Zhongyang Cheng Auburn University
Vivek Bharti 3M Company
Zhuo Xu Xi’an Jiaotong University
Debra A. Wrobleski Los Alamos National Laboratory
HH1: Dielectric Elastomers
Monday AM, November 29, 2010
Back Bay B (Sheraton)
9:30 AM - **HH1.1
Hydrostatically Coupled Dielectric Elastomer Actuators: New Opportunities for Haptics.
Federico Carpi 1 , Gabriele Frediani 1 , Danilo De Rossi 1 Show Abstract
1 Interdpt. Res. Centre 'E. Piaggio', University of Pisa, Pisa Italy
Dielectric elastomer actuators (DEAs) have been demonstrated to represent today a high-performance technology for electromechanical transducers based on electroactive polymers. As a means to improve versatility and safety of 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 their promising potential application in the field of haptics. In particular, the first part of the paper describes a static and dynamic characterization of a prototype actuator made of two pre-stretched membranes (20 mm wide, 1.8 mm high, and 61 µm thick) of 3M VHB acrylic elastomer, coupled via silicone grease. The actuator exhibited a maximum stress of 1.3 kPa at 4.4 kV, a relative displacement of -80% at 4.4 kV, a -3dB bandwidth of 3 Hz, and a resonance frequency of 160 Hz. The second part of the paper presents possible applications of the tested actuator configuration for haptic interfaces. Two 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 of usage, an up-scaled prototype version of an 8-dots refreshable cell for dynamic Braille displays is shown. Each Braille pin consists of a miniature HC-DEA, with a diameter lower than 2 mm. Both types of application clearly show the potential of the new technology and the prospective opportunities for haptics.
10:00 AM - HH1.2
Highly Compliant Pressure Sensor Using Conductive Fluid in an Elastomeric Sheet.
Rebecca Kramer 1 , Yong-Lae Park 1 , Carmel Majidi 1 , Phil Berard 1 , Robert Wood 1 Show Abstract
1 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
Emerging technologies such as wearable computing and stretchable electronics require the development of highly compliant and stretchable sensors that register the location and intensity of pressure or strain over a large area. We present a rapid monolithic fabrication technique for the development of an elastomeric sheet embedded with a network of conductive micro-channels that senses the location and intensity of localized pressure. The micro-channels achieve conductivity through the implantation and encapsulation of a conductive liquid, such as non-toxic eutectic gallium indium (eGaIn, BASF). Pressing or straining the surface of the elastomeric sheet at any point deforms the cross-section of nearby channels and changes their electrical resistance. The relative change in the electrical resistance of all of the channels within the network yields the location and intensity of applied pressure or strain. Sensitivity and resolution of the elastomeric pressure sensor is controlled by the geometry and spacing of the conductive micro-channels as well as the thickness and elasticity of the elastomer matrix. Pressure sensors with channel dimensions ranging from 25 μm to 1000 μm have been fabricated by casting polydimethylsiloxane (PDMS; Sylgard 184, Dow Corning; 10:1 mass ratio of elastomer base to curing agent) in a photoresist (SU-8 2010) mold that is patterned by means of a laser-based direct-write photolithography technique. Micro-channels of the desired dimensions are introduced into silicon wafers via direct-write laser exposure using a diode-pumped solid-state (DPSS) 355nm laser micromachining system. The system was previously calibrated to provide good exposure for SU-8 spin-coated to 40 μm in thickness. Elastomer micro-channels have been demonstrated with dimensions as small as 25 μm by 40 μm. Micro-channels of this size, and of other various dimensions, have been filled with conductive eGaIn and shown to maintain sensing functionality. Enhanced sensitivity of the elastomeric pressure sensor can be achieved through continued reduction of the micro-channel dimensions and increased density of the channel network. Multi-layered elastomeric channel networks may provide greater sensing capabilities due to perpendicular but non-intersecting channel designs. Moreover, the elastomeric sheet may be easily integrated with wearable electronics or robotic systems for combined on-board circuitry and sensing functionality.
10:15 AM - HH1.3
Controlled Improvement of Nanocomposite Properties for Dielectric Elastomer Actuators.
