Patawee Mesawad

This study presents a low-cost Internet of Things (IoT)-based antenna-measurement system that integrates automated dual-axis positioning, mobile data visualization, antenna-related calculations, and data export within a unified platform. The system employs a NodeMCU ESP8266, Arduino Uno R3, servo-driven θ- and ϕ-axis positioning mechanism, NETPIE IoT communication, and a mobile application, while a FieldFox vector network analyzer is used for RF measurements. Positioning performance was evaluated at angular steps of 4°, 5°, 6°, and 10° under unloaded and antenna-loaded conditions. Across all 16 test conditions, the maximum positioning error did not exceed 0.3°, remaining below the predefined ±1° requirement. The far-field distance and antenna-gain calculation functions were also validated against independently calculated theoretical reference values, with gain differences arising only from two-decimal-place display rounding. Radiation-pattern measurements at 2.4 GHz using dipole and Yagi–Uda antennas demonstrated the expected approximately omnidirectional H-plane response of the dipole and the more directional response of the Yagi–Uda antenna. Comparison with CST simulations and ME1300 reference measurements showed agreement in the principal radiation characteristics, including main-lobe direction and overall pattern behavior. The developed system provides an accessible platform for antenna radiation-pattern measurement, with future development focused on automated RF data acquisition.

This paper presents a systematic numerical investigation of a hybrid plasmonic–photonic Panda-ring antenna with an embedded gold grating, designed to enable efficient dual-mode radiation for optical and terahertz communication systems. The proposed structure integrates high-Q whispering-gallery mode (WGM) confinement in a multi-ring dielectric resonator with plasmonic out-coupling at the metal–dielectric interface, allowing controlled conversion of resonantly stored photonic energy into free-space radiation. The electromagnetic behavior is analyzed through a hierarchical structural evolution, progressing from a linear silicon waveguide to single-ring, add–drop, and Panda-ring resonator configurations. Gold is modeled using a dispersive Drude formulation with complex permittivity to accurately capture frequency-dependent plasmonic response at 1.55 µm. Power redistribution within the resonator system is described using coupled-mode theory, with coupling and loss parameters evaluated consistently from full-wave numerical simulations. Full-wave simulations using OptiFDTD and CST Studio Suite demonstrate that purely photonic resonators exhibit strong WGM confinement but negligible radiation, while plasmonic gratings alone suffer from low efficiency due to the absence of coherent photonic excitation. In contrast, the proposed hybrid Panda-ring antenna achieves stable and directive far-field radiation under WGM excitation, with a realized gain of approximately 8.05 dBi at 193.5 THz. The performance enhancement originates from synergistic hybrid SPP–WGM coupling, establishing a WGM-driven radiation mechanism suitable for Li-Fi and terahertz wireless applications.

This work presents a computational study of a hybrid plasmonic–photonic Panda-ring antenna embedded with a gold grating for dual-mode optical and terahertz (THz) transmission. The proposed structure integrates whispering gallery modes (WGMs) supported by a multi-ring resonator with surface plasmon polariton (SPP) excitation at a metal–dielectric interface, enabling strong near-field confinement and efficient far-field radiation. A systematic structural evolution—from a linear silicon waveguide to single-ring, add-drop, and Panda-ring configurations—is investigated to clarify the role of resonant coupling and power routing. Full-wave simulations using Optiwave FDTD and CST Microwave Studio are employed to analyze electric-field distributions, spectral power intensity, and radiation characteristics. The results demonstrate that the embedded gold grating facilitates effective SPP–WGM hybridization, allowing confined photonic energy to be converted into directional radiation with a peak gain exceeding 5 dBi near 1.52–1.55 µm. The proposed antenna exhibits stable dual-mode operation, making it a promising candidate for Li-Fi transmitters, THz wireless links, and integrated photonic–plasmonic communication systems.

Rapid and reliable detection of pesticide residues in vegetables is essential for food safety and sustainable agriculture. This work presents a four-port closed-loop ring resonator (CLRR) sensor for quantitative detection of carbamate residues in leafy vegetables. Operating through the S₃₁ transmission path, the sensor enhances electric-field coupling and sensing resolution in the high-field region. Four resonance modes were identified at 1.05, 2.10, 3.12, and 4.11 GHz, with the third mode (3.12 GHz) showing the most stable and linear response. Vegetable extracts of Chinese kale and Choy sum were prepared with carbamate concentrations of 0–8% (w/v). Increasing concentration caused a red-shift in resonance frequency corresponding to a reduction in dielectric constant. Regression analysis revealed a strong linear correlation between frequency shift and concentration (R² = 0.9855–0.9988). The CLRR achieved average normalized sensitivities of 6.39% and 6.54% per unit dielectric variation, outperforming most planar and metamaterial sensors. Fabricated on a single-layer FR-4 substrate, the sensor combines high sensitivity, low cost, and excellent repeatability, offering a practical, label-free, non-destructive tool for on-site monitoring of pesticide contamination in leafy vegetables.

Cassava is a critical crop in tropical regions due to its high starch content. Traditional methods of measuring starch content are often laboratory-based, time-consuming, costly, and require specialized equipment and expertise, making them impractical for on-site assessments. This study aims to develop an accurate and efficient method for measuring cassava starch content using a moisture sensor integrated with an Arduino Pro Mini. The proposed device measures moisture content, which inversely correlates with starch levels, providing a rapid and non-destructive estimation of starch content. The prototype was tested on cassava samples from 20 farmers, showing a strong correlation (r=0.985) and R2=0.9711 between sensor readings and actual starch content. The results, compared to the GENIX GX3000 device, demonstrate the prototype's reliability and accuracy in measuring starch content, offering a practical solution for farmers and processing factories.

This research investigates the process of designing, practical implementation, and modification of features in a sectoral antenna for mobile communication technology. The study employs the principles of a magneto-electric dipole and metamaterials to achieve its objectives. The antenna comprises a pair of magneto-electric curved strip dipoles arranged in a cross configuration for feeding. The antenna superstructure is constructed using a metamaterial consisting of three layers of metallic rods and a U-shaped reflector plane. The feeding component is oriented orthogonally to the ground plane at angles of ±45 degrees and is powered by two crossed-shaped strips to achieve dual polarization. Circular polarization can be attained through a three-layer metamaterial, providing control over the electric field’s magnitude and phase. Additionally, the U-shaped reflector plane reflects waves, effectively increasing the sectoral antenna’s beamwidth. The sectoral antenna achieves a peak gain of 15.35 dBi, representing an improvement over the initial gain of 9.8 dBi achieved solely through the use of magneto-electric curved strip dipoles. This proposed methodology can be adapted to enable circular polarization for mobile communication.