This paper describes the design methodology of a compact multiband microstrip patch antenna intended for next-generation wireless communication applications. The proposed antenna operates over seven distinct frequency bands: 1.25-1.32 GHz, 2.30-2.44 GHz, 2.50-2.75 GHz, 2.92-3.25 GHz, 3.40-3.65 GHz, 3.70-4.23 GHz, and 4.70-6.0 GHz. These operating bands support a wide range of wireless services, including LTE, 5G communications, Wi-MAX, ISM applications, radar systems, and broadband wireless communications. Multiband performance is achieved through the incorporation of three strategically placed slits in the radiating patch along with a square split-ring resonator (SSRR). By adjusting the dimensions of the slits and the position of the SSRR, the operating frequency bands can be effectively tuned. The proposed antenna occupies a compact footprint of 40 × 40 mm² and consists of a radiating patch, a partial ground plane, and an SSRR structure. Simulation results demonstrate resonant frequencies at 1.3, 2.38, 2.66, 3.0, 3.5, 4.2, 4.9, and 5.7 GHz. Owing to its compact size, multiband capability, and simple structure, the proposed antenna offers advantages in terms of reduced cost, lower system complexity, and miniaturization, making it suitable for modern wireless communication systems.

Due to the high electrical conductivity, relative permittivity, and magnetic permeability of seawater, the propagation behavior of electromagnetic fields differs significantly from that in air. The conductive nature of seawater causes strong eddy current loss and magnetic field attenuation, thereby reducing the effective coupling coefficient and resulting in frequency detuning between the transmitter and receiver coils. Moreover, the marine environment introduces parasitic impedance paths and additional energy dissipation due to the conductive medium, which further decreases transmission efficiency. These unique electromagnetic characteristics make the design and optimization of wireless power transfer (WPT) systems in seawater more complex and challenging than in air, motivating this study to develop and analyze a dual-receiver WPT architecture that improves midrange transmission efficiency under underwater conditions. To address this issue, a single-transmitter dual-receiver (1TX-2RX) WPT system operating in the 300-550 kHz frequency range is designed and implemented. Experimental results demonstrate that, under midrange transmission in seawater, the efficiency of the proposed 2RX architecture improves markedly from 12% in the 1RX system to 25%, while maintaining stable output performance under various receiver coil misalignment conditions. In addition, compared with operation in air, the optimal operating frequency of the 2RX system in seawater shifts leftward from approximately 460 kHz to 410 kHz. To better characterize the impact of seawater on transmission performance, complex impedance and mutual inductance parameters are incorporated into the conventional circuit model, enabling effective representation of the additional losses and coupling attenuation induced by the conductive medium. The predicted load voltage is consistent largely with the experimental measurements, validating the accuracy and applicability of the proposed modeling approach. Overall, this study not only verifies experimentally the feasibility of improving midrange transmission efficiency through a dual-receiver architecture but also establishes theoretically a circuit modeling method suited better for seawater environments, providing useful insights for the design and optimization of marine WPT systems.

This paper introduces an ultra-miniaturized, reconfigurable antenna for wireless communication applications. The suggested reconfigurable antenna is fabricated on an FR4-epoxy substrate (20 × 20 × 1.6 mm³, ε!= 4.4), and it provides a miniature factor 79% which is an outstanding value. Frequency reconfiguration can be achieved using two PIN diodes, which make the proposed antenna capable of working in various frequencies, including 5G/6G, WLAN, HiperLAN, V2X, WiMAX, Wi-Fi 6E/7/8, and S/C/X/Ku bands. With the analysis performed by CST Studio Suite, the proposed antenna shows outstanding quantitative results without any sacrifice in its size, cost, or complexity. In this context, the antenna shows dual-band impedance bandwidths of 1.36 GHz and 6.4 GHz. Additionally, it has 2 dBi of peak gain and 79% high radiation efficiency.

