Stretching and Twisting Sensing With Liquid-Metal Strain Gauges Printed on Silicone Elastomers

Kim, Seokbeom; Lee, Jungchul; Choi, Byungcho

doi:10.1109/jsen.2015.2462314

Cited by 48 publications

(45 citation statements)

References 9 publications

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“…For the resistor, the relative resistance change Δ R / R increases by stretching along the length direction and decreases by stretching along the width direction, as shown in Figure b. This behavior can be simply explained by the effect of geometry changes on the resistance R = ρl /( wt) , considering the Poisson's ratio of the elastomeric materials . In the case of the planar spiral inductor ( d out = 11 mm, d in = 5 mm, and n (number of turns) = 2), the measured inductance was 43.7 nH, which agreed well with the simulated value <15% deviation (Figure S4a,b, Supporting Information).…”

Section: Resultssupporting

confidence: 73%

Multiscale and Uniform Liquid Metal Thin‐Film Patterning Based on Soft Lithography for 3D Heterogeneous Integrated Soft Microsystems: Additive Stamping and Subtractive Reverse Stamping

Kim

Alrowais

et al. 2018

Adv Materials Technologies

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to healthcare. [5,6] Unlike conventional solid-state electronics, soft electronics can be lightweight, stretchable, and reconfigurable, with biocompatible characteristics for skin-mountable and wearable sensing electronics. [7,8] Thereby, flexible and stretchable characteristics are achieved by using either 2D or 3D compliant wave-like, solid metal patterns [9,10] or elastic conductors based on conductive nanomaterials embedded in a polymer matrix. [11,12] An alternative approach to realize all-soft microsystems is the use of intrinsically soft conductors, such as gallium-based liquid metal (eutectic gallium-indium alloy, EGaIn). EGaIn-based soft electronics benefits from its nontoxicity, mechanical stability (unlimited stretchability, but ultimately limited by the mechanical properties of the encasing material), thermal conductivity (κ = 26.6 W m −1 K −1 ), and electrical conductivity (σ = 3.4 × 10 6 S m −1 ). [13][14][15] The low melting temperature (M P < 15 °C) and negligible vapor pressure of EGaIn facilitate room-temperature and ambient pressure manufacturing processing. [13][14][15] Moreover, thanks to the formation of a thin oxide layer (t ≈ 1-3 nm) on the EGaIn surface under atmospheric oxygen level, EGaIn structures maintain their mechanical shapes, [16,17] allowing 2D/3D EGaIn patterns on a soft elastomeric substrate, such as poly(dimethylsiloxane) (PDMS).The moldable characteristic of EGaIn has enabled a broad range of patterning methods based on lithography-enabled stamping and stencil printing, injection, as well as additive and subtractive direct write/patterning processes, [18][19][20] as summarized in Table S1 in the Supporting Information. Thereby, printing using lithography-defined stencils [21][22][23][24] yields simple and high throughput EGaIn patterning on elastomeric substrates with small features of w (width) ≈200 µm/t (thickness) ≈50 µm using metal stencil films, [21] w ≈ 20 µm/t ≈ 2 µm using microfabricated metal stencil films, [22] and w ≈ 20 µm/t ≈ 10 µm using polymer stencil films. [23] Limitations of this approach are the relatively low resolution, rough EGaIn surface, and excessive EGaIn loss during the stencil lift-off process. SubtractiveThe use of intrinsically soft conductors, such as gallium-based liquid metal (eutectic gallium-indium alloy, EGaIn), has enabled bioinspired and skin-like soft electronics. Thereby, creating patterned, smooth, and uniform EGaIn thin films with high resolution and size scalability is one of the primary technical hurdles. Soft lithography using wetting/nonwetting surface modifications and 3D heterogeneous integration can address current EGaIn patterning challenges. This paper demonstrates multiscale and uniform EGaIn thin-film patterning by utilizing an additive stamping process for large-scale (mm-cm) soft electronics and a subtractive reverse stamping process for microscale (µm-mm) soft electronics. While EGaIn patterning based on stamping is regarded as the least reliable patterning technique, this paper highlights multiscale and uniform thin-fi...

