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Open Access Publications from the University of California

Scholarly Works (8 results)

  • Thesis
  • Peer Reviewed
UC Berkeley Electronic Theses and Dissertations (2020)

Soft and deformable electronics and actuators have attracted high research interests toward practical applications. This work focuses on two goals: (1) applying the concept of elastic instability in the structural design for soft systems; and (2) exploring rapid and low-cost schemes for their facile fabrications. Specifically, Kirigami, curved serpentines, auxetics, bistable and multistable structures, have all been utilized in different electronics and actuator systems to obtain unique and desirable properties, such as ultrahigh deformability, omnidirectional stretchability, and impact-resistant mechanics in this work.

First, a construct inspired by Kirigami designs has been developed to make highly deformable micro-supercapacitor patches with high areal coverages of electrode and electrolyte materials. These patches are fabricated in simple and efficient steps by a laser assisted graphitic conversion and cutting process, utilizing different laser power and scanning speeds on a laser cutter. The Kirigami cuts significantly increase the structural compliance such that individual segments in the patches can buckle, rotate, bend and twist to accommodate large overall deformations with only a small strain in active electrode areas. Electrochemical testing results have proved that electrochemical performances are preserved under large deformations up to 282.5% of overall structural elongations.

A time- and cost-effective fabrication approach to construct stretchable electronics with the “island-bridge” constructs has been established without using photomasks. A low-cost commercially available vinyl cutter is used to define patterns by adjusting the cutting force and depth on the blade. Metal interconnects and pads can be patterned via the “tunnel cut” process and the flexible overall structure can be defined via the “through cut” process. The capabilities of the proposed method is shown by two demonstration devices, a skin-mounted module for monitoring breathing and a water-resistant supercapacitor array with omni-directionally stretchable capability. These devices can accommodate large deformations through the buckling and post-buckling instability without affecting their functions.

Finally, a class of magnetically powered, untethered soft actuators has been built based on a bioinspired “flesh-and-bone” construct. This construct has both key attributes of fast actuation and compliant impact-resistant mechanics and it also renders a simple fabrication process using generic 3D printers and off-the-shelf neodymium magnets as well as silicone elastomers. Actuators of diverse shapes of elastomeric “fleshes” and different placements of magnetic “bones” have displayed several distinct types of tasks, including auxetic expansion and shrinking, out-of-plane transformations, transition among multiple stable states, and manipulation of small objects.

