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SPIE Photonics West 2020, San Francisco, USA

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


Polarization Independent Flat Metasurface Lens for Millimeter-Wave Beam Focusing

Wonwoo Lee, Semin Jo, Kanghyeok Lee, Hong Soo Park, Junhyuk Yang, Changkun Park, Sun K. Hong and Hojin Lee


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Abstract


  In this paper, we propose a new polarization independent ultra-thin (<λ/10) single-layer metasurface lens to focus incident electromagnetic waves at millimeter-wave frequency. The proposed metasurface focusing lens consists of the 13 x 13 array supercells with different shapes and sizes representing differential gradient phase at 33GHz range. In addition, each supercell could cover enough phase range to make a focal point at desired distance by arranging the discrete phase distribution for each supercell of the metasurface and controlling the phase of the scattering electromagnetic waves. To confirm the focusing characteristics, the power density distribution of scattering field at the focal plane was analyzed, and the maximum power density was formed at the focal length of 50mm which is half-wavelength distance both on x-z plane and y-z plane for incident plane wave. Base on the experimental results, we could confirm that the wavefront and electromagnetic wave could be successfully manipulated and focused. We expect that the proposed ultrathin and high-efficiency metasurface lens can be widely used in various millimeter-wave applications.

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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



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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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KIEEME 2020, Pyeongchang, Korea

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


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

Hojin Lee (Invited Talk)


Abstract 


  Metamaterials, that possesses powerful ability to manipulate the electromagnetic (EM) waves exhibiting the unprecedented EM properties, 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 compound (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. When i-TPU electrolyte was exposed to VOCs, diffusivity of ionic liquid increases leading to decrease in resistance of i-TPU electrolyte that can be identified with differential harvested energy level induced from resonance property variation of the EH-MM. By analyzing variation of the energy-harvesting rate as output DC voltage levels, proposed sensor system could provide sensitive and accurate VOCs sensing results without complicated analyzing system. Also, using multi-analyte sensing capability of i-TPU electrolyte, the EH-MM sensor could classify differential VOCs including toluene, hexane, ethanol, and acetone that causes harmful effects for human by simply displaying the differential output voltage levels. Furthermore, the EH-MM sensor shows fast responses (< 1 sec), wide range of VOCs concentration (> 1000 ppm) and high stability (> 1 month) in ambient condition. As a result, a novel method for designing the simple and portable VOCs sensing system is presented offering the satisfactory sensing abilities with easily accessible sensing platform. It is expected that the proposed sensor system is expected to offer new route to real-time and wireless sensor systems which make it possible for the proposed sensor to be widely used in the various sensing applications.

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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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KIEES 2020, Jeju Island, Korea

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


원우_학회.png


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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