Abstract Climacteric fruit respiration generates carbon dioxide (CO2), making its real-time monitoring crucial for optimizing storage and transport conditions, minimizing economic losses and waste. This work demonstrates the application of Wavelength Modulation Spectroscopy (WMS) for the development of a sensor capable of measuring CO2 concentration in real time with high precision and reproducibility. For the technique, a Distributed-Feedback diode laser was used, tuned to the 1572.3 nm CO2 absorption line. The temporal evolution of CO2 concentration released by tomato and banana at different ripening stages was measured. The sensor exhibited a detection limit for CO2 variations ranging from 122 to 488 parts per million (ppm). The results demonstrate the applicability of WMS for monitoring fruit respiration. The normalization technique second harmonic/first harmonic (2f/1f) proved essential for mitigating thermal effects, as the 1f signal corrects for laser power and non-absorption losses, thus enhancing data reliability. Analysis of CO2 evolution curves suggests the potential to study gas diffusion phenomena within fruits, evidenced by the sigmoidal profile. This sensor has potential for future applications in modified atmosphere packaging (MAP) and quality control.
Abstract This paper presents the development and experimental validation of a low-cost Direction of Arrival (DoA) estimation system using Software-Defined Radio (SDR) technology. The system employs an NI USRP B-210 with two printed log-periodic dipole antennas in a coherent configuration, implementing beamforming algorithms through GNU Radio software. Experimental validation was conducted in different environments at 3 GHz across a ±90◦ range. The system maintains accurate DoA estimates with interference levels up to 8 dB below the signal of interest. Performance limitations include front-back ambiguity inherent to two-element arrays and sensitivity to multipath effects. This work demonstrates the feasibility of replacing expensive commercial DoA systems with affordable SDR-based alternatives, with advantages such as easy deployment and reconfigurability.
Abstract As a simulation-based exploratory study, a novel and improved dual-mode resonator is proposed in this paper. By exploiting two asynchronous resonance modes that can be generated within the proposed resonator, such architectures can be utilized to construct dual-band filters. In addition, the new cavity introduces an anti-resonance mode that can be used to create a transmission zero within the rejection band of dual-band filters, thereby enhancing filter selectivity while maintaining a simple inline filter structure. The simulation results demonstrate an improvement in the quality factor and a reduction in the overall resonator size compared to conventional designs, while preserving the characteristic impedance at the two resonance frequencies. Furthermore, the quality factors of the modes and the anti-resonance frequency remain stable as the resonance frequencies vary. Based on this novel resonator, the design of a dual-band filter is presented, starting from the equivalent circuit and coupling configuration to the complete filter synthesis methodology, including the determination of the coupling matrix. A tenth-order dual-band filter is designed to validate the proposed concept. The simulation results indicate that the filter meets the required specifications for both passband widths and center frequencies.
Abstract The article presents a design optimization method for microwave resonators. This method is based on the development of an artificial neural network (ANN) to calculate the physical parameters of resonators used in microwave resonators, which results in resonator characteristics according to the operating frequency requirements of the design. The proposed approach uses a resonator with a T-inverted geometry as the basis for modeling and validating the artificial neural network. The designed resonator is manufactured and measured according to the physical parameters provided by the network. The results obtained from the simulations of the resonator designed by the proposed method and the measurements show good agreement. For the provided examples, the prediction error of the model reaches 2.55%, indicating an accuracy of over 97%, confirming the validity of the proposed approach.
Abstract This work presents a closed-form formulation for analyzing perturbed resonant cavities with metallic walls, implemented using Substrate Integrated Waveguide (SIW) technology. In particular, it focuses on planar SIW filters in which the perturbations consist of grounded metallic vias. Codified in MATLAB, the proposed formulation provides a powerful tool for the design of microwave filters based on these structures. The proposed approach computes the internal electric and magnetic field distributions, scattering parameters, and derived properties such as group delay. Moreover, the code solves the circuits up to 100 times faster than full-wave simulators while using approximately 50% less RAM. The model is validated through comparisons with full-wave simulators as well as by the design, fabrication, and testing of a C-band SIW filter.
Abstract In this work, polynomial regression was used for prediction of the first and second resonance frequencies, first and second cut-off frequencies at -3 dB of planar bandstop filters based on matryoshka geometry, considering the S21 curve and given certain constraints. The results were validated, considering the mean absolute error (MAE) and the mean absolute percentage error (MAPE) in the test data, calculated for each output variable. The higher values observed were 0.023 GHz for MAE and 2.30% for MAPE. Further validation was performed in new independent test data, which also showed good values for MAE and MAPE. A prototype of a filter was fabricated, and the simulated and predicted results agreed with the measured ones.
