Michael Wissler

Bio: Michael Wissler is an academic researcher from Swiss Federal Laboratories for Materials Science and Technology. The author has contributed to research in topics: Electroactive polymers & Actuator. The author has an hindex of 10, co-authored 12 publications receiving 1503 citations. Previous affiliations of Michael Wissler include École Polytechnique Fédérale de Lausanne.

Electromechanical coupling in dielectric elastomer actuators

Abstract: In this paper the electromechanical coupling in dielectric elastomer actuators is investigated. An equation proposed by Pelrine et al. [R.E. Pelrine, R.D. Kornbluh, J.P. Joseph, Electrostriction of polymer dielectrics with compliant electrodes as a means of actuation, Sens. Actuators A 64 (1998) 77–85] is commonly used for the calculation of the electrostatic forces in dielectric elastomer systems. This equation is analyzed here with (i) energy consideration and (ii) numerical calculations of charge and force distribution. A new physical interpretation of the electrostatic forces acting on the dielectric elastomer film is proposed, with contributions from in-plane and out-of-plane stresses. Representation of this force distribution using Pelrine's equation is valid for an incompressible material, such as the acrylic elastomer VHB 4910. Experiments are performed for the measurement of the dielectric constant ɛ r of the acrylic elastomer VHB 4910 for different film deformations. The values of ɛ r are shown to decrease with increasing pre-stretch ratio λ p , from 4.7 for the un-stretched film, down to 2.6 for equi-biaxial deformation with λ p = 5. This result is important in that it corrects the constant value of 4.7 largely applied in literature for pre-stretched dielectric elastomer actuator modeling. With the results of this work the predictive capabilities of a model describing the three-dimensional passive and active actuator behavior are remarkably improved.

Mechanical behavior of an acrylic elastomer used in dielectric elastomer actuators

Abstract: The paper reports on extensive experimental work for the characterization of a dielectric elastomer used as base material for electroactive polymer (EAP) actuators. The mechanical behavior of the acrylic elastomer VHB 4910 is characterized using large strain experiments (uniaxial and equibiaxial deformation) under force and displacement controlled loading conditions. Next to tensile and relaxation tests, experiments were conducted also using the so-called circular actuators. Over 40 actuators were produced (with different in-plane pre-strain levels) and activated with voltages between 2000 and 3500 V. The experimental data are useful for determining constitutive model parameters as well as for validating models and simulation procedures for electromechanical coupling in EAP actuators. A novel approach is proposed for finite element analysis of dielectric elastomer actuator, which has been used in the present work for the evaluation of the experimental observations from circular actuators. Material parameters of different visco-hyperelastic models have been determined from a subset of the experimental data and the predictive capabilities of the models evaluated through comparisons with the remaining data. The prediction of the circular actuator behavior was satisfactory so that the proposed models might be useful for actuator design and optimization purposes. Limitations of the proposed constitutive model formulation are presented.

Modeling and simulation of dielectric elastomer actuators

Abstract: Dielectric elastomers are used as base material for so-called electroactive polymer (EAP) actuators. A procedure and a specific constitutive model (for the acrylic elastomer VHB 4910) are presented in this work for finite element modeling and simulation of dielectric elastomer actuators of general shape and set-up. The Yeoh strain energy potential and the Prony series are used for describing the large strain time-dependent mechanical response of the dielectric elastomer. Material parameters were determined from uniaxial experiments (relaxation tests and tensile tests). Thereby the inverse problem was solved using iterative finite element calculations. A pre-strained circular actuator was built and activated with a predefined voltage. A three-dimensional finite element model of the circular actuator was created and the electromechanical activation process simulated. Simulation and actual measurements agree to a great extent, thus leading to a validation of both the constitutive model and the actuator simulation procedure proposed in this work.

Modeling of a pre-strained circular actuator made of dielectric elastomers

Abstract: Dielectric elastomers are used for the realization of actuators with large deformations and belong to the group of so-called electroactive polymers (EAP). Models are required for the design and optimization of EAP actuators. Thereby the constitutive behavior of the elastomer is of crucial importance and typically uniaxial experiments are performed in order to determine the mechanical properties of these materials. In this paper a pre-strained circular actuator made of a dielectric elastomer is investigated: constitutive models based on uniaxial data are verified by comparing calculation results with experimental observations. An analytical model is derived for the instantaneous response to an activation voltage in the pre-strained circular actuator and a finite element model is used to simulate the time-dependent behavior. Hyperelastic models are used and three strain energy formulations (Yeoh, Ogden and Mooney-Rivlin) are compared in their predictive capabilities. The results of the calculations with the three strain energy forms differ significantly, although all forms were successfully fitted to the same uniaxial data set. Predictions of the actuator behavior with the Yeoh form agree to a great extent with the measurements. The results of the present work show that the circular actuator set-up represents a valid model system for the characterization and optimization of the electromechanical behavior of dielectric elastomers.

