Browsing by Author "Lee, Hee-Jo"

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    A Compact Ultra-Wideband Monocone Antenna with Folded Shorting Wires for Vehicle-to-Everything (V2X) Applications
    (MDPI, 2023) Lee, Martin Wooseop; Abushakra, Feras; Choffin, Zachary; Kim, Sangkil; Lee, Hee-Jo; Jeong, Nathan; University of Alabama Tuscaloosa; Pusan National University; Daegu University
    In this paper, a capacitively-fed, ultra-wideband (UWB), and low-profile monocone antenna is proposed for vehicle-to-everything (V2X) applications. The proposed antenna consists of a monocone design with an inner set of vias. Additionally, an outer ring is added with a small gap from the monocone and shorted with six folded wires of different lengths to extend the operating band. The proposed antenna covers the frequency range from 0.75 GHz to 7.6 GHz and has a 164% fractional bandwidth, with a gain value varying between 2 and 10 dBi. The dimensions of the antenna are 0.37?(L) x 0.37?(L) x 0.067?(L). The antenna was fabricated using a 3D printer with low-cost polylactic acid plastic (PLA) material and then sprayed with aerosol copper nanoparticles. The efficiency was approximately 90% throughout the frequency bands of interest. Finally, the proposed antenna was installed on a vehicle and tested with an OBU (onboard unit) and a RSU (roadside unit) in the field. The results show a longer wireless communication range for V2X applications.
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    Microwave Properties of Coplanar Waveguide-Based PEDOT:PSS Conducting Polymer Line in Ethanol Gas Atmosphere
    (MDPI, 2020) Lee, Hee-Jo; Jeong, Nathan; Choi, Hyang Hee; Daegu University; University of Alabama Tuscaloosa; Yonsei University
    This study aims to investigate the microwave properties of coplanar waveguide (CPW)-based poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) conducting polymer line in an ethanol gas atmosphere, with the frequency range of 0.5-2 GHz. For an ethanol-exposed PEDOT:PSS line (test sample), the transmission coefficient (S-21) decreased immediately; moreover, the microwave effective conductivity (sigma(m/w)) decreased simultaneously, compared with the ethanol-free PEDOT:PSS line (reference sample). The immediate variations in Delta S-21 ( = S-21,S-ethanol - S-21,S-free) and Delta sigma(m/w) ( = sigma(m/w,ethanol) - sigma(m/w,free)) were approximately 10.2 dB and 2.7 x 10(4) S/m, respectively. Furthermore, in the analysis of the circuit model of the PEDOT:PSS line, the characteristic impedance and distributed elements, i.e., resistance (R) and inductance (L) per length, of the test sample increased, compared with the reference sample. However, upon stopping the exposure to ethanol gas, the microwave properties of the test sample instantaneously recovered to those of the reference sample. According to these critical observations, we could confirm that the coplanar waveguide with a PEDOT:PSS line shows a significant difference in the diverse microwave properties, through rapid response to the ethanol gas at room temperature.