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KIEEME 2021, Pyeongchang, Korea

June 30 - July 2, 2021 (Wed. - Fri.), Alpensia


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Electromagnetic Wave Focusing Metasurface based Novel Wireless Power Transfer System for Bio-Implantable Device

Semin Jo, Wonwoo Lee, and Hojin Lee


Abstract


  Implantable devices require miniaturization, stability, and long-term operation characteristics for monitoring and stimulation within the tissue. Generally, batteries have been used in the implantable device for long-term operation ability. However, implantable devices using batteries have limitations such as large size, short lifetime, and periodical replacement surgery. Therefore, wireless power transfer (WPT) system has been reported as alternative method to long-term operation of implantable devices. Recently, WPT systems based on metasurfaces, that exhibit exotic electromagnetic (EM) characteristics with sub-wavelength thickness, were introduced in bioelectronics to improve the efficiency and to reduce the geometrical dimension of WPT system.

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2014 SPIE Optics + Photonics, San Diego, USA

August 17-21, 2014 (Sunday - Thursday), San Diego Convention Center

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<Poster Session : 9160-100>

Anisotropy modeling of polarization dependent terahertz metamaterials

Hyunseung Jung and Hojin Lee

 

Abstract

We propose a novel anisotropy modeling of the polarization dependent meta-atoms at terahertz frequencies. The proposed anisotropic metamaterials are composed of metallic microstructures combined with various numbers of H-shaped meta-atoms. We confirm that the proposed metamaterials successfully realize the unique properties that can modulate the resonance frequency for the specific polarization of an incident wave, while can keep one identical resonance frequency for their orthogonal polarization direction, simultaneously. Moreover, regardless of the number of H-shaped meta-atoms as well as the polarization direction, their bandwidth can be kept identical by coupling effects between adjacent meta-atoms and their excited electric dipole moments.

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2015 MRS fall Meeting, Boston, USA

November 29 - December 4, 2015 (Mon - Fri), John B. Hynes Veterans Memorial Convention Center

 

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<Poster Session : BB3-32>

Photolithography-Adaptive Organic Semiconductors for High-Resolution Flexible Tandem Electronics

Han wool  Park1, Keun-Yeong  Choi2, Hojin  Lee2, Do Hwan  Kim1

 

 

Abstract

Organic electronics has recently attracted a great deal of interest because of its solution-processed potential applications in flexible, wearble, and even stretchable devices. This, however, serves as a trade-off when one tries to implement these processes in assembling practical electronic devices, since the as-deposited films would be fragile to subsequent solution processes. Consequently, conventional photolithography is hardly applicable to solution-processed organic semiconductor layers for getting high-resolution pattern. In this talk, we demonstrate the whole new type of organic materials based on sol-gel chemistry, which is capable of remarkably showing chemical and mechanical stability during photolithography process. The critical step in a sol-gel reaction is the formation of a highly cross-linked network out of molecular precursors through hydrolysis and condensation reactions. By carefully manipulating this step, we could prepare self-assembled structures of either quasi-3D random or ladder characteristics. The resulting structures yielded films that are highly tolerant against harsh external stimuli. Moreover, the peculiar topology of organometallic gel network containing with molecular pores could be successfully utilized as a template to form a heterogeneous interpenetrated network (HIPN) with functional electronic organic units. As a result, we could achieve micron scaled patterns of organic semiconductor through the standard photolithography. Based on electrical properties of thin-film transistors with patterned organic semiconductor layers, we successfully designed and demonstrated a CMOS inverter circuit with micro-patterned n- and p-type channels based orthogonal organic semiconductor gels through sequential solution processes.

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SPIE Photonics West 2020, San Francisco, USA

February 1 - 6, 2020 (Sun. - Thur.), Moscone Centor


Tandem structured 3-color micro-polymer light-emitting diodes (μ-PLEDs)

Keun-Yeong Choi, Han Wool Park, Do Hwan kim, and Hojin Lee




근영_SPIE.jpg





Abstract


  In this study, we proposed a tandem structured 3-color micro-patterned polymer light-emitting diodes (μ-PLEDs) for super high-resolution organic light-emitting diode (OLED) micro displays. The proposed 3-color polymer light-emitting diodes consisted of red, green, and blue colored polymers patterned down to 20 μm. For the tandem structure, we adopted the recently developed sol-gel process to obtain the orthogonality of organic semiconductor against the solvents and chemicals so that we could apply the standard photolithography and dry-etch process to achieve micron-size patterns of light-emitting polymers. Experimental results showed that we could achieve the 3 distinct color emissions from our tandem PLEDs fabricated by the standard process, the which was confirmed by EL spectrum and CIE chromaticity diagram.

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SPIE Photonics West 2020, San Francisco, USA

February 1 - 6, 2020 (Sun. - Thur.), Moscone Centor


Wireless-Powered VOC Sensor based on Wi-Fi Energy-Harvesting Metamaterial with i-TPU

Heejoo Park, Wonwoo Lee, Hyunseung Jung, So Young Kim, Do Hwan Kim, and Hojin Lee



희주_SPIE.jpg




Abstract


  In this paper, we propose a wireless-powered VOC sensor system based on energy-harvesting metamaterial combined with ionic thermoplastic polyurethane (i-TPU) channel. The sensor consists of the SRR, rectifier circuit to harvest the RF energy by converting electromagnetic energy into DC voltage, and i-TPU channel to detect VOC with the variation of resistance. For the practical wireless sensing system, we utilized widespread and easily accessible commercial 2.4 GHz Wi-Fi source as external electromagnetic wave energy, and the energy-harvesting metamaterial was designed and optimized to resonate at 2.4 GHz. When i-TPU was exposed to acetone gas as target gas, the diffusivity of ionic liquid (IL) increases leading to decrease in resistance of i-TPU that can be identified with the differential harvested energy induced from variation for resonance property. As a result, according to variation of energy-harvesting rate, the proposed sensor could provide the highly sensitive and ultra-stable wireless VOC sensor system without bulky and complicated measurement system offering great accessibility and simplicity for the sensor systems. In addition, it is expected that the proposed system can be applied to not only for VOC sensors but also for dynamic environmental sensing systems.

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