1,721,310 research outputs found
ll diritto processuale civile e la Scuola bolognese
No full textIl contributo analizza la storia della scuola bolognese di diritto processuale civile
Dielectric elastomer cylindrical actuators: electromechanical modelling and experimental evaluation
No full textThis paper presents an experimentally validated electromechanical model of cylindrical actuators made of dielectric elastomers with compliant electrodes. Modelling was based on independent electrical and mechanical analyses of the specific configuration of the device. The expressions of the electrostatic pressures exerted by the electrodes in response to an applied voltage were formulated and inserted into the expressions of the actuator mechanical deformations, obtained by assuming linearly elastic stress–strain constitutive equations of the material for small strains. Values of axial strains expected from the model well fit those recorded from a realised actuator, electrically stimulated by step-wise high voltages. This actuator has carbon grease electrodes smeared on a cylinder-shaped silicone elastomer, showing a room-temperature-relative dielectric constant of 3 within a wide frequency range (10–109 Hz). An axial strain of 4.5% due to a voltage per unit wall thickness of 100 V/μm was measured at a 5% axial prestrain, around which the material held a Young's modulus of 5 MPa
Perspectives for new dielectric elastomers with improved electromechanical actuation performance: composites versus blends
No full textThis work presents a comparison between composites and blends as two alternative approaches for the development of new dielectric elastomers offering superior electromechanical properties at lower driving electric fields. Silicone- and polyurethane- based dielectric elastomers were modified by either making particulate composites with high-permittivity ceramic fillers or by blending with different polymeric phases. Both previous and new data are considered. Experimental observations are compared and discussed to assess which one of the aforementioned approaches might be more generally preferable. Due to a consequent worsening of the mechanical properties, pure composite architectures yielded only limited results. While with the blend approach both an increase of the dielectric permittivity and an unexpected reduction of the tensile elastic modulus were observed, leading to an overall increase of the electromechanical response. The blending approach permits one to obtain a new dielectric elastomer with improved electromechanical properties by simply combining two low-dielectric-constant polymers. This is the first time such a type of result has been reported. This study indicates that formulating all-polymeric compounds may represent a very promising route for obtaining new dielectric elastomers with improved actuation performance
ELECTROACTIVE POLYMER BASED DEVICES FOR E-TEXTILES IN BIOMEDICINE
No full textThis paper describes the early conception and latest developments of electroactive polymer (EAP)-based sensors, actuators, electronic components, and power sources, implemented as wearable devices for smart electronic textiles (e-textiles). Such textiles, functioning as multifunctional wearable human interfaces, are today considered relevant promoters of progress and useful tools in several biomedical fields, such as biomonitoring, rehabilitation, and telemedicine. After a brief outline on ongoing research and the first products on e-textiles under commercial development, this paper presents the most highly performing EAP-based devices developed by our lab and other research groups for sensing, actuation, electronics, and energy generation/storage, with reference to their already demonstrated or potential applicability to electronic textiles
Elastomeric contractile actuators for hand rehabilitation splints
No full textThe significant electromechanical performances typically shown by dielectric elastomer actuators make this polymer technology particularly attractive for possible active orthoses for rehabilitation. Folded contractile actuators made of dielectric elastomers were recently described as a simple configuration, suitable to easily implement linear contractile devices. This paper describes an application of folded actuators for so-called hand splints: they consist of orthotic systems for hand rehabilitation. The dynamic versions of the state-of-the-art splints typically include elastic bands, which exert a passive elastic resistance to voluntary elongations of one or more fingers. In order to provide such splints with the possibility of electrically modulating the compliance of the resistive elements, the substitution of the passive elastic bands with the contractile actuators is here described. The electrical activation of the actuators is used to vary the compliance of the system; this enables modulations of the force that acts as an antagonist to voluntary finger movements, according to programmable rehabilitation exercises. The paper reports results obtained from the first prototype implementations of such a type of system
Effects of Corona Treatment on Electrical and Mechanical Properties of a Porous Dielectric Elastomer
No full textThe main problem of dielectric elastomer (DE) actuators is today represented by the high driving electric fields (orders of 10-100 V/μm) 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
Bioinspired actuation of the eyeballs of an android robotic face: concept and preliminary investigations
No full textThis paper describes the concept and preliminary investigations related to the development of simple bioinspired actuation mechanisms for the eyeballs of an android robotic face. Two design solutions for a one-degree-of-freedom mechanism are proposed and analytically studied according to linear models. Both of them are based on new contractile actuators made of electroactive polymers, employed as pseudomuscular devices. The actuators consist of dielectric elastomers and are capable of electrically driven linear contractions. The arrangement and the functionality of the actuators were conceived to mimic those of rectus-type human ocular muscles. Both the presented solutions rely on a couple of agonist-antagonist actuators, in order to enable bidirectional rotations of the eyeball around an axis. The two configurations basically differ in the presence/absence of pulleys, guiding tendon-like wires which connect the actuators to the eyeball. The influence on the system performances of both rest length and elastic modulus of the actuators was studied for both configurations. Geometrical constraints allow the configuration with pulleys to perform more than the other, despite a potential intrinsic superior efficacy of the latter. The paper describes also the assembly of a simple prototype version of the system and presents the results of preliminary tests. These permitted us to assess the feasibility of the proposed concept and suggested possible improvements
Improvement of electromechanical actuating performances of a silicone dielectric elastomer by dispersion of titanium dioxide powder
No full textThis paper presents the first reported data on the embedding of highly dielectric ceramic inclusions in a rubbery host medium as a means to increase the electromechanical material response for dielectric elastomer actuation. The studied polymer/ceramic composite, consisting of a silicone matrix in which titanium dioxide powder was dispersed, exhibited, in comparison with pure silicone, a decreased elastic modulus, as well as an increased dielectric constant. The measured low frequency permittivity resulted in accordance with several classical dielectric mixing rules. The use of this material as elastomeric dielectric for planar actuators enabled a reduction of the driving electric fields, so that a transverse strain of 11% at 10 V/μm and a transverse stress of 16.5 kPa at 9 V/μm were obtained. These levels of strain and stress were respectively more than eight and four times higher than the corresponding values generated with the pure polymer matrix for analogous electrical stimuli
COLOURS FROM ELECTROACTIVE POLYMERS: ELECTROCHROMIC, ELECTROLUMINESCENT AND LASER DEVICES BASED ON ORGANIC MATERIALS
No full textThis paper focuses on the most relevant devices currently used in order to achieve electrically stimulated generations of colours from electroactive polymers, either as coloured light emissions from the material or as modifications of its intrinsic colour properties. For this purpose, most relevant materials, fundamental principles of operations, latest developments and current applications of organic-based electrochromic, electroluminescent and lasing devices are reviewed here. The very promising performances resulting from the analysis of state-of-the-art products, and in particular of those which are currently approaching commercial applications, suggest likely roles played by such devices for niche applications in the very near future
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