32 results on '"Youngoh Lee"'
Search Results
2. Ultrasensitive Multimodal Tactile Sensors with Skin‐Inspired Microstructures through Localized Ferroelectric Polarization
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Young‐Eun Shin, Yong‐Jin Park, Sujoy Kumar Ghosh, Youngoh Lee, Jonghwa Park, and Hyunhyub Ko
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healthcare ,interlocked microstructure ,multifunctional sensor ,self‐powered sensor ,skin‐inspired tactile sensor ,temperature sensor ,Science - Abstract
Abstract Multifunctional electronic skins have attracted considerable attention for soft electronics including humanoid robots, wearable devices, and health monitoring systems. Simultaneous detection of multiple stimuli in a single self‐powered device is desired to simplify artificial somatosensory systems. Here, inspired by the structure and function of human skin, an ultrasensitive self‐powered multimodal sensor is demonstrated based on an interlocked ferroelectric copolymer microstructure. The triboelectric and pyroelectric effects of ferroelectric microstructures enable the simultaneous detection of mechanical and thermal stimuli in a spacer‐free single device, overcoming the drawbacks of conventional devices, including complex fabrication, structural complexity, and high‐power consumption. Furthermore, the interlocked microstructure induces electric field localization during ferroelectric polarization, leading to enhanced output performance. The multimodal tactile sensor provides ultrasensitive pressure and temperature detection capability (2.2 V kPa−1, 0.27 nA °C−1) over a broad range (0.1–98 kPa, −20 °C < ΔT
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- 2022
- Full Text
- View/download PDF
3. A Triple-Mode Flexible E-Skin Sensor Interface for Multi-Purpose Wearable Applications
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Sung-Woo Kim, Youngoh Lee, Jonghwa Park, Seungmok Kim, Heeyoung Chae, Hyunhyub Ko, and Jae Joon Kim
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electronic skin ,readout integrated circuit ,sensor interface ,wearable device ,triple-mode ,multi-purpose ,Chemical technology ,TP1-1185 - Abstract
This study presents a flexible wireless electronic skin (e-skin) sensor system that includes a multi-functional sensor device, a triple-mode reconfigurable readout integrated circuit (ROIC), and a mobile monitoring interface. The e-skin device’s multi-functionality is achieved by an interlocked micro-dome array structure that uses a polyvinylidene fluoride and reduced graphene oxide (PVDF/RGO) composite material that is inspired by the structure and functions of the human fingertip. For multi-functional implementation, the proposed triple-mode ROIC is reconfigured to support piezoelectric, piezoresistance, and pyroelectric interfaces through single-type e-skin sensor devices. A flexible system prototype was developed and experimentally verified to provide various wireless wearable sensing functions—including pulse wave, voice, chewing/swallowing, breathing, knee movements, and temperature—while their real-time sensed data are displayed on a smartphone.
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- 2017
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- View/download PDF
4. A Multi-Functional Physiological Hybrid-Sensing E-Skin Integrated Interface for Wearable IoT Applications.
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Kwangmuk Lee, Hee Young Chae, Kyeonghwan Park, Youngoh Lee, Seungse Cho, Hyunhyub Ko, and Jae Joon Kim
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- 2019
- Full Text
- View/download PDF
5. Frequency-selective acoustic and haptic smart skin for dual-mode dynamic/static human-machine interface
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Jonghwa Park, Dong-hee Kang, Heeyoung Chae, Sujoy Kumar Ghosh, Changyoon Jeong, Yoojeong Park, Seungse Cho, Youngoh Lee, Jinyoung Kim, Yujung Ko, Jae Joon Kim, and Hyunhyub Ko
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Multidisciplinary - Abstract
Accurate transmission of biosignals without interference of surrounding noises is a key factor for the realization of human-machine interfaces (HMIs). We propose frequency-selective acoustic and haptic sensors for dual-mode HMIs based on triboelectric sensors with hierarchical macrodome/micropore/nanoparticle structure of ferroelectric composites. Our sensor shows a high sensitivity and linearity under a wide range of dynamic pressures and resonance frequency, which enables high acoustic frequency selectivity in a wide frequency range (145 to 9000 Hz), thus rendering noise-independent voice recognition possible. Our frequency-selective multichannel acoustic sensor array combined with an artificial neural network demonstrates over 95% accurate voice recognition for different frequency noises ranging from 100 to 8000 Hz. We demonstrate that our dual-mode sensor with linear response and frequency selectivity over a wide range of dynamic pressures facilitates the differentiation of surface texture and control of an avatar robot using both acoustic and mechanical inputs without interference from surrounding noise.
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- 2022
6. A cutaneous receptors-mimicking system for real-time and multimodal detection of tactile stimuli
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Bo-Yeon Lee, Seonggi Kim, Sunjong Oh, Youngoh Lee, Jonghwa Park, Hyunhyub Ko, Ja Choon Koo, Young-Do Jung, and Hyuneui Lim
- Abstract
A human can intuitively perceive and comprehend complicated tactile information, when interacting with objects, owing to the different cutaneous receptors distributed in the fingertip skin. Many research groups have attempted to mimic the structure and receptors of the skin to develop next-generation tactile sensors that can precisely and seamlessly deliver the overall tactile sensation. In this study, we propose a real-time multimodal tactile system that mimics the sensing qualities of cutaneous receptors entirely by simultaneously acquiring four types of decoupled tactile information in real time using multiple sensors integrated into three dimensions (3D), a signal-processing module, and a transmission module. The interconnections between 3D-integrated sensors and the signal-processing module were manufactured by 3D printing methods to have an adaptable shape. Furthermore, the proposed system can differentiate between various tactile stimuli, texture characteristics, and consecutive complex motions depending on the decoupled tactile sensing signals of pressure, shear force, vibration, and temperature. We believe that the results of this study can provide a novel design for a skin-like, perceivable, tactile sensing system for application in soft robotics, human-machine interfaces, health monitoring systems, and biomedical devices.
