Journal of the Korean Society for Precision Engineering

Emerging Patterning Strategies for Intrinsically Stretchable Conductors: Materials, Architectures, and Device-level Performance: Donghyeon Seo, Seongsik Jeong, Hae-Jin Kim; J. Korean Soc. Precis. Eng. 2025;42(10):789-816.
Published online October 1, 2025; DOI: https://doi.org/10.7736/JKSPE.D.25.00003

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Intrinsically stretchable electronics enable seamless integration with dynamic biological tissues and curved surfaces, making them vital for next-generation wearables, biointerfaces, and intelligent robotics. Yet, precise, high-resolution patterning of stretchable electrodes and circuits remains challenging, limiting practical applications. Traditional lithography offers excellent resolution but is hindered by thermal and chemical incompatibilities with soft substrates. Consequently, alternative approaches such as soft lithography, laser-based patterning, printing methods, and electrospray deposition have gained importance. Soft lithography provides an economical, low-temperature option suitable for delicate materials like liquid metals. Laser-based techniques deliver high resolution and design flexibility but require careful parameter tuning for specific substrates. Mask-free printing methods, including direct ink writing and inkjet printing, enable versatile patterning of complex geometries, while electrospray deposition supports precise, non-contact patterning on stretchable surfaces. Collectively, these techniques advance the fabrication of robust stretchable displays, wireless antennas, and bioelectronic interfaces for accurate physiological monitoring. Despite progress, challenges persist, particularly in achieving large-area uniformity, multilayer stability, and sustainable processing. Addressing these issues demands interdisciplinary collaboration across materials science, fluid dynamics, interfacial engineering, and digital manufacturing. This review highlights recent progress and remaining hurdles, offering guidance for future research in stretchable electronics.

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Air- and Bone-conduction Effects in Vehicle Interior Noise and Vibration Evaluation: A 12-DOF Human Model-head Finite Element Study: Jongyeon Yoon, Daeun Jeong, Namkeun Kim; J. Korean Soc. Precis. Eng. 2025;42(9):713-721.
Published online September 1, 2025; DOI: https://doi.org/10.7736/JKSPE.025.085

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The rise of electric vehicles (EVs) has led to a reduction in engine noise, making suspension and road noise more noticeable. However, most assessments focus only on air-conducted (AC) pathways and overlook bone-conducted (BC) transmission. This study identifies key sources of vehicle noise and implements a finite-element simulation to replicate real-world driving conditions. A 12-degree-of-freedom (DOF) human body model quantifies how vibrations transmit from the vehicle structure to the head. Additionally, a detailed finite-element model of the human head evaluates basilar-membrane (BM) vibrations for both AC and BC inputs. The results indicate that BC dominates below 10 Hz, producing BM velocities up to 50 dB greater than AC. Above 10 Hz, AC prevails, showing a difference of approximately 40 dB. Notably, at frequencies of 33, 46, 67, and 80 Hz, the AC–BC difference narrows to below 10 dB, highlighting significant BC effects even at higher frequencies. These findings reveal that neglecting bone-conduction pathways can lead to an underestimation of occupant exposure to low-frequency vibrations. Therefore, comprehensive evaluations and control methods for vehicle noise should consider both AC and BC transmission mechanisms to accurately reflect human perception

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Phasic and Tonic Coordination among Upper-limb Muscles in Different Speeds of Reaching Movement: Min-Jae Kim, Ju-Hee Kim, Hyeon-Soo Shin, Sean-Min Lee, Na-Yeon Kim, Gwang-Moon Eom; J. Korean Soc. Precis. Eng. 2025;42(2):105-120.
Published online February 1, 2025; DOI: https://doi.org/10.7736/JKSPE.024.112

