A tactile sensor using a conductive graphene-sponge composite

Chun, Sungwoo,Hong, Ahyoung,Choi, Yeonhoi,Ha, Chunho,Park, Wanjun The Royal Society of Chemistry 2016 Nanoscale Vol.8 No.17

<P>For sensors that emulate human tactile perception, we suggest a simple method for fabricating a highly sensitive force sensor using a conductive polyurethane sponge where graphene flakes are self-assembled into the porous structure of the sponge. The complete sensor device shows a sensitive and reliable detection response for a broad range of pressure and dynamic pressure that correspond to human tactile perception. Sensitivity of the sensor to detect vibration is also confirmed with vertical actuations due to slipping over micro-scale ridge structures attached on the sensors. Based on the sensor's ability to detect both pressure and vibration, the sensor can be utilized as a flexible tactile sensor.</P>

Flexible pressure sensors using highly-oriented and free-standing carbon nanotube sheets

Chun, Sungwoo,Son, Wonkyeong,Choi, Changsoon Elsevier 2018 Carbon Vol.139 No.-

<P><B>Abstract</B></P> <P>Carbon allotropes are strong candidates for pressure sensing materials in flexible electronics due to their extraordinary mechanical and electrical properties. However, the complexity of the conventional transfer process for these allotropes, the success of which is strongly dependent on the surface conditions of the substrates, limits their feasibility for use as pressure sensors. Thus, we propose a method to create flexible pressure sensors using highly-oriented and free-standing hydrophobic carbon nanotube (CNT) sheets. When drawn from a sidewall of a carbon nanotube forest, these sheets only require a single transfer process without any chemical treatment, thereby facilitating a simple, cost-effective transfer method. The resulting sensors exhibit high sensitivity and fast response characteristics for both statically and dynamically applied pressures. In addition, the highly-oriented structure of these CNT sheets results in distinctive response characteristics for bi-axially applied bending strains. It was also confirmed that the sheets can be easily transferred onto any substrate, including those with rough surfaces, due to the naturally formed free-standing structure. In this work, we present the intact transfer of a CNT sheet onto a micro-patterned substrate representing a rough surface and demonstrate the accompanying typical piezoresistive responses of the resulting pressure sensor.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

A highly sensitive pressure sensor using a double-layered graphene structure for tactile sensing

Chun, Sungwoo,Kim, Youngjun,Oh, Hyeong-Sik,Bae, Giyeol,Park, Wanjun The Royal Society of Chemistry 2015 Nanoscale Vol.7 No.27

<P>In this paper, we propose a graphene sensor using two separated single-layered graphenes on a flexible substrate for use as a pressure sensor, such as for soft electronics. The working pressure corresponds to the range in which human perception recognizes surface morphologies. A specific design of the sensor structure drives the piezoresistive character due to the contact resistance between two graphene layers and the electromechanical properties of graphene itself. Accordingly, sensitivity in resistance change is given by two modes for low pressure (−0.24 kPa<SUP>−1</SUP>) and high pressure (0.039 kPa<SUP>−1</SUP>) with a crossover pressure (700 Pa). This sensor can detect infinitesimal pressure as low as 0.3 Pa with uniformly applied vertical force. With the attachment of the artificial fingerprint structure (AFPS) on the sensor, the detection ability for both the locally generated shear force and actual human touch confirms recognition of the surface morphology constructed by periodic structures.</P>

Water-Resistant and Skin-Adhesive Wearable Electronics Using Graphene Fabric Sensor with Octopus-Inspired Microsuckers

Chun, Sungwoo,Son, Wonkyeong,Kim, Da Wan,Lee, Jihyun,Min, Hyeongho,Jung, Hachul,Kwon, Dahye,Kim, A-Hee,Kim, Young-Jin,Lim, Sang Kyoo,Pang, Changhyun,Choi, Changsoon American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.18

<P>Wearable and skin-attachable electronics with portable/wearable and stretchable smart sensors are essential for health-care monitoring devices or systems. The property of adhesion to the skin in both dry and wet environments is strongly required for efficient monitoring of various human activities. We report here a facile, low-cost, scalable fabrication method for skin-adhesive graphene-coated fabric (GCF) sensors that are sensitive and respond fast to applied pressure and strain. With octopus-like patterns formed on the side of the GCF that touches the skin, the GCF adheres strongly to the skin in both dry and wet environments. Using these characteristics, we demonstrate efficient monitoring of a full range of human activities, including human physiological signals such as wrist pulse and electrocardiography (ECG), as well as body motions and speech vibrations. In particular, both measurements of ECG and wrist-bending motions were demonstrated even in wet conditions. Our approach has opened up a new possibility for wearable and skin-adherent electronic fabric sensors working even in wet environments for health-care monitoring and medical applications in vitro and in vivo.</P> [FIG OMISSION]</BR>

A tactile sensor using single layer graphene for surface texture recognition

Chun, Sungwoo,Choi, Yeonhai,Suh, Dong Ik,Bae, Gi Yoon,Hyun, Sangil,Park, Wanjun The Royal Society of Chemistry 2017 Nanoscale Vol.9 No.29

<P>Tactile sensors capable of texture recognition are essential for artificial skin functions. In this work, we describe a tactile sensor with a single sensor architecture made of single layer graphene that can recognize surface texture based on the roughness of the interacting surface. Resistance changes due to the local deformation of a local area of the single layer graphene are reflected in the resistance of the entire sensor. By introducing microstructures inspired by human finger prints, surface texture was successfully defined through fast Fourier transform analysis, and spatial resolution was easily achievable. This work provides a simple method utilizing a single sensor for surface texture recognition at the level of human sensation without using a matrix architecture which requires high density integration technology with force and vibration sensor elements.</P>