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- 2022
7. Flexible Pyroresistive Graphene Composites for Artificial Thermosensation Differentiating Materials and Solvent Types
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Youngoh Lee, Jonghwa Park, Ayoung Choe, Young-Eun Shin, Jinyoung Kim, Jinyoung Myoung, Seungjae Lee, Youngsu Lee, Young-Kyung Kim, Sung Won Yi, Jin Nam, Jeongeun Seo, and Hyunhyub Ko
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Touch ,General Engineering ,Solvents ,General Physics and Astronomy ,Humans ,General Materials Science ,Graphite ,Skin Temperature ,Skin - Abstract
When we touch an object, thermosensation allows us to perceive not only the temperature but also wetness and types of materials with different thermophysical properties (i.e., thermal conductivity and heat capacity) of objects. Emulation of such sensory abilities is important in robots, wearables, and haptic interfaces, but it is challenging because they are not directly perceptible sensations but rather learned abilities via sensory experiences. Emulating the thermosensation of human skin, we introduce an artificial thermosensation based on an intelligent thermo-/calorimeter (TCM) that can objectively differentiate types of contact materials and solvents with different thermophysical properties. We demonstrate a TCM based on pyroresistive composites with ultrahigh sensitivity (11.2% °Csup-1/sup) and high accuracy (lt;0.1 °C) by precisely controlling the melt-induced volume expansion of a semicrystalline polymer, as well as the negative temperature coefficient of reduced graphene oxide. In addition, the ultrathin TCM with coplanar electrode design shows deformation-insensitive temperature sensing, facilitating wearable skin temperature monitoring with accuracy higher than a commercial thermometer. Moreover, the TCM with a high pyroresistivity can objectively differentiate types of contact materials and solvents with different thermophysical properties. In a proof-of-principle application, our intelligent TCM, coupled with a machine-learning algorithm, enables objective evaluation of the thermal attributes (coolness and wetness) of skincare products.
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- 2022
8. A Triple-Mode Flexible E-Skin Sensor Interface for Multi-Purpose Wearable Applications.
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Sung-Woo Kim, Youngoh Lee, Jonghwa Park, Seungmok Kim, Hee Young Chae, Hyunhyub Ko, and Jae Joon Kim
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- 2018
- Full Text
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9. Stimuli-responsive micro/nanoporous hairy skin for adaptive thermal insulation and infrared camouflage
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Young-Eun Shin, Jinyoung Kim, Yeju Kwon, Ayoung Choe, Hyunhyub Ko, Jeonghee Yeom, and Youngoh Lee
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Materials science ,Infrared ,Nanoporous ,business.industry ,Process Chemistry and Technology ,Hairy skin ,Control reconfiguration ,Nanotechnology ,Human skin ,Shape-memory polymer ,Mechanics of Materials ,Thermal insulation ,Camouflage ,General Materials Science ,Electrical and Electronic Engineering ,business - Abstract
Hairs in homeothermic animals have multiple functions essential for survival, such as regulation of body temperature and camouflage, through adaptable reconfiguration in response to external environments. By contrast, humans wear clothes because the human skin is ineffective for thermoregulation and camouflage, but clothes do not exhibit dynamic responsiveness. In this work, we demonstrate a smart reconfigurable hairy skin based on a hair-patterned shape memory polymer (SMP) containing hierarchical porous micro/nanostructures, which has unique functions of dynamically responsive thermal insulation and camouflage from infrared surveillance. The hairy SMP exhibits high thermal insulation due to the long tortuous path of thermal transport in the micro/nanopores. The programmable shape of the hairy SMP enables the reversible reconfiguration of the hair geometry in response to temperature, leading to the dynamic control of thermal insulation by more than 61.4%. As a proof-of-concept, the smart hairy skin can be used as wearable thermal camouflage or thermal encryption films.
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- 2020
10. Ultrasensitive Multimodal Tactile Sensors with Skin-Inspired Microstructures through Localized Ferroelectric Polarization
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Young‐Eun Shin, Yong‐Jin Park, Sujoy Kumar Ghosh, Youngoh Lee, Jonghwa Park, and Hyunhyub Ko
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Wearable Electronic Devices ,Touch ,General Chemical Engineering ,General Engineering ,General Physics and Astronomy ,Medicine (miscellaneous) ,Humans ,General Materials Science ,Electronics ,Biochemistry, Genetics and Molecular Biology (miscellaneous) ,Skin - Abstract
Multifunctional electronic skins have attracted considerable attention for soft electronics including humanoid robots, wearable devices, and health monitoring systems. Simultaneous detection of multiple stimuli in a single self-powered device is desired to simplify artificial somatosensory systems. Here, inspired by the structure and function of human skin, an ultrasensitive self-powered multimodal sensor is demonstrated based on an interlocked ferroelectric copolymer microstructure. The triboelectric and pyroelectric effects of ferroelectric microstructures enable the simultaneous detection of mechanical and thermal stimuli in a spacer-free single device, overcoming the drawbacks of conventional devices, including complex fabrication, structural complexity, and high-power consumption. Furthermore, the interlocked microstructure induces electric field localization during ferroelectric polarization, leading to enhanced output performance. The multimodal tactile sensor provides ultrasensitive pressure and temperature detection capability (2.2 V kPa
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- 2021
11. Spatiotemporal Measurement of Arterial Pulse Waves Enabled by Wearable Active-Matrix Pressure Sensor Arrays
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Sanghoon Baek, Youngoh Lee, JinHyeok Baek, Jimin Kwon, Seongju Kim, Seungjae Lee, Karl-Philipp Strunk, Sebastian Stehlin, Christian Melzer, Sung-Min Park, Hyunhyub Ko, and Sungjune Jung
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Wearable Electronic Devices ,Heart Rate ,Cardiovascular Diseases ,Printing, Three-Dimensional ,General Engineering ,General Physics and Astronomy ,Humans ,General Materials Science ,Pulse Wave Analysis - Abstract
Wearable pressure sensors have demonstrated great potential in detecting pulse pressure waves on the skin for the noninvasive and continuous diagnosis of cardiac conditions. However, difficulties lie in positioning conventional single-point sensors on an invisible arterial line, thereby preventing the detection of adequate signal amplitude for accurate pulse wave analysis. Herein, we introduce the spatiotemporal measurements of arterial pulse waves using wearable active-matrix pressure sensors to obtain optimal pulse waveforms. We fabricate thin-film transistor (TFT) arrays with high yield and uniformity using inkjet printing where array sizes can be customizable and integrate them with highly sensitive piezoresistive sheets. We maximize the pressure sensitivity (16.8 kPasup-1/sup) and achieve low power consumption (10sup1/supnW) simultaneously by strategically modulating the TFT operation voltage. The sensor array creates a spatiotemporal pulse wave map on the wrist. The map presents the positional dependence of pulse amplitudes, which allows the positioning of the arterial line to accurately extract the augmentation index, a parameter for assessing arterial stiffness. The device overcomes the positional inaccuracy of conventional single-point sensors, and therefore, it can be used for medical applications such as arterial catheter injection or the diagnosis of cardiovascular disease in daily life.
