous interest as soft biomimetic actuators and sensors in various bioengineering and human affinity applications, such as artificial muscles and actuators, aquatic propulsors, robotic end-effectors, and active catheters. Main challenges in developing biomimetic actuators are the attainment of high strain and actuation force at low operating voltage. Here we first report a nanostructured electrode surface design for IPMC comprising platinum nanothorn assemblies with multiple sharp tips. The newly developed actuator with the nanostructured electrodes shows a new way to achieve highly enhanced electromechanical performance over existing flat-surfaced electrodes. We demonstrate that the formation and growth of the nanothorn assemblies at the electrode interface lead to a dramatic improvement (3- to 5-fold increase) in both actuation range and blocking force at low driving voltage (1–3 V). These advances are related to the highly capacitive properties of nanothorn assemblies, increasing significantly the charge transport during the actuation process.

A bio-inspired multi degree of freedom actuator based on a novel cylindrical ionic polymer-metal composite material

In this work, we explore a promising electroactive polymer (EAP), called ionic polymer-metal composite (IPMC) as a material to use as a multi degree of freedom actuator. Configuration of our interest is a cylindrical IPMC with 2-DOF electromechanical actuation capability. The desired functionality was achieved by fabricating unique inter-digitated electrodes. Firstly, a 3D finite element (FE) model was introduced as a design tool to validate if the concept of cylindrical actuators would work. The FE model is based upon the physical transport processes — field induced migration and diffusion of ions. Secondly, based upon the FE modeling we fabricated a prototype exhibiting desired electromechanical output. The prototype of cylindrical IPMC has a diameter of 1 mm and a 20 mm length. We have successfully demonstrated that the 2-DOF bending of the fabricated cylindrical IPMCs is feasible. Furthermore, the experimental results have given new insight into the physics that is behind the actuation phenomenon of IPMC.

Physics-based modeling of mechano-electric transduction of tube-shaped ionic polymer-metal composite

In this study, tube-shaped ionic polymer-metal composite (IPMC) mechanoelectrical transducers have been examined through simulation and experimental investigation for use as multi-directional sensor devices. It should be noted that cation migration simulations provide keen insight into the differences in actuation and sensing phenomena in IPMC transducers. COMSOL Multiphysics 4.3b is used to achieve 3D time-based finite element simulations, including all relevant physics. A physics-based model is proposed to simulate mechanoelectrical transduction of 3D shaped IPMCs. Configuration of interest is a tube-shaped IPMC with multi-directional transducer capabilities. Also, the fabricated IPMCs have an outer diameter of 1 mm and a length of 20–25 mm. Multi-directional sensing results are presented. The cation rise in a very small (roughly 10 micrometers) sub-surface layer near the electrodes is several orders of magnitude larger in case of actuation than in case of sensing. Furthermore, the signal produced from sensing is of opposite charge direction as that provided as input for actuation to achieve the same displacement. However, cation rise is in the same direction, indicating anion concentration change as the primary effect in sensing. The proposed model is independent of general geometry and can be readily applied to IPMC sensors of other complex 3D shapes.

Biomimetic robotic artificial muscles

Introduction Physical Principles of Ionic Polymer-Metal Composites New IPMC Materials and Mechanisms A Systems Perspective on Modeling of Ionic Polymer-Metal Composites Conjugated Polymer Actuators: Modeling and Control Synthetic Dielectric Elastomer Materials Dielectric Elastomer Actuator Integrated Sensory Feedback for EAP Actuators Device and Robotic Applications of EAPs.

Characterization of sectored-electrode IPMC-based propulsors for underwater locomotion

Ionic polymer-metal composite (IPMC) actuators with sectored (patterned) electrodes have been fabricated for realizing bending and twisting motion. Such IPMCs can be used to create next-generation artificial fish-like propulsors that can mimic the undulatory, flapping, and complex motions of real fish fins. Herein, a thorough experimental study is performed on sectored IPMCs to characterize their performance. Specifically, results are presented to show (1) the achievable twisting response; (2) blocking force and torque; (3) power consumption and effectiveness; and (4) propulsion characteristics. The results can be utilized to guide the design of practical marine systems driven by IPMC propulsors. The design of an example underwater robotic system is also described which employs the IPMC actuators, and the performance of the robotic system is reported.Copyright

Improving electromechanical output of IPMC by high surface area Pd-Pt electrodes and tailored ionomer membrane thickness

In this study, we attempt to improve the electromechanical performance of ionic polymer–metal composites (IPMCs) by developing high surface area Pd-Pt electrodes and tailoring the ionomer membrane thickness. With proper electroless plating techniques, a high dispersion of palladium particles is achieved deep in the ionomer membrane, thereby increasing notably the interfacial surface area of electrodes. The membrane thickness is increased using 0.5 and 1 mm thick ionomer films. For comparison, IPMCs with the same ionomer membranes, but conventional Pt electrodes, are also prepared and studied. The electromechanical, mechanoelectrical, electrochemical and mechanical properties of different IPMCs are characterized and discussed. Scanning electron microscopy-energy dispersive X-ray (SEM-EDS) is used to investigate the distribution of deposited electrode metals in the cross section of Pd-Pt IPMCs. Our experiments demonstrate that IPMCs assembled with millimeter thick ionomer membranes and newly developed Pd-Pt electrodes are superior in mechanoelectrical transduction, and show significantly higher blocking force compared to conventional type of IPMCs. The blocking forces of more than 0.3 N were measured at 4V DC input, exceeding the force output of typical Nafion® 117-based Pt IPMCs more than two orders of magnitude. The newly designed Pd-Pt IPMCs can be useful in more demanding applications, e.g., in biomimetic underwater robotics, where high stress and drag forces are encountered.