This paper presents a single-port concentric multi-ring circular monopole in which each ring is a separate characteristic-mode resonator, and cross spokes force the ring currents in phase so that the individual ring resonances merge into one continuous impedance band. This ring-per-mode partitioning distinguishes the design from single-mode monopoles, and characteristic mode analysis (CMA) is used to place and order the modes rather than explain a finished geometry. The radiator occupies 0.27λ₀ × 0.39λ₀ on a 33 × 23 × 0.8 mm³ RT/Duroid 5880 substrate (ε_r = 2.2, tan δ = 0.0009), a low-permittivity laminate that resists miniaturisation. A central disc of radius 5.5 mm and three concentric rings of mean radii 6.27, 7.79, and 10.14 mm are excited by a 50 Ω microstrip line whose 2.465 mm width follows directly from Hammerstad synthesis, and a triangular tapered partial ground of height 10.66 mm - one quarter-wavelength at band centre completes the match. Closed-form ring resonances of 3.72, 4.84 and 6.02 GHz agree with the modal spectrum and with the measured lower resonance at 3.65 GHz to within 1.9%. The measured impedance band spans 3.50-6.15 GHz, a fractional bandwidth of 54.9% centered at 4.83 GHz, and covers the 5G NR n77, n78 and n79 bands together with the 5.5 GHz WLAN band in one continuous match. A physically partitioned equivalent circuit, one series-RLC branch per ring with every branch resonance fixed to its closed-form value, reproduces the full-wave reflection response with a 0.72 dB RMS error. The design gives a compact, single-layer, single-feed route to full sub-6 GHz coverage with an analysis chain that ties every dimension to a resonant mechanism.

This paper proposes and investigates a dual-band four-element MIMO antenna structure. The antenna operates across several frequency bands, including U6G, 5G n256, 4G LTE, WiMAX, and WLAN 5G, while maintaining its intended functionality. The proposed CPW-fed antenna adopts slot radiators and occupies a compact volume of 103.72 × 103.72 × 0.8 mm³. A trident-shaped branch enhances bandwidth, and the antenna's dual-band performance comes from etching a semi-elliptical ring slot. Experimental results show that the antenna provides two impedance bandwidths of 2200 MHz (1.81-4.01 GHz) and 2380 MHz (4.85-7.23 GHz). These bandwidths fully cover the required operating ranges, including WLAN 5G (5.15-5.35 GHz and 5.725-5.825 GHz), U6G (6.425-7.125 GHz), 5G n256 (1.98-2.01 GHz and 2.17-2.2 GHz), 4G LTE (2.3-2.39 GHz and 2.555-2.655 GHz) and WiMAX (3.3-3.8 GHz). Furthermore, the proposed antenna achieves a peak gain of 4.08 dB at 2.5 GHz and 6.42 dB at 6 GHz. The ECC remains less than 0.003, and the DG exceeds 9.99, indicating superior diversity performance. These findings indicate that the proposed dual-band four-element MIMO antenna is highly suitable for use in 5G sub-6 GHz and U6G communication systems.

Flux reversal permanent magnet machine (FRPMM), owing to their high power density and excellent low-speed high-torque capability, is considered promising for low-speed direct-drive hydropower generation systems. However, the vibration and noise caused by radial electromagnetic force hinder the development of the FRPMM. A novel FRPMM with a permanent magnet (PM) chamfer on the stator is proposed. First, the radial force density, average torque, and torque ripple are taken as optimization objectives. The multi-objective genetic algorithm (MOGA) is used to optimize the machine. Next, the space-time characteristics of air-gap flux density and radial force density are obtained based on finite-element simulation. The modal analysis and harmonic response analysis of the stator are carried out. The results show that the radial force density of the proposed FRPMM is significantly reduced, and the machine's vibration characteristics are optimized.

This paper presents power divider that combines broadside coupling and coplanar waveguides. This structure enables the tuning of the coupling coefficient by changing the microstrip line width on the top and bottom surfaces as well as the slot spacing between the line and the ground plane. This developed power divider can be easily fabricated with a single-layer structure, without requiring complex multilayer manufacturing of a printed circuit board. To verify the effectiveness of this proposed structure, simulation and measurement were performed at a center frequency of 2 GHz. The measurement results of the implemented power divider agreed well with the simulation results.