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- 2021
12. Molecular structure engineering of dielectric fluorinated polymers for enhanced performances of triboelectric nanogenerators
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Jinyoung Kim, Yeon Sik Jung, Youngoh Lee, Chang Won Ahn, Seungwon Song, Hyunhyub Ko, Minsoo Kim, Yoon Hyung Hur, Jonghwa Park, and Youngsu Lee
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chemistry.chemical_classification ,Materials science ,Renewable Energy, Sustainability and the Environment ,Annealing (metallurgy) ,chemistry.chemical_element ,02 engineering and technology ,Polymer ,Dielectric ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Methacrylate ,01 natural sciences ,0104 chemical sciences ,Molecular engineering ,chemistry ,Chemical engineering ,Fluorine ,Molecule ,General Materials Science ,Electrical and Electronic Engineering ,0210 nano-technology ,Triboelectric effect - Abstract
Fluorinated polymers have been widely used in triboelectric sensors, displays, and energy harvesting devices because of their superior electron affinity, which leads to the negative triboelectric materials. While previous reports have shown that the control of dielectric constants of fluorinated polymers can increase the triboelectric output performance, the exact relationship between the molecular structures of fluorinated polymers and the resulting triboelectric properties is still elusive. In this study, we demonstrate that the molecular chain structures of the fluorinated polymers depending on the number of fluorine units, the molecular weight (Mw), and conditions such as spin rate and annealing temperature directly affect the relative dielectric constants of dielectric layers and the triboelectric polarity, which are closely related to the triboelectric output performance. We observe that the polymer chain packing structures result in the increase of the relative dielectric constants, thus leading to the improvement of triboelectric output currents. Among the fluorinated polymers used in this study, a poly (2,2,2-trifluoroethyl methacrylate) polymer with three fluorine units and Mw of ~ 20 kg/mol shows the best triboelectric output performance. Our molecular engineering strategy to control the dielectric constants of fluorinated polymers can be a robust platform for the fundamental studies of triboelectric materials and their applications in diverse energy harvesting and sensing devices.
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- 2018
13. Bioinspired Gradient Conductivity and Stiffness for Ultrasensitive Electronic Skins
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Seungjae Lee, Jinyoung Kim, Youngsu Lee, Jinyoung Myoung, Chunggi Baig, Youngoh Lee, Hochan Lee, Soowon Cho, Jonghwa Park, and Hyunhyub Ko
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Materials science ,business.industry ,General Engineering ,Electronic skin ,General Physics and Astronomy ,Linearity ,02 engineering and technology ,Acoustic wave ,Conductivity ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Piezoresistive effect ,0104 chemical sciences ,Stress (mechanics) ,Optoelectronics ,Waveform ,General Materials Science ,0210 nano-technology ,business ,Tactile sensor - Abstract
Hierarchical and gradient structures in biological systems with special mechanical properties have inspired innovations in materials design for construction and mechanical applications. Analogous to the control of stress transfer in gradient mechanical structures, the control of electron transfer in gradient electrical structures should enable the development of high-performance electronics. This paper demonstrates a high performance electronic skin (e-skin) via the simultaneous control of tactile stress transfer to an active sensing area and the corresponding electrical current through the gradient structures. The flexible e-skin sensor has extraordinarily high piezoresistive sensitivity at low power and linearity over a broad pressure range based on the conductivity-gradient multilayer on the stiffness-gradient interlocked microdome geometry. While stiffness-gradient interlocked microdome structures allow the efficient transfer and localization of applied stress to the sensing area, the multilayered structure with gradient conductivity enables the efficient regulation of piezoresistance in response to applied pressure by gradual activation of current pathways from outer to inner layers, resulting in a pressure sensitivity of 3.8 × 105 kPa-1 with linear response over a wide range of up to 100 kPa. In addition, the sensor indicated a rapid response time of 0.016 ms, a low minimum detectable pressure level of 0.025 Pa, a low operating voltage (100 μV), and high durability during 8000 repetitive cycles of pressure application (80 kPa). The high performance of the e-skin sensor enables acoustic wave detection, differentiation of gas characterized by different densities, subtle tactile manipulation of objects, and real-time monitoring of pulse pressure waveform.
