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KIEEME 2020, Pyeongchang, Korea

July 8 - 10, 2020 (Wed. - Fri.), Phoenix Park

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Metamaterial based Wireless Power Transfer System for Neuro Stimulator

Semin Jo, Wonwoo Lee, and Hojin Lee


Abstract 


  

Bioelectronic devices require miniaturization, stability, and long-term operation characteristics for sustainable monitoring and stimulation within human body. In this regard, batteries have been widely used for the implantable device due to the long-term operation ability, but the battery working based implantable devices have some challenges in bulky size, limited lifetime, and need for replacement that essentially requires surgical method. Therefore, wireless power transfer (WPT) have been attracted significant attention as the alternative approach to enable the long-term operation of bioelectronic devices, and WPT based charging system for the implantable bioelectronic devices have been reported using near-field coil-pair coupling methods. Despite the satisfied charging capacity, however, the miniaturization of the WPT system is remained as a critical problem since the efficiency and power transfer depth strongly depends on the dimensions of coils. Recently, metasurface, that exhibit exotic electromagnetic (EM) characteristics with sub-wavelength thickness, based WPT system was introduced in Bioelectronics to enhance the efficiency and to reduce the geometrical dimension of WPT system. In this work, we propose a novel WPT method for biomedical implantable device using EM focusing metasurface at 5.8 GHz. The proposed metasurface has dimensions of length (l) = 49 mm, width (w) = 49 mm size, and thickness (t) = 4.69 mm which is much smaller than the operating wavelength (<l/10). The proposed metasurface consists of the 7 x 7 array unit cells with various shapes and sizes that shows gradient phase distribution to control the phase front of the transmit EM wave. Also, the proposed metasurface is designed to have 4 different layers to realize full 2p phase coverage for focusing the EM wave at specific depth in biological tissue. To confirm the EM wave focusing characteristics, the electric and magnetic field distribution of transmit field at the focal point was analyzed, and the proposed metasurface could successfully form a focal point at 4 mm depth of the biological tissue as desired. Furthermore, the proposed WPT enhanced the EM waves propagation efficiency from 16 % to 23 % into biological tissue by reducing the reflection loss at the air-tissue interface.

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2018.09.07 13:48

2018 iMiD, Busan, Korea

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2018 iMiD, Busan, Korea

August 28 - 31, 2017 (Tue. - Fri.), Exhibition Center I, BEXCO 



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Coplanar a-InGaZnO Thin Film Transistors with Photo-Patterned Ionic-Polymer Gate Dielectric

Dayoon Lee, Yongchan Kim, and Hojin Lee

 

 Abstract

Currently electrolyte-gated thin-film transistors (TFTs) have been actively studied due to their advantages of high-density carrier accumulation in the channel, ultra-low operation voltage, and low-temperature process. For patterning the electrolyte to be used as a gate dielectric, there have been many different approaches reported so far, such as ‘cut and stick’ method, aerosol printing process, or using additional mold to isolate the ionic liquid. However, most of previous methods have challenges on realizing micron-sized fine patterns. In this paper, we adopted photo-patternable ionic-polymer as a gate dielectric for coplanar TFT structures where the gate, source, and drain electrodes deposited by single lift-off process. After electrodes and a-InGaZnO active layer was patterned in sequence, photo-patternable ionic polymer dielectric was patterned using photo cross-linking reactions to UV light. The measured transfer characteristics of the fabricated TFTs are shown in Fig. 1. According to measurement results, we confirmed the high field-effect mobility (~4.36 cm2/V·s), high on-off ratio (~106), and good sub-threshold swing (~108 mV/decade) could be achieved at drain voltage of 1V.

