2023.10.05 15:06

PIERS 2023, Prague, Czech

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PIERS 2023, Prague, Czech

July 3 - July 6, 2023 (Mon. - Thur.), Prague Congress Center


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Patch-Type Electromagnetic Wave Focusing Metasurface for Wireless Power Transfer in Bio-Implantable Devices 

Wonwoo LEE, Semin Jo, and Hojin Lee


Abstract


 With the advances in biomedical technologies, convenient, long-term operable, and sustainable implantable devices are required to be used within the human body, including drug delivery, stimulators, sensors, and post-stimulation monitoring. In general, batteries are used as power sources in these implantable devices, but bioimplantable devices using batteries have challenges in limited lifetime, bulky size, and need for replacement that essentially requires surgical operations. In this regard, wireless power transfer systems (WPT) have been employed as alternatives method to eliminate the use of battery and inevitable surgery for replacement. Recently, WPT systems using metasurfaces exhibiting exotic electromagnetic (EM) characteristics were introduced in bioimplantable devices to enhance the efficiency and to reduce the geometrical dimension. Herein, we propose a patch-type metasurface that improves the power transmission to the tissue by reducing the reflection loss of electromagnetic waves at the air–skin interface and forming a focal point at a specific location. The subwavelength-thickness (< λ/10) metasurface is introduced that focuses electromagnetic waves to a desired depth in multilayered biological tissues to enhance the transferred power for implantable devices. The stable focusing performance is demonstrated by confirming the robust focal point and field intensity profiles for varying incident angles and polarization directions with enhanced field of approximately 11.1 dBmV at a depth of 10 mm in in-vitro environment. By applying the patch-type metasurface to an actual wireless power transfer system, transmission coefficient is improved by 6.37 dB at a depth of 10 mm compared with that of a system without the metasurface patch.

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SID Display Week 2023, Los Angeles, USA

May 22 - May 26, 2023 (Mon. - Fri.), Los Angeles Convention Center


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Ultra-high Resolution Full-Color OLEDs Patterned by Photo-Lithography

Ryungyu Lee, Keun-Yeong Choi, Hyukmin Kweon, Borina Ha, Do Hwan Kim, and Hojin Lee


Abstract


   In this paper, we present an ultra-high resolution organic light-emitting diodes (OLEDs) pixels patterned by conventional photo-lithography via imbuing high chemical and physical resistance to commercial light-emitting polymers through the silicon networked orthogonal gel process. Especially, when silicon networked orthogonal polymers gel layers are pattered by reactive ion etch, a in-situ non-volatile etch-blocking layer (EBL) is formed to prevent pattern distortion or damage. This unique feature not only slows the etch rate but also enhances the anisotropy of etch direction, leading to achieve ultra-high resolution multicolor OPSG-based OLED patterns (up to 4,500 pixels per inch) through photolithography. This patterning strategy is expected to provide a novel paradigm toward ultrahigh-resolution OLED microdisplays.


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SID Display Week 2023, Los Angeles, USA

May 22 - May 26, 2023 (Mon. - Fri.), Los Angeles Convention Center


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An AMOLED Pixel Circuit Compensating for Variation of Sub-threshold Swing and Threshold Voltage Based on Double Gate a-IGZO TFTs 

Hyunwoo Kim, Yongchan Kim, and Hojin Lee

Abstract

   In this paper, an AMOLED pixel circuit based on amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs) compensating for variations in sub-threshold swing (SS) and threshold voltage (VTH) of driving TFT is proposed. The proposed pixel circuit is composed of five TFTs and one capacitor. From the simulation results, when the SS and VTH shifts of the driving up to ±10% and ±1 V, the maximum OLED current error can be suppressed to 3.6% and 7.2%, respectively. 

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Metamaterials 2022, Siena, Italy

September 12 - September 17, 2022 (Mon. - Sat.), Siena Univ.


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Trans-Reflective Dual-Mode Terahertz Spatial Light Modulator Using Electrically Tunable Metasurface

Wonwoo Lee, and Hojin Lee


Abstract

  

Terahertz imaging systems have been extensively studied due to its high-resolution and non-destructive characteristics implementing the considerable potential for security inspection, bio-chemical material identification, and real-time imaging technologies. Despite remarkable progresses, conventional terahertz imaging systems require high power source, expensive detector, and complicate and time-consuming systems. In this regard, single-pixel imaging technique has been implemented into the terahertz range to realize compressive and real-time imaging. However, previous researches only allow the transmissive or reflective imaging technique owing to the passive or absorption type spatial light modulators (SLM). In this work, transmissionreflection dual-mode terahertz spatial light modulator is presented using electrically tunable metasurface based on ion-gel gating graphene metasurface. By applying differential driving voltage on the proposed SLM, differential respective object images could be successfully obtained simultaneously both for transmission and reflection mode exhibiting high correspondence with real objects.

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2022.11.11 20:39

IMID 2022, Pusan, Korea

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IMID 2022, Pusan, Korea

August 23 - August 26, 2022 (Tue. - Fri.), Bexco


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Monolithic Circuit Integrated with VOC Sensor Based on a-IGZO TFT

Eseudeo Yun, Yongchan Kim, Hanbin Choi, Do Hwan Kim, and Hojin Lee


Abstract

  

As volatile organic compound (VOCs) gases generated in industrial production lines is harmful to the human body, study on detecting VOCs gases has attracted much interest. For detection of various VOCs, Amorphous oxide semiconductors (AOS) have been highly researched to produce high-sensitivity chemoresistive-type VOCs gas sensors. Especially, amorphous indium gallium zinc oxide (a-IGZO) thin film transistors (TFTs) are considered the most promising candidate for gas sensors, thanks to their high field-effect mobility, low leakage current, good uniformity, and superior electrical stability with the low-temperature process. However, a-IGZObased gas sensors reported so far still remain in an early stage such as for resistor-type sensor or a single TFT. In this talk, we proposed a monolithic sensor circuit with high sensitivity capable of amplifying the sensing signal of the solution-processed a-IGZO sensor TFT. 

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