Electroactive Polymer Transducers Research Articles

An investigation of the electrical dynamics in electroactive polymer transducers with resistive electrodes

To pursue a variable-capacitance working principle, transducers based on soft electroactive polymers (EAPs) need deformable electrodes that match the compliance and stretchability of the EAP polymeric substrates. A variety of manufacturing procedures are available to create conductive materials that can achieve this, including solutions that can provide remarkably low resistivity. However, the simplest and most feasible options often involve the use of particle-filled (e.g. carbon-filled) polymer composites, which, while easy to produce, tend to exhibit relatively high resistivity. This high level of resistivity, combined with the inherent capacitance of EAP transducers, introduces dynamic effects in the devices electrical activation, which may affect performance. This paper investigates the impact of electrode resistivity on the electrical dynamics of EAP devices, combining continuum models and experimental validations. We use a continuum generalisation of known resistive-capacitive (RC) transmission line models to accurately predict voltage gradients on the surfaces of electrostatic transducers subject to rapidly varying voltages. We then present an experimental validation by measuring the spatial voltage distributions over carbon-based polymeric electrodes of dielectric elastomer (DE) transducers, and find a good agreement with our model predictions. We use our validated model to provide general estimates of the typical charging time and limit working frequency ranges of DE devices as a function of their dimensional scale and electrode sheet resistance. Our model provides useful indications for designing compliant electrodes in EAP transducers given target performance, or to understand the working limits of devices with given geometry and dielectric-electrode properties.

An airbrush 3D printer: Additive manufacturing of relaxor ferroelectric actuators

The additive manufacturing of electroactive polymer (EAP) devices poses significant challenges due to their distinct structure and dissimilar properties of their constituent materials. It requires deposition of multiple functional materials with different properties, achieving μm-scale resolution in layer thickness, and executing incremental deposition and curing steps while preserving the previously deposited functional material layers. This study introduces an airbrush 3D printer concept and employs it for fabricating EAP transducers. An airbrush 3D printer was constructed by adapting a standard extrusion printer platform and integrating it with a two fluid atomizer (i.e. an airbrush) as the deposition tool. A process was developed for printing of the bending P(VDF-TrFE-CTFE) actuators with carbon black electrodes, and actuators with a single and dual EAP layers were fabricated. The airbrush printer attained in-plane resolution of 0.5mm, thickness resolutions of 0.63 μm and allowed atomizing up to 7% P(VDF-TrFE-CTFE) solutions. The 18 mm × 4 mm EAP actuators achieved 340μm (440 Vpp) and 3.7 mm (400 Vpp, 104 Hz) tip deflections respectively in quasi-static and resonant operation. Airbrush printing therefore proved to be a robust method for printing precursor materials with a wide range of properties, and is anticipated to be a versatile approach for printing other passive and stimuli-responsive materials and devices.

Development of ionic liquid-based electroactive polymer composites using nanotechnology

Abstract This review is intended to provide an overview of the design and fabrication of ionic liquid-based ionic electroactive polymer (IL-iEAP) transducers for advanced applications in biological and electronic fields. The iEAP is a class of smart materials that can perform sensing or actuating functions by controlling the movement of cations and anions in the active layer. This type of material can deform under low voltage stimulation and generate electrical signals when undergoing mechanical deformation because of ion redistribution. Numerous research attention has been focused on studying the deformation mechanisms and the potential for actuation, sensing, and energy harvesting applications. Compared to the traditional water-based iEAP, the non-volatile IL-iEAP delivers a wider electrochemical window and a more stable actuation performance. In this paper, the classification of iEAP with different actuation mechanisms is first outlined, followed by introducing various preparation methods including nanotechnology for IL-iEAPs, and discussing the key factors governing their actuation performance. In addition, the advanced functions of IL-iEAP in actuating and sensing, especially self-sensing in bionics and electromechanical equipment applications, are reviewed. Finally, novel nanotechnologies used for fabricating IL-iEAPs and the prospects of their microelectromechanical system (MEMS) applications are discussed.

Modeling, fabrication, and characterization of motion platform actuated by carbon polymer soft actuator

Carbon polymer composites (CPC) are kind of soft actuators belonging to the category of ionic electroactive polymer transducers. In this work, we present design, modeling, fabrication, and characterization of a novel parallel manipulation system actuated by the CPC actuators. In this system, four actuators are operated in parallel to manipulate an end effector or a platform to generate motion along the different axis. The major advantage of the current system is that the platform and the actuators are fabricated as a single structure using the simple layer-by-layer spray-deposition method with selective masking. The proposed system is highly dexterous and is capable of generating three degrees of motions, namely, roll, pitch, and piston. The initial structural design and its deformation are optimized by modeling and simulating using finite element method and followed by fabrication and characterization to examine its workspace. The experimental results have demonstrated high levels of manipulability from the CPC actuators that are outstanding in the class of soft ionic actuators while keeping the fabrication method simple, scalable and cost-effective. The proposed configuration has potential application in micromanipulation systems that require large deformation in a confined space.

