• Journal of Sensor Science and Technology
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• v.31 no.5
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• pp.307-311
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• 2022

With the development of Internet of Things (IoT) technologies, numerous people worldwide connect with various electronic devices via Human-Machine Interfaces (HMIs). Considering that HMIs are a new concept of dynamic interactions, wearable electronics have been highlighted owing to their lightweight, flexibility, stretchability, and attachability. In particular, wearable strain sensors have been applied to a multitude of practical applications (e.g., fitness and healthcare) by conformally attaching such devices to the human skin. However, the stretchable elastomer in a wearable sensor has an intrinsic stretching limitation; therefore, structural advances of wearable sensors are required to develop practical applications of wearable sensors. In this study, we demonstrated a 3-dimensional (3D), porous, and piezoelectric strain sensor for sensing body movements. More specifically, the device was fabricated by mixing polydimethylsiloxane (PDMS) and polyvinylidene fluoride nanoparticles (PVDF NPs) as the matrix and piezoelectric materials of the strain sensor. The porous structure of the strain sensor was formed by a sugar cube-based 3D template. Additionally, mixing methods of PVDF piezoelectric NPs were optimized to enhance the device sensitivity. Finally, it is verified that the developed strain sensor could be directly attached onto the finger joint to sense its movements.

• Journal of the Korea Institute of Military Science and Technology
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• v.26 no.3
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• pp.262-272
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• 2023

A polymer-based mechanical low-pass filter(m-LPF) for high-g accelerometers makes it possible to remove high-frequency transient noises from acceleration signals, thus ensuring repeatable and reliable measurement on high-g acceleration. We establish a prediction model for performance of m-LPF by combining a fundamental vibration model with the fractional derivative standard linear solid(FD SLS) model describing the storage modulus and loss modulus of polymers. Here, the FD SLS model is modified to consider the effect of m-LPF shape factor (i.e., thickness) on storage modulus and loss modulus. The prediction accuracy is verified by comparing the displacement transmissibility(or cut-off frequency) estimated using our model with that measured from 3 kinds of polymers(polysulfide rubber(PSR), silicone rubber(SR), and polydimethylsiloxane(PDMS)). Our findings will contribute a significant growth of m-LPF for high-g accelerometers.

• Journal of Korean Ophthalmic Optics Society
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• v.11 no.3
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• pp.259-265
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• 2006

We polymerized material of AA(Acrylic acid) and BMA(butyl methacrylate) to make up for the weak points of hydrogel contact lens. The synthesis process of silicone synthesis is as follows. Acrylate-PDMS(Polydimethylsiloxane)-Urethane prepolymer was composed after Diisocynate reacted with HEMA(2-hydroxyethylmethacrylate) under the catalyst and it reacted again with bis(hydroxyalkyl) terminated poly(dimethylsiloxane) with high oxygen transmissibility characteristics. HEMA(2-hydroxyethylmethacrylate) was used to make prepolymer that can be polymerized and the urethane was used to improve elasticity and oxygen transmissibility, copolymerization was performed with conventional hydrogel contact lens materials to make silicone hydrogel contact lens with higher oxygen transmissibility. For manufacturing of contact lens, We added BMA(Butyl methacrylate) with better elasticity and flexibility, and AA(Acrylic acid) with higher moisturizing to used contact lens materials. AIBN (Azobis2-methylpropionitrile) as initiator and EGDMA(Ethylene Glycol Dimethacrylat) as crosslinking agent were used and the lens with higher oxygen transmissibility and better moisturizing were manufactured complying with basic contact lens properties, which have several combination trial of each monomer characteristics. Compounding SN which included SILICONE, HEMA, NVP and EGDMA etc was showed by swelling ratio of 9.38% and water content of 23.7%. SN was showed by swelling ratio of 9.38%, water content of 23.7% and a visible ray transmissibility of 89%. SB which added BMA in the SN was showed by swelling ratio of 12.50%, water content of 18.56% and a visible ray transmissibility of 88%. SAB which added both AA and BMA in the SN was showed by swelling ratio of 8.33%, water content of 12.93% and a visible ray transmissibility of 88%.

• Science of Emotion and Sensibility
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• v.22 no.1
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• pp.15-22
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• 2019