Abstract This paper presents the design and experimental validation of a compact, single-layer, triple-band Frequency Selective Surface (FSS) based on triple square loops. The proposed structure targets resonant frequencies at 1.56 GHz, 2.45 GHz, and 3.50 GHz, corresponding to the GPS L1, Wi-Fi, and 5G bands, respectively. An equivalent circuit model (ECM) was developed to guide the initial parametric design, reducing reliance on computationally intensive full-wave simulations. The structure was optimized using HFSS and fabricated on a low-cost FR-4 substrate. Simulated and measured results show good agreement, with three well-defined stop bands exhibiting low insertion loss and stable resonant frequencies. Experimental measurements under oblique incidence up to 45° confirm the angular stability of the design for both TE and TM polarizations. Compared to prior works, the proposed FSS offers simpler geometry, lower fabrication complexity, closely spaced resonances with minimal frequency shift under angular variation, and low pass-band insertion losses. These features make the proposed FSS a strong candidate for compact and low-profile solutions in GPS, Wi-Fi, and 5G systems requiring multiband electromagnetic filtering.
Abstract This paper presents an analytical and design-oriented enhancement of the cascaded single-stage distributed amplifier (CSSDA) aimed at improving its gain-bandwidth performance. The proposed approach, referred to as the Enhanced Cascaded Single-Stage Distributed Amplifier (ECSSDA), is based on leaving the input artificial transmission line of the CSSDA open-circuited. This configuration leads to a theoretical 6 dB gain increase at low frequencies due to voltage doubling at the gate of the first stage but also introduces input mismatch and frequency-dependent gain behavior. To overcome these limitations, the transducer gain of the ECSSDA is analytically derived and approximated using Chebyshev polynomials. This approximation can be interpreted as an impedance-shaping technique that stabilizes the frequency response and limits gain ripple up to the cutoff frequency. Circuit-level simulations demonstrate a broadband gain improvement of approximately 7.24 dB and a bandwidth extension of about 3 GHz compared to the conventional CSSDA, while maintaining acceptable matching conditions. Since the proposed method relies on normalized parameters, it can be extended to other transistor technologies and distributed amplifier implementations.
Abstract In the study of Electromagnetic Compatibility (EMC) for electric vehicle motor drive systems, the simulation and prediction of conducted Electromagnetic Interference (EMI) require consideration of uncertainty factors. The application of uncertainty analysis methods within this system can effectively enhance the reliability of simulation model predictions. Due to its enormous computational cost, the commonly used Monte Carlo Method (MCM) is often impractical for engineering applications. This paper introduces two representative high-efficiency uncertainty analysis methods, the Stochastic Collocation Method (SCM) and the Kriging method, into the simulation study of conducted EMI in this system, comparing their performance from multiple perspectives. By comparing simulation results, it can be found that under the premise that the time costs required by the two methods are similar, SCM can better reflect data fluctuations. Additionally, the Mean Equivalent Area Method (MEAM) is employed to evaluate the analysis results. Of these, the SCM evaluation results are above 0.9, while the Kriging method falls below 0.85. In the simulation of this system, SCM has better applicability. This study provides a method support for the EMC optimization design of an electric vehicle motor drive system considering uncertainty in practical engineering applications.
Abstract The increasing demand for bandwidth in modern communication networks has highlighted the need for efficient and dynamic resource allocation. Elastic Optical Networks address this challenge by enabling flexible spectrum and power assignment. This paper proposes an advanced resource allocation technique based on multi-objective optimization (MOO) to jointly optimize spectrum and power, mitigating nonlinear impairments and enhancing network performance. When a connection request arrives at the Call Admission Control, all possible frequency slot demands are generated by combining the requested bit rate with the available modulation formats. The Min Slot Continuity Capacity Loss (MSCL) heuristic selects routes and slot sets to minimize allocation capacity loss for each modulation level. From this process, a matrix of frequency slot combinations is built and subsequently explored by the MOO framework. The proposed method integrates the MSCL heuristic with power assignment to reduce spectrum fragmentation and select optimal power levels, thereby improving the optical signal-to-noise ratio. By jointly considering spectrum positioning, channel powers, amplified spontaneous emission noise, and nonlinear effects, the approach achieves significant performance gains. Simulation results demonstrate that the proposed method outperforms the Power and MSCL (P-MSCL) algorithm, achieving an approximately 11% reduction in blocking probability under a 180 Erlang load in the NSFNET topology with identical parameters.
