iMechanica - dielectric elastomer membrane
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enJournal Club Theme of August 2011: Energy Harvesting Using Soft Materials
https://imechanica.org/node/10723
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/171">materials modeling</a></div><div class="field-item odd"><a href="/taxonomy/term/257">MEMS</a></div><div class="field-item even"><a href="/taxonomy/term/590">energy research</a></div><div class="field-item odd"><a href="/taxonomy/term/1425">Ocean Energy</a></div><div class="field-item even"><a href="/taxonomy/term/2877">dielectric elastomer membrane</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>
Energy harvesting is the process of converting energy that will otherwise be dissipated into the ambient environment, into useful energy to do work. I shall focus this discussion on motion-based energy harvesting. Motion-based energy harvesting is the process of converting dissipated mechanical energy into electrical energy. Sources of mechanical energy include the ocean waves, wind, human motion, vehicular traffic, and vibrations in buildings and bridges. This source of energy is ubiquitous and pervasive, and yet, it is one of the least developed energy harvesting technology.
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Traditional methods of motion-based energy harvesting adopt piezoelectric, electrostatic MEMS and electromagnetic (EM) generators as the media of conversion. These techniques are incapable of packing a huge amount of mechanical energy as they are either too stiff (piezos), or too compliant (electrostatic MEMS and EM generators). This results in poor yield-to-size energy conversion ratio. Typical piezoelectric systems are able to produce a yield in the region of uJ (micro-joules), with an energy conversion efficiency of less than 10%. EM generators are able to produce energy at a much larger scale, but it requires an enormous system to do so. Typical yield of EM generators is in the region of mJ/g of the system, with a conversion efficiency of about 20%.
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I shall focus on a technology using dielectric elastomers as energy harvesters. This technology was proposed by Pelrine et. al., in 2001. Dielectric elastomers are thin membrane of polymers sandwiched between compliant electrodes. When subject to a voltage through the thickness of the membrane, the elastomer thins down and expands in area. It works as an actuator. On the other hand, when a pre-stretched and pre-charged elastomer is mechanically relaxed in the open-circuit condition, voltage across the electrodes may be boosted. It works as a generator. In Pelrine’s work (2001), they used a thin membrane of polyacrylate, very-high-bond (VHB) adhesive tape (manufactured by 3M), and sandwiched the membrane between compliant electrodes made from carbon grease. They managed to produce a voltage boost of five times the input voltage, and computed a potential energy conversion capacity of 400 mJ/g.
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Inspired by their work, me and my coworkers at Harvard and Johannes-Kepler University in Linz, Austria, performed theoretical calculations to estimate the maximum amount of energy that may be converted using a dielectric elastomer generator (DEG). We assume that a DEG will cease to produce useful energy if one or more of the following occurs: Rupture, electrical breakdown, electromechanical instability and loss of tension. Using equilibrium thermodynamics, we estimated that VHB has the potential to produce 1.7 J/g of energy, and that natural rubber produces a comparable amount at 1.3 J/g. We expect the actual yield of VHB to be very poor due to the large mechanical and electrical dissipation in that material. On the other hand, natural rubber looks to be a promising material due to its low dissipation, and high resistance to electrical breakdown. We further proposed that the energy of conversion scales linearly with the dielectric constant, and to the square of the dielectric strength. Our analysis shows that a material with a dielectric constant of 6.0, and dielectric strength of 100 MV/m, is capable of converting 1.0 J/g of energy when cycled at 100% strain. This amount of energy conversion, if realized, will be orders of magnitude higher than current technologies.
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There is much work left to be done in this field. The mechanisms of dissipation in dielectric elastomers are not well-understood. This hampers the evaluation, design and optimization of energy harvesting systems using DEGs. Furthermore, experiments conducted on dielectric elastomer as generators are limited to only VHB and silicone elastomers. There is a wealth of materials out there waiting to be discovered. Finally, the durability of elastomer materials may be a crucial factor in determining if this technology takes off or not. Fracture and fatigue of elastomers must be better understood.