- Published
- 2020
14. Binary Spiky/Spherical Nanoparticle Films with Hierarchical Micro/Nanostructures for High-Performance Flexible Pressure Sensors
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Dong-hee Kang, Sujoy Kumar Ghosh, Jinyoung Kim, Hyunhyub Ko, Youngoh Lee, Minsoo Kim, Jonghwa Park, and Young-Ryul Kim
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Materials science ,Nanostructure ,Fabrication ,Electronic skin ,Nanoparticle ,Nanotechnology ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Pressure sensor ,0104 chemical sciences ,chemistry.chemical_compound ,chemistry ,Polyaniline ,Nano ,General Materials Science ,0210 nano-technology ,Nanoscopic scale - Abstract
Flexible pressure sensors have been widely explored for their versatile applications in electronic skins, wearable healthcare monitoring devices, and robotics. However, fabrication of sensors with characteristics such as high sensitivity, linearity, and simple fabrication process remains a challenge. Therefore, we propose herein a highly flexible and sensitive pressure sensor based on a conductive binary spiky/spherical nanoparticle film that can be fabricated by a simple spray-coating method. The sea-urchin-shaped spiky nanoparticles are based on the core-shell structures of spherical silica nanoparticles decorated with conductive polyaniline spiky shells. The simple spray coating of binary spiky/spherical nanoparticles enables the formation of uniform conductive nanoparticle-based films with hierarchical nano/microstructures. The two differently shaped particles-based films (namely sea-urchin-shaped and spherical) when interlocked face-to-face to form a bilayer structure can be used as a highly sensitive piezoresistive pressure sensor. Our optimized pressure sensor exhibits high sensitivity (17.5 kPa-1) and linear responsivity over a wide pressure range (0.008-120 kPa), owing to the effects of stress concentration and gradual deformation of the hierarchical microporous structures with sharp nanoscale tips. Moreover, the sensor exhibits high durability over 6000 repeated cycles and practical applicability in wearable devices that can be used for healthcare monitoring and subtle airflow detection (1 L/min).
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- 2020
15. Micro/nanostructured surfaces for self-powered and multifunctional electronic skins
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Youngoh Lee, Hyunhyub Ko, Seungse Cho, Jonghwa Park, and Minjeong Ha
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Materials science ,business.industry ,Biomedical Engineering ,Wearable computer ,Nanotechnology ,Robotics ,02 engineering and technology ,General Chemistry ,General Medicine ,Strain sensor ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Wireless ,General Materials Science ,Electronics ,Artificial intelligence ,0210 nano-technology ,business ,Energy harvesting ,Wearable technology ,Healthcare system - Abstract
Flexible electronic devices are regarded as one of the key technologies in wearable healthcare systems, wireless communications and smart personal electronics. For the realization of these applications, wearable energy and sensor devices are the two main technologies that need to be developed into lightweight, miniaturized, and flexible forms. In this review, we introduce recent advances in the controlled design of device structures into bioinspired micro/nanostructures and 2D/3D structures for the enhancement of energy harvesting and multifunctional sensing properties of flexible electronic skins. In addition, we highlight their potential applications in flexible/wearable electronics, sensors, robotics and prosthetics, and biomedical devices.
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- 2020
16. A Multi-Functional Physiological Hybrid-Sensing E-Skin Integrated Interface for Wearable IoT Applications
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Hee Young Chae, Seungse Cho, Hyunhyub Ko, Jae Joon Kim, Youngoh Lee, Kyeonghwan Park, and Kwangmuk Lee
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Functional verification ,Computer science ,business.industry ,Interface (computing) ,Noise reduction ,Biomedical Engineering ,Wearable computer ,Blood Pressure Determination ,Reduction (complexity) ,Wearable Electronic Devices ,Readout integrated circuit ,Electric Impedance ,Humans ,Electrical and Electronic Engineering ,business ,Electrodes ,Computer hardware ,Wearable technology ,Electronic circuit - Abstract
This paper presents a flexible multi-functional physiological sensing system that provides multiple noise-immune readout architectures and hybrid-sensing capability with an analog pre-processing scheme. The proposed multi-functional system is designed to support five physiological detection methodologies of piezo-resistive, pyro-resistive, electro-metric, opto-metric and their hybrid, utilizing an in-house multi-functional e-skin device, in-house flexible electrodes and a LED-photodiode pair. For their functional verification, eight representative physiological detection capabilities were demonstrated using wearable device prototypes. Especially, the hybrid detection method includes an innovative continuous measurement of blood pressure (BP) while most previous wearable devices are not ready for it. Moreover, for effective implementation in the form of the wearable device, post-processing burden of the hybrid method was much reduced by integrating a proposed analog pre-processing scheme, where only simple counting process and calibration remain to estimate the BP. This multi-functional sensor readout circuits and their hybrid-sensing interface are fully integrated into a single readout integrated circuit (ROIC), which is designed to implement three readout paths: two electrometric readout paths and one impedometric readout path. For noise-immune detection of the e-skin sensor, a pseudo-differential front-end with a ripple reduction loop is proposed in the impedometric readout path, and also state-of-the-art body-oriented noise reduction techniques are adopted for the electrometric readout path. The ROIC is fabricated in a CMOS process and in-house e-skin devices and flexible electrodes are also fabricated.