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In the rehabilitation of upper limb function impaired by stroke, facilitating the coordinated activation of multiple muscles is desirable. This study aims to analyze the coordination patterns of the tonic and phasic components of EMG during a reaching task and to investigate how the phasic component changes in relation to reaching speed. The analysis focused on the shoulder and elbow joints. EMG was recorded at five different speeds, with the slowest speed selected to represent the tonic component. The tonic component was then removed from the total EMG at the other four speeds to extract the phasic component. Correlation coefficients were calculated between the tonic component and joint angles, as well as between the phasic component and joint angular accelerations. For the tonic component, as joint angle increased during reaching, muscle activation also increased to counteract gravitational moments and enhance joint stiffness. For the phasic component, as reaching speed increased, the correlation between acceleration-deceleration patterns and muscle activation also increased. This suggests a greater synergistic contraction for enhanced acceleration and deceleration, as well as increased antagonistic contraction to ensure dynamic stability during faster movements

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Fabrication of Electrospun Nanofibers with Direct-write Sprayed Conductive Patterns: Jeong Hwa Kim, Semih Akin, Yujin Lee, Martin B.-G. Jun, Yong Jun Yoon, Young Hun Jeong; J. Korean Soc. Precis. Eng. 2024;41(4):287-293.
Published online April 1, 2024; DOI: https://doi.org/10.7736/JKSPE.023.148

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The demand for flexible electronic materials used in wearable devices has experienced a significant surge in recent years. Wearable devices typically incorporate an electronic material or system that can be mounted on a human body. It is imperative that these materials are composed of substances compatible with the human body. Consequently, numerous studies have been undertaken to develop flexible electronic devices with various performance capabilities. In this study, nanowire patterns were manufactured on nanofibers and utilized as patches. To create a nanowire pattern, a direct-write spraying process was employed to investigate changes in electrical characteristics using process variables. The process involved depositing silver nanowires on the surface of nanofibers using a pneumatic spray nozzle. Generated patterns were found to be suitable for use as sensors capable of withstanding skin-attached deformation.

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Effects of the Wearable Assistive Suit on Muscle Activity during Lifting Tasks: Kwang Hee Lee, Chul Un Hong, Mi Yu, Tae Kyu Kwon; J. Korean Soc. Precis. Eng. 2024;41(1):47-53.
Published online January 1, 2024; DOI: https://doi.org/10.7736/JKSPE.023.103

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Quick picking and heavy lifting are the most common problems in current workplaces. They can cause lumbar muscle damage. The operator then must spend energy, time, and money for recovery or rehabilitation. To solve this problem, we developed a passive-type assistive suit using air mesh material, elastic band, and wire. To determine the strength support effect of the passive-type assistive suit, electromyography (EMG) was performed for eight muscles and the maximum voluntary contraction (MVC) was analyzed when lifting weights of 0%, 15%, and 30% of the subject’s weight in a Semisquat motion. Results showed that MVC increased as the weight of the heavy object increased. However, its increase was not proportional to the decrease in MVC according to the presence or absence of assistive suits or the weight of the heavy object. The highest MVC was observed for the erector spinae muscle under all conditions. The greatest decrease in MVC according to working clothes was measured for the vastus lateralis muscle (lifting: 17.7±2.95%, lowering: 18.3±0.55%). These results show that lifting work performed while wearing a passive-type assistive suit using wires and elastic bands is effective in assisting muscle activity.

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EMG and Usability Assessment of Adjustable Stiffness Passive Waist-Assist Exoskeletons for Construction Workers
Jung Sun Kang, Bo Ra Jeong, Eung-Pyo Hong, Bok Man Lim, Byung June Choi, Youn Baek Lee, Yun Hee Chang
International Journal of Precision Engineering and Manufacturing.2025; 26(1): 227. CrossRef

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Development of Passive Upper Limb Exoskeleton Device (H-Frame) for Augment the Load Carrying Capability of the Human: Dong-Hyun Jeong, Do Yeon Kang, Ji Seck Lee; J. Korean Soc. Precis. Eng. 2023;40(4):283-289.
Published online April 1, 2023; DOI: https://doi.org/10.7736/JKSPE.022.113

