Elastomeric actuator devices for magnetic resonance imaging

The present invention is directed to devices and systems used in magnetic imaging environments that include an actuator device having an elastomeric dielectric film with at least two electrodes, and a frame attached to the actuator device. The frame can have a plurality of configurations including, such as, for example, at least two members that can be, but not limited to, curved beams, rods, plates, or parallel beams. These rigid members can be coupled to flexible members such as, for example, links wherein the frame provides an elastic restoring force. The frame preferably provides a linear actuation force characteristic over a displacement range. The linear actuation force characteristic is defined as .+-.20% and preferably 10% over a displacement range. The actuator further includes a passive element disposed between the flexible members to tune a stiffness characteristic of the actuator. The passive element can be a bi-stable element. The preferred embodiment actuator includes one or more layers of the elastomeric film integrated into the frame. The elastomeric film can be made of many elastomeric materials such as, for example, but not limited to, acrylic, silicone and latex

Artificial Muscles

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Dielectric Elastomer Actuated Systems and Methods

The system of the present invention includes an actuator having at least two electrodes, an elastomeric dielectric film disposed between the two electrodes, and a frame attached to the elastomeric dielectric film. The frame provides a linear actuation force characteristic over a displacement range. The displacement range is preferably the stroke of the actuator. The displacement range can be about 5 mm and greater. Further, the frame can include a plurality of configurations, for example, at least a rigid members coupled to a flexible member wherein the frame provides an elastic restoring force. In preferred embodiments, the rigid member can be, but is not limited to, curved beams, parallel beams, rods and plates. In a preferred embodiment the actuator can further include a passive element disposed between two flexible members such as, for example, links to tune a stiffness characteristic of the actuator. The passive element can be a bi-stable element. Further, the actuator can include a plurality of layers of the elastomeric dielectric film integrated into the frame. The elastomeric film can be made of different materials such as, for example, acrylic, silicone and latex

The effect of morphology on poly(vinylidene fluoride-trifluoroethylene- chlorotrifluoroethylene)-based soft actuators: Films and electrospun aligned nanofiber mats

This paper analyzes soft actuators realized as unimorph cantilever beams, in which the active layer can have two different morphologies, i.e., either an extruded film or an aligned electrospun nanofiber mat of the poly (vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene). Six different soft actuators are fabricated, with active layers of varying thicknesses and morphologies, to study the electrostrictive effect of the polymer and to evaluate the stiffening properties, the mechanical work, and the blocking forces of the actuators when stimulated by different direct current electric fields. The comparison between the different actuators is performed by introducing weight specific properties, i.e., specific stiffness and specific work, showing improved specific properties for the nanofibers-based actuators. Moreover, the blocking forces, the tip deflections, and the leakage currents of the actuators are evaluated when stimulated by alternating current electric fields. The experiments show faster viscoelastic relaxation and lower electrical power consumption for the nanofibers-based actuators. This study concludes that, thank to its electro-mechanical properties, the poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) in the form of aligned electrospun nanofiber mat has high potential to be used as the active layer of electrostrictive unimorph beam soft actuators

Finite element modeling of dielectric elastomer actuators for space applications

A special actuator device with passive sensing capability based on dielectric elastomer was studied and specialized to be used in space applications. The work illustrates the research project modeling procedure adopted to simulate the mechanical behavior of this material based on a finite element theory approach. The Mooney-Rivlin’s hyperelastic and Maxwell’s electrostatic models provide the theoretical basis to describe its electro-mechanic behavior. The validation of the procedure is performed through a numerical-experimental correlation between the response of a prototype of actuator developed by the Risø Danish research center and the 3D finite element model simulations. An investigation concerning a possible application in the space environment of dielectric elastomer actuators (DEA) is also presented

Micromechanics of smart electrostrictive materials

Two micromechanics models have been developed to estimate the local fields, the effective properties, and the electro-mechanical coupling in smart electrostrictive materials. The first model is based on the laminated plate theory. The nonlinear relations between the polarization and the electric field are considered in the model and an iterative formulation has been developed. Closed-form solutions are also obtained by ignoring the nonlinear terms in the constitutive relations between the polarization and the electric field. The effects of material properties, and the thickness and the number of plies on the mechanical and electrical response of the electrostrictive composite are studied. The model focuses on laminated composites and considers not only applied mechanical loads but also prescribed electric fields. However, it is not able to predict the deformation in the thickness direction of the composites. The second model considers electrostrictive materials containing periodically distributed inhomogeneities. The local fields and the effective properties of three dimensional electrostrictive composites are predicted using the equivalent inclusion method (Esheby, 1957) and the Fourier series (Nemat-Nasser et al, 1993). Linear constitutive relations between the polarization and the electric field are employed in the model, which involves very few assumptions and can be applied to a broad class of electrostrictive composites. Furthermore, the effective properties of electrostrictive materials containing periodically distributed, aligned two dimensional (2-D) line cracks are studied. A 2-D line crack can be considered as a limiting case of a flat elliptical cylindrical void with its thickness approaching zero. Thus, a limiting process is employed to estimate the effective properties of an electrostrictive solid with periodically distributed, aligned 2-D line cracks

Construction Techniques and Statistical Analysis of Dielectric Elastomer Actuators

In this study, a series of experiments were conducted to investigate and improve upon existing construction methods of dielectric elastomer actuators (DEAs). First, a proof of concept was built, which utilized a DEA as an active diaphragm to reproduce sound. Next, two electrode sizes and construction methods were compared via statistical analysis of electrode strain. In an attempt to develop an easier and more efficacious electrode construction method, the substance used for electrodes was then dissolved in six solvents. A commercially available graphite spray was compared against the solutions and determined to be the most promising on the basis of measured surface conductivity and observed particle dispersion. Finally, an actuator was tested with graphite spray electrodes; it was discovered that the spray hardens when dried and was thus not able to produce in-plane deformation