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- 2019
17. Tailoring force sensitivity and selectivity by microstructure engineering of multidirectional electronic skins
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Jae Joon Kim, Jaehyung Hong, Sung-Woo Kim, Hochan Lee, Hyunhyub Ko, Seungse Cho, Jin Young Kim, Youngoh Lee, Sung Youb Kim, and Jonghwa Park
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Materials science ,lcsh:Biotechnology ,Electronic skin ,02 engineering and technology ,Bending ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Piezoresistive effect ,0104 chemical sciences ,Stress (mechanics) ,Shear (sheet metal) ,lcsh:TP248.13-248.65 ,Modeling and Simulation ,Ultimate tensile strength ,lcsh:TA401-492 ,Shear stress ,lcsh:Materials of engineering and construction. Mechanics of materials ,General Materials Science ,Composite material ,0210 nano-technology ,Contact area - Abstract
Electronic skins (e-skins) with high sensitivity to multidirectional mechanical stimuli are crucial for healthcare monitoring devices, robotics, and wearable sensors. In this study, we present piezoresistive e-skins with tunable force sensitivity and selectivity to multidirectional forces through the engineered microstructure geometries (i.e., dome, pyramid, and pillar). Depending on the microstructure geometry, distinct variations in contact area and localized stress distribution are observed under different mechanical forces (i.e., normal, shear, stretching, and bending), which critically affect the force sensitivity, selectivity, response/relaxation time, and mechanical stability of e-skins. Microdome structures present the best force sensitivities for normal, tensile, and bending stresses. In particular, microdome structures exhibit extremely high pressure sensitivities over broad pressure ranges (47,062 kPa−1 in the range of
- Published
- 2018
18. MXene-enhanced β-phase crystallization in ferroelectric porous composites for highly-sensitive dynamic force sensors
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Youngoh Lee, Sun Sook Lee, Youngsu Lee, Jinyoung Kim, Moonjeong Jang, Yeoheung Yoon, Ki-Seok An, Jeonghee Yeom, Young-Ryul Kim, Jonghwa Park, Seungyeon Yu, Geonyoung Jeong, Ayoung Choe, Soowon Cho, and Hyunhyub Ko
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Materials science ,Renewable Energy, Sustainability and the Environment ,Nucleation ,Polyvinylidene fluoride ,Ferroelectricity ,Piezoelectricity ,law.invention ,chemistry.chemical_compound ,chemistry ,law ,Phase (matter) ,General Materials Science ,Electrical and Electronic Engineering ,Crystallization ,Composite material ,Contact area ,Stress concentration - Abstract
Piezoelectric polyvinylidene fluoride (PVDF) has been widely utilized in flexible and self-powered tactile sensors, which require high ferroelectricity of polar phase PVDF. Herein, we demonstrate self-powered piezoelectric e-skins with high sensitivity and broad sensing range based on 3D porous structures of MXene (Ti3C2Tx)/PVDF. MXene was used as a nucleation agent to increase the ferroelectric properties of PVDF. This was carried out considering its 2D geometry and abundant surface functional groups that facilitate intermolecular hydrogen bonding between the surface functional groups of MXene and the CH2 group of PVDF. In addition, porous structures can increase the variation in contact area and localized stress concentration in response to applied pressure. This further enhances the piezoelectric sensitivity. Owing to structural deformation and localized stress concentration, the piezoelectric sensitivity of porous MXene/PVDF e-skin is 11.9 and 1.4 nA kPa−1 for low (
- Published
- 2021
19. A Hierarchical Nanoparticle-in-Micropore Architecture for Enhanced Mechanosensitivity and Stretchability in Mechanochromic Electronic Skins
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Ravi Shanker, Chunggi Baig, Youngoh Lee, Hyunhyub Ko, Soowon Cho, Stephen L. Craig, Jinyoung Kim, Jinyoung Myoung, Minsoo Kim, Meredith H. Barbee, Seungse Cho, and Jonghwa Park
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Materials science ,Electronic skin ,Soft robotics ,Nanoparticle ,Color ,Nanotechnology ,02 engineering and technology ,Tensile strain ,010402 general chemistry ,01 natural sciences ,Wearable Electronic Devices ,Tensile Strength ,General Materials Science ,Mechanical Phenomena ,chemistry.chemical_classification ,Normal force ,Mechanical Engineering ,Microporous material ,Polymer ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,chemistry ,Mechanics of Materials ,Nanoparticles ,Stress, Mechanical ,0210 nano-technology ,Hydrophobic and Hydrophilic Interactions ,Porosity - Abstract
Biological tissues are multiresponsive and functional, and similar properties might be possible in synthetic systems by merging responsive polymers with hierarchical soft architectures. For example, mechanochromic polymers have applications in force-responsive colorimetric sensors and soft robotics, but their integration into sensitive, multifunctional devices remains challenging. Herein, a hierarchical nanoparticle-in-micropore (NP-MP) architecture in porous mechanochromic polymers, which enhances the mechanosensitivity and stretchability of mechanochromic electronic skins (e-skins), is reported. The hierarchical NP-MP structure results in stress-concentration-induced mechanochemical activation of mechanophores, significantly improving the mechanochromic sensitivity to both tensile strain and normal force (critical tensile strain: 50% and normal force: 1 N). Furthermore, the porous mechanochromic composites exhibit a reversible mechanochromism under a strain of 250%. This architecture enables a dual-mode mechanochromic e-skin for detecting static/dynamic forces via mechanochromism and triboelectricity. The hierarchical NP-MP architecture provides a general platform to develop mechanochromic composites with high sensitivity and stretchability.
- Published
- 2018
20. Capillary Printing of Highly Aligned Silver Nanowire Transparent Electrodes for High-Performance Optoelectronic Devices
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Seo-Jin Ko, Bright Walker, Youngoh Lee, Jin Young Kim, Hyunhyub Ko, Saewon Kang, Ayoung Choe, Taehyo Kim, and Seungse Cho
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chemistry.chemical_classification ,Materials science ,Organic solar cell ,business.industry ,Mechanical Engineering ,Bioengineering ,Percolation threshold ,General Chemistry ,Polymer ,Condensed Matter Physics ,chemistry ,Percolation ,Electrode ,Optoelectronics ,General Materials Science ,business ,Electrical conductor ,Sheet resistance ,Diode - Abstract
Percolation networks of silver nanowires (AgNWs) are commonly used as transparent conductive electrodes (TCEs) for a variety of optoelectronic applications, but there have been no attempts to precisely control the percolation networks of AgNWs that critically affect the performances of TCEs. Here, we introduce a capillary printing technique to precisely control the NW alignment and the percolation behavior of AgNW networks. Notably, partially aligned AgNW networks exhibit a greatly lower percolation threshold, which leads to the substantial improvement of optical transmittance (96.7%) at a similar sheet resistance (19.5 Ω sq(-1)) as compared to random AgNW networks (92.9%, 20 Ω sq(-1)). Polymer light-emitting diodes (PLEDs) using aligned AgNW electrodes show a 30% enhanced maximum luminance (33068 cd m(-2)) compared to that with random AgNWs and a high luminance efficiency (14.25 cd A(-1)), which is the highest value reported so far using indium-free transparent electrodes for fluorescent PLEDs. In addition, polymer solar cells (PSCs) using aligned AgNW electrodes exhibit a power conversion efficiency (PCE) of 8.57%, the highest value ever reported to date for PSCs using AgNW electrodes.