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Carrying heavy objects in agricultural and industrial sites is the most basic labor, which requires a lot of energy. Many equipment such as crane, chain block, elevator, and forklift truck has been developed to reduce human power. Nevertheless, many tasks require human labor. In addition, rapid aging is increasing musculoskeletal diseases in industrial workers. Consequently, various muscle auxiliary wear robots and devices are being developed. In this study; a passive upper limbs exoskeleton (H-Frame) was developed to help carry over 20 kg of weight in industrial and agricultural sites. For the functional test of the developed H-Frame, tests were carried out for 20, 30, and 40 kg of each box. To measure the objective and numerical data of the H-Frame, various sensor values such as EMG (Electromyography), harness compression force sensor, and load cell value of side support and rope were measured. EMG and metabolic experiments were also performed on 8 subjects before and after wearing the device. The average value of the upper extremity muscle showed a 44% reduction effect after wearing. The device helped the wearer when carrying heavy objects. It could help prevent musculoskeletal diseases in industrial and agricultural fields.

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Comparative Analysis between IMU Signal-based Neural Network Models for Energy Expenditure Estimation
Chang June Lee, Jung Keun Lee
Journal of the Korean Society for Precision Engineering.2024; 41(3): 191. CrossRef

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Finite Element Analysis of the Difference of Bone-Conducted Responses according to the Young’s Modulus of Skull: Jongwoo Lim, Soomin Lee, Namkeun Kim; J. Korean Soc. Precis. Eng. 2022;39(9):663-667.
Published online September 1, 2022; DOI: https://doi.org/10.7736/JKSPE.022.078

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The bone compression and the inertia from cochlear fluid or middle ear (ME) ossicles, are generally considered to be important components inducing bone-conducted (BC) hearing. To clarify the bone compression effect on the BC hearing caused by variation of Young’s modulus of skull, two different types of three-dimensional finite-element models were used in this study. The FE models were (1) Isolated cochlea model comprising ME and cochlea containing basilar membrane (BM) and (2) Head model comprising the isolated cochlea structure. The model was validated by comparison of cochlear responses such as BM velocities with those of otosclerosis patients’ clinical data. Additionally, results showed that the bone compression effects on a BC hearing is highly depended on the Young’s modulus of a skull. Also, the bone compression effects could be underestimated at low frequencies in temporal bone experiments, whereas the effects could be overestimated at high frequencies in cadaver experiments.

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Design and Evaluation of Soft Actuators Including Stretchable Conductive Fibers: Hye Won Lee, Yeji Han, Minchae Kang, Ju-Hee Lee, Min-Woo Han; J. Korean Soc. Precis. Eng. 2022;39(4):307-313.
Published online April 1, 2022; DOI: https://doi.org/10.7736/JKSPE.021.113

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In this study, soft actuators comprising conductive fibers, flexible polymers, and shape memory alloys, which can be used as textile products, are introduced. Conductive fibers play an important role because they can be used as sensors in wearable devices. The conductive fiber introduced in this study is a form that can be combined with a polymer, and it comprises a form wrapped around a flexible polymer. When an electric current is applied to the shape memory alloy embedded in the polymer, macroscopic deformation occurs due to phase transformation from the Martensite to the Austenite phase. Conductive fibers used in soft actuators are affected by resistive heat generated by the shape memory alloy and bending deformation of the actuator. Accordingly, changes in the conduction properties of conductive fibers were observed due to bending deformation and temperature changes. We also fabricated soft actuators with different types of polymers and observed the differences. The soft actuator presented in this study is a one-piece combination of a conductor and an actuator using a textile-type conductor, and it is likely to be used in smart clothing applications.

