Person: Keplinger, Christoph
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Keplinger
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Christoph
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Keplinger, Christoph
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Publication Natural rubber for sustainable high-power electrical energy generation(Royal Society of Chemistry (RSC), 2014) Kaltseis, Rainer; Keplinger, Christoph; Adrian Koh, Soo Jin; Baumgartner, Richard; Goh, Yu Feng; Ng, Wee Hoe; Kogler, Alexander; Tröls, Andreas; Foo, Choon Chiang; Suo, Zhigang; Bauer, SiegfriedClean, renewable and abundant sources of energy, such as the vast energy of ocean waves, are untapped today, because no technology exists to convert such mechanical motions to electricity economically. Other sources of mechanical energy, such as motions of people and vibrations of buildings and bridges, can potentially power portable electronics and distributed sensors. Here we show that natural rubber can be used to construct generators of high performance and low cost. Natural rubber has higher elastic modulus, fracture energy and dielectric strength than a commonly studied acrylic elastomer. We demonstrate high energy densities (369 mJ g−1) and high power densities (200 mW g−1), and estimate low levelized cost of electricity (5–11 ct kW−1 h−1). Soft generators based on natural rubber enable clean, low-cost, large-scale generation of electricity.Publication Charge localization instability in a highly deformable dielectric elastomer(AIP Publishing, 2014) Lu, Tongqing; Keplinger, Christoph; Arnold, Nikita; Bauer, Siegfried; Suo, ZhigangThis paper shows that a highly deformable capacitor made of a soft dielectric and two conformal electrodes can switch between two states discontinuously, by a first-order transition, as the total charge varies gradually. When the total charge is small, it spreads evenly over the area of the capacitor, and the capacitor deforms homogeneously. When the total charge is large, it localizes in a small region of the capacitor, and this region thins down preferentially. The capacitor will survive the localization without electrical breakdown if the area of the electrode is small. Such a bistable system may lead to useful devices.Publication 25th Anniversary Article: A Soft Future: From Robots and Sensor Skin to Energy Harvesters(BlackWell Publishing Ltd, 2013) Bauer, Siegfried; Bauer-Gogonea, Simona; Graz, Ingrid; Kaltenbrunner, Martin; Keplinger, Christoph; Schwödiauer, ReinhardScientists are exploring elastic and soft forms of robots, electronic skin and energy harvesters, dreaming to mimic nature and to enable novel applications in wide fields, from consumer and mobile appliances to biomedical systems, sports and healthcare. All conceivable classes of materials with a wide range of mechanical, physical and chemical properties are employed, from liquids and gels to organic and inorganic solids. Functionalities never seen before are achieved. In this review we discuss soft robots which allow actuation with several degrees of freedom. We show that different actuation mechanisms lead to similar actuators, capable of complex and smooth movements in 3d space. We introduce latest research examples in sensor skin development and discuss ultraflexible electronic circuits, light emitting diodes and solar cells as examples. Additional functionalities of sensor skin, such as visual sensors inspired by animal eyes, camouflage, self-cleaning and healing and on-skin energy storage and generation are briefly reviewed. Finally, we discuss a paradigm change in energy harvesting, away from hard energy generators to soft ones based on dielectric elastomers. Such systems are shown to work with high energy of conversion, making them potentially interesting for harvesting mechanical energy from human gait, winds and ocean waves.Publication Ionic skin(Wiley-Blackwell, 2014) Sun, Jeong-Yun; Keplinger, Christoph; Whitesides, George; Suo, ZhigangElectronic skins (i.e., stretchable sheets of distributed sensors) report signals using electrons, whereas natural skins report signals using ions. Here, ionic conductors are used to create a new type of sensory sheet, called “ionic skin”. Ionic skins are highly stretchable, transparent, and biocompatible. They readily measure strains from 1% to 500%, and pressures as low as 1 kPa.Publication Stretchable Conductive Composites Based on Metal Wools for Use as Electrical Vias in Soft Devices(Wiley-Blackwell, 2015) Lessing, Joshua; Morin, Stephen A.; Keplinger, Christoph; Tayi, Alok S.; Whitesides, GeorgeSoft devices can be bent, stretched, and compressed reversibly, but conventional wires are rigid. This work describes stretchable composites that are easily fabricated with simple tools and commodity materials, and that can provide a strategy for electrical wiring that meets certain needs of soft devices. These composites are made by combining metal wool and elastomeric polymers. Embedding fine (average fiber width ≈25 μm) steel wool (or other metal wools) in a silicone polymer creates an electrically conductive path through the nonconductive elastomer. This composite is flexible, stretchable, compressible, inexpensive, and simple to incorporate into the bodies of soft devices. It is also electrically anisotropic, and shows maximum conductivity along the majority axis of the fibers, but maximum extension perpendicular to