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Vertechy R.,Sant'Anna School of Advanced Studies | Frisoli A.,Sant'Anna School of Advanced Studies | Bergamasco M.,Sant'Anna School of Advanced Studies | Carpi F.,Queen Mary, University of London | And 4 more authors.
Smart Materials and Structures | Year: 2012

Buckling dielectric elastomer actuators are a special type of electromechanical transducers that exploit electro-elastic instability phenomena to generate large out-of-plane axial-symmetric deformations of circular membranes made of non-conductive rubbery material. In this paper a simplified explicit analytical model and a general monolithic finite element model are described for the coupled electromechanical analysis and simulation of buckling dielectric elastomer membranes which undergo large electrically induced displacements. Experimental data are also reported which validate the developed models. © 2012 IOP Publishing Ltd.


Carpi F.,University of Pisa | Carpi F.,Technology and Life Institute | Kornbluh R.,SRI International | Sommer-Larsen P.,Technical University of Denmark | Alici G.,University of Wollongong
Bioinspiration and Biomimetics | Year: 2011

Electroactive polymer (EAP) actuators are electrically responsive materials that have several characteristics in common with natural muscles. Thus, they are being studied as 'artificial muscles' for a variety of biomimetic motion applications. EAP materials are commonly classified into two major families: ionic EAPs, activated by an electrically induced transport of ions and/or solvent, and electronic EAPs, activated by electrostatic forces. Although several EAP materials and their properties have been known for many decades, they have found very limited applications. Such a trend has changed recently as a result of an effective synergy of at least three main factors: key scientific breakthroughs being achieved in some of the existing EAP technologies; unprecedented electromechanical properties being discovered in materials previously developed for different purposes; and higher concentration of efforts for industrial exploitation. As an outcome, after several years of basic research, today the EAP field is just starting to undergo transition from academia into commercialization, with significant investments from large companies. This paper presents a brief overview on the full range of EAP actuator types and the most significant areas of interest for applications. It is hoped that this overview can instruct the reader on how EAPs can enable bioinspired motion systems. © 2011 IOP Publishing Ltd.


Galantini F.,University of Pisa | Gallone G.,University of Pisa | Gallone G.,Technology and Life Institute | Carpi F.,Technology and Life Institute | And 3 more authors.
Proceedings - International Symposium on Electrets | Year: 2011

The results reported show that electret elastomers may represent a new promising way for obtaining dielectric elastomers with improved dielectric constant to be used as actuators. To this purpose two main issues have to be faced: first a way to keep charges over time (see TABLE II); second, a study on how the pore dimension/dispersion influences the dielectric and electromechanical response. © 2011 IEEE.


Carpi F.,University of Pisa | Carpi F.,Technology and Life Institute | Frediani G.,University of Pisa | Turco S.,University of Pisa | And 2 more authors.
Advanced Functional Materials | Year: 2011

Optical lenses with tunable focus are needed in several fields of application, suchas consumer electronics, medical diagnostics and optical communications. To address this need, lenses made of smart materials able to respond to mechanical, magnetic, optical, thermal, chemical, electrical or electrochemical stimuli are intensively studied. Here, we report on an electrically tunable lens made of dielectric elastomers, an emerging class of "artificial muscle" materials for actuation. The optical device is inspired by the architecture of the crystalline lens and ciliary muscle of the human eye. It consists of a fluid-filled elastomeric lens integrated with an annular elastomeric actuator working asanartificial muscle. Upon electrical activation, the artificial muscle deforms the lens, so that a relative variation of focal length comparable to that of the human lens is demonstrated. The device combined optical performance with compact size, low weight, fast andsilent operation, shock tolerance, no overheating, low power consumption, and possibilityof implementation with inexpensive off-the-shelf elastomers. Results show that combing bioinspired design with the unique properties of dielectric elastomers as artificial muscle transducers has the potential to open new perspectives on tunable optics. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Carpi F.,University of Pisa | Carpi F.,Technology and Life Institute | Frediani G.,University of Pisa | De Rossi D.,University of Pisa | De Rossi D.,Technology and Life Institute
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2012

Electrical control of optical focalisation is important in several fields, such as consumer electronics, medical diagnostics and optical communications. As an alternative to complex, bulky and expensive current solutions based on shifting constant-focus lenses, here we report on an electrically tunable lens made of dielectric elastomers as 'artificial muscle' materials. The device is inspired to the architecture of the crystalline lens and ciliary muscle of the human eye. A fluid-filled elastomeric lens is integrated with an annular elastomeric actuator that works as an artificial muscle. Electrical activation of the artificial muscle deforms the lens, with a relative variation of focal length comparable to that of the human lens. Optical performance is achieved with compact size, low weight, fast and silent operation, shock tolerance, no overheating, low power consumption, and inexpensive off-the-shelf materials. Results show that combing bio-inspired design with dielectric elastomer artificial muscles can open new perspectives on tunable optics. © 2012 Springer-Verlag.