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A Study on the Effect of Soft Wearable Suit Using Elastic Band: Eun Hye Cha, Seong Young Oh, Chul Un Hong, Mi Yu, Tae Kyu Kwon; J. Korean Soc. Precis. Eng. 2022;39(1):59-67.
Published online January 1, 2022; DOI: https://doi.org/10.7736/JKSPE.021.037

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Many of the workers are exposed to work that burdens the musculoskeletal system, and musculoskeletal diseases, such as low back pain, are increasing every year. Various muscle support systems, such as wearable robots, have been developed to prevent musculoskeletal diseases at industrial sites, but the system is bulky. Therefore, the total weight is high, it is inconvenient to wear, and the wearer cannot freely perform the activities when power is not supplied. In this paper, in order to compensate for the shortcomings of the hard-type wearable robot system, a soft-type wearable suit using an elastic band was manufactured so that it is light and portable, as it does not require an actuator. The experiment was conducted to verify the effect of muscle strength assistance through an experiment (Measurement of Maximum Waist Torque and Measurement of the Approximate Dose) on the effect of the soft wearable suit. In addition, by making two different types of elastic bands in the wearable suit, it was possible to classify the more effective types for the waist and lower extremities according to the elasticity by comparing the muscle strength assisting effect according to the elastic band.

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EMG and Usability Assessment of Adjustable Stiffness Passive Waist-Assist Exoskeletons for Construction Workers
Jung Sun Kang, Bo Ra Jeong, Eung-Pyo Hong, Bok Man Lim, Byung June Choi, Youn Baek Lee, Yun Hee Chang
International Journal of Precision Engineering and Manufacturing.2025; 26(1): 227. CrossRef
Development of lifting-assistive passive functional pants for construction works
Jin Zhi Chen, Jeong Eun Yoon, Zi Ying Liu, Sung Kyu Lee, Sumin Helen Koo
Textile Research Journal.2025;[Epub] CrossRef
Effects of the Wearable Assistive Suit on Muscle Activity during Lifting Tasks
Kwang Hee Lee, Chul Un Hong, Mi Yu, Tae Kyu Kwon
Journal of the Korean Society for Precision Engineering.2024; 41(1): 47. CrossRef
Design development and evaluation of arm movement-assistive suits for lifting and movement for industrial workers considering wearability
Jiwon Chung, Jung Eun Yoon, Soah Park, Hyunbin Won, Suhyun Ha, Sumin Helen Koo
International Journal of Industrial Ergonomics.2024; 103: 103616. CrossRef
Enhancing wearability: designing wearable suit platforms for industrial workers
Jiwon Chung, Hyunbin Won, Hannah Lee, Soah Park, Hyewon Ahn, Suhyun Pyeon, Jeong Eun Yoon, Sumin Koo
International Journal of Clothing Science and Technology.2024; 36(3): 526. CrossRef

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Fabrication of Conductive Patterns by Selective Laser Sintering of Silver Nanoparticles-Photopolymer Ink: Gil-Yong Lee, Geo-Sung Lee; J. Korean Soc. Precis. Eng. 2021;38(7):537-547.
Published online July 1, 2021; DOI: https://doi.org/10.7736/JKSPE.021.021

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Recent developments in additive manufacturing (AM) process have led us to fabricate many mechanical and electrical components or devices into complex geometries. Within existing AM processes, laser is widely used as an energy source to selectively sinter particles with a powder bed fusion (PBF) process or cure photopolymers with a vat photopolymerization (VPP) process. This study investigated the applicability of the SLS process for silver nanoparticles (Ag NPs)-photopolymer inks to fabricate micro-scale conductive patterns. With Ag NPs-photopolymer inks prepared with different mixture ratios and pasted on a polyethylene terephthalate (PET) substrate, a pulse width modulation (PWM) signal-controlled 405 nm laser was applied to these inks to selectively sinter and cure the Ag NPs and the photopolymer simultaneously. The final conductive patterns were obtained after a rinse in ethanol to remove un-sintered and un-cured regions of the inks. Microstructures, thickness profiles, pattern width, electrical resistance, and resistivity of the fabricated patterns were investigated by varying the PWM duty and the laser exposure time. Effects of different numbers of scan lines in the pattern and nanoparticle mixture ratios were also investigated. The proposed method is cost effective and easy with fast patterning capabilities. It will leverage practical advances in AM industries.