Abstract The present research proposes a methodology to develop a model to predict Path Loss in a mixed environment comprising urban areas with tree-lined streets. Based on cross-validation and utilizing Artificial Intelligence (AI) and Machine Learning (ML) algorithms that employ various training functions, architectures, and numbers of neurons, the goal is to optimize the model’s performance in predicting Path Loss (PL) in mixed environments. The model is structured in layers, incorporating geolocation, non-line-of-sight loss, urban density, and vegetation coverage to predict PL. Within this model, Bayesian optimization is applied to select the best hyperparameters. Experimental results demonstrate its effectiveness, with a mean Root Mean Square Error (RMSE) per k-folds of 4.91 dB and Standard Deviation (STD) 4.76 dB for more forested areas.
Abstract A novel design of an Ultra-wideband (UWB) antenna based on a grounded coplanar waveguide element, featuring an edge engraved square patch antenna is proposed. This antenna configuration integrates a square patch with carved corners as the primary radiating element, along with coplanar waveguide components and Frequency Selective Surface (FSS) elements. The coplanar waveguide elements and carved corners serve to enhance both impedance matching and radiation directivity in this prototype. To further augment gain, an 8×8-unit cell is positioned beneath the antenna. The FSS component is constructed through a combination of square and circular structures. The optimized dimensions of the proposed antenna measure 40×40×1.6 mm3, utilizing FR4 substrate material. Experimental validation confirms the performance of proposed design, with simulation outcomes closely reiterate measured results. The antenna exhibits resonant characteristics throughout the ultra-wideband frequency range of 1.9-14.4 GHz. The proposed edge-engraved square patch antenna exhibits a fractional bandwidth of 153.3% and a maximum efficiency of 96%, while the incorporation of FSS elements provides an average gain enhancement of 4 dBi and a peak gain of 9.6dBi observed across the UWB range.
Abstract This work investigates the optimization of silicon waveguide crossings using a hybrid GRASP-Simulated Annealing (GRASP-SA) algorithm coupled with two-dimensional finite element method (2D-FEM) analysis. An inverse design approach was adopted to systematically modify geometric parameters and enhance transmission efficiency at the design wavelength of 1.55 μm. Different values of the control parameter μ were evaluated, and the best-performing configuration was selected for further spectral analysis. The optimized structure achieved transmission efficiencies above 97%, corresponding to approximately 0.13 dB insertion loss. A wavelength sweep from 1.50 to 1.60 μm confirmed the stability of the optimized geometry. The results demonstrate that the proposed hybrid metaheuristic framework is an effective alternative for the design of high-performance photonic waveguide crossings.
Abstract This paper introduces a new approach to reconfiguring an antenna’s operating frequencies by switching between an inverted-F antenna (IFA) mode and a loop mode. This frequency agility is achieved by incorporating a switch at the end of the antenna trace, which connects or disconnects the trace from the antenna ground, thereby altering the antenna's resonant behavior depending on the selected mode. To validate the concept, a prototype antenna was fabricated, and the measured results showed strong alignment with simulation predictions. In the IFA mode, the antenna exhibits two resonant frequencies around 1 GHz and 2 GHz, while in the loop mode, it achieves two close resonances approximately at 1.4 GHz and 1.7 GHz. This ability to switch between modes and cover multiple frequency bands makes the proposed design particularly well-suited for LTE-enabled mobile devices that demand wide or multi-band operation.
Abstract A lower cross polarization level in the radiation pattern of microstrip antenna is needed for achieving the pattern and polarization purity. The main source of cross-polar radiation in microstrip antenna is the residual contribution of higher order resonant modes present at the fundamental resonant mode frequency. In this paper, designs of circular microstrip antenna either loaded with ground plane 900 Sectoral slots or shorting posts placed on the patch or the combination of slots and shorting posts, are proposed for the cross-polar level reduction at the fundamental mode. These techniques increase the spacing of TM21 mode frequency with respect to TM11 mode that achieves reduction in the cross-polar levels. Amongst all the techniques presented, design with five shorting posts yields cross-polar reduction by 48 dB in the broadside direction, whereas combination of shorting posts and 900 Sectoral slots achieves 45 dB cross-polar reduction against the circular patch employing the conventional square ground plane. An experimental validation for the simulated results has been carried out that shows a closer agreement.