The purpose of this study is to develop a strain sensor based on a nanoweb by applying electrical conductivity to a polyurethane nanoweb through the use of Graphene. For this purpose, 1% Graphene ink was pour-coated on a polyurethane nanoweb and post-treated with PDMS (Polydimethylsiloxane) to complete a wearable strain sensor. The surface characteristics of the specimens were evaluated using a field emission scanning electron microscope (FE-SEM) to check whether the conductive material was well coated on the surface of the specimen. Electrical properties of the specimens were measured by using a multimeter to measure the linear resistance of the specimen and comparing how the line resistance changes when 5% and 10% of the specimens are tensioned, respectively. In order to evaluate the performance of the specimen, the gauge factor was obtained. The evaluation of the clothing was performed by attaching the completed strain sensor to the dummy and measuring the respiration signal according to the tension using MP150 (Biopac system Inc., USA) and Acqknowledge (ver. 4.2, Biopac system Inc., U.S.A.). As a result of the evaluation of the surface characteristics, it was confirmed that all the conductive nanoweb specimen were uniformly coated with the Graphen ink. As a result of measuring the resistance value according to the tensile strength, the specimen G, which was treated with just graphene had the lowest resistance value, the specimen G-H had the highest resistance value, and the change of the line resistance value of the specimen G and the specimen G-H is increased to 5% It is found that it increases steadily. Unlike the resistance value results, specimen G showed a higher gauge rate than specimen G-H. As a result of evaluation of the actual clothes, the strain sensor made using the specimen G-H measured the stable peak value and obtained a signal of good quality. Therefore, we confirmed that the polyurethane nanoweb treated with Graphene ink plays a role as a breathing sensor.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.4
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• pp.247-255
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• 2018

In this work, glucose solution and sodium chloride solution were distinguished noninvasively using a microwave complementary split-ring resonator (CSRR). Based on the electrical properties of the two solutions measured using a open-ended coaxial probe, a CSRR was designed and fabricated for operation at a specific frequency that facilitates differentiating the two solutions. Furthermore, a polydimethylsiloxane mold was fabricated to concentrate the solution at a region where the electric field of the resonator was strongest, and a laminating film was used to prevent contact between the solution and resonator. Experiments were performed by dropping $50{\mu}L$ of the solution in steps of 100 mg/dL up to a maximum human blood glucose level of 400 mg/dL. Our experiments confirmed that the transmission coefficients ($S_{21}$) of glucose solution and sodium chloride solution exhibit variations of -0.06 dB and 0.14 dB, respectively, per 100 mg/dL concentration change at the resonance frequency. Thus, the opposite trends in the variation of $S_{21}$ with change in the concentration of the two solutions can be used to distinguish between them.

• Journal of Korean Society of Environmental Engineers
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• v.36 no.6
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• pp.387-395
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• 2014

A highly sensitive analytical method based on stir bar sorptive extraction (SBSE) technique and gas chromatography/tandem mass spectrometry (GC-MS/MS) has been developed, allowing the simultaneous multi-analyte determination of 11 synthetic fragrances (SFs) in water samples. The stir bar coated with polydimethylsiloxane (PDMS) was added to 40 mL of water sample at pH 3 and stirred at 1,100 rpm for 120 min. Other SBSE parameters (salt effect and presence of organic solvent) were optimised. The method shows good linearity (coefficients > 0.990) and reproducibility (RSD < 10.9%). The extraction efficiencies were above 83% for all the compounds. The limits of detections (LOD) and limits of quantification (LOQ) were 2.1~4.1 ng/L and 6.6~12.9 ng/L, respectively. The developed method offers the ability to detect 11 SFs at ultra-low concentration levels with only 40 mL of sample volume. Matrix effects in tap water, river water, wastewater treatment plant (WWTP) final effluent water and seawater were investigated and it was shown that the method is suitable for the analysis of trace level of 11 SFs. The method developed in the present study has the advantage of being rapid, simple, high-sensitive and both user and environmentally friendly.

• Korean Journal of Acupuncture
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• v.38 no.4
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• pp.282-289
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• 2021

Objectives : The purpose of this study is to construct a model of the possible thermal runaway of electronic moxibustion and to implement an appropriate risk management method. Methods : To reproduce the system error situation of the electronic moxibustion circuit equipped with microcontroller unit, temperature sensor and heater, a code was set to disable the signal input to temperature sensor and maintain "high" heating signal to heater. The temperature change of electronic moxibustion was compared between 3 types of heater module; module 1 consisting of a combination of heater+0 ohm+0 ohm resistance, module 2 consisting of a combination of heater+Polymeric Positive Temperature Coefficient (PPTC)+0 ohm resistance, and module 3 consisting of a combination of heater+PPTC+10 ohm resistance. The temperature change was measured using a polydimethylsiloxane (PDMS) silicone phantom. After maintaining surface temperature of the phantom at 31~32℃ for 20 seconds, electronic moxibustion was applied. After operating electronic moxibustion, the temperature change was measured for 660 seconds on the surface and 900 seconds at 2 mm depth. Results : Regardless of the module type, the time-dependent change in temperature showed a rapid rise followed by a gentle curve, and a sharp drop in temperature after reaching the maximum temperature about 10 minutes after the switching the moxibustion on. Temperature measured at the depth of 2 mm below the surface increased slower and to a lesser extent. Module 1 reached highest peak temperature with largest change of temperature at both depths followed by module 2, and 3. Conclusions : Through the combination of PPTC+resistance with the heater of electronic moxibustion, it is possible to limit the rise in temperature even with the software error. Thus, this setting can be used as an independent safety measure for the electronic moxibustion control unit.