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Design of Prosthetic Robot Hand and Electromyography-Based Hand Motion Recognition: Ho Myoung Jang, Jung Woo Sohn; J. Korean Soc. Precis. Eng. 2020;37(5):339-345.
Published online May 1, 2020; DOI: https://doi.org/10.7736/JKSPE.019.138

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In this paper, a prosthetic robot hand was designed and fabricated and experimental evaluation of the realization of basic gripping motions was performed. As a first step, a robot finger was designed with same structural configuration of the human hand and the movement of the finger was evaluated via kinematic analysis. Electromyogram (EMG) signals for hand motions were measured using commercial wearable EMG sensors and classification of hand motions was achieved by applying the artificial neural network (ANN) algorithm. After training and testing for three kinds of gripping motions via ANN, it was observed that high classification accuracy can be obtained. A prototype of the proposed robot hand is manufactured through 3D printing and servomotors are included for position control of fingers. It was demonstrated that effective realization of gripping motions of the proposed prosthetic robot hand can be achieved by using EMG measurement and machine learning-based classification under a real-time environment.

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Development of a Caterpillar-Type Walker for the Elderly People
Yeon-Kyun Lee, Chang-Min Yang, Sol Kim, Ji-Yong Jung, Jung-Ja Kim
Applied Sciences.2021; 12(1): 383. CrossRef
Remote Control of Mobile Robot Using Electromyogram-based Hand Gesture Recognition
Daun Lee, Jung Woo Sohn
Transactions of the Korean Society for Noise and Vibration Engineering.2020; 30(5): 497. CrossRef

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Effect of Thermal Conductivity of Coil Insulator Material on the Temperature Variation of High Voltage Motor: Jaehyun Park, Seung Ho Paek, Hyun Woo Lee, Heesung Park; J. Korean Soc. Precis. Eng. 2020;37(5):355-360.
Published online May 1, 2020; DOI: https://doi.org/10.7736/JKSPE.019.119

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It has been an on-going issue to develop a high voltage motor with high capacity and reliability. In this study, we investigated the effective coil insulator materials in terms of thermal conductivity. To quantify the contribution of the coil insulator material, two different motors with and without the cooling structure were numerically studied. Based on the measured thermal conductivity of six different coil insulators, we have achieved the effectiveness of thermal conductivity. Consequently, the high voltage motor can be developed with the proposed effectiveness of thermal conductivity regarding coil insulator materials. Our study of fundamental material characteristics will be beneficial in enhancing thermal management technology of a high voltage motor.

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Improved thermal conductivity of anticorona insulation paint for high-voltage motor application
Xia Zhao, Hui Zhang, Yongxin Sun, Tiandong Zhang
Journal of Materials Science: Materials in Electronics.2023;[Epub] CrossRef

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A Study of the Thermal Effectiveness of Pyrolytic Graphite Sheet in the Transmit Receive Module Housing: Sang Hyeok Ahn, Sung Hwan Yim, Jun Woo Park, Young Eun Ra; J. Korean Soc. Precis. Eng. 2020;37(2):99-106.
Published online February 1, 2020; DOI: https://doi.org/10.7736/JKSPE.019.093

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In this study, pyrolytic graphite was applied to overcome the conventional cooling system. Pyrolytic graphite is an anisotropic material with high thermal conductivity in the X-Y direction and low thermal conductivity in the Z direction. The advantage of high thermal conductivity in the plane direction is applied to improve the performance of the cooling capacity transceiver module housing made of aluminum. In comparison with the housing using the aluminum, the housing applied to the PGS plate shows a higher cooling performance on the average temperature of chips and the temperature variations by 2.79% and 49.98%. The heat dissipation performance was investigated according to the thickness of the PGS and the via the shape. When the factor of thickness in PGS plate was “0.375”, the average temperature of the chip was the lowest, and the temperature variation decreased due to increasing the factor of thickness in the PGS plate. In the case of the via shape, the “separation plate” showed the lowest average temperature of chips and the “plate” showed the lowest temperature variation.