A multi-layered approach to product architecture modeling: Applied to technology prototypes

Companies that wish to include novel technology in the product portfolio may need to test and evaluate the technology with the use of prototypes to learn its benefits. Without clear knowledge of the benefits of the technology to the products in the portfolio, in the form of increased performance, added functions, or material savings, the prototype development can be hard to manage. In this article, two contributions are made. The first adds to the vocabulary of prototyping, defining technology prototype, a prototype used for testing a novel technology in the context of an existing product. The second is a tool to model and manage technology prototypes: the Technology Prototype Product Architecture Tool (TePPAT). The TePPAT is a product architecture tool with three main sections: Purpose, Concept, and Architecture. The TePPAT was tested in four industry cases, all part of a public–private partnership project to support the development of technology prototypes using electro-active polymer transducer technology. The findings showed that the TePPAT supported the development teams in the four cases. It is concluded that the TePPAT can support multidisciplinary development teams in modeling and managing technology prototypes and can be correlated with improvements in the team collaboration, communication, and development performance.

Design of an improved signal conditioning circuit for ionic polymer sensors based on the streaming potential hypothesis

Ionic polymer transducers also known as ionic polymer metal composites belong to the family of electroactive polymer transducers. Electroactive polymers are flexible and lightweight devices that operate as sensors and actuators without having any internally moving parts. The absence of moving parts offers a more efficient and cost-effective transducer with increased reliability. As actuators, ionic polymer transducers have the ability to generate bending strains on the order of 5% when +2 V potential is applied across their thickness. However, as sensors, the ionic polymer transducer has superior sensitivity as compared to other electroactive polymer materials. This is especially true when a charge or current amplifier is used as the signal conditioning circuit. These sensors operate in a wide spectrum and specifically at small strains. In this article, a new signal conditioning circuit is designed with superior sensing capabilities compared to the conventional circuit. In the new design, the ionic polymer transducer is biased with a small voltage on the order of 5 to 25 mV. Experimental results demonstrate a 27% enhancement in the current generated and the signal-to-noise ratio as compared to the conventional circuit. Furthermore, this circuit enables the use of ionic polymer transducer polymers with larger capacitance compared to the previous current sensing circuit. Earlier research demonstrates that the capacitance of an ionic polymer transducer is proportional to its actuation performance, and it is believed to affect the sensing performance. To increase the capacitance, the direct assembly process is used in the fabrication of ionic polymer transducer. Previously, using the conventional current amplifiers, it was impossible to use a direct assembly process–fabricated ionic polymer transducer with a large capacitance as a sensor, since it would saturate the operational amplifier circuit. In this study, three types of operational amplifier circuits are investigated, and their ability to bring the sensor to a short-circuit condition is measured. The signal-to-noise ratio of the operational amplifiers is measured and the OP177 has proved to be the best in both experiments.

A model of the electrodynamic field distribution for optimized electrode design for dielectric electroactive polymer transducers

Dielectric electroactive polymers belong to a new class of smart materials, whose functional principle is based on electrostatic forces. They can either be used as actuators to provide considerable stretch ratios or as generators to convert mechanical strain energy into electrical energy based on an electrostatic energy converter concept. Since the polymer material and also the covering compliant electrodes have non-ideal electrical properties, such as, respectively, finite resistivity and conductivity, design rules are usually required to optimize the devices. The electrode conductivity combined with the polymer resistivity causes a voltage drop along the electrode surface, resulting in a reduced actuation strain or energy conversion. To minimize its parasitic effects, the influence of this effect is studied, firstly, for the transient and steady state behavior and, secondly, in order to derive design rules for the optimal placement of electrode contacts.

ELECTROACTIVE POLYMER TRANSDUCERS BIASED FOR OPTIMAL OUTPUT

Electroactive polymer transducers are disclosed. They are biased in a manner that provides for increased force and/or stroke output, thereby offering improved work potential and power output capacity. The biasing may offer additional or alternate functional advantage in terms of matching transducer performance with a given application such as a normally-closed valve. The improved biasing (including increased output biasing) may utilize negative spring rate biasing and/or a combination of negative or zero-rate biasing with positive rate biasing to achieve the desired ends.

Compliant Electroactive Polymer Transducers for Sonic Applications

Described herein are compliant electroactive polymer transducers for use in acoustic applications. A compliant electroactive polymer transducer includes a compliant electroactive polymer at least two electrodes. For sound production, circuitry in electrical communication with the transducer electrodes is configured to apply a driving signal that causes the electroactive polymer to deflect in the acoustic range.

