Abstract
Dielectric elastomer actuators (DEA) are smart lightweight flexible materials integrating actuation, sensing, and structural functions. The field of DEAs has been progressing rapidly, with actuation strains of over 300% reported, and many application concepts demonstrated. However many DEAs are slow, exhibit large viscoelastic drift, and have short lifetimes, due principally to the use of acrylic elastomer membranes and carbon grease electrodes applied by hand. Here a DEA‐driven tunable lens, the world's fastest capable of holding a stable focal length, is presented. By using low‐loss silicone elastomers rather than acrylics, a settling time shorter than 175 μs is obtained for a 20% change in focal length. The silicone‐based lenses show a bandwidth 3 orders of magnitude higher compared to lenses of the same geometry fabricated from the acrylic elastomer. Stretchable electrodes, a carbon black and silicone composite, are precisely patterned by pad‐printing and subsequently cross‐linked, enabling strong adhesion to the elastomer and excellent resistance to abrasion. The lenses operate for over 400 million cycles without degradation, and show no change after more than two years of storage. This lens demonstrates the unmatched combination of strain, speed, and stability that DEAs can achieve, paving the way for complex fast soft machines.
Highlights
Soft actuators enable many applications and features that are not feasible with conventional approaches based on hard materials
We found that the Sylgard 184 silicone pre-polymer, used by Carpi et al for a tuneable lens based on a VHB acrylic elastomer membrane,[4] was the best choice for silicone membranes.[13]
The response speed of that lens is in the range of hundreds of millisecond, [5] probably mostly due to the use of acrylic elastomer as dielectric membrane rather than to the effect of inertia or fluidic impedance
Summary
Soft actuators enable many applications and features that are not feasible with conventional approaches based on hard materials. The concept is based on the bioinspired and DEA-driven design introduced by Carpi et al in 2011.[4] a low-mechanical loss silicone (Nusil CF19-2186) is used here as dielectric membrane, instead of acrylic elastomer This leads to the world’s fastest tuneable lens with the ability to hold a very stable position, and demonstrates the integration of actuation, fast response speed and long lifetime in a soft device. The process forms solid electrodes with a strong adhesion to the dielectric membrane (Figure S1) and an excellent resistance to mechanical abrasion and wear, leading to reproducible devices with long lifetime Because of their large actuation strain, DEAs are interesting in the field of adaptive optics.[5] Deformable optical lenses with electrically controllable focus present numerous advantages over the traditional approach consisting in translating rigid lenses. For driving fields smaller than 100 V/ μm, the Strehl ratio is higher than 0.8, which is usually regarded as good for high quality optical systems, making these soft tuneable lenses suitable for imaging applications
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