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Chhetry, Ashok,Yoon, Hyosang,Park, Jae Yeong The Royal Society of Chemistry 2017 Journal of Materials Chemistry C Vol.5 No.38
<P>In this study, a flexible and highly sensitive capacitive pressure sensor has been fabricated by coating a microporous polydimethylsiloxane (PDMS) elastomeric dielectric onto conductive fibers. Conductive fibers were prepared by depositing silver nanoparticles (AgNPs) in poly(styrene-<I>block</I>-butadiene-styrene) (SBS) polymer on the surface of Twaron fibers. The configuration obtained by cross-stacking of two microporous PDMS-coated fibers imitates a capacitive sensor, which responds to compressive stress by increasing the contact area and decreasing the separation between the fiber electrodes. Moreover, the gradual closure of micropores under pressure increases the effective permittivity of the dielectric, thereby enhancing the sensitivity of the sensor. A relatively high sensitivity of 0.278 kPa<SUP>−1</SUP>for a low pressure region (<2 kPa), negligible hysteresis of 6.3%, a dynamic response time in the millisecond range (∼340 ms), a low detection limit of 38.82 Pa and an excellent repeatability of over 10 000 cycles were achieved. Finally, the practicality of the sensor was also demonstrated by loading small objects (∼9.4 mg) and gentle finger touches (<10 kPa). By virtue of its excellent sensitivity, low pressure detection and cost-effective fabrication process, our sensor is applicable for next-generation advanced touch panels with a more human-friendly interface, non-invasive health monitoring systems, and artificial robot arms.</P>
A sandpaper-inspired flexible and stretchable resistive sensor for pressure and strain measurement
Chhetry, Ashok,Das, Partha Sarati,Yoon, Hyosang,Park, Jae Yeong Elsevier 2018 Organic Electronics Vol.62 No.-
<P><B>Abstract</B></P> <P>We report very small shape-factored microstructures developed via a simple and cost-effective approach, enabling a high degree of sensitivity in a low-pressure regime (<2.67 kPa). The surface intertexture on the counter electrode and irregular microstructures with a high surface area developed on the base electrode help reduce the shape factor, allowing the device to deform more easily under pressure. Moreover, the irregular patterns with higher unloaded surface area strengthen the tunneling current sufficiently at low pressure. Furthermore, the fabricated features enable the device to perform as a flexible and stretchable sensing mechanism; the outstanding performance was achieved through a novel and feasible fabrication from a low-surface-energy template without surfactant coating. An ultra-low hysteresis of 3.17%, a high sensitivity of 0.3954 kPa<SUP>−1</SUP>, a fast response time of 0.49 s and stability over 6000 cycles were achieved. Finally, the sensing capability was examined by gentle finger tapping and arbitrary movement of the sensor placed on the forefinger. The current platform can be a key component for diverse applications such as muscle movement, speech detection, and health monitoring systems.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Flexible and stretchable resistive sensor for pressure and strain sensing capability. </LI> <LI> Very small shape-factored microstructures were generated from sandpaper template. </LI> <LI> An ultra-low hysteresis of 3.17%, a high sensitivity of 0.3954 kPa<SUP>−1</SUP> and stability over 6000 cycles were achieved. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Chhetry, Ashok,Kim, Jiyoung,Yoon, Hyosang,Park, Jae Yeong American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.3
<P>The rapid development of pressure sensors with distinct functionalities, notably, with increased sensitivity, fast response time, conformability, and a high degree of deformability, has increased the demand for wearable electronics. In particular, pressure sensors with an excellent sensitivity in the low-pressure range (<2 kPa) and a large working range simultaneously are strongly demanded for practical applications in wearable electronics. Here, we demonstrate an emerging class of solid polymer electrolyte obtained by incorporating a room-temperature ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide with poly(vinylidene fluoride-<I>co</I>-hexafluoropropylene) as a high-capacitance dielectric layer for interfacial capacitive pressure sensing applications. The solid polymer electrolyte exhibits a very high interfacial capacitance by virtue of mobile ions that serve as an electrical double layer in response to an electric field. The randomly distributed microstructures created on the solid electrolyte help the material to elastically deform under pressure. Moreover, the interfacial capacitance is improved by utilizing a highly conductive porous percolated network of silver nanowires reinforced with poly(dimethylsiloxane) as the electrodes. An ultrahigh-pressure sensitivity of 131.5 kPa<SUP>-1</SUP>, a low dynamic response time of ∼43 ms, a low limit of detection of 1.12 Pa, and a high stability for over 7000 cycles are achieved. Finally, we demonstrate the application of the sensor for international Morse code detection, artery pulse detection, and eye blinking. Owing to the ultrahigh sensitivity, the as-fabricated sensor will have great potential for wearable devices in health status monitoring, motion detection, and electronic skin.</P> [FIG OMISSION]</BR>
A Flexible Capacitive Pressure Sensor for Wearable Respiration Monitoring System
Park, Seong Won,Das, Partha Sarati,Chhetry, Ashok,Park, Jae Yeong IEEE 2017 IEEE Sensors Journal Vol. No.
<P>This paper presents the design, fabrication, and characterization of a wearable capacitive pressure sensor for respiration-monitoring systems. For the dielectric layer of the proposed capacitive sensor, Porous Ecoflex with a porosity of similar to 36% was prepared from a manually made sugar cube via a simple melting process. A polydimethylsiloxane-based silver nanowire and carbon fibers thin films were used for the sensor electrodes. The fabricated flexible pressure sensor exhibited a high sensitivity of 0.161 kPa(-1) for low pressure regime (<10 kPa), a wide working pressure range of <200 kPa, and a high durability over 6000 cycles. Since the proposed sensor is flexible and resizable, it can be integrated into clothes and easily placed at any location of the human body. Finally, the practicality of the sensor was successfully demonstrated by integrating the sensor into a waist belt to monitor the real-time respiration signal of the human being. The finding is highly useful to monitor respiration signal for the detection of diseases, such as sleep apnea, asthma, and others.</P>