Abstract This work presents a numerical analysis of a multilayer graphene-based absorber, composed of SiO₂, graphene, and metals (Ag, Au). The device structure is SiO₂/Graphene/SiO₂/metal, each material significantly influencing optical properties. The model, insensitive to the relaxation rate, exhibits high response time, beneficial for high-performance all-optical communication devices, resonators, and perfect absorbers. SiO₂ provides a stable, transparent dielectric base for wave propagation. Various Kubo formula references for graphene's conductivity were examined. Resonances were analyzed using different Ag and Au data sets from Rakic, Johnson, and Palik. The results demonstrate that the interaction of these components is crucial for realistic simulations aligned with experimental data.
Abstract Nonuniform Large Antenna Arrays (NULaA) represent a possible approach for 5G and forthcoming wireless communication technologies. This comprehensive study analysed NULaA geometry, performance benefits, and drawbacks in 5G applications. Compared to uniform arrays, NULaA feature better beamforming, less mutual coupling, and higher spectral efficiency. The uneven spacing of antenna elements allows for more array design flexibility, better sidelobe suppression, spatial resolution, and power efficiency. Linear, circular, planar, fractal, and sparse NULaA geometries were evaluated to determine their suitability for 5G applications. NULaA offer enhanced spatial selectivity, less interference, and tiny designs for urban applications, according to this review. NULaA introduce complex optimisation processes, calibration and maintenance challenges in large deployments, and economical considerations connected to bespoke designs and sophisticated production methods. Current research trends and future directions highlight AI-driven optimisation, new materials, and NULaA' integration with other 5G technologies. Feature Selective Validation (FSV) is applied to selected references with simulated and measured results, yielding Good to Excellent agreements (GDM < 0.32), confirming NULaA's performance superiority. This review sheds light on how NULaA will shape wireless communication and 5G networks.
Abstract This paper proposes a Defected Ground Structure (DGS) hairpin filter based on the Thue Morse sequence for Sband applications. The filter operates between frequencies ranging from 2.15 to 2.37 GHz and is built on a printed circuit board with a copper foil and FR-4 substrate, which has a permittivity of 4.4. The measured insertion losses were 1.79 dB, the measured insertion loss was 1.79 dB, the bandwidth was approximately 220 MHz, and the reflection coefficient reached -25 dB. Although there was a small shift in the response value for return loss between the measured and simulated values, the proposed filter can be applied to frequencies in the S range from 2 to 4 GHz.
This study proposes a wireless power transfer (WPT) system based on inductive coupling for powering implantable medical devices (IMDs). The system operates at 403 MHz within the Medical Implant Communication Service (MICS) band. It consists of two resonators utilizing split-ring loops geometry. The transmitter and receiver feature compact dimensions of $25 ~\text{mm} \times 25 ~\text{mm} \times 1.52 ~\text{mm}$ and $14 ~\text{mm} \times 14 ~\text{mm} \times 1.27 ~\text{mm}$, respectively. These are among the smallest dimensions reported for resonators based on planar split-ring loop geometry. Electromagnetic (EM) simulations were performed to optimize the geometry for maximum efficiency while maintaining reduced dimensions transfer distance. A measured power transfer efficiency (PTE) of 16.58 % is achieved at a transfer distance of $\mathbf{1 2. 0 ~ m m}$. According to numerical analyzes results, the maximum received power, limited by specific absorption rate (SAR) regulations, reaches 105.5 mW at 8 mm and 29.44 mW at 12 mm.
Abstract Triangular trihedral corner reflectors (TTCRs) are widely used passive radar targets for evaluating radar system performance due to their high structural rigidity and predictable backscattering behavior. The Radar Cross Section (RCS) of a TTCR is critical for assessing system characterization parameters and understanding backscatter properties. This paper presents an RCS characterization of three different TTCR sizes under clear weather conditions, specifically considering an airport runway environment. A comprehensive analysis is conducted using both electromagnetic simulations in the 90–100 GHz millimeter-wave range and experimental measurements. Field measurements were carried out at Runway 2 of Kuala Lumpur International Airport using a 93.1 GHz Frequency Modulated Continuous Wave (FMCW) radar system. The study uniquely considers radar incident angles and runway transverse slope effects, contributing valuable insights into the real-world performance of high-frequency radar systems in airfield applications. The simulation models, experimental setup, and observed results are detailed to support future development of radar-based Foreign Object Debris (FOD) detection systems.
