Ionic Polymer Metal Composite Strip Research Articles

A thermodynamic model for ionic polymer–metal composites and finite volume-finite element solution

The transient electromechanical response of an ionic polymer–metal composite (IPMC) is modeled within a thermodynamic framework using the Euler–Bernoulli beam theory coupled with electrostatically driven diffusion to account for the flow of the ionic fluid phase. A finite volume-finite element model to handle general electromechanical load conditions has been developed based on the new beam theory. The model has been shown to simulate various electromechanical responses of IPMC strips including initial overshoot followed by a back-relaxation, and anode and cathode side equilibrium configurations. Water–polymer interaction has been shown to be sufficient to capture these responses. The model can be used in both actuator and sensor applications of IPMC beams.

Curled actuated shapes of ionic polymer metal composites strips

The curled actuated shapes of ionic polymer metal composites (IPMCs) are described within a nonlinear physics-based model of IPMC actuators. A key characteristic of the model is the refined, even if black box based, modeling of the relative permittivity of the IPMCs which strongly influences the actuation performances of the IPMC, when voltages higher than 1 V are involved. A varying-along-the-thickness relative permittivity is proposed to take into account the highly heterogeneous layers resulting from electrode deposition, where a charge redistribution occurs. Moreover, the presence of the metal electrodes has been considered as hampering the IPMCs' bending deformations, so reducing the actuation performances of the IPMC. A series of numerical tests have been planned and discussed to show the characteristics of the model; in particular, the model is shown to be strong enough to catch the not monotonic behavior of IPMCs, when back relaxation is manifested.

Aquatic Ionic-Polymer-Metal-Composite Insectile Robot With Multi-DOF Legs

Ionic polymer-metal composite (IPMC) is used in various bioinspired systems, such as fish- and tadpole-like robots swimming in water. The deflection of this smart material results from several external factors, such as water distribution and concentration. IPMC strips with a variety of water concentration on the surfaces and the surface conductivity show various deflection patterns. In this paper, IPMC strips in four initial wetness conditions (100%, 50%, 0% wet on the anode surfaces but 100% wet on the cathode surfaces, and the last one submerged in deionized water) were tested. Even without any external excitation, the strips can bend due to nonuniform water distribution. In order to understand the effects of surface conductivity in an aquatic environment, an IPMC strip with two wires connected to two distinct spots was used to demonstrate the power loss due to the surface resistance. Three types of input signals, sawtooth, sinusoidal, and square waves, were used to compare the difference between the input and output signals measured at the two spots. Thick (1 mm) IPMC strips were fabricated and employed in this study to sustain and drive the robot with sufficient forces. Finally, an aquatic walking robot (102 × 80 × 43 mm, 39 g) with six 2-degree-of-freedom (2-DOF) legs has been designed, implemented, and walked in water at the speed of 0.5 mm/s. The average power consumption is 8 W per leg. Each leg has a thigh and a shank to generate 2-DOF motions. Each set of three legs walked together as a tripod to maintain the stability in operation.

Model study of IPMC beam electroactive response based on root deformation

Ionic polymer-metal composite (IPMC) is a type of electroactive polymer (EAP). In this paper, based on Nemat-Nasser model, an improved model is developed to explain the initial nonlinear response of electric actuation on the fixed end deformation. Three IPMC strip samples with different surface resistance are chosen for analysis. Further, from simulation and experiment results, it is found that the root deformation made the tip movement of the IPMC strip with little surface resistance, but this effect was less and less when the surface resistance reduced. The calculation results of this model for the fixed end show a more accurate simulation for the actual deformation of IPMC strips.

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.

SYNTHESIS, EXPERIMENTAL CHARACTERIZATION AND PARAMETRIC IDENTIFICATION OF IONIC-POLYMER METAL COMPOSITE BENDING ACTUATORS

Ionic polymer metal composite (IPMC) actuator is a sandwiched structure with a thin polyelectrolyte strip or membrane plated with metal electrodes on both sides. Under a low applied voltage the IPMC strip bends toward either electrode depending on its polarity, forming a soft actuator for potential diverse applications. We report in details our methodologies for synthesizing IPMC with high quality electrode morphologies. We describe our experimental setup for measuring the physical and mechanical properties of IPMC. In conjunction with the experimental characterization, we finally present a parameter identification scheme to identify two key parameters for establishing relationship between unbalanced charge density and the associated electrostatic eigenstress, a constitutive law widely used in IPMC literature. The experimental and simulation procedures presented herein pave the avenue for fabrication, characterization and development of novel IPMC-based sensors and actuators.