Full-wave electromagnetic simulation is computationally intensive during parametric antenna design and optimization. This study proposes a Support Vector Regression (SVR) based framework to predict the reflection coefficient of an Artificial Magnetic Conductor-Perfect Electric Conductor (AMC-PEC) metasurface antenna array in the X-band. The antenna comprises circular AMC cells and rectangular/grid PEC radiating elements arranged in a spatially optimized architecture. A dataset of 500 samples was generated using openEMS full-wave simulations, with antenna geometrical parameters as inputs and S₁₁ as the target response. An SVR model with a radial basis function kernel was trained and validated against simulations and measurements of a fabricated multilayer prototype. The predicted, simulated, and measured resonances occurred at approximately 9.8, 9.9, and 10.0 GHz, respectively, while measurements confirmed broadband impedance matching from 9.04 to 11.0 GHz. The SVR achieved a Mean Absolute Error (MAE) of 0.20 dB, Root Mean Square Error (RMSE) of 0.26 dB, and coefficient of determination (R²) of 0.998, outperforming Artificial Neural Network (ANN) and Gaussian Process Regression (GPR) models trained on the same dataset. Predictions were generated in under one second, providing a speedup of approximately three orders of magnitude over full-wave simulation. The results demonstrate accurate and computationally efficient prediction for antenna design and optimization.

This paper proposes a compact, independently fed hybrid antenna array featuring reconfigurable frequency and radiation patterns for adaptive wireless applications, employing PIN diodes. The hybrid arrangement incorporates independently driven elements with diode-controlled current pathways to enable concurrent spectral and spatial tuning within a single structure. Frequency agility is achieved through PIN-diode switching configurations; five representative states are presented, due to the similarity among the other responses, with resonant frequencies derived from the minima of the S-parameters. Multiband operation is demonstrated in simulation from 3.8 to 6.49 GHz and in measurement from 4.18 to 6.56 GHz; the mutual coupling suppression is achieved by an independently fed architecture, maintaining inter-port isolation better than 18-20 dB throughout the operating band, which signifies effective suppression of mutual coupling within the operating band. Radiation pattern reconfigurability is achieved via PIN diode switching, yielding directional radiation-pattern reconfigurability through electronic switching via controlled redistribution of surface current. The design remains compact at 40 × 44 mm² and uses only four PIN diodes, reducing switching complexity while preserving stable gain and radiation performance. Measured results show good agreement with simulations, validating the design's effectiveness. The proposed antenna provides a compact and low-complexity solution for adaptive sub-6 GHz wireless communication systems requiring simultaneous frequency and radiation-pattern reconfigurability.

This paper presents a compact 39 × 39 mm² quad-port ultra-wideband (UWB) MIMO antenna with dual band-notches and enhanced inter-element isolation. Four orthogonally arranged microstrip-fed circular radiators are employed to reduce mutual coupling, while two U-shaped slots etched on each radiator suppress interference from the C-band (3.1-4.3 GHz) and Wireless LAN (5.2-5.6 GHz) bands. We investigate the antenna using Characteristic Mode Analysis through modal significance and modal current distributions. The proposed diversity antenna is evaluated using envelope correlation coefficient, diversity gain, total active reflection coefficient, channel capacity loss, multiplexing efficiency, and simulated group delay. The antenna achieves an impedance spectrum covering 2.9-10.6 GHz, radiation efficiency of 90%, gain of 5.2 dBi, ECC < 0.02, and isolation of -20 dB. The results demonstrate that the proposed antenna provides an effective combination of small size and high isolation, making it viable for UWB applications.