    • Article
    • Peer Reviewed
    UC Berkeley Previously Published Works (2018)
    The design and functionality of extremely flexible, foldable, and rollable microsupercapacitors (MSCs) with in-plane interdigital electrodes that consist of single-walled carbon nanotube (SWCNT) networks on an ultrathin polyimide substrate are demonstrated through experiments and finite element simulations. The all-solid-state MSCs can be reversibly bent, folded, and rolled purely elastically without degradation of their electrical performance. The simulation results confirm that the deformation in bent, folded, and rolled MSCs is purely elastic. The high power density (1125 W cm-3) and small time constant (1 ms) of the present MSCs are comparable to those of aluminum electrolytic capacitors. The MSCs operate at scan rates of up to 1000 V s-1, are characterized by a volumetric capacitance of 18 F cm-3 and an energy density of 1.6 mWh cm-3, and exhibit superior electrochemical stability with 96% capacity retention even after 100,000 charge/discharge cycles. The developed MSCs demonstrate high potential for integration in flexible and wearable electronic systems.
      Cover page: Highly flexible, foldable, and rollable microsupercapacitors on an ultrathin polyimide substrate with high power density
      • Article
      • Peer Reviewed
      UC Berkeley Previously Published Works (2024)
      Soft actuators with unique mechanics have gained significant interests for unique capabilities and versatile applications. However, their actuation mechanisms (usually driven by light, heat, or chemical reactions) result in long actuation times. Reported magnetically actuated soft actuators can produce rapid and precise motions, yet their complex manufacturing processes may constrain their range of applications. Here, the “bone-in-flesh” is proposed that constructs combining rigid magnetic structures encapsulated within soft polymers to create untethered magnetic soft actuators. This approach enables these soft, impact-resistant, agile actuators with a significantly simplified fabrication process. As demonstration examples, multiple soft actuators are fabricated and tested, including actuators for auxetic properties, 2D–3D transformations, and multi-stable states. As such, this work offers a promising solution to challenges associated with soft actuators to potentially expand their applications in various domains.
        Cover page: Ultrafast Biomimetic Untethered Soft Actuators with Bone‐In‐Flesh Constructs Actuated by Magnetic FieldCreative Commons 'BY' version 4.0 license
        • Article
        • Peer Reviewed
        UC Berkeley Previously Published Works (2022)
        The geometric designs of MEMS devices can profoundly impact their physical properties and eventual performances. However, it is challenging for researchers to rationally consider a large number of possible designs, as it would be very time- and resource-consuming to study all these cases using numerical simulation. In this paper, we report the use of deep learning techniques to accelerate the MEMS design cycle by quickly and accurately predicting the physical properties of numerous design candidates with vastly different geometric features. Design candidates are represented in a nonparameterized, topologically unconstrained form using pixelated black-and-white images. After sufficient training, a deep neural network can quickly calculate the physical properties of interest with good accuracy without using conventional numerical tools such as finite element analysis. As an example, we apply our deep learning approach in the prediction of the modal frequency and quality factor of disk-shaped microscale resonators. With reasonable training, our deep learning neural network becomes a high-speed, high-accuracy calculator: it can identify the flexural mode frequency and the quality factor 4.6 × 103 times and 2.6 × 104 times faster, respectively, than conventional numerical simulation packages, with good accuracies of 98.8 ± 1.6% and 96.8 ± 3.1%, respectively. When simultaneously predicting the frequency and the quality factor, up to ~96.0% of the total computation time can be saved during the design process. The proposed technique can rapidly screen over thousands of design candidates and promotes experience-free and data-driven MEMS structural designs.
          Cover page: Deep learning for non-parameterized MEMS structural design
          • Article
          • Peer Reviewed
          UC Berkeley Previously Published Works (2021)
          A variety of autonomous oscillations in nature such as heartbeats and some biochemical reactions have been widely studied and utilized for applications in the fields of bioscience and engineering. Here, we report a unique phenomenon of moisture-induced electrical potential oscillations on polymers, poly([2-(methacryloyloxy)ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide-co-acrylic acid), during the diffusion of water molecules. Chemical reactions are modeled by kinetic simulations while system dynamic equations and the stability matrix are analyzed to show the chaotic nature of the system which oscillates with hidden attractors to induce the autonomous surface potential oscillation. Using moisture in the ambient environment as the activation source, this self-excited chemoelectrical reaction could have broad influences and usages in surface-reaction based devices and systems. As a proof-of-concept demonstration, an energy harvester is constructed and achieved the continuous energy production for more than 15,000 seconds with an energy density of 16.8 mJ/cm2. A 2-Volts output voltage has been produced to power a liquid crystal display toward practical applications with five energy harvesters connected in series.
            Cover page: Moisture-induced autonomous surface potential oscillations for energy harvesting
            • Article
            • Peer Reviewed
            UC Berkeley Previously Published Works (2018)
            The recent developments in material sciences and rational structural designs have advanced the field of compliant and deformable electronics systems. However, many of these systems are limited in either overall stretchability or areal coverage of functional components. Here, we design a construct inspired by Kirigami for highly deformable micro-supercapacitor patches with high areal coverages of electrode and electrolyte materials. These patches can be fabricated in simple and efficient steps by laser-assisted graphitic conversion and cutting. Because the Kirigami cuts significantly increase structural compliance, segments in the patches can buckle, rotate, bend and twist to accommodate large overall deformations with only a small strain (<3%) in active electrode areas. Electrochemical testing results have proved that electrical and electrochemical performances are preserved under large deformation, with less than 2% change in capacitance when the patch is elongated to 382.5% of its initial length. The high design flexibility can enable various types of electrical connections among an array of supercapacitors residing in one patch, by using different Kirigami designs.
              Cover page: Kirigami-inspired, highly stretchable micro-supercapacitor patches fabricated by laser conversion and cutting
              • Article
              • Peer Reviewed
              UC Berkeley Previously Published Works (2024)
              Dehydration has been a key limiting factor for the operation of conductive hydrogels in practical application. Here, we report self-healable ionic skins that can self-regulate their internal moisture level by capturing extenral moistures via hygroscopic ion-coordinated polymer backbones through antipolyelectrolyte effect. Results show the ionic skin can maintain its mechanical and electrical functions over 16 months in the ambient environment with high stretchability (fracture stretch ∼2216 %) and conductivity (23.5 mS/cm). The moisture self-regulating capability is further demonstrated by repeated exposures to harsh environments such as 200°C heating, freezing, and vacuum drying with recovered conductivity and stretchability. Their reversible ionic and hydrogen bonds also enable self-healing feature as a sample with the fully cut-through damage can restore its conductivity after 24 h at 40 % relative humidity. Utilizing the ionic skin as a building block, self-healing flexible piezoelecret sensors have been constructed to monitor physiological signals. Together with a facile transfer-printing process, a self-powered sensing system with a self-healable supercapacitor and humidity sensor has been successfully demonstrated. These results illustrate broad-ranging possibilities for the ionic skins in applications such as energy storage, wearable sensors, and human-machine interfaces.
                Cover page: Moisture self-regulating ionic skins with ultra-long ambient stability for self-healing energy and sensing systems
                • Article
                • Peer Reviewed
                UC San Diego Previously Published Works (2016)
                Power supply represents a critical challenge in the development of body-integrated electronic technologies. Although recent research establishes an impressive variety of options in energy storage (batteries and supercapacitors) and generation (triboelectric, piezoelectric, thermoelectric, and photovoltaic devices), the modest electrical performance and/or the absence of soft, biocompatible mechanical properties limit their practical use. The results presented here form the basis of soft, skin-compatible means for efficient photovoltaic generation and high-capacity storage of electrical power using dual-junction, compound semiconductor solar cells and chip-scale, rechargeable lithium-ion batteries, respectively. Miniaturized components, deformable interconnects, optimized array layouts, and dual-composition elastomer substrates, superstrates, and encapsulation layers represent key features. Systematic studies of the materials and mechanics identify optimized designs, including unusual configurations that exploit a folded, multilayer construct to improve the functional density without adversely affecting the soft, stretchable characteristics. System-level examples exploit such technologies in fully wireless sensors for precision skin thermography, with capabilities in continuous data logging and local processing, validated through demonstrations on volunteer subjects in various realistic scenarios.
                  Cover page: Soft, thin skin-mounted power management systems and their use in wireless thermography
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