Engineering topics
Publications and source records attributed to Yu, Cunjiang.
Scissoring in thick bars suppresses buckling behavior in serpentine traces that have thicknesses greater than their widths, as detailed in a systematic set of analytical and experimental studies. Scissoring in thick copper traces enables elastic stretchability as large as ≈350%, corresponding to a sixfold improvement over previously reported values for thin geometries (≈60%).
We describe and characterize elementary designs for electrochemical micro- and macro-scale chemomechanical hydrogel actuators. The actuation of a pH-sensitive cross-linked polyacrylic acid (PAA) hydrogel is driven in the model devices through the oxygen reduction reaction (ORR) occurring at the electrodes of an embedded Au mesh micro-electrochemical array. Proton consumption by the ORR at the cathode of the embedded electrochemical cell leads to the formation of a localized pH gradient that in turn drives the strain response in the composite actuators. The dynamics result from the ionization of the carboxylic acid moieties of the PAA network in the high pH region, yielding an osmotic pressure that drives a volumetric expansion due to water imbibition. This system actuates both stably and reversibly; when the electrochemically-induced ORR is halted, the localized pH gradient dissipates due to diffusive mixing, which in turn relaxes the induced strains. Two approaches to the fabrication of hydrogel actuators were examined in this work. The first method adopted a design based on small flagella (~0.2 mm × 1.5 mm × 60 μm, width × length × height) in which the actuating PAA structures are molded atop a set of fixed electrodes mounted on a supporting substrate. These hydrogel actuators show fast, large-amplitude, and largely reversible responses in the ORR mediated chemomechanical dynamics. We also investigated larger hydrogel actuators (~4.5 mm × 11 mm × 1 mm, width × length × height), based on an autonomous design that embeds an open mesh stretchable micro-electrode array within the hydrogel. Furthermore, the significant and design-dependent impacts of mass transfer on the chemomechanical dynamics are evidenced in each case, a feature examined to elucidate more efficient mesoscopic design rules for actuators of this form.
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This paper presents a class of hydration monitor that uses ultrathin, stretchable sheets with arrays of embedded impedance sensors for precise measurement and spatially multiplexed mapping. The devices contain miniaturized capacitive electrodes arranged in a matrix format, capable of integration with skin in a conformal, intimate manner due to the overall skin-like physical properties. These “epidermal” systems noninvasively quantify regional variations in skin hydration, at uniform or variable skin depths. Experimental results demonstrate that the devices possess excellent uniformity, with favorable precision and accuracy. Theoretical models capture the underlying physics of the measurement and enable quantitative interpretation of the experimental results. Furthermore, these devices are appealing for applications ranging from skin care and dermatology, to cosmetology and health/wellness monitoring, with the additional potential for combined use with other classes of sensors for comprehensive, quantitative physiological assessment via the skin.
An important trend in electronics involves the development of materials, mechanical designs and manufacturing strategies that enable the use of unconventional substrates, such as polymer films, metal foils, paper sheets or rubber slabs. The last possibility is particularly challenging because the systems must accommodate not only bending but also stretching. Although several approaches are available for the electronics, a persistent difficulty is in power supplies that have similar mechanical properties, to allow their co-integration with the electronics. In this study we introduce a set of materials and design concepts for a rechargeable lithium ion battery technology that exploits thin, low modulus silicone elastomers as substrates, with a segmented design in the active materials, and unusual ‘self-similar’ interconnect structures between them. The result enables reversible levels of stretchability up to 300%, while maintaining capacity densities of ~1.1 mAh cm ⁻2 . Stretchable wireless power transmission systems provide the means to charge these types of batteries, without direct physical contact.
The use of shape memory polymers is demonstrated for deformable, programmable, and shape-memorizing micro-optical devices. A semi-crystalline shape memory elastomer, crosslinked poly(ethylene-co-vinyl acetate), is used to prepare various micro-optic components, ranging from microlens and microprism arrays to diffraction gratings and holograms. Here, the precise replication of surface features at the micro- and nanoscale and the formation of crosslinked shape memory polymer networks can be achieved in a single step via compression molding. Further deformation via hot pressing or stretching of micro-optics formed in this manner allows manipulation of the microscopic surface features, and thus the corresponding optical properties. Due to the shape memory effect, the original surface structures and the optical properties can be recovered and the devices be reprogrammed, with excellent reversibility in the optical properties. Furthermore, arrays of transparent resistive microheaters can be integrated with deformed micro-optical devices to selectively trigger the recovery of surface features in a spatially programmable manner, thereby providing additional capabilities in user-definable optics.