A Novel Determination Method of IPMC Young’s Modulus Based on Cantilever Resonance Theory

The research is aimed at presenting a novel determination method of IPMC (Ionic Polymer Metal Composites) Young’s Modulus. This method would fill up some deficiencies, such as damaging the tested IPMC strip, having low precision and so on, in the traditional method like tensile test and bending test. The paper presents a novel determination method based on cantilever resonance theory. Cantilever resonance theory is one of the methods to determinate the Young’s modulus of metal wire and metal strip. This method adopts Euler-Bernoulli beam to build a vibration differential equation of the beam. Then, by using the separate variable method, the general solution of the equation would be obtained. Considering the boundary conditions, a formula about the relation of the Young’s modulus and the first natural frequency is obtained. Limited by the experimental equipment and test method, this method has not been applied in the composite material. This paper attempts to apply this method in the IPMC material. The laser probing DISP (displacement) technique is applied in the test experiment. The laser displacement transducer is a kind of accurate un-contact laser displacement measurement set. The distance measured, which could be used to measure the change in position of the tested object, is based on the triangle principle.

Preparation and performance of IPMC actuators with electrospun Nafion ®–MWNT composite electrodes

A new ionic polymer actuator was prepared with Nafion ®-117 membrane and electrodes made of an electrospun Nafion ®/multiwalled carbon nanotube (MWNT) web. The surfaces of composite electrodes were ion-beam coated with gold layers of 2–3 μm thickness to reduce the surface resistance. The composite electrodes offer several advantages over conventional platinum electrodes prepared via electroless plating process, i.e. flexibility, simple processability in large scales, and batch-to-batch reproducibility. The new ionic polymer–metal composite (IPMC) actuators showed a rapid and large bending motion. Under an applied potential of 3 V dc, the maximum horizontal displacement ( δ max) measured at the tip of IPMC strip (cantilever length: 20 mm) was 16.7 mm, the tip velocity in the initial linear region was 10.5 mm/s, 88% of the δ max was reached within initial 5 s, and the generated strain% was 0.79 (13.6 mm, 7.2 mm/s, 85%, and 0.88, respectively for a conventional Nafion ®–IPMC made via the electroless plating of platinum). It was noted that the energy efficiency of strain was over 10 times higher than that of the conventional Nafion ®–IPMC. And the crack formation of metal electrode after repeated bending deformation significantly reduced with the introduction of relatively flexible electrode assembly into the IPMC architecture. The remarkable improvements in its performance were considered to be due to the efficient quantum chemical and double-layer electrostatic effects in a charge injection model, induced by the good dispersion of MWNTs through a typical electrospinning technique.

A helical ionic polymer–metal composite actuator for radius control of biomedical activestents

Helical ionic polymer–metal composite (IPMC) actuators are newly developed to controlthe radius of biomedical active stents. The helix-shaped IPMC actuator is fabricatedthrough the thermal treatment of an IPMC strip helically coiled on a glass rod. Thehelical IPMC actuator can be used to realize not only bending motion but alsotorsional and longitudinal motion. In particular, the dynamic responses of the helicalIPMC actuators are evaluated according to various structural parameters such asdiameter, pitch and width of the helical configuration. The present experimentalresults for the harmonic responses and frequency response functions show thatdiameter, among the structural parameters, plays an important role in the actuationperformance required to efficiently control the radius of the helical stent. The staticand dynamic responses of the helical IPMC actuators are also investigated withstep and harmonic electrical inputs, a voltage–current diagram and a mechanicalcompression test. This study shows that a helical IPMC actuator can be usedfor biomedical smart systems capable of controlling the radius of active stents.

Development of an ionic polymer–metal composite stepper motor using a novel actuator model

A novel ionic polymer–metal composite (IPMC) actuated stepper motor was developed in order to demonstrate an innovative design process for complete IPMC systems. The motor was developed by utilizing a novel model for IPMC actuators integrated with the complete mechanical model of the motor. The dynamic, nonlinear IPMC model can accurately predict the displacement and force actuation in air for a large range of input voltages as well as accounting for interactions with mechanical systems and external loads. By integrating this geometrically scalable IPMC model with a mechanical model of the motor mechanism an appropriate size IPMC strip has been chosen to achieve the required motor specifications. The entire integrated system has been simulated and its performance verified. The system has been built and the experimental results validated to show that the motor works as simulated and can indeed achieve continuous 360° rotation, similar to conventional motors. This has proven that the model is an indispensable design tool for integrated IPMC actuators into real systems. This newly developed system has demonstrated the complete design process for smart material actuator systems, representing a large step forward and aiding in the progression of IPMCs towards wide acceptance as replacements for traditional actuators.