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Section: Resultssupporting

confidence: 73%

Multiscale and Uniform Liquid Metal Thin‐Film Patterning Based on Soft Lithography for 3D Heterogeneous Integrated Soft Microsystems: Additive Stamping and Subtractive Reverse Stamping

Kim

Alrowais

et al. 2018

Adv Materials Technologies

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“…By leveraging these unique characteristics, researchers have recently demonstrated advances in reconfigurable, responsive, and stretchable electronic devices. [5][6][7][8] Select applications of liquid metals include soft electronic skins, [9,10] dynamic and flexible antennas, [11][12][13][14] and self-healing and elastic electronics. [15,16] Moreover, the fluid nature of GaLMAs such as eutectic gallium-indium (eGaIn) enables broad process compatibility with additive printing methods such as direct write, inkjet, transfer, and 3D printing.…”

mentioning

confidence: 99%

Wiring up Liquid Metal: Stable and Robust Electrical Contacts Enabled by Printable Graphene Inks

Secor

Cook

Tabor

et al. 2017

Adv Elect Materials

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electronic materials. By leveraging these unique characteristics, researchers have recently demonstrated advances in reconfigurable, responsive, and stretchable electronic devices. [5][6][7][8] Select applications of liquid metals include soft electronic skins, [9,10] dynamic and flexible antennas, [11][12][13][14] and self-healing and elastic electronics. [15,16] Moreover, the fluid nature of GaLMAs such as eutectic gallium-indium (eGaIn) enables broad process compatibility with additive printing methods such as direct write, inkjet, transfer, and 3D printing. [17][18][19][20][21][22][23] As such, research toward the control and integration of GaLMAs for printed, stretchable, and reconfigurable electronics has attracted broad scientific and practical interest.Despite their promise, the development of liquid metal electronics must overcome several challenges for widespread application. In particular, stable electrical contacts have been identified as a critical challenge for the integration of GaLMAs in electronic circuits and systems. [4] Since gallium alloys rapidly with most metals, GaLMAs lead to unstable or mechanically sensitive interfaces when combined with metal electrodes or interconnects, thereby preventing the reliable integration of eGaIn functionality with conventional electronics. In a recent dramatic demonstration of this effect, Dickey and coworkers exploited the aggressive alloying of eGaIn with silver to direct the motion of liquid metal droplets across a surface, completely removing the silver in the process. [24] Therefore, to enable broader application of eGaIn with conventional circuits, interfacial alloying needs to be suppressed without compromising electrical or mechanical properties.Here, we demonstrate printed graphene as a reliable and high-performance interfacial layer to enable electrical connections to eGaIn. In contrast to conventional metals, sp 2 -bonded carbon materials are stable to alloy formation with liquid metals. [25,26] To leverage this property in a platform that is suitable for printed GaLMAs, graphene inks based on cellulose derivatives are used for robust contacts to liquid metal. This class of graphene inks has shown broad process compatibility with excellent electrical conductivity, mechanical durability, and environmental stability. [27][28][29][30] A thin film (≈100 nm) of fewlayer graphene flakes printed between conventional silver leads and eGaIn acts as a physical barrier, effectively passivating the surface against alloying while retaining the ability to conduct current across the interface. Moreover, graphene interfacial Gallium-based liquid metal alloys (GaLMAs) are a unique class of advanced materials with the potential to offer unprecedented opportunities in stretchable and reconfigurable electronics. Despite their promise, the development of liquid metal electronics must overcome several challenges for widespread application. In particular, stable electrical contacts have been identified as a critical challenge for the integration of GaLMAs in electronic...

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“…[33] Conductive liquids belong to another class of materials suitable for deployment in soft and stretchable sensing platforms. [37] Microfluidic devices based on the liquid metals have therefore been increasingly employed as wearable pressure sensors, [38] strain sensors, [39] temperature sensors, [40] and even more recently as a thermotherapy platform. As such, they are highly patternable and reconfigurable.…”

mentioning

confidence: 99%

“…[37] Microfluidic devices based on the liquid metals have therefore been increasingly employed as wearable pressure sensors, [38] strain sensors, [39] temperature sensors, [40] and even more recently as a thermotherapy platform. [37] Microfluidic devices based on the liquid metals have therefore been increasingly employed as wearable pressure sensors, [38] strain sensors, [39] temperature sensors, [40] and even more recently as a thermotherapy platform.…”

