DESIGN, MANUFACTURING, AND CHARACTERIZATION OF SOFT, CAPACITIVE ACTUATORS AND ARCHITECTED DIELECTRIC ELASTOMERS

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Abstract
Elastomeric, dielectric architectures exhibit versatile functionality. Depending on their material properties and geometric structure, dielectric architectures can facilitate the transformation of an object’s shape, sense local deformation, or even alter the transmission of electromagnetic waves in the surrounding envi- ronment. This work develops and characterizes soft material systems and fab- rication frameworks for multi-dimensional mobility and topological morphing. A comprehensive material system is introduced for the additive manufactur- ing of soft, electrohydraulic tentacle actuators. A photo-curable, elastomeric silicone-urethane with strong dielectric properties (εr ≈ 8.8 at 1 kHz) serves as the encapsulating material for ionically-conductive hydrogel and silver paint electrodes that displace a vegetable-based liquid dielectric under an applied electric field. A fully-encapsulated and 3D printed electrohydraulic tentacle actuator—containing a three-dimensional array of 30 actuators—demonstrates the use of this material system in a synthetic hydrostat with multi-dimensional motion. This technology is extended to toplogical morphing with dual-phase capacitive actuators to design conformable reflectarray antennas with beam- steering capabilities. A silicone-urethane membrane with carbon and copper electrodes encapsulates a dual gas-liquid working fluid (N2 gas and Envirotemp FR3 liquid, εr = 3.2) to create a lightweight and rapid reconfiguration mech-anism. A pair of the capacitive actuators can exhibit a free displacement of ∆d ≈ 1.4 mm with only 0.34 g of working fluid (46wt% N2 gas). This work also introduces a numerical and experimental study of dielec- tric elastomer architectures that can serve as flexible metamaterials for adaptive electronics. The unit cell design and porosity of two dielectric elastomeric archi- tectures provides a tuning mechanism for the onset of a mechanical instability in the structure; a shift in effective permittivity is observed due to the increase in matrix volume and the rearrangement of the electric field distribution in the cells. Additive fabrication allows rapid customization of the unit cell geome- try and scale for tuning the matrices’ electromechanical response. We observed effective permittivity shifts ∆ε2 > 0.7 under compressive strains γ < 0.35. With the ability to tune their effective mechanical behavior, the architected elastomers are more flexible than their bulk polyurethane counterpart for flexible electronic applications. A demonstration of the 3D printed architectures as soft, flexible substrates for a microstrip patch antenna show tunable shifts in resonance fre- quency
∆ fr
> 110 MHz under compression.
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145 pages
Supplemental file(s) description: Supplemental Video for Chapter 2.
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2021-12
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Shepherd, Robert F.
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Lal, Amit
Petersen, Kirstin Hagelskjaer
Degree Discipline
Mechanical Engineering
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Ph. D., Mechanical Engineering
Degree Level
Doctor of Philosophy
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dissertation or thesis
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