Tyler Stalbaum

A multiple-shape memory polymer-metal composite actuator capable of programmable control, creating complex 3D motion of bending, twisting, and oscillation.

Development of biomimetic actuators has been an essential motivation in the study of smart materials. However, few materials are capable of controlling complex twisting and bending deformations simultaneously or separately using a dynamic control system. Here, we report an ionic polymer-metal composite actuator having multiple-shape memory effect, and is able to perform complex motion by two external inputs, electrical and thermal. Prior to the development of this type of actuator, this capability only could be realized with existing actuator technologies by using multiple actuators or another robotic system. This paper introduces a soft multiple-shape-memory polymer-metal composite (MSMPMC) actuator having multiple degrees-of-freedom that demonstrates high maneuverability when controlled by two external inputs, electrical and thermal. These multiple inputs allow for complex motions that are routine in nature, but that would be otherwise difficult to obtain with a single actuator. To the best of the authors’ knowledge, this MSMPMC actuator is the first solitary actuator capable of multiple-input control and the resulting deformability and maneuverability.

Soft but Powerful Artificial Muscles Based on 3D Graphene–CNT–Ni Heteronanostructures

Bioinspired soft ionic actuators, which exhibit large strain and high durability under low input voltages, are regarded as prospective candidates for future soft electronics. However, due to the intrinsic drawback of weak blocking force, the feasible applications of soft ionic actuators are limited until now. An electroactive artificial muscle electro-chemomechanically reinforced with 3D graphene-carbon nanotube-nickel heteronanostructures (G-CNT-Ni) to improve blocking force and bending deformation of the ionic actuators is demonstrated. The G-CNT-Ni heteronanostructure, which provides an electrically conductive 3D network and sufficient contact area with mobile ions in the polymer electrolyte, is embedded as a nanofiller in both ionic polymer and conductive electrodes of the ionic actuators. An ionic exchangeable composite membrane consisting of Nafion, G-CNT-Ni and ionic liquid (IL) shows improved tensile modulus and strength of up to 166% and 98%, respectively, and increased ionic conductivity of 0.254 S m-1 . The ionic actuator exhibits enhanced actuation performances including three times larger bending deformation, 2.37 times higher blocking force, and 4 h durability. The electroactive artificial muscle electro-chemomechanically reinforced with 3D G-CNT-Ni heteronanostructures offers improvements over current soft ionic actuator technologies and can advance the practical engineering applications.

A comprehensive physics-based model encompassing variable surface resistance and underlying physics of ionic polymer-metal composite actuators

The ionic polymer-metal composite (IPMC) is an emerging smart material in actuation and sensing applications, such as artificial muscles, underwater actuators, and advanced medical devices. However, the effect of the change in surface electrode properties on the actuating of IPMC has not been well studied. To address this problem, we theoretically predict and experimentally investigate the dynamic electro-mechanical response of the IPMC thin-strip actuator. A model of the IPMC actuator is proposed based on the Poisson-Nernst-Planck equations for ion transport and charge dynamics in the polymer membrane, while a physical model for the change of surface resistance of the electrodes of the IPMC due to deformation is also incorporated. By incorporating these two models, a complete, dynamic, physics-based model for IPMC actuators is presented. To verify the model, IPMC samples were prepared and experiments were conducted. The results show that the theoretical model can accurately predict the actuating performance of IPMC actuators over a range of dynamic conditions. Additionally, the charge dynamics inside the polymer during the oscillation of the IPMC is presented. It is also shown that the charge at the boundary mainly affects the induced stress of the IPMC. The current study is beneficial for the comprehensive understanding of the surface electrode effect on the performance of IPMC actuators.

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.

Chapter 5:Modeling Ionic Polymer Metal Composites with COMSOL: Step-by-Step Guide

Considerable effort has been put into modeling the physics of the electromechanical transduction phenomenon of ionic polymer metal composites (IPMCs). A broad way to categorize the existing models is by how the underlying physics is described. The first category is made up of rather empirical current-displacement relation models, often based on the electric circuit equivalent description. The second category of the models explicitly considers the ionic flux inside the material. In this chapter, we consider the latter, namely physics-based IPMC electromechanical and mechanoelectrical transduction models. Although the basic equations of the physics-based models of IPMCs have been established, it can take a significant amount of time and effort to implement them for calculations. Furthermore, freely available basic models of IPMCs would greatly benefit researchers and engineers by being a basis for developing more complicated models according to the research or design needs. To make the fundamental models of IPMCs more applicable in system and application designs, an explicit foundation of how to implement the equations is needed. Therefore, the FEM-based implementation of the model with all necessary boundary conditions is presented—this is called the modeling framework of IPMCs. Step-by-step guidelines of how to implement a basic model of IPMCs in COMSOL Multiphysics® modeling software are provided. COMSOL Multiphysics® is a registered trademark of COMSOL AB. The underlying equations and boundary conditions for the electromechanical and mechanoelectrical transduction model implementations are explicitly described first. Thereafter, sample models with illustrations are introduced followed by a brief analysis of modeling results.