Temporally-resolved hydrodynamics in the vicinity of a vibrating ionic polymer metal composite

In this paper, we study the hydrodynamics induced by an ionic polymer metal composite (IPMC) cantilever vibrating in a quiescent fluid. Time-resolved particle image velocimetry is used to measure the velocity field in the vicinity of the vibrating IPMC strip and a control volume analysis is utilized to estimate the thrust production per unit IPMC width. The governing fluid dynamics dimensionless parameters are varied parametrically to ascertain the influence of the Reynolds number, the peak tip displacement to IPMC length ratio, and the IPMC aspect ratio. It is found that the Reynolds number is the dominant parameter in determining the thrust produced by the IPMC, while the relative tip displacement and aspect ratio play secondary roles. An increase in the relative tip displacement has a minimal effect on the produced thrust, while an increase in the aspect ratio results in a mild decrease in thrust production. It is further found that estimating the thrust from the mean velocity field significantly underpredicts the thrust estimate.

IPMC gripper static analysis based on finite element analysis

Recently, a type of flexible grippers with low power supply (0–5 V) has been designed and developed for grasping small but precision parts. In previous work, the authors manufactured a soft gripper whose actuating components are made of ionic polymer-metal composite (IPMC) materials; however, there is not a comprehensive model to analyze the complete mechanics for this IPMC gripper. Therefore, this paper provides a finite element method for analyzing its static mechanics characteristics in the state with maximal stress and strain (i.e., the gripper opening largest, including the IPMC deformation, stress, and strain). Further, these electromechanical coupling relationships can be simulated by using the piezoelectric analysis module based on ANSYS software. The simulation results show that the maximal tip displacement of IPMC strips can nearly reach their own free length, the maximal stress is 54 MPa in the center of copper electrodes, and the maximal strain is 0.0286 on the IPMC strip. The results provide detailed numerical solutions and appropriate finite element analysis methodologies beneficial for further research on the optimization design, forecast analysis, and control field.

Three nonlinear performance relationships in the start-up state of IPMC strips based onfinite element analysis

Ionic polymer–metal composites (IPMC) are a class of electroactive polymers (EAP), andthey currently attract numerous researchers to study their performance characteristics andapplications. However, research on its start-up characteristics still requires more attention.In the IPMC start-up state (the moment of applying an actuation voltage at the verybeginning), its mechanical performance is different in the stable working state (working forat least 10 min). Therefore, this paper focuses on three performance relationships of anIPMC strip between its maximal tip deformation and voltage, its maximal stressand voltage, as well as its maximal strain and voltage, both in the two states.Different from other reports, we found that they present nonlinear tendencies inthe start-up state rather than linear ones. Therefore, based on the equivalentbimorph beam model, a finite element electromechanical coupling calculationmodule in the ANSYS software was utilized to simulate these characteristics.Furthermore, a test system is introduced to validate the phenomena. As a whole,these three relationships and the FEA method may be beneficial for providingcontrol strategies effectively to IPMC actuators, especially in their start-up states.

Self‐sensing ionic polymer–metal composite actuating device with patterned surface electrodes

AbstractElectroactive polymers are materials that change their properties (e.g. size and shape) while stimulated by an electric field/current. Conversely, they produce an electrical signal if bent. As both actuators and sensors, they are considered attractive for various applications, e.g. in biomedicine and robotics. Self‐sensing actuators made of these materials are still a topic of great interest among researchers. This paper proposes a new self‐sensing ionic polymer–metal composite (IPMC) actuating device. By specially patterning the opposite metal electrodes of an IPMC strip, an actuator and a sensor are formed on a single piece of the material. Self‐sensitivity is attained by measuring the changing resistance of the sensor part of the structure. This paper introduces the methods for patterning the surface of an IPMC strip and measuring the resistance change during the actuator work cycle, and gives experimental evidence of the suitability of the proposed method for the realization of a smart motion actuator. Copyright © 2009 Society of Chemical Industry

Modeling of bending behavior of IPMC beams using concentrated ion boundary layer

Ionic polymer metal composites (IPMCs) are an emerging class of electroactive polymers (EAP), which have many potential applications as sensors and actuators. Recently, IPMCs have been intensively studied because of their huge potential in medical, mechanical, electronic, and aerospace engineering. However, before the benefits of these materials can be effectively exploited for practical use, a mathematical model must be established to enhance understanding and predictability of IPMC actuation. The coupled electrical-chemical-mechanical response of an IPMC depends on the structure of the polyelectrolyte membrane, the morphology and conductivity of the metal electrodes, the cation properties, and the level of hydration. With this in mind, the purpose of this study is to establish a finite element model for bending behavior of IPMC beams. With reference to their operation principle, it is assumed that an IPMC beam has three virtual layers. We draw an analogy between thermal strain and real strain in IPMC due to volume change. This is a coupled structure/thermal model, and the finite element method is used to solve this model. The ion concentration distribution in the IPMC boundary layer is mimicked with the temperature distribution, and the electromechanical coupling coefficient is mimicked with the thermal expansion coefficient. Theoretical and experimental results demonstrate that our suggested model is practical and effective enough in predicting the blocking force of IPMC strips for different input voltages and strip thicknesses.