- Published
- 2015
21. Flexible Ferroelectric Sensors with Ultrahigh Pressure Sensitivity and Linear Response over Exceptionally Broad Pressure Range
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Jinyoung Kim, Soowon Cho, Saewon Kang, Jinyoung Myoung, Hyunhyub Ko, Seungse Cho, Chunggi Baig, Youngoh Lee, Jonghwa Park, Hochan Lee, and Young-Eun Shin
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Materials science ,business.industry ,General Engineering ,General Physics and Astronomy ,Response time ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Pressure sensor ,Ferroelectricity ,0104 chemical sciences ,Linear range ,Miniaturization ,Optoelectronics ,General Materials Science ,Dynamic pressure ,0210 nano-technology ,business ,Sensitivity (electronics) ,Tactile sensor - Abstract
Flexible pressure sensors with a high sensitivity over a broad linear range can simplify wearable sensing systems without additional signal processing for the linear output, enabling device miniaturization and low power consumption. Here, we demonstrate a flexible ferroelectric sensor with ultrahigh pressure sensitivity and linear response over an exceptionally broad pressure range based on the material and structural design of ferroelectric composites with a multilayer interlocked microdome geometry. Due to the stress concentration between interlocked microdome arrays and increased contact area in the multilayer design, the flexible ferroelectric sensors could perceive static/dynamic pressure with high sensitivity (47.7 kPa–1, 1.3 Pa minimum detection). In addition, efficient stress distribution between stacked multilayers enables linear sensing over exceptionally broad pressure range (0.0013–353 kPa) with fast response time (20 ms) and high reliability over 5000 repetitive cycles even at an extremely hi...
- Published
- 2018
22. Skin-Inspired Hierarchical Polymer Architectures with Gradient Stiffness for Spacer-Free, Ultrathin, and Highly Sensitive Triboelectric Sensors
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Chunggi Baig, Youngoh Lee, Soowon Cho, Sangyoon Na, Seongdong Lim, Hyunhyub Ko, and Minjeong Ha
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chemistry.chemical_classification ,animal structures ,Materials science ,Nanoporous ,Effective stress ,technology, industry, and agriculture ,General Engineering ,General Physics and Astronomy ,Stiffness ,02 engineering and technology ,Polymer ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Highly sensitive ,Stress (mechanics) ,chemistry ,medicine ,General Materials Science ,Composite material ,medicine.symptom ,0210 nano-technology ,Elastic modulus ,Triboelectric effect - Abstract
The gradient stiffness between stiff epidermis and soft dermis with interlocked microridge structures in human skin induces effective stress transmission to underlying mechanoreceptors for enhanced tactile sensing. Inspired by skin structure and function, we fabricate hierarchical nanoporous and interlocked microridge structured polymers with gradient stiffness for spacer-free, ultrathin, and highly sensitive triboelectric sensors (TESs). The skin-inspired hierarchical polymers with gradient elastic modulus enhance the compressibility and contact areal differences due to effective transmission of the external stress from stiff to soft layers, resulting in highly sensitive TESs capable of detecting human vital signs and voice. In addition, the microridges in the interlocked polymers provide an effective variation of gap distance between interlocked layers without using the bulk spacer and thus facilitate the ultrathin and flexible design of TESs that could be worn on the body and detect a variety of pressing, bending, and twisting motions even in humid and underwater environments. Our TESs exhibit the highest power density (46.7 μW/cm
- Published
- 2018
23. Transparent and conductive nanomembranes with orthogonal silver nanowire arrays for skin-attachable loudspeakers and microphones
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Jonghwa Park, Saewon Kang, Seungse Cho, Hyunhyub Ko, Hochan Lee, Ravi Shanker, Youngoh Lee, and Doo-Seung Um
- Subjects
Materials science ,Silver ,Microphone ,Materials Science ,ComputingMethodologies_IMAGEPROCESSINGANDCOMPUTERVISION ,02 engineering and technology ,Substrate (printing) ,010402 general chemistry ,01 natural sciences ,Signal ,GeneralLiterature_MISCELLANEOUS ,chemistry.chemical_compound ,Wearable Electronic Devices ,Engineering ,Hardware_GENERAL ,Humans ,Electronics ,Electrical conductor ,Electrodes ,Triboelectric effect ,Research Articles ,Monitoring, Physiologic ,Skin ,Multidisciplinary ,Polydimethylsiloxane ,business.industry ,Nanowires ,Electric Conductivity ,SciAdv r-articles ,Acoustics ,Equipment Design ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,chemistry ,Applied Sciences and Engineering ,ComputerSystemsOrganization_MISCELLANEOUS ,Optoelectronics ,Loudspeaker ,0210 nano-technology ,business ,Research Article - Abstract
Nanomembranes and nanowires build tiny, transparent loudspeakers and sensitive, voice-recognition microphones that attach to skin., We demonstrate ultrathin, transparent, and conductive hybrid nanomembranes (NMs) with nanoscale thickness, consisting of an orthogonal silver nanowire array embedded in a polymer matrix. Hybrid NMs significantly enhance the electrical and mechanical properties of ultrathin polymer NMs, which can be intimately attached to human skin. As a proof of concept, we present a skin-attachable NM loudspeaker, which exhibits a significant enhancement in thermoacoustic capabilities without any significant heat loss from the substrate. We also present a wearable transparent NM microphone combined with a micropyramid-patterned polydimethylsiloxane film, which provides excellent acoustic sensing capabilities based on a triboelectric voltage signal. Furthermore, the NM microphone can be used to provide a user interface for a personal voice-based security system in that it can accurately recognize a user’s voice. This study addressed the NM-based conformal electronics required for acoustic device platforms, which could be further expanded for application to conformal wearable sensors and health care devices.