Bioinspired travelling wave generation in soft-robotics using ionic polymer-metal composites

Biology inspired inventions have been of great interest to the researcher and engineer. Biomimicry offers special insight into nature’s methods of motion control, with significance in thrust and drag control for swimming and flying lifeforms. An array of actuators designed in an artificial wing could be used to control aerodynamic effects to adjust drag or lift according to given wind conditions for improved flight, or to control stability prior to touchdown for a smooth landing, providing an additional means of aerodynamic stability control. In this study, a method of generating a travelling wave motion in attempt to mimic that observed in the wings of flying-fish (Exocoetidae) during descent are presented. Ionic polymer-metal composite actuators were arranged in an array and oscillated in a travelling wave motion. The arrays were held rigid between glass slides and embedded into a flexible substrate to create the soft “wing” surface for free-end displacement measurements. Using a microcontroller and motor drivers, a controllable travelling wave motion was created. Additionally, an array of actuators was connected to a 3D printed wing skeleton based on the dimensions of a four-wing flying-fish like structure. The results indicate the travelling wave motion can be controlled with ionic polymer-metal composite actuators as arranged in several configurations. This offers an experimental platform for further study of the aerodynamic effects of a travelling wave across a wing during flight.

Modeling of a soft multiple-shape-memory ionic polymer-metal composite actuator

The multiple-shape-memory ionic polymer-metal composite (MSM-IPMC) actuator can demonstrate complex 3D deformation. The MSM-IPMC have two characteristics, which are the electro-mechanical actuation effect and the thermal-mechanical shape memory effect. The bending, twisting, and oscillating motions of the actuator could be controlled simultaneously or separately by means of thermal-mechanical and electro-mechanical transactions. In our study, we theoretically modelled and experimentally investigated the MSM-IPMC. We proposed a new physical principle to explain the shape memory behavior. A theoretical model of the multiple shape memory effect of MSMIPMC was developed. It is based on the assumption that the multiple shape memory effect is caused by the thermal stress and each individual Young’s modulus is ‘memorized’ during the previous programming process. As the MSM-IPMC was reheated to each temperature, the corresponding thermal stress was applied on the MSM-IPMC, and the Young’s modulus was recovered, which result in the shape recovery of the MSM-IPMC. To verify the model, a MSM-IPMC sample was prepared. Experimental tests of MSM-IPMC were conducted. By comparing the simulation results and the experimental results, both results have a good agreement. The current study is beneficial for the better understanding of the underlying physics of MSM-IPMC.

Multi degree of freedom IPMC sensor

Ionic polymer-metal composite (IPMC) has been examined through simulation and experimental tests as a material for use in multi degree of freedom (DOF) sensor applications. Mechanoelectrical transduction, the ability to generate current from imposed mechanical deformation, enables IPMCs to be applied as sensor devices. This phenomenon has been reported and is reasonably well described by various models. In this study, a physics-based model is applied to predict performance of an IPMC sensor over a range of conditions. Configuration of our interest is cylindrical IPMC with 2-DOF mechanoelectrical sensor capabilities. The prototype of cylindrical IPMC has an outer diameter of 1 mm and a 25 mm length. Application of deformation induced voltage of the fabricated cylindrical IPMCs as a means of mechanoelectrical transduction have been simulated and experimentally verified. The performance of the prototype IPMC under several operating conditions was also analyzed, and experimental results have provided keen insight into the physical phenomenon of mechanoelectical IPMC transduction.

A model framework for actuation and sensing of ionic polymer-metal composites: prospective on frequency and shear response through simulation tools

Ionic polymer-metal composite (IPMC) is a promising material for soft-robotic actuator and sensor applications. This material system offers large deformation response for low input voltage and has an aptitude for operation in hydrated environments. Researchers have been developing IPMC actuators and sensors for applications with examples of self-sensing actuators, artificial fish fins and biomimicry of other aquatic lifeforms, and in medical operations such as in guided catheter devices. IPMCs have been developed in a range of geometric configurations, with tube or cylindrical and flat-plate rectangular as the most common shapes. Several mathematical and physics-based models have been developed for describing the transduction effects of IPMCs. In this work, the underlying theories of electromechanical and mechanoelectrical transduction in IPMCs are discussed, and simulated results of frequency response and shear response are presented. A model backbone is utilized which is primarily based on ion-transport and charge dynamics within the polymer membrane. The electromechanical model, that is with an IPMC as an actuator, is caused when an electric field is applied across the membrane causing ionic migration and swelling in the polymer membrane, which is based on the Poisson-Nernst-Planck equations and solid mechanics models. The mechanoelectric model is similar in underlying physics; however, the primary mechanisms of transduction are of different significance, where anion concentrations are as important as cations. COMSOL Multiphysics is utilized for simulations. Example applications of the modeling framework are presented. The simulated results provide additional support for the underlying physics theories discussed.

Numerical and experimental investigation of a biomimetic robotic jellyfish actuated by Ionic Polymer-Metal Composite

A biomimetic jellyfish robot is explored. The robot will be actuated by Ionic Polymer-Metal Composites arranged in a silicone dome. Computational Analysis is used to optimize thrust production by the jellyfish robot. Preliminary experiments will be conducted to analyze the deformation, thrust, displacement, and velocity. The two analyses will be compared to further optimize the design.