this axis. The utility of this composite for creating an electrically conductive path through an elastomer was demonstrated in several devices, including: a soft, solderless breadboard, a soft touch sensor, and a soft strain gauge.Publication Pneumatic Networks for Soft Robotics that Actuate Rapidly(Wiley-Blackwell, 2014) Mosadegh, Bobak; Polygerinos, Panagiotis; Keplinger, Christoph; Wennstedt, Sophia; Shepherd, Robert F.; Gupta, Unmukt; Shim, Jongmin; Bertoldi, Katia; Walsh, Conor; Whitesides, GeorgeSoft robots actuated by pressurization and inflation of a pneumatic network (a “pneu-net”) of small channels in elastomeric materials are appealing for their ability to produce sophisticated motions with simple controls. Although current designs of pneu-nets achieve motion with large amplitudes, they do so relatively slowly (that is, over seconds). This paper describes a new design for pneu-nets that reduces the amount of gas that must be transported for inflation of the pneu-net, and thus increases its speed of actuation. A simple actuator can bend from a linear shape to a quasi-circular shape in 50 milliseconds when pressurized at ΔP = 345 kPa. At high rates of pressurization and inflation, the path along which the actuator bends depends on this rate. When inflated fully, the channels and chambers of this new pneu-net design experience only one-tenth the change in volume of that required for a motion of equal amplitude using the previous design. This small change in volume requires comparably low levels of strain in the material at maximum amplitudes of actuation, and commensurately low rates of fatigue and failure. This actuator can operate over a million cycles without significant degradation of performance. This design for soft robotic actuators combines high rates of actuation with high reliability of the actuator, and opens new areas of application for them.Publication Buckling Pneumatic Linear Actuators Inspired by Muscle(Wiley-Blackwell, 2016) Yang, Dian; Verma, Mohit Singh; So, Ju-Hee; Mosadegh, Bobak; Keplinger, Christoph; Lee, Benjamin; Khashai, Fatemeh; Lossner, Elton; Suo, Zhigang; Whitesides, GeorgeThe mechanical features of biological muscles are difficult to reproduce completely in synthetic systems. A new class of soft pneumatic structures (vacuum-actuated muscle-inspired pneumatic structures) is described that combines actuation by negative pressure (vacuum), with cooperative buckling of beams fabricated in a slab of elastomer, to achieve motion and demonstrate many features that are similar to that of mammalian muscle.Publication Soft Actuators and Robots that Are Resistant to Mechanical Damage(Wiley-Blackwell, 2014) Martinez, R; Glavan, Ana; Keplinger, Christoph; Oyetibo, Alexis I.; Whitesides, GeorgeThis paper characterizes the ability of soft pneumatic actuators and robots to resist mechanical insults that would irreversibly damage or destroy hard robotic systems—systems fabricated in metals and structural polymers, and actuated mechanically—of comparable sizes. The pneumatic networks that actuate these soft machines are formed by bonding two layers of elastomeric or polymeric materials that have different moduli on application of strain by pneumatic inflation; this difference in strain between an extensible top layer and an inextensible, strain-limiting, bottom layer causes the pneumatic network to expand anisotropically. While all the soft machines described here are, to some extent, more resistant to damage by compressive forces, blunt impacts, and severe bending than most corresponding hard systems, the composition of the strain-limiting layers confers on them very different tensile and compressive strengths.Publication Inkjet Printing of Conductive Inks with High Lateral Resolution on Omniphobic “R F Paper” for Paper-Based Electronics and MEMS(Wiley-Blackwell, 2014) Lessing, Joshua; Glavan, Ana; Walker, S. Brett; Keplinger, Christoph; Lewis, Jennifer; Whitesides, GeorgeThe use of omniphobic “fluoroalkylated paper” as a substrate for inkjet printing of aqueous inks that are the precursors of electrically conductive patterns is described. By controlling the surface chemistry of the paper, it is possible to print high resolution, conductive patterns that remain conductive after folding and exposure to common solvents.Publication Stretchable, Transparent, Ionic Conductors(Association for the Advancement of Science, 2013) Keplinger, Christoph; Sun, Jeong Yun; Foo, Choon Chiang; Rothemund, Philipp Josef Michael; Whitesides, George; Suo, ZhigangExisting stretchable, transparent conductors are mostly electronic conductors. They limit the performance of interconnects, sensors, and actuators as components of stretchable electronics and soft machines. We describe a class of devices enabled by ionic conductors that are highly stretchable, fully transparent to light of all colors, and capable of operation at frequencies beyond 10 kilohertz and voltages above 10 kilovolts. We demonstrate a transparent actuator that can generate large strains and a transparent loudspeaker that produces sound over the entire audible range. The electromechanical transduction is achieved without electrochemical reaction. The ionic conductors have higher resistivity than many electronic conductors; however, when large stretchability and high transmittance are required, the ionic conductors have lower sheet resistance than all existing electronic conductors.