Energy harvesting from base excitation of ionic polymer metal composites in fluidenvironments

In this paper, we analytically and experimentally study the energy harvestingcapability of submerged ionic polymer metal composites (IPMCs). We considerbase excitation of an IPMC strip that is shunted with an electric impedance andimmersed in a fluid environment. We develop a modeling framework to predictthe energy scavenged from the IPMC vibration as a function of the excitationfrequency range, the constitutive and geometric properties of the IPMC, and theelectric shunting load. The mechanical vibration of the IPMC strip is modeledthrough Kirchhoff–Love plate theory. The effect of the encompassing fluid on theIPMC vibration is described by using a linearized solution of the Navier–Stokesequations, that is traditionally considered in modeling atomic force microscopecantilevers. The dynamic chemo-electric response of the IPMC is described through thePoisson–Nernst–Planck model, in which the effect of mechanical deformations of thebackbone polymer is accounted for. We present a closed-form solution for thecurrent flowing through the IPMC strip as a function of the voltage across itselectrodes and its deformation. We use modal analysis to establish a handleableexpression for the power harvested from the vibrating IPMC and to optimize theshunting impedance for maximum energy harvesting. We validate theoretical findingsthrough experiments conducted on IPMC strips vibrating in aqueous environments.

An IPMC Actuated 3D Swimming Microrobot and its Propulsive Efficiency Analysis

An Ionic polymer metal composites (IPMC) actuated 3D swimming microrobot is presented first. Inspired by biologic fins, passive plastic fin is attached to the IPMC strip to increase the thrust. Infrared sensors are equipped for wireless control and autonomous navigation. Then propulsive efficiency analyses are carried out. From the water electrolysis influence analysis of the IPMC, the best working voltage is confirmed. Finally, a two parts IPMC actuator is presented to improve the propulsive efficiency of the microrobot after the analysis of propulsive efficiency of caudal fin.

Verification of Beam Models for Ionic Polymer-Metal Composite Actuator

Ionic Polymer-Metal Composite (IPMC) can work as an actuator by applying a few voltages. A thick IPMC actuator, where Nafion-117 membrane was synthesized with polypyrrole/alumina composite filler, was analyzed to verify the equivalent beam and equivalent bimorph beam models. The blocking force and tip displacement of the IPMC actuator were measured with a DC power supply and Young's modulus of the IPMC strip was measured by bending and tensile tests respectively. The calculated maximum tip displacement and the Young's modulus by the equivalent beam model were almost identical to the corresponding measured data. Finite element analysis with thermal analogy technique was utilized in the equivalent bimorph beam model to numerically reproduce the force-displacement relationship of the IPMC actuator. The results by the equivalent bimorph beam model agreed well with the force-displacement relationship acquired by the measured data. It is confirmed that the equivalent beam and equivalent bimorph beam models are practically and effectively suitable for predicting the tip displacement, blocking force and Young's modulus of IPMC actuators with different thickness and different composite of ionic polymer membrane.

A Camera Based Method for the Measurement of Motion Parameters of IPMC Actuators

A visual measurement technique that is specifically developed to monitor the movements of ionic polymer metal composite (IPMC) materials in underwater conditions is presented. The proposed method is based on the extraction of appropriate information about the movement of an IPMC strip from subsequent picture frames. Since the time difference between these pictures is known, the system calculates both the displacement and the speed of the moving part. The processing algorithm implements a fully automated procedure for the localization of the point of interest (i.e., the edge of a microrobotic wing) and calculates the distance (displacement) between subsequent frames. This method is particularly useful for rather large and slow movements of the IPMC strips, as found in underwater microrobotic applications. The experimental results are compared with concurrent reference measurements by a high-accuracy laser-positioning system. A setup based on a low-cost camera offers a resolution of 0.5 mm or better, which is quite good for the specific application.

A Particle Image Velocimetry Study of Vibrating Ionic Polymer Metal Composites in Aqueous Environments

Low power consumption and activation voltage combined with high flexibility and minimal weight make ionic polymer metal composites (IPMCs) well-suited for miniaturized underwater propulsion systems. In the present study, we investigate the flow field generated by an IPMC strip vibrating in a quiescent aqueous environment using planar particle image velocimetry. We use the time-averaged flow field to compute the momentum transfer to the fluid and estimate the mean thrust generated by the vibrating actuator. We find that the mean thrust produced by the vibrating IPMC increases with the Reynolds number, defined by the maximum tip speed and IPMC width, and is only marginally affected by the relative vibration amplitude. The results of this study can guide the optimization of IPMC-based propulsion systems for miniature biomimetic robotic swimmers.