A comparison between silicone and acrylic elastomers as dielectric materials in electroactive polymer actuators

Abstract: Soft elastomers, mostly silicones and acrylics, are interesting candidates as dielectric materials in electroactive polymer actuator technology. Generally, characteristics like large strain, high stress, high energy density, good efficiency and high response speed are required for actuator applications. However, some of these material properties may be contradictory. For this reason a comparison between Dow Corning silicone and 3M acrylic elastomers was made based on a set of six electromechanical tests for actuator applications. The silicone elastomer shows a fast electromechanical response (3 s) with good reproducibility and the dissipated work is negligible and not frequency dependent. It also shows a stable mechanical behaviour over a wide temperature range. In contrast, the acrylic elastomer shows a slow electromechanical response with poor reproducibility. The dissipated work of the acrylic elastomer is significant: a strong frequency and temperature dependency of the dissipated work is observed for this material. The Dow Corning silicone (DC 3481) is a better material for many applications, where activation strains of less than 10% are sufficient. However, in applications where higher strains are required, it might be obligatory to use acrylic elastomers, because only these have the potential for use with activation strains beyond 10%. The electrical activation of a circular specimen is most useful in order to evaluate a material as a dielectric in electroactive polymer actuators. Copyright © 2009 Society of Chemical Industry

Stretchable, Transparent, Ionic Conductors

Abstract: Existing stretchable, transparent conductors are mostly electronic conductors. They limit the performance of interconnects, sensors, and actuators as components of stretchable electronics and soft machines. We describe a class of devices enabled by ionic conductors that are highly stretchable, fully transparent to light of all colors, and capable of operation at frequencies beyond 10 kilohertz and voltages above 10 kilovolts. We demonstrate a transparent actuator that can generate large strains and a transparent loudspeaker that produces sound over the entire audible range. The electromechanical transduction is achieved without electrochemical reaction. The ionic conductors have higher resistivity than many electronic conductors; however, when large stretchability and high transmittance are required, the ionic conductors have lower sheet resistance than all existing electronic conductors.

Embedded 3D Printing of Strain Sensors within Highly Stretchable Elastomers

Abstract: A new method, embedded-3D printing (e-3DP), is reported for fabricating strain sensors within highly conformal and extensible elastomeric matrices. e-3DP allows soft sensors to be created in nearly arbitrary planar and 3D motifs in a highly programmable and seamless manner. Several embodiments are demonstrated and sensor performance is characterized.

Advances in dielectric elastomers for actuators and artificial muscles.

Abstract: A number of materials have been explored for their use as artificial muscles Among these, dielectric elastomers (DEs) appear to provide the best combination of properties for true muscle-like actuation DEs behave as compliant capacitors, expanding in area and shrinking in thickness when a voltage is applied Materials combining very high energy densities, strains, and efficiencies have been known for some time To date, however, the widespread adoption of DEs has been hindered by premature breakdown and the requirement for high voltages and bulky support frames Recent advances seem poised to remove these restrictions and allow for the production of highly reliable, high-performance transducers for artificial muscle applications

Soft Robotics: Review of Fluid‐Driven Intrinsically Soft Devices; Manufacturing, Sensing, Control, and Applications in Human‐Robot Interaction

Abstract: The emerging field of soft robotics makes use of many classes of materials including metals, low glass transition temperature (Tg) plastics, and high Tg elastomers. Dependent on the specific design, all of these materials may result in extrinsically soft robots. Organic elastomers, however, have elastic moduli ranging from tens of megapascals down to kilopascals; robots composed of such materials are intrinsically soft − they are always compliant independent of their shape. This class of soft machines has been used to reduce control complexity and manufacturing cost of robots, while enabling sophisticated and novel functionalities often in direct contact with humans. This review focuses on a particular type of intrinsically soft, elastomeric robot − those powered via fluidic pressurization.