Galantini F.,University of Pisa | Gallone G.,University of Pisa | Carpi F.,University of Pisa | Carpi F.,Technology and Life Institute
IEEE Transactions on Dielectrics and Electrical Insulation | Year: 2012

The main problem of dielectric elastomer (DE) actuators is today represented by the high driving electric fields (orders of 10-100 V/m) necessary for their activation. Although several attempts have been made in order to increase strains by enhancing the dielectric constant (ε') of such matrices and keeping low elastic moduli (Y) to control the ε/Y ratio, currently several challenges have still to be faced. In this work, a new approach is presented to enhance the electrical properties of DE elastomers. Soft elastomeric polyurethane (PU) matrices with foam structure were electrically modified via Corona process. Such matrices showed electret-like properties, possibly due to the presence of macro-dipoles established both at the matrix/pore surfaces and inside the bulk. Morphological (SEM, Bet), dielectric and dynamic-mechanical (DMA) analyses were performed in order to characterize the material. Results showed that Corona charging may represent a new promising route to obtain dielectric elastomers with improved dielectric properties, although ways to promote charge trapping and retention are still do be found. © 1994-2012 IEEE.


Carpi F.,University of Pisa | Carpi F.,Technology and Life Institute | Frediani G.,University of Pisa | De Rossi D.,University of Pisa | De Rossi D.,Technology and Life Institute
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2011

As a means to improve versatility and safety of dielectric elastomer actuators (DEAs) for several fields of application, so-called 'hydrostatically coupled' DEAs (HC-DEAs) have recently been described. HC-DEAs are based on an incompressible fluid that mechanically couples a DE-based active part to a passive part interfaced to the load, so as to enable hydrostatic transmission. This paper presents ongoing developments of HC-DEAs and potential applications in the field of haptics. Three specific examples are considered. The first deals with a wearable tactile display used to provide users with tactile feedback during electronic navigation in virtual environments. The display consists of HC-DEAs arranged in contact with finger tips. As a second example, an up-scaled prototype version of an 8-dots refreshable cell for dynamic Braille displays is shown. Each Braille dot consists of a miniature HC-DEA, with a diameter lower than 2 mm. The third example refers to a device for finger rehabilitation, conceived to work as a sort of active version of a rehabilitation squeezing ball. The device is designed to dynamically change its compliance according to an electric control. The three examples of applications intend to show the potential of the new technology and the prospective opportunities for haptic interfaces. © 2011 SPIE.


Carpi F.,University of Pisa | Carpi F.,Technology and Life Institute | Frediani G.,University of Pisa | Nanni M.,University of Pisa | And 2 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2011

So-called 'hydrostatically coupled' dielectric elastomer actuators (HC-DEAs) have recently been shown to offer new opportunities for actuation devices made of electrically responsive elastomeric insulators. HC-DEAs include an incompressible fluid that mechanically couples a dielectric elastomer based active part to a passive part interfaced to the load, so as to enable hydrostatic transmission. Drawing inspiration from that concept, this paper presents a new kind of actuators, analogous to HC-DEAs, except for the fact that the fluid is replaced by fine powder. The related technology, here referred to as 'granularly coupled' DEAs (GC-DEAs), relies entirely on solid-state materials. This permits to avoid drawbacks (such as handling and leakage) inherent to usage of fluids, especially those in liquid phase. The paper presents functionality and actuation performance of bubble-like GC-DEAs, in direct comparison with HC-DEAs. For this purpose, prototype actuators made of two pre-stretched membranes of acrylic elastomer, coupled via talcum powder (for GC-DEA) or silicone grease (for HC-DEA), were manufactured and comparatively tested. As compared to HC-DEAs, GC-DEAs showed a higher maximum stress, the same maximum relative displacement, and nearly the same bandwidth. The paper presents characterization results and discusses advantages and drawbacks of GC-DEAs, in comparison with HC-DEAs. © 2011 SPIE.


Carpi F.,University of Pisa | Carpi F.,Technology and Life Institute | Frediani G.,University of Pisa | Frediani G.,Technology and Life Institute | And 2 more authors.
IEEE/ASME Transactions on Mechatronics | Year: 2012

The so-called hydrostatically coupled dielectric elastomer actuators (HC-DEAs) have recently been described as a means to improve versatility and safety of electroactive polymer actuators made of DEs. HC-DEAs use an incompressible fluid that mechanically couples a DE-based active part to a passive part interfaced to the load. In this paper, we present the ongoing development of linear contractile HC-DEAs. The actuator is made of two rigid disks (circular frames) that support an active membrane, consisting of a DE film coated with compliant electrodes. The frames and the membrane delimit a closed chamber, filled with the fluid. The pressure of the fluid is used to provide the actuator with a barrel-like shape, while keeping the length of the structure limited by a counteracting element (such as an internal spring or the external load itself); combining this element with the internal pressure allows the structure to be axially precompressed. As a result of an electrical activation of the membrane, outward radial buckling and related axial contraction of the device are achieved. This paper presents preliminary assessment of static electromechanical performance of prototypes made of silicone and water, studying combined effects of precompression, voltage, and stress relaxation. © 2012 IEEE.


Wang H.,Zhejiang University | Wang H.,Harvard University | Cai S.,Zhejiang University | Carpi F.,University of Pisa | And 2 more authors.
Journal of Applied Mechanics, Transactions ASME | Year: 2012

A hydrostatically coupled dielectric elastomer (HCDE) actuator consists of two membranes of a dielectric elastomer, clamped with rigid circular rings. Confined between the membranes is a fixed volume of a fluid, which couples the movements of the two membranes when a voltage or a force is applied. This paper presents a computational model of the actuator, assuming that the membranes are neo-Hookean, capable of large and axisymmetric deformation. The voltage-induced deformation is described by the model of ideal dielectric elastomer. The force is applied by pressing a rigid flat punch onto one of the membranes over an area of contact. The computational predictions agree well with experimental data. The model can be used to explore nonlinear behavior of the HCDE actuators. © 2012 American Society of Mechanical Engineers.

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