- Published
- 2017
24. Bioinspired Interlocked and Hierarchical Design of ZnO Nanowire Arrays for Static and Dynamic Pressure-Sensitive Electronic Skins
- Author
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Youngoh Lee, Hyunhyub Ko, Seongdong Lim, Minjeong Ha, Doo-Seung Um, and Jonghwa Park
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Materials science ,business.industry ,Nanowire ,Electronic skin ,Response time ,Nanotechnology ,Static pressure ,Condensed Matter Physics ,Piezoelectricity ,Piezoresistive effect ,Electronic, Optical and Magnetic Materials ,Biomaterials ,Electrochemistry ,Optoelectronics ,Dynamic pressure ,business ,Sound pressure - Abstract
The development of electronic skin (e-skin) is of great importance in human-like robotics, healthcare, wearable electronics, and medical applications. In this paper, a bioinspired e-skin design of hierarchical micro- and nano-structured ZnO nanowire (NW) arrays in an interlocked geometry is suggested for the sensitive detection of both static and dynamic tactile stimuli through piezoresistive and piezoelectric transduction modes, respectively. The interlocked hierarchical structures enable a stress-sensitive variation in the contact area between the interlocked ZnO NWs and also the efficient bending of ZnO NWs, which allow the sensitive detection of both static and dynamic tactile stimuli. The flexible e-skin in a piezoresistive mode shows a high pressure sensitivity (−6.8 kPa−1) and an ultrafast response time (
- Published
- 2015
25. Ultrasensitive Piezoresistive Pressure Sensors Based on Interlocked Micropillar Arrays
- Author
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Youngsu Lee, Youngoh Lee, Jonghwa Park, Youngdo Jung, Hyunhyub Ko, Hyuneui Lim, and Seongdong Lim
- Subjects
Materials science ,business.industry ,Contact resistance ,Biomedical Engineering ,Electronic skin ,Response time ,Bioengineering ,Nanotechnology ,Pressure sensor ,Signal ,Piezoresistive effect ,Optoelectronics ,business ,Contact area ,Wearable technology - Abstract
The development of wearable electronic skins is drawing many interests due to potential applications in prosthetic limbs, robotic skins, and human healthcare monitoring devices. Here, we demonstrate piezoresistive wearable electronic skins based on conductive composite elastomers with interlocked geometry of micropillar arrays. The interlocked micropillar arrays enable the huge variation of contact area and thus the contact resistance between interlocked micropillar arrays when they are deformed in response to external pressure stimuli. In this study, we show that the contact resistance is strongly affected by the variation of diameter, pitch size, and shape of micropillar arrays. The pressure sensor with optimized micropillar dimension shows an ultrahigh pressure sensitivity (−22.8 kPa−1) and response time (∼0.07 s). Finally, we demonstrate that the wearable electronic skin attached on the fingertip is capable of detecting the pressure and vibration signal simultaneously.
- Published
- 2014
26. Giant Tunneling Piezoresistance of Composite Elastomers with Interlocked Microdome Arrays for Ultrasensitive and Multimodal Electronic Skins
- Author
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Jaehyung Hong, Youngoh Lee, Jonghwa Park, Minjeong Ha, Sung Youb Kim, Youngdo Jung, Hyuneui Lim, and Hyunhyub Ko
- Subjects
Materials science ,Finite Element Analysis ,Composite number ,Electronic skin ,General Physics and Astronomy ,Artificial Limbs ,Nanotechnology ,Prosthesis Design ,Elastomer ,Signal ,Materials Testing ,Electrochemistry ,Pressure ,Humans ,General Materials Science ,Electronics ,Monitoring, Physiologic ,Skin ,Nanotubes, Carbon ,General Engineering ,Reproducibility of Results ,Robotics ,Piezoresistive effect ,Elastomers ,Contact area ,Tactile sensor - Abstract
The development of flexible electronic skins with high sensitivities and multimodal sensing capabilities is of great interest for applications ranging from human healthcare monitoring to robotic skins to prosthetic limbs. Although piezoresistive composite elastomers have shown great promise in this area of research, typically poor sensitivities and low response times, as well as signal drifts with temperature, have prevented further development of these materials in electronic skin applications. Here, we introduce and demonstrate a design of flexible electronic skins based on composite elastomer films that contain interlocked microdome arrays and display giant tunneling piezoresistance. Our design substantially increases the change in contact area upon loading and enables an extreme resistance-switching behavior (ROFF/RON of ∼10(5)). This translates into high sensitivity to pressure (-15.1 kPa(-1), ∼0.2 Pa minimum detection) and rapid response/relaxation times (∼0.04 s), with a minimal dependence on temperature variation. We show that our sensors can sensitively monitor human breathing flows and voice vibrations, highlighting their potential use in wearable human-health monitoring systems.