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References<br />
Pelrine et. al., Proc. SPIE <strong>4329</strong>, pp. 148–156, 2001.<br />
S. J. A. Koh, X. Zhao & Z. Suo, Appl. Phys. Lett. <strong>94</strong>, 262902, 2009.<br />
S. J. A. Koh, C. Keplinger, T. Li, S. Bauer and Z. Suo, IEEE/ASME Trans. Mech. <strong>16</strong>, 33–41, 2010.<br />
T. McKay et. al., Smart Mater. Struct. <strong>19</strong>, 055025, 2010.<br />
T. McKay et. al., Appl. Phys. Lett. <strong>97</strong>, 062911, 2010.<br />
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<tr class="odd"><td><span class="file"><img class="file-icon" alt="PDF icon" title="application/pdf" src="/modules/file/icons/application-pdf.png" /> <a href="https://imechanica.org/files/Dielectric%20Elastomers%20-%20Generator%20Mode%20Fundamentals%20%26%20Applications.pdf" type="application/pdf; length=994418" title="Dielectric Elastomers - Generator Mode Fundamentals &amp; Applications.pdf">Dielectric Elastomers - Generator Mode Fundamentals & Applications.pdf</a></span></td><td>971.11 KB</td> </tr>
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</div></div></div>Mon, 01 Aug 2011 07:12:51 +0000Adrian S. J. Koh10723 at https://imechanica.orghttps://imechanica.org/node/10723#commentshttps://imechanica.org/crss/node/10723Equilibrium and stability of dielectric elastomer membranes undergoing inhomogeneous deformation
https://imechanica.org/node/3953
<div class="field field-name-taxonomy-vocabulary-6 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/76">research</a></div></div></div><div class="field field-name-taxonomy-vocabulary-8 field-type-taxonomy-term-reference field-label-hidden"><div class="field-items"><div class="field-item even"><a href="/taxonomy/term/85">suo group research</a></div><div class="field-item odd"><a href="/taxonomy/term/2877">dielectric elastomer membrane</a></div></div></div><div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>
Dielectric elastomers are capable of large deformation subject to an electric voltage, and are promising for uses as actuators, sensors and generators. Because of large deformation, nonlinear equations of state, and diverse modes of failure, modeling the process of electromechanical transduction has been challenging.<span> </span>This paper studies a membrane of a dielectric elastomer deformed into an out-of-plane, axisymmetric shape, a configuration used in a family of commercial devices known as the Universal Muscle Actuators.<span> </span>
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The kinematics of deformation and charging, together with thermodynamics, lead to field equations that govern the state of equilibrium, as well as the conditions under which the state of equilibrium is stable.<span> </span>Numerical results indicate that the field in the membrane can be very inhomogeneous, and that the membrane is susceptible to several modes of failure, including electrical breakdown, electromechanical instability, loss of tension, and rupture by stretch.<span> </span>Care is needed in design to balance the requirements of averting various modes of failure while using the material efficiently.
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<tr class="odd"><td><span class="file"><img class="file-icon" alt="PDF icon" title="application/pdf" src="/modules/file/icons/application-pdf.png" /> <a href="https://imechanica.org/files/Equilibrium%20and%20stability%20of%20dielectric%20elastomer%20membranes%20undergoing%20inhomogeneous%20deformation.pdf" type="application/pdf; length=271065" title="Equilibrium and stability of dielectric elastomer membranes undergoing inhomogeneous deformation.pdf">Equilibrium and stability of dielectric elastomer membranes undergoing inhomogeneous deformation.pdf</a></span></td><td>264.71 KB</td> </tr>
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</div></div></div>Fri, 03 Oct 2008 21:14:38 +0000Tianhu He3953 at https://imechanica.orghttps://imechanica.org/node/3953#commentshttps://imechanica.org/crss/node/3953Error | iMechanica