Denis McCarthy 1 , Hristiyan Stoyanov 1 , Dmitry Rychkov 1 , Huelya Ragusch 1 , Sebastian Risse 1 , Guggi Kofod 1 Show Abstract
1 Institute of Physics & Astronomy, University of Potsdam, Potsdam, Brandenburg, Germany
High permittivity nanocomposites are being studied for use in a variety of fields. Classical theories, such as Bruggeman and Lichteneker, predict small permittivity increases at low amounts of high permittivity filler where the processing and mechanical properties of the composites are practical. Much higher permittivity increases than these predictions have been observed with nanocomposites suggesting large improvements are possible. The large increases observed in nanocomposites are normally accompanied by increased A.C. conductivity and different mechanisms have been suggested to explain these increases. Although none of these have been conclusive, it is clear the interface between the fillers and the host matrix is the source and control of the interaction between the fillers and matrix is key to achieving new, high performance nanocomposites in all fields. Increased conductivity of the interface layers in nanocomposites contributes strongly to the increased permittivity of composites, but it also influences the electrical breakdown and mechanical properties. It has been shown that increases in permittivity can be achieved without compromising the desired polymer properties.Dielectric elastomer actuators (DEA) are simple electrostatic actuators similar in design to a soft capacitor. Due to their low cost, simple production and impressive performance - stresses up to 7 MPa and strains of over 200%, DEA allow the design of new devices, and can replace other actuators in current devices. These devices also require new high permittivity materials, while maintaining high electrical breakdown, low losses and elastomeric mechanical properties in order to reduce operating voltages and increase actuation performance.We report the results of an investigation into TiO2-elastomer composites for DEA. We show that modifying the TiO2 particle surface changes the interaction between the polymer and filler and this can be used to achieve high permittivity composites with low loss, low mechanical reinforcement and improved actuation. By studying a range of TiO2 particles with different surface functionalisation the effects of the different filler particles, their surfaces can be identified and the requirements for improved composites identified. As predicted by the classical theories, increased filler content leads to increased permittivity, but the greater effect is the increased interface. Unlike the predictions of these theories, even at low filler content the permittivity of the filler has a significant effect on the composite permittivity. By controlling the interface we can increase the permittivity without degrading the other material properties, thus improving the actuation performance. Percolation of the interface layers and the particles is observed and this leads to detrimental effects on the electrical and mechanical properties. A targeted method to achieve improved composites will be suggested from these results.
10:30 AM - HH1.4
Dielectric Elastomer Generators: How Much Energy Can be Converted?
Soo Jin Adrian Koh 1 2 , Christoph Keplinger 3 2 , Tiefeng Li 4 2 , Siegfried Bauer 3 , Zhigang Suo 2 Show Abstract
1 Large-Scale Complex Systems, Institute of High Performance Computing, Singapore Singapore, 2 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States, 3 Soft-Matter Physics, Johannes Kepler University, Linz Austria, 4 Institute of Applied Mechanics, Zhejiang University, Hangzhou, Zhejiang, China
Dielectric elastomers are being developed as generators to harvest energy from renewable sources, such as human movements and ocean waves. We model a dielectric elastomer generator as a system of two degrees of freedom, represented either on the stress-stretch plane, or the voltage-charge plane. A point on such a plane represents a state of the generator, a curve represents a path of operation, a contour represents a cycle of operation, and the area enclosed by the contour represents the energy of conversion per cycle. Each mechanism of failure is represented by a curve in the plane. The curves of all the known mechanisms of failure enclose a region of allowable states. The area enclosed by these curves gives the theoretical maximum amount of energy that can be converted. Using realistic material models, it is found that natural rubber outperforms VHB elastomer as a generator at operating strains of less than 15%. Furthermore, by varying key material parameters like the small-strain shear stiffness, dielectric strength or dielectric constant, energy of conversion of 1.0 J/g is possible. The method presented in this study could aid in the selection and evaluation of elastomer materials as generators.
11:15 AM - **HH1.5
Environmental Power From Dielectric Elastomers.
Iain Anderson 1 2 , Thomas McKay 1 , Benjamin O'Brien 1 Show Abstract
1 Biomimetics Laboratory, Auckland Bioengineering Institute, Auckland, Auckland, New Zealand, 2 Engineering Science, University of Auckland, Auckland New Zealand