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Hybrid battery thermal management system coupled with paraffin/copper foam composite phase change material
Seunghoon Lee, Hyoseong Lee, Yong Joo Jun, Hoseong Lee
Applied Energy.2024; 353: 122043. CrossRef

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Triple-Conducting Oxide as a Cathode for Solid Oxide Fuel Cells : Review: Taehyun Park; J. Korean Soc. Precis. Eng. 2018;35(12):1141-1146.
Published online December 1, 2018; DOI: https://doi.org/10.7736/KSPE.2018.35.12.1141

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Solid oxide fuel cells (SOFCs) are at a technological level close to commercialization, which could be enabled by new material research. Especially, not only an electrolyte, but also a cathode material becomes very important to further increase electrochemical performance, due to the effort to lower operating temperature of SOFCs to intermediate range (400-600℃) to take advantage of high and low temperature operation. Unfortunately, this trend inevitably results in demand for new cathode materials with high oxygen reduction reaction activity, as well as high mechanical durability. Recently, ceramic materials which conduct oxygen ion, proton, and electron, thereby called ‘triple conducting oxide’ are being highlighted, due to their excellent material properties, to be used for cathodes of SOFCs. This paper reviews the three representative triple-conducting oxides, which were already used and tested in SOFC operating conditions.

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Recent advances in layered Ln2NiO4+δnickelates: fundamentals and prospects of their applications in protonic ceramic fuel and electrolysis cells
Artem P. Tarutin, Julia G. Lyagaeva, Dmitry A. Medvedev, Lei Bi, Aleksey A. Yaremchenko
Journal of Materials Chemistry A.2021; 9(1): 154. CrossRef

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The Development of Foldable Electric Wheelchair with Separable Power Module: Dae Jin Jang, Yong Cheol Kim, Shin Ki Kim, Je Cheong Ryu; J. Korean Soc. Precis. Eng. 2018;35(10):1007-1014.
Published online October 1, 2018; DOI: https://doi.org/10.7736/KSPE.2018.35.10.1007

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This study shows the 4 - Bar linkage design process and static/dynamic stability analysis of a foldable electric wheelchair that can be loaded into a vehicle for long-distance trips. Conventional foldable electric wheelchairs have been developed for indoor use because the safety of the disabled is not secure enough for outdoor use. However, the disabled have generally used foldable electric wheelchairs for outdoor use, potentially putting themselves in a dangerous situation. The body of a foldable electric wheelchair consists of a double 4 - Bar linkage system that shares one link. The architecture of the wheelchair’s four-bar linkage frame was synthesized using four finitely separated design positions. This simple method can design a planar four-bar mechanism through the use of four finitely separated poses (orientation and position). The power driving module includes a battery and controller, and can be separated to load into a car easily. An analysis of the tip-over measurement was performed using ADAMS and LifeMOD during a maneuver on the ground. by force-moment stability metric. Several elements, including the center of gravity position, rotational radius, and acceleration, were evaluated how to affect stability metric.

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A study on the formative usability testing for modular powered wheelchair
Jin Hong Kim, Yu Ri Kim, Mi Hyang Han, Soul Han, Eun hye Jeon, Eun Young Hwang, Jae Won Yang, Seon Yeong Lee, Gangpyo Lee
Disability and Rehabilitation: Assistive Technology.2025; 20(2): 452. CrossRef