- Published
- 2014
27. Mimicking Human and Biological Skins for Multifunctional Skin Electronics
- Author
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Jonghwa Park, Jinyoung Kim, Ayoung Choe, Seungse Cho, Hyunhyub Ko, and Youngoh Lee
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Biomaterials ,Materials science ,business.industry ,Electrochemistry ,Nanotechnology ,Electronics ,Condensed Matter Physics ,business ,Wearable technology ,Electronic, Optical and Magnetic Materials - Published
- 2019
28. Particle-on-Film Gap Plasmons on Antireflective ZnO Nanocone Arrays for Molecular-Level Surface-Enhanced Raman Scattering Sensors
- Author
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Tae Kyung Lee, Minjung Ha, Youngoh Lee, Hyunhyub Ko, Jiwon Lee, Sang Kyu Kwak, and Jonghwa Park
- Subjects
Nanostructure ,Materials science ,business.industry ,Surface plasmon ,Nanowire ,Nanotechnology ,symbols.namesake ,Semiconductor ,symbols ,General Materials Science ,Nanorod ,Raman spectroscopy ,business ,Plasmon ,Raman scattering - Abstract
When semiconducting nanostructures are combined with noble metals, the surface plasmons of the noble metals, in addition to the charge transfer interactions between the semiconductors and noble metals, can be utilized to provide strong surface plasmon effects. Here, we suggest a particle-film plasmonic system in conjunction with tapered ZnO nanowire arrays for ultrasensitive SERS chemical sensors. In this design, the gap plasmons between the metal nanoparticles and the metal films provide significantly improved surface-enhanced Raman spectroscopy (SERS) effects compared to those of interparticle surface plasmons. Furthermore, 3D tapered metal nanostructures with particle-film plasmonic systems enable efficient light trapping and waveguiding effects. To study the effects of various morphologies of ZnO nanostructures on the light trapping and thus the SERS enhancements, we compare the performance of three different ZnO morphologies: ZnO nanocones (NCs), nanonails (NNs), and nanorods (NRs). Finally, we demonstrate that our SERS chemical sensors enable a molecular level of detection capability of benzenethiol (100 zeptomole), rhodamine 6G (10 attomole), and adenine (10 attomole) molecules. This work presents a new design platform based on the 3D antireflective metal/semiconductor heterojunction nanostructures, which will play a critical role in the study of plasmonics and SERS chemical sensors.
- Published
- 2015
29. A Triple-Mode Flexible E-Skin Sensor Interface for Multi-Purpose Wearable Applications
- Author
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Hyunhyub Ko, Youngoh Lee, Sung-Woo Kim, Hee Young Chae, Seungmok Kim, Jonghwa Park, and Jae Joon Kim
- Subjects
triple-mode ,Engineering ,sensor interface ,Movement ,Interface (computing) ,Electronic skin ,Wearable computer ,wearable device ,02 engineering and technology ,lcsh:Chemical technology ,010402 general chemistry ,electronic skin ,readout integrated circuit ,multi-purpose ,01 natural sciences ,Biochemistry ,Article ,Analytical Chemistry ,Wearable Electronic Devices ,Readout integrated circuit ,Heart Rate ,Humans ,Pulse wave ,Wireless ,Array data structure ,lcsh:TP1-1185 ,Electrical and Electronic Engineering ,Instrumentation ,Skin ,business.industry ,Electrical engineering ,021001 nanoscience & nanotechnology ,Piezoelectricity ,Atomic and Molecular Physics, and Optics ,0104 chemical sciences ,Embedded system ,Graphite ,0210 nano-technology ,business - Abstract
This study presents a flexible wireless electronic skin (e-skin) sensor system that includes a multi-functional sensor device, a triple-mode reconfigurable readout integrated circuit (ROIC), and a mobile monitoring interface. The e-skin device's multi-functionality is achieved by an interlocked micro-dome array structure that uses a polyvinylidene fluoride and reduced graphene oxide (PVDF/RGO) composite material that is inspired by the structure and functions of the human fingertip. For multi-functional implementation, the proposed triple-mode ROIC is reconfigured to support piezoelectric, piezoresistance, and pyroelectric interfaces through single-type e-skin sensor devices. A flexible system prototype was developed and experimentally verified to provide various wireless wearable sensing functions-including pulse wave, voice, chewing/swallowing, breathing, knee movements, and temperature-while their real-time sensed data are displayed on a smartphone.
- Published
- 2017
30. Triboelectric generators and sensors for self-powered wearable electronics
- Author
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Youngoh Lee, Jonghwa Park, Minjeong Ha, and Hyunhyub Ko
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Flexibility (engineering) ,Electric Power Supplies ,Computer science ,business.industry ,Textiles ,General Engineering ,Electrical engineering ,General Physics and Astronomy ,Nanotechnology ,Identification (information) ,Electricity ,Wireless ,Humans ,General Materials Science ,Electronics ,business ,Electromagnetic Phenomena ,Triboelectric effect ,Wearable technology ,Mechanical Phenomena - Abstract
In recent years, the field of wearable electronics has evolved at a rapid pace, requiring continued innovation in technologies in the fields of electronics, energy devices, and sensors. In particular, wearable devices have multiple applications in healthcare monitoring, identification, and wireless communications, and they are required to perform well while being lightweight and having small size, flexibility, low power consumption, and reliable sensing performances. In this Perspective, we introduce two recent reports on the triboelectric generators with high-power generation achieved using flexible and lightweight textiles or miniaturized and hybridized device configurations. In addition, we present a brief overview of recent developments and future prospects of triboelectric energy harvesters and sensors, which may enable fully self-powered wearable devices with significantly improved sensing capabilities.
- Published
- 2015
31. Capillary Printing of Highly Aligned Silver Nanowire Transparent Electrodes for High-Performance Optoelectronic Devices.
- Author
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Saewon Kang, Taehyo Kim, Seungse Cho, Youngoh Lee, Ayoung Choe, Walker, Bright, Seo-Jin Ko, Jin Young Kim, and Hyunhyub Ko
- Published
- 2015
- Full Text
- View/download PDF
32. Transparent and conductive nanomembranes with orthogonal silver nanowire arrays for skin-attachable loudspeakers and microphones.
- Author
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Saewon Kang, Seungse Cho, Shanker, Ravi, Hochan Lee, Jonghwa Park, Doo-Seung Um, Youngoh Lee, and Hyunhyub Ko
- Subjects
- *
NANOSTRUCTURED materials , *ELECTRONICS , *DETECTORS , *WEARABLE technology , *NANOCOMPOSITE materials - Abstract
The article offers information on a study which addresses the nanomembranes (NM)-based conformal electronics required for acoustic device platforms, which could be further expanded for application to conformal wearable sensors and health care devices. It mentions that conventional hybrid NMs containing nanomaterials exhibit enhanced mechanical properties relative to pure polymer NMs due to the reinforcing effect of the fillers in the nanocomposite.
- Published
- 2018
- Full Text
- View/download PDF
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