Bioinspired Hairy Skin Electronics for Detecting the Direction and Incident Angle of Airflow

Chun, Sungwoo,Son, Wonkyeong,Choi, Changsoon,Min, Hyeongho,Kim, Jiwon,Lee, Heon Joon,Kim, Dongjin,Kim, Changhwan,Koh, Je-sung,Pang, Changhyun American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.14

<P>The human skin has inspired multimodal detection using smart devices or systems in fields including biomedical engineering, robotics, and artificial intelligence. Hairs of a high aspect ratio (AR) connected to follicles, in particular, detect subtle structural displacements by airflow or ultralight touch above the skin. Here, hairy skin electronics assembled with an array of graphene sensors (16 pixels) and artificial microhairs for multimodal detection of tactile stimuli and details of airflows (e.g., intensity, direction, and incident angle) are presented. Composed of percolation networks of graphene nanoplatelet sheets, the sensor array can simultaneously detect pressure, temperature, and vibration, all of which correspond to the sensing range of human tactile perceptions with ultrahigh response time (<0.5 ms, 2 kHz) for restoration. The device covered with microhairs (50 μm diameter and 300 μm height, AR = 6, hexagonal layout, and ∼4400/cm<SUP>2</SUP>) exhibits mapping of electrical signals induced by noncontact airflow and identifying the direction, incident angle, and intensity of wind to the sensor. For potential applications, we implement the hairy electronics to a sailing robot and demonstrate changes in locomotion and speed by detecting the direction and intensity of airflow.</P> [FIG OMISSION]</BR>

All-graphene strain sensor on soft substrate

Chun, Sungwoo,Choi, Yeonhoi,Park, Wanjun Elsevier 2017 Carbon Vol.116 No.-

<P>We propose a transparent and stretchable all-graphene strain sensor that can detect various types of strain induced via stretching, bending, and torsion. The sensor is fabricated by introducing single-layer graphene as a force sensing material with a conductive film composed of graphene flake for the electrode. With the exclusive use of flexible materials, the completed strain sensor is fully flexible. Using a serpentine-shaped pattern for the single-layer graphene, the sensor is capable of stretching up to 20% with a high gauge factor (42.2). In addition, the sensor provides functional extension to bi-directional responses. This sensor can detect infinitesimal strain as low as 0.1% with a relative resistance change (Delta R/R-0) of similar to 0.005. Finally, sensitive detection of strains induced via bending and torsion are successfully demonstrated. (C) 2017 Elsevier Ltd. All rights reserved.</P>

A Stretchable Graphene Thin-Film Sensor for Detecting All of Lateral and Vertical Strains

Chun, Sungwoo,Son, Wonkyeong,Park, Wanjun American Scientific Publishers 2019 Journal of nanoscience and nanotechnology Vol.19 No.3

Self-Powered Pressure- and Vibration-Sensitive Tactile Sensors for Learning Technique-Based Neural Finger Skin

Chun, Sungwoo,Son, Wonkyeong,Kim, Haeyeon,Lim, Sang Kyoo,Pang, Changhyun,Choi, Changsoon American Chemical Society 2019 Nano letters Vol.19 No.5

<P>Finger skin electronics are essential for realizing humanoid soft robots and/or medical applications that are very similar to human appendages. A selective sensitivity to pressure and vibration that are indispensable for tactile sensing is highly desirable for mimicking sensory mechanoreceptors in skin. Additionally, for a human-machine interaction, output signals of a skin sensor should be highly correlated to human neural spike signals. As a demonstration of fully mimicking the skin of a human finger, we propose a self-powered flexible neural tactile sensor (NTS) that mimics all the functions of human finger skin and that is selectively and sensitively activated by either pressure or vibration stimuli with laminated independent sensor elements. A sensor array of ultrahigh-density pressure (20 × 20 pixels on 4 cm<SUP>2</SUP>) of interlocked percolative graphene films is fabricated to detect pressure and its distribution by mimicking slow adaptive (SA) mechanoreceptors in human skin. A triboelectric nanogenerator (TENG) was laminated on the sensor array to detect high-frequency vibrations like fast adaptive (FA) mechanoreceptors, as well as produce electric power by itself. Importantly, each output signal for the SA- and FA-mimicking sensors was very similar to real neural spike signals produced by SA and FA mechanoreceptors in human skin, thus making it easy to convert the sensor signals into neural signals that can be perceived by humans. By introducing microline patterns on the top surface of the NTS to mimic structural and functional properties of a human fingerprint, the integrated NTS device was capable of classifying 12 fabrics possessing complex patterns with 99.1% classification accuracy.</P> [FIG OMISSION]</BR>

Recognition, classification, and prediction of the tactile sense

Chun, Sungwoo,Hwang, Inyoung,Son, Wonkyeong,Chang, Joon-Hyuk,Park, Wanjun The Royal Society of Chemistry 2018 Nanoscale Vol.10 No.22

<P>The emulation of the tactile sense is presented with the encoding of a complex surface texture through an electrical sensor device. To achieve a functional capability comparable to a human mechanoreceptor, a tactile sensor is designed by employing a naturally formed porous structure of a graphene film. The inherent tactile patterns are achievable by means of proper analysis of the electrical signals that the sensor provides during the event of touching the interacting objects. It is confirmed that the pattern-recognition method using machine learning is suitable for quantifying human tactile sensations. The classification accuracy of the tactile sensor system is better than that of human touch for the tested fabric samples, which have a delicate surface texture.</P>