Exosomal surface proteins are emerging as minimally invasive liquid-biopsy biomarkers for breast cancer, yet their trace-level abundance poses challenges for biosensor sensitivity and multiplexing capacity, and conventional assays miss the substantial cargo in vesicles. Here, we report a mass-amplification-enhanced multiplexed SPR platform coupling antibody-directed magnetic enrichment with a phase-interrogated Ag/ZnSe waveguide chip for simultaneous detection of EpCAM, VEGF, and CD63, with a proof-of-concept extension to the immune-activation marker IFN-γ. A bimetallic Zr/Ce-MOF@Fe₃O₄ nanocomposite (confirmed by SEM-EDS) provided high refractive-index mass loading and magnetic separability, interfaced with a multi-channel Ag/ZnSe/APTES/GO chip (anti-EpCAM, anti-VEGF, anti-CD63) via a phase-polarization-modulation SPR system and PDMS microfluidics. MOF amplification improved the LOD for EpCAM from 0.86 to 0.07 pg mL^-1 (12.3-fold) and for VEGF from 2.45 to 0.21 pg mL^-1 (11.7-fold). Intact exosomes gave antibody-specific responses on anti-EpCAM (6.22°), anti-VEGF (3.09°), and anti-CD63 (9.54°), with signal-to-background ratios up to 106.0 and cross-reactivity below 0.4°; in matched healthy and patient serum, MOF-amplified responses were consistently higher in patients across all three markers (6.5-fold EpCAM, 6.2-fold VEGF, 8-fold CD63), with comparable discrimination extended to urine on the CD63 channel. Lysates analyzed on anti-EpCAM channels showed negligible healthy signals (0.29° without MOF, 1.63° with MOF) versus a patient increase from 5.80° to 18.4° (3.17-fold), corresponding to an apparent 41 pg mL^-1 total solubilized EV-associated EpCAM. As proof of concept for immune-status phenotyping, CD63-captured exosomes from a patient with clinical suspicion of immune activation showed a 12-fold higher IFN-γ signal than healthy samples (9-fold with MOF), with Langmuir kinetics indicating higher apparent binding affinity in the patient. Nanoparticle tracking confirmed exosome populations within the characteristic 30-150 nm range (mean 66.5-92.8 nm), and inter-chip/inter-channel reproducibility were 2.72% and 0.64% CV. As a complementary label-free imaging readout, the EV/MOF workflow was also implemented on a differential guided-mode resonance (dGMR) platform, where intact whole-EV binding produced MOF-amplified resonance-stripe pixel shifts without vesicle lysis; patient-derived EVs showed ~9.4-fold enhancement (vs 6.86-fold by phase-interrogated SPR), and healthy-derived EVs showed $\sim10.8$-fold enhancement, pushing the dGMR whole-EV response into a near-order-of-magnitude amplification regime. In a comparative discussion, sandwich SERS detection of EV-associated IFN-γ in CAR-T therapy further demonstrated that molecular fingerprint-based SERS can resolve specific immune markers, complementing the quantitative strengths of SPR and extending the platform toward immune-status monitoring. This platform demonstrates proof-of-concept feasibility for multiplexed exosomal marker detection directly in crude clinical matrices, with larger cohort studies required to establish diagnostic utility.

This study proposes a triple-band high-efficiency electromagnetic absorber constructed using a lossy resonant layer, an air spacer, and a bandpass frequency-selective surface (FSS) boundary. The lossy layer adopts bent multi-section metal resonators loaded with two types of lumped resistors to generate a multi-band resonant loss, while the underlying slot-type bandpass FSS provides frequency-dependent boundary responses: it serves as a reflective boundary at the lower two absorption bands and couples with the top-layer resonance at the higher band, while retaining out-of-band transmission. The simulated results reveal effective absorption (absorptivity > 80%) at 5.2-6.1 GHz, 14.5-16.0 GHz, and 20.8-22.2 GHz, with peak absorptivities of 0.92, 1.00, and 0.97, respectively. Thanks to the centrosymmetric layout, the absorber is insensitive to TE/TM polarizations and maintains stable absorption up to 30° under oblique incidence. The operating frequencies can be flexibly tuned the via slot dimensions, metal line size, and resistance values. Due to its low profile and easy processing, the proposed design is suitable for stealth, radar cross-section reduction, and electromagnetic interference mitigation.

This paper presents a compact dual-band two-element multiple-input multiple-output (MIMO) antenna for terminal-device wireless communication. The antenna element is based on a rectangular patch, and miniaturization is achieved by combining slot loading with a partial ground plane. A complementary split-ring resonator (CSRR) introduces an additional resonant mode, enabling dual-band operation. A 2 × 1 MIMO configuration is formed by arranging two elements in parallel. To reduce mutual coupling, a four-stage T-shaped hybrid-slot decoupling structure with E-, L-, window-, and spiral-shaped slots is introduced on a common ground plane, effectively suppressing surface current coupling. The dimension of the antenna is 0.45λ₀ × 0.31λ₀ × 0.019λ₀. The antenna operates over 3.17-4.37 GHz and 4.76-5.02 GHz, with a port isolation better than -20 dB over both bands, reaching -34.58 dB at 3.52 GHz and -22.79 dB at 4.87 GHz. The envelope correlation coefficient (ECC) is below 0.005, and the diversity gain (DG) is approximately 10 dB. The measured results agree with the simulated ones. These results indicate that the proposed antenna achieves a good balance between compact size and high isolation, making it suitable for size-constrained terminal MIMO applications.