High-performance electroactive polymer transducers

Electroactive polymer constructions that convert electrical energy to mechanical energy and vice versa are disclosed. The subject transducers (actuators, generators, sensors or combinations thereof) share the requirement of a frame or fixture element used in preloading elastomeric film electrodes and dielectric polymer in a desired configuration. The structures are either integrally biased in a push-pull arrangement or preloaded/biased by another element.

Single-Walled Carbon Nanotubes — Ionic Polymer Electroactive Hybrid Transducers

Ionic electroactive polymers, sometimes referred to as artificial muscles, have the ability to generate large bending strain and moderate stress at low applied voltages. Typical types of ionic electroactive polymer transducers include ionic polymers, conducting polymers, and carbon nanotubes. Preliminary research combining multiple types of materials proved to enhance certain transduction properties. Bennett and Leo (Materials Research Society Symposium Proceedings, vol. 785, 2003b) showed that the speed of response, maximum strain, and quasi-static actuation are improved by adding a layer of conducting polymer on an ionic polymer transducer. In this work, a recently developed fabrication method called the direct assembly process (DAP) plating is used to build SWNT/RuO2 hybrid transducers. The DAP consists of mixing a conducting powder with an ionomer solution. This technique has demonstrated improved response time and strain output as compared to previous methods. Electrodes applied using this new technique of mixing RuO2 (surface area 45—65 m2/g) particles and NafionTMdispersion provided 5× the displacement and 10× the force compared to a transducer made with conventional methods. Furthermore, previous studies demonstrated that the response speed of the transducer is optimized by varying the composition of metal in the electrode (Akle, B.J., Bennett, M.D., Leo, D.J., Wiles, K.B. and McGrath, J.E. 2007. "Direct Assembly Process: A Novel Fabrication Technique for Large Strain Ionic Polymer Transducers,'' Journal of Mat. Sci., 42:7031—7041). For RuO2, the optimal loading was approximately 45vol%, while carbon nanotubes electrodes have an optimal performance at 30vol%. Due to low percolation threshold, carbon nanotubes actuators perform better at a lower loading compared to other conducting powders. The addition of single-walled carbon nanotubes (SWNT) to the electrode increases both the strain rate and the maximum strain of the hybrid actuator. The strain rate of the transducer increased proportional to the ratio of SWNT to RuO2 in the electrode. A maximum peak-to-peak strain of 10.6% (±2V) is attained in a 15vol% SWNT/30 vol% RuO2 hybrid transducer. The maximum strain rate of 2.7%/s is generated by a 20vol% SWNT/25 vol% RuO2 hybrid transducer.

Stretched rolled electroactive polymer transducers and method of producing same

A transducer is designed and fabricated using stretched rolled electroactive polymers. The invention includes the design, fabrication, and integration of a stretched rolled actuator system with corresponding sensing, control and power subsystems. The invention presented is based on the improved performance of electroactive polymer transducers that can be achieve by prestretching the polymeric material. In this invention, the preferred stretch is maintained in a rolled configuration by introducing structural elements to the transducer. The structural elements facilitate fabrication of the transducer as well as provide a compact and efficient means of maintaining stretch and the desired boundary conditions on the electroactive polymer during operation. These conditions together are used to improve and tailor the strain response of the transducer.

Variable stiffness electroactive polymer systems

The invention relates to systems that provide variable stiffness and/or variable damping using an electroactive polymer transducer. Systems described herein offer several techniques that provide variable and controlled stiffness and/or damping. A transducer may be implemented using open loop control, thereby providing simple systems that inactively deliver a desired stiffness and/or damping performance. Alternately, closed loop control techniques permit electroactive polymer transducer designs that actively adapt the stiffness and/or damping performance of a system. Further, transducers may be implemented in a device whose stiffness changes with deflection of the polymer.

MEMS Technologies for Ubiquitous Computing World: Silicon to Silicone: Stretching the Capabilities of Micromachines with Electroactive Polymers

Electroactive polymer transducers have many features that are desirable for MEMS devices. An especially attractive type of electroactive polymer is dielectric elastomer. Dielectric elastomers, transducers that couple the deformation of a rubbery polymer film to an applied electric field, show particular promise with features such as simple fabrication in a variety of size scales, high strain and energy density, high efficiency and fast speed of response, and inherent flexibility, environmental tolerance, and ruggedness. A variety of actuator configurations has been demonstrated at the small size scales needed for MEMS devices, including rolled “artificial muscle actuators, framed and bending beam actuators for efficient opto-mechanical switches, and diaphragm and thickness mode actuators for pumps and valves. The performance benefits of electroactive polymers can allow for new generations of devices in microrobotics, communications, and biotechnology. Several challenges remain for electroactive polymers, including microfabrication, integration with driving electronics, and operational lifetime.