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.

This work presents a study of the ring resonator circuit, the objective was to develop a microwave sensor that would detect pesticide residues. A closed-ring structure with two transmission lines is presented. It concentrates on the transmission coefficient's resonance frequency response analysis when tested with organic vegetable juice. The results indicated that resonance frequency had changed to a lower frequency as a resultant shift in the electrical permittivity of the test materials and the characterization of the resonance frequency to a narrow band. It was a sensor property that qualifies it for its application as a detection device.

In this study, we present the design and analysis of high-gain InP-based hybrid plasmonic nanoantennas incorporating a SiO 2 -Graphene-Au stacked waveguide. The proposed nanoantenna leverages the superior optical properties of Indium Phosphide (InP), integrated with a hybrid waveguide structure consisting of SiO 2 , graphene, and gold (Au). The inclusion of SiO 2 serves as a low-loss dielectric layer, graphene enhances light-matter interactions, and Au provides strong plasmonic effects. Our simulation results, obtained using CST, demonstrate that the proposed design achieves a significant enhancement in gain and directivity compared to traditional configurations. Specifically, the proposed nanoantenna exhibits a remarkable gain of 13.27 dB at a resonant frequency of 193.45 THz (1550 nm), highlighting its potential for high-performance photonic applications.