mentioning

confidence: 99%

“…Among which, Gallistan and eutectic gallium-indium (eGaIn) are two widely reported electrically conductive liquid metallic alloys that are nontoxic and highly deformable. [37] Microfluidic devices based on the liquid metals have therefore been increasingly employed as wearable pressure sensors, [38] strain sensors, [39] temperature sensors, [40] and even more recently as a thermotherapy platform. [41] However, the macroscopic monolithic film format of microfluidics may not fully meet the requirements of imperceptibility and affect conformability due to many subtle but nonflat topologies on the surface of human skin.…”

mentioning

confidence: 99%

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Ultrathin and Wearable Microtubular Epidermal Sensor for Real‐Time Physiological Pulse Monitoring

Yeo

et al. 2017

Adv Materials Technologies

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high performance of these sensors, their complicated structures, in many cases, require more expensive and complex production routes, limiting its scalability and reproducibility. [33] Conductive liquids belong to another class of materials suitable for deployment in soft and stretchable sensing platforms. These liquids assume the shape of the microchannels within the soft silicone elastomer due to the weak intermolecular forces of attraction between particles. As such, they are highly patternable and reconfigurable. [34][35][36] Recently, several liquid metals that exist in a fluid state in room temperatures are gaining popularity. Among which, Gallistan and eutectic gallium-indium (eGaIn) are two widely reported electrically conductive liquid metallic alloys that are nontoxic and highly deformable. [37] Microfluidic devices based on the liquid metals have therefore been increasingly employed as wearable pressure sensors, [38] strain sensors, [39] temperature sensors, [40] and even more recently as a thermotherapy platform. [41] However, the macroscopic monolithic film format of microfluidics may not fully meet the requirements of imperceptibility and affect conformability due to many subtle but nonflat topologies on the surface of human skin. Thus, an ultrasensitive tactile sensor that is ultrathin, ultralight, and shape configurable is highly desirable.Here, we report an ultrathin microtubular resistive sensor that is soft, flexible, stretchable, and simple to manufacture. The microtube facilitates the deployment of liquid metallic alloy eGaIn which serves as a thin flexible conduit with excellent electrical conductivity and mechanical deformability. Specifically, by considering the radius and thickness of the microtube, we realize an ultrasensitive liquid-based tactile sensor with high flexibility and durability. The self-sustaining fiber-like shape of the sensor is entirely conformal to human interfaces due to its ability to twist around 3D curvatures and objects. In addition, its tiny footprint of 120 µm in diameter makes it almost imperceptible when worn on bare skin. The results of this work establish an attractive option for imperceptible epidermal healthcare diagnostics and monitoring platform.To achieve sensitive force measurements, we utilize liquid metallic alloy within a tubular structure in a submillimeter regime. Liquid metal core fiber of ≈400 µm inner diameter and ≈100 µm in wall thickness has been previously demonstrated as a strain sensor. [42] However, in our current study, we developed a facile manufacturing strategy to achieve an ultrathin, soft core fiber that was previously unattainable. The fabrication process A flexible, stretchable, soft, and ultrathin wearable microtubular sensor that is highly sensitive to mechanical perturbations is developed. The sensor comprises a unique architecture consisting of a liquid-state conductive element core within a soft silicone elastomer microtube. The microtubular sensor can distinguish forces as small as 5 mN and possesses a high force sensitivity ...

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Stretching and Twisting Sensing With Liquid-Metal Strain Gauges Printed on Silicone Elastomers

Cited by 48 publications

References 9 publications

Multiscale and Uniform Liquid Metal Thin‐Film Patterning Based on Soft Lithography for 3D Heterogeneous Integrated Soft Microsystems: Additive Stamping and Subtractive Reverse Stamping

Multiscale and Uniform Liquid Metal Thin‐Film Patterning Based on Soft Lithography for 3D Heterogeneous Integrated Soft Microsystems: Additive Stamping and Subtractive Reverse Stamping

Wiring up Liquid Metal: Stable and Robust Electrical Contacts Enabled by Printable Graphene Inks

Ultrathin and Wearable Microtubular Epidermal Sensor for Real‐Time Physiological Pulse Monitoring

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