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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2024.01.11 17:21

NK2023, Oslo, Norway

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NK2023, Oslo, Norway

Sept 26 - Sept 29, 2023 (Tue. - Fri.), Scandic Holmenkollen Park Hotel


Energy Focusing Single-Layer Metasurface for Powering Small Unmanned Vehicles 

Wonwoo Lee, and Hojin Lee


Abstract

 Metasurfaces, that is artificially engineered two-dimensional planar metamaterials, are attracting significant consideration to achieve various functionalities including negative refractive index, anomalous refraction, and planar lenses owing to their capability in manipulating the phase, amplitude, and polarization of electromagnetic waves. In particular, due to their low profile and ease of fabrication characteristics, metasurface lenses that convert an incident plane wavefront into a spherical wavefront could be respectable candidate to solve the problem of power reception and efficiency degradation by focusing the spreading electromagnetic waves, and have become indispensable elements for planar optical devices, compared to conventional optical devices generally rely on gradual phase accumulation in bulk materials. Especially, phase gradient metasurfaces have been highlighted as a promising candidate for realizing electromagnetic-wave-focusing characteristics by manipulating the wavefront through controlling the spatial phase and transmission profiles of metasurfaces. Herein, we propose a single-layer phase-gradient metasurface lens that is capable of effectively controlling the spatial phase and transmission distribution with low-Q resonance properties, as well as with incident angle independency over a wide operating frequency band. From the experimental results, we confirm that the proposed metasurface exhibits electromagnetic-wave-focusing characteristics at 22.5 GHz and maintains a spatially fixed focal point at 13 mm for incident angles from − 30° to 30°. Further, to validate the metasurface based energy-harvesting applications, a low-power and scaled-down small unmanned vehicle powering experiment is performed with an ionic polymer actuator. Based on the energy-harvesting capability of the proposed metasurface for powering small unmanned devices, we could demonstrate the low power unmanned "bug", and the unmanned actuator moved forward about 26 mm in 25 seconds validating the feasibility of the proposed WPT system for powering small unmanned devices, which can be potentially extended to full-scale, high power, longer range operation.

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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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2019.07.31 12:56

META 2019, Lisbon, Portugal

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META 2019, Lisbon,  Portugal

July 23 - 26, 2019 (Tue. - Fri.), Instituto Superior Tecnico


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Selectively reconfigurable molecularization of terahertz meta-atoms

Hyunseung Jung, Hyunwoo Jo, Wonwoo Lee, Moon Sung Kang, and Hojin Lee


Abstract


  In this study, we propose selectively reconfigurable terahertz meta-molecules by controlling the micro-patterned ion-gel gate structures to change the conductance of graphene bridges between adjacent meta-atoms. Moreover, we experimentally verify that the proposed structures can change the resonance frequency of metamaterial from 1.40, 1.10, to 0.74 THz, by changing the metamaterial unit cell from the individual atom to dimeric and tetrameric molecules, respectively.

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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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