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.

IMID 2023, Pusan, Korea

August 22 - August 25, 2023 (Tue. - Fri.), Bexco

a-InGaZnO TFT Scan Driver for Extra Period Function with Compensating Depletion-mode 

Jinho Moon, Yongchan Kim, Hyunwoo Kim, and Hojin Lee

Abstract

 Recently, with the development of future technologies that enable high-resolution displays, interest in higher frame rates and larger display areas has increased. However, these displays face issues with limited pixel areas, and external pixel compensation circuits are necessary. Nevertheless, external pixel compensation cannot be properly performed due to a lack of sensing time. To overcome this problem, we propose a scan driver based on a-InGaZnO transistors, which are responsible for controlling the switching TFTs in the pixel circuit. To further improve compensation, we combined a memory function block at the input of the scan driver, which provides extra sensing periods for pixel circuits, thereby improving compensation accuracy. Additionally, we utilized the capacitive coupling effect to enhance the performance of the scan driver and also to improve the depletion-mode operation, which can be caused by oxide TFTs. The proposed scan driver allows for improved signal transfer between the pixel circuit and the scan driver, resulting in better compensation accuracy.

CLEO 2022, San Jose, USA

May 16 - May 20, 2022 (Mon. - Fri.), McEnery Convention Center

CLEO 2019, San Jose, California, USA

May 10 - 15, 2019 (Mon. - Fri.), San Jose Convention Centor

Terahertz Single-Pixel Imaging System with Electrically Tunable Metamaterial Spatial Light Modulator

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

Abstract

  Due to its penetrability and straightness of terahertz wave, terahertz imaging system has been extensively studied for real-time, high-resolution and accurate imaging systems. However, these imaging systems require high power sources or expensive and complex detectors and usually take a long time to acquire a single image. To overcome the limitations mentioned before, a single-pixel imaging system that had been used in optical imaging technique has been introduced into the terahertz range. In particular, through a single-pixel imaging system, it is possible to construct a terahertz imaging system using only a lamp and a bolometer detector instead of telescopic systems consisting of hundreds of terahertz parts, which gives great possibility for commercialization. In this work, we present electrically tunable terahertz spatial light modulator (SLM) based on ion-gel gating graphene metamaterials. From experimental results, we confirmed that the terahertz image could be successfully reconstructed corresponding to 93 % with the real object image at maximum.

IEEE-NEMS 2023, Jeju, Korea

May 14 - May 17, 2023 (Sun. - Wed.), Ramada Plaza Hotel

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

Wonwoo Lee, Semin Jo, and Hojin Lee

Abstract

 Herein, a patch-type metasurface is proposed that improves the power transferred to the skin 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 energy 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 oblique incident angles and polarization directions with enhanced voltage of approximately 11.1 dBmV at a depth of 10 mm in an in-vitro environment. By applying the patch-type metasurface to an actual implemented wireless power transfer system, an improved transmission coefficient of 6.37 dB is realized at a depth of 10 mm compared with that of a system without the metasurface patch.