To address speed-tracking degradation and torsional vibration caused by flexible-shaft coupling and load disturbances in PMSM dual-inertia systems, this paper proposes a high-order nonsingular fast integral terminal sliding mode control (HONFITSMC) method integrated with dual finite-time extended sliding mode disturbance observers (FTESMDOs). First, a third-order load-side dynamic model is derived to explicitly describe the effects of shaft torque and load disturbance. Next, the HONFITSMC method is developed using an inner integral sliding surface, an outer high-order sliding surface, and a dual-power reaching law. Furthermore, a weighting function is introduced to adapt the convergence speed across different error regions, reducing chattering and improving speed-tracking accuracy. Then, dual FTESMDOs are designed for the motor side and load side to estimate the shaft torque and load-side disturbances, and the estimated values are fed forward into the control law for real-time compensation. The simulated and experimental results demonstrate that the proposed control scheme significantly improves the system's disturbance rejection capability and overall robustness.

Rotor water friction loss is a critical determinant of the overall performance and efficiency of water-filled submersible permanent magnet synchronous motors (WSPMSMs) employed in mining applications. This study analyzes the electromagnetic performance and rotor water friction loss of a 500\,kW WSPMSM using the finite element method and computational fluid dynamics (CFD), respectively. From a structural optimization perspective, the effects of the air-gap length and stator slot shape on rotor water friction loss were examined. A multi-objective optimization method incorporating rotor water friction loss was proposed, featuring variable stratification and differentiated reduction of optimization ranges. Firstly, an orthogonal array was constructed using the Taguchi method, and both electromagnetic finite element and CFD simulations were performed. Secondly, analysis of variance (ANOVA) classified design variables as significant and insignificant. Based on the multiple performance characteristic index (MPCI) analysis, the optimization ranges of two types of variables were narrowed to different extents. Finally, for significant variables, the response surface method (RSM) coupled with the non-dominated sorting genetic algorithm III (NSGA-III) was applied for precise optimization. For insignificant variables, the Taguchi method or parameter scanning was used for rapid optimization, depending on their number. By comparing the optimization results of the proposed method with those of existing methods, the effectiveness and superiority of the proposed method were verified.

This work demonstrates the design of a terahertz (THz) antenna that utilizes graphene to achieve frequency-reconfigurable multiband operation. The proposed design integrates electrically controlled graphene switches within precisely defined slots to dynamically modify the distribution of surface currents, enabling a highly multi-band, frequency-reconfigurable antenna. The antenna consists of perpendicular (vertical and horizontal) slots, supported by six graphene switches, whose operating frequencies are adjusted by controlling the graphene's chemical potential. The proposed antenna covers a wide frequency range from 0.288 to 2.501 THz, operating at 63 resonant frequencies and 58 impedance bands, achieved through 11 reconfiguration states (C1-C11). The proposed antenna is created on a 10 μm-thick Rogers RO3003 substrate with overall dimensions of 268 μm × 240 μm × 10 μm. The performance of the proposed antenna, including the reflection coefficient, gain, and radiation efficiency, was evaluated under different operating conditions. Due to its ability to reconfigure multiple frequency bands, this antenna is an ideal solution for dynamically adjustable, tunable THz communication systems.

Existing wideband circularly polarized (CP) antennas generally face trade-offs among wide impedance bandwidth, broad axial ratio (AXR) bandwidth, gain, and compactness in single-layer implementation. Furthermore, a number of reported designs are multi-layer or metasurface-based or require complex feeding networks, making them more complex to manufacture, resulting in increased fabrication costs. In this paper, we develop a wideband circularly polarized (CP) antenna design using an active central patch with four parasitic patches on an FR4 substrate. The CP condition is obtained by exciting two orthogonal modes of equal magnitude and $90^\circ$ phase difference, which are attained by perturbing the active patch and placing a diagonal coaxial feed on it. We enhance the broadside gain and bandwidth by loading parasitic patches around the active patch via electromagnetic coupling. This type of coupling improves aperture efficiency, impedance matching, and axial ratio bandwidth (ARBW). Characteristic Mode Analysis (CMA) is used to determine and optimize the dominant orthogonal modes responsible for circular polarization and radiation enhancement. The fabricated prototype shows a measured -10 dB impedance bandwidth (IBW) of 18.12% (5.42-6.50 GHz), an ARBW of 17.87% (5.35-6.40 GHz), and a broadside gain of 8.5 dBi. The measured and simulated results show excellent agreement, confirming the functionality of the designed antenna. The antenna's compact size, wide bandwidth, and high broadside gain make it a potential solution for broadband wireless communication, satellite-based systems, and C-band antenna applications.