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2016 MRS fall Meeting, Boston, USA

November 27 - December 2, 2016 (Mon - Fri), John B. Hynes Veterans Memorial Convention Center

 

 

<Poster Session : BM4-16.12>

High-Speed Electroactive Polymer Actuator Engineered by Microstructured Ion Channel for Artificial Muscle 

Eunah Heo, Sangsik Park, Yongchan Kim, So Young Kim, Do Hwan Kim, and Hojin Lee

 

 MRS 김용찬.jpg

 

 

Abstract

Creating artificial muscle that emulates the capability of human muscle has been a big challenge in stretchable haptic research. In particular, ionic electroactive polymer (i-EAP) actuator has been regarded as a promising candidate for mimicking human muscle due to low operational voltage and mechanical flexibility. Artificial muscles by i-EAP actuators, however, suffer from keeping displacement and stability consistent in high operation frequencies, which comes from slow ion migration into active channel. In this manner, engineering of an optimal ion transport in the ionic films as well as mechanical properties of actuators is strongly required to allow fast actuation under electrical stimuli in the solid-state.

In this talk, we describe an unprecedented high-speed i-EAP actuator by engineering microstructure of ion channel at the interface of ionic elastomer and flexible conducting polymer electrode, Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS). To this end, the PEDOT:PSS electrodes are formed onto both sides of ionic elastomer with an optimal content of ions using well-controlled spray-coating method. The actuator implemented by us was successfully operated with a large displacement up to 4mm (strain=0.55%) at an operating frequency of 0.1Hz under an applied voltage of 1.5V. Further, the actuator shows high-speed response under the bending strain of 0.15% and the displacement of 0.92mm even at frequency of 30Hz, which is equivalent to 100 folds improvement compared to the values reported in the literature. This result indicates that controlling an interpenetration depth of PEDOT:PSS chains into the ionic elastomer not only decreases an internal resistance between two electrodes, but also forms more effective and microstructured ion conducting channel, thereby leading to larger displacement and faster response of actuators even under low voltage bias.

We believe that high-speed i-EAP actuator demonstrated by us will be an effective way to implement human-interactive smart haptics capable of recognizing the human-environment interface and a novel engineering design for smart artificial muscle capable of physiologically actuating under electrical stimuli. 

 

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KIEES 2020, Jeju Island, Korea

August 19 - 22, 2020 (Wed. - Sat.), Ramada Plaza Jeju


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Wi-Fi Energy-Harvesting Metamaterial and Ionic Polymer Based Wireless VOCs Sensor System

Wonwoo Lee, Heejoo Park, Junho Kim, Sung-Min Park, and Hojin Lee


Abstract


  Metamaterials have attracted considerable attention as new sensing platform having great sensing capability of high sensitivity, rapid sensing response, and non-destructive detection. However, conventional metamaterial based sensor systems require expensive and complicated measurement system that limits real-time application. In this paper, wireless-powered volatile organic compounds (VOCs) sensor is presented by combining energy-harvesting metamaterial (EH-MM) as wireless sensing platform and ionic thermoplastic polyurethane (i-TPU) electrolyte as a VOCs sensing material. Especially, to accomplish the practical wireless-powered sensing system, proposed EH-MM based sensor is designed to operate by harvesting the widespread commercial 2.4 GHz Wi-Fi source.

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2016 APCCAS, Jeju, Republic of Korea

October 25 - 28, 2016 (Tue - Fri), Ramada Plaza Jeju Hotel

 

 

<Special Session : Display Driver Interface Circuits>

Design of Low-Dropout Regulator Using a-InGaZnO Thin-Film Transistors

Yongchan KimHojin Lee

 

 APCCAS 김용찬.jpg

 

 

 

Abstract

In this paper, we presented a low-dropout (LDO) regulator composed with amorphous indium-gallium-zinc-oxide thin-film transistors (a-InGaZnO TFTs) for display driving systems. Through extensive simulation works, we confirmed that the proposed LDO regulator successfully could control the output voltage levels to follow the reference input voltages, and the output voltage ripple could be suppressed below 48mV when input reference voltage was changed from 14V to 15V with 100mV fluctuation.

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