This paper proposes a wideband, low-profile, circularly polarized (CP) crossed-dipole antenna with an artificial magnetic conductor (AMC) reflector. The antenna consists mainly of a pair of orthogonal half-wavelength dipoles, two 90$^\circ$ phase-delay rings, four parasitic patches, four pairs of vertically arranged metallic strips, an AMC reflector, and a square ground plane. CP radiation is generated by exciting bow-tie dipole arms via phase-delay rings. Introducing parasitic patches and vertical metallic strips optimizes the surface current distribution, broadening the impedance-matching bandwidth and axial ratio bandwidth (ARBW). Meanwhile, using the AMC structure as a reflector effectively reduces the antenna profile. We fabricate a prototype of the proposed antenna to verify consistency between simulated and measured results. The measured results show that impedance bandwidth (IBW) is 1.51-2.54 GHz (50.9%), and ARBW is 1.53-2.51 GHz (48.5%). The antenna achieves a peak gain of 8.5 dBic and an average gain of 7.05 dBic across the entire operating band. Furthermore, the antenna features an ultra-low profile of 0.12λ_L at the lowest operating frequency.

In this paper, we propose a compact quad-band bandpass filter by using short-ended stepped-impedance resonators (SE-SIRs) and open-ended stepped-impedance resonators (OE-SIRs) in a hybrid structure. The proposed design uses the odd- and even-mode resonances of the two types of resonators to produce four independent passbands in a compact multilayer structure. The first and second passbands are set by SE-SIR resonators at 1.56 and 2.5\,GHz, respectively. The third and fourth passbands are centered at 3.5 and 5.2\,GHz, respectively, due to the OE-SIR resonators. To achieve the quad-band response in a compact size, a multilayer arrangement with electromagnetic broadside coupling between the feeding structure and resonators has been adopted. Finally, the filter is designed, simulated, fabricated, and measured using a Rogers-Ceramic RO4360 substrate with a permittivity of ε_r = 6.15 and thicknesses of (h₁ = 0.3, h₂ = 0.508) mm. Simulated insertion losses were 0.29, 0.26, 0.43, and 0.66 dB, and return losses were 28.65, 15.05, 14.04, and 17.3 dB in each of the four operating bands, respectively. Filter responses from simulation and measurement are contrasted and discussed. The produced filter is very small, covering a circuit area of about 129 mm², without feeding ports.

This paper presents the design, numerical modeling, and experimental validation of a compact, collocated multi-port reconfigurable antenna array optimized for high-density WLAN access points. The proposed structure supports robust dual-band operation covering the 2.4-2.5 GHz and 5.2-5.8 GHz frequency ranges, exhibiting a measured reflection coefficient well below -10 dB across both bands. Polarization diversity is successfully achieved through orthogonally oriented, horizontally and vertically polarized radiation elements, ensuring an isolation higher than 17 dB between adjacent ports. Furthermore, an integrated electronic switching network based on PIN diodes enables flexible radiation pattern control, allowing seamless switching between a 360° omnidirectional coverage mode and multiple directive beam states. The omnidirectional configuration provides a stable baseline for wide-area connectivity, while the directive modes focus electromagnetic energy into specific spatial sectors, boosting the peak total gain from 5.16 dBi to 7.14 dBi. This dynamic beam-steering capability significantly mitigates multi-path fading and optimizes Multiple-Input Multiple-Output (MIMO) system performance in complex indoor environments. The entire array architecture occupies a compact physical footprint of only 200 mm × 200 mm, with excellent agreement between simulated and measured results, confirming its suitability for next-generation WLAN infrastructure.