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 presents a low-coupling ultra-wideband (UWB) antenna based on a metamaterial structure. The proposed metamaterial exhibits single-negative characteristics with a negative permittivity (ε) in the 3.3-4 GHz and 6.4-10.1 GHz bands, effectively reducing inter-element coupling. Through simulation and experimental measurement, the antenna is demonstrated to operate from 3.1 to 11.4 GHz, achieving an absolute bandwidth of 11.31 GHz and a relative bandwidth of 114.5% (S₁₁ < -10 dB). By integrating the metamaterial to suppress inter-element coupling, the antenna maintains low mutual coupling across the entire operating band (S₂₁ < -20  dB), with an envelope correlation coefficient (ECC) below 0.0045 and a radiation efficiency ranging from 70% to 95%. These outstanding performance metrics render the antenna well-suited for indoor high-precision positioning scenarios, providing stable and high-speed data transmission capabilities.

We present the design, fabrication, and experimental characterization of two 150 mm Luneburg lenses for X-band (10 GHz), produced by FFF using standard PLA. The printed PLA permittivity was measured with a 7 mm coaxial cell and EpsiMu, yielding ε_{r, PLA} ≈ 2.5 at 100% infill; a volume-weighted mixing model with perimeter correction was used to set discrete radial infill fractions. Two infill patterns (grid and gyroid) were tested, and waveguide mounts were integrated for reproducible alignment. Insertion-loss tests give 1.5 dB (grid) and 1.1 dB (gyroid) at 10 GHz. Far-field measurements (R = 1.5 m) and Friis-based estimates yield peak gains of 20.5 dBi (grid) and 19.4 dBi (gyroid) (simulation: 20.8 dBi); the waveguide reference gain is 4.9 dBi. Near-field tests at R = 0.15 m show an on-axis S₂₁ improvement of +2.33 dB, which corresponds to a low apparent near-field aperture efficiency (1.8-2.3%) while far-field efficiencies inferred from the measured gains are substantially higher (35-45%). These results confirm that discrete infill grading in low-cost FFF-printed PLA can realize effective Luneburg lenses at X-band, with quantifiable trade-offs among insertion loss, infill geometry, and realized aperture efficiency.

Flux observers have been extensively employed in the sensorless control of permanent magnet synchronous motors (PMSMs). Traditional flux observers are susceptible to DC offset and high-order harmonics during flux estimation. To address this issue, this paper proposes an improved third-order generalized integrator (TOGIFO-X), which combines a third-order generalized integrator with a low-pass filter. First, the relationship between the flux observation error and rotor position error is established. Then, through rigorous mathematical derivation and Bode-plot analysis, the proposed TOGIFO-X was compared with three conventional flux observers, demonstrating its capability to effectively eliminate both the DC component and high-order harmonic components in the estimated rotor flux without introducing any adverse effects on the amplitude or phase of the fundamental wave. Finally, the effectiveness of the improved third-order generalized integrator is verified via simulations and a 0.75  kW surface-mounted PMSM (SPMSM) experimental platform. The experimental results indicate that TOGIFO-X significantly enhances the reduction in flux estimation error and the elimination of DC bias, thereby contributing to improved position estimation accuracy and advances in sensorless control technology.

In the design of a precision operational amplifier (OPA), cancellation of the input bias current is a challenging issue, which is primarily limited by the current mirror mismatch and the low β value of the PNP transistors. This article proposes a new base current compensation design, which enables zero input-bias-current theoretically. The input stage of the circuit is an active load differential pair with a new common-mode feedback (CMFB) circuit based on the current reuse technique, which can provide a stable common-mode voltage for the amplifier without additional power consumption and area occupation. The proposed OPA is designed in a bipolar process with a core area of 2.85 mm × 1.5 mm. Simulation results show that this OPA achieves a 134 dB open-loop-gain, 50 pA input-bias-current @25˚C, and a low supply current of 0.9 mA, which suggests a concise architecture of the OPA for low offset, low noise, low input bias current, and high gain.

This study proposes a two-element Vivaldi antenna array that achieves broadband mutual coupling suppression and gain enhancement. First, by etching multiple spoof surface plasmon polariton (SSPP) slots on the ground plane to suppress surface-wave coupling, the inter-element isolation has increased from 20-31 dB to 20-45 dB, with an improvement of 5-10 dB (a peak of 20 dB) within the operating band of 1.8-4.5 GHz. Then, a quasi-transparent metasurface (MS) is placed above the aperture to enable phase compensation, converting spherical wavefronts to quasi-planar ones and thereby improving the gain of 0.5-2 dBi across the operating band. Finally, the designed Vivaldi antenna array is fabricated and measured, which exhibits S₁₁ < -10 dB (1.3-4.5 GHz), enhanced isolation, and stable gain performance.

The manuscript presents the design and validation of an inverted bowtie dual-polarized antenna for 5G base station applications. The paper initiates with a comprehensive examination of antenna design, divided into two distinct phases: the evolving stage and the final stage. In the evolving stage, the antenna consists of two pairs of planar inverted bowtie dipoles, which are oriented perpendicularly to one another along their central axes. A balanced feed configuration has been effectively devised to facilitate optimal feeding to the bowtie antennas. The antenna, which is in an evolving stage of development, is engineered to operate at frequencies of 2.8 GHz on port 1 and 3.2 GHz on port 2. It features dual-polarization characteristics. The system ensures an isolation level exceeding 24 dB throughout the entire operational frequency range between the two ports. Additionally, it demonstrates an exceptional radiation efficiency of over 97% at the resonant frequencies. The maximum gain of this evolving stage antenna is 2.3 dBi. A 100 mm × 100 mm square ground plane has been integrated into the suggested antenna design in the final stage of design. Implemented on an FR4 substrate, the suggested antenna has a broad impedance bandwidth appropriate for 5G base-station services. This design has significantly improved gain, isolation, and radiation efficiency, as well as a broad-band resonant frequency range. The antenna proposed in the final stage is designed to operate within a frequency range of 2.66 GHz to 4.4 GHz, demonstrating wide-band characteristics. The design has been meticulously manufactured and calibrated to operate at a central frequency of 3.5 GHz. A -10 dB reflection coefficient with a wide band of 49.5% (which spans from 2.66 GHz to 4.4 GHz) is obtained from the measurements. Antenna-C, the suggested antenna discussed in this article, has a wide bandwidth of 1720 MHz for port 1, which spans the frequency range from 2.66 GHz to 4.4 GHz, and a wide bandwidth of 1710 MHz for port 2, which spans the frequency range from 2.91 GHz to 4.62 GHz. The isolation observed between the two ports has reached a maximum of -39.7 dB. Additionally, this optimization ensures a consistent level above -35 dB is maintained across the entire bandwidth. The results obtained from the proposed antenna, which incorporates a reflector, indicate that cross-polarization remains below -25 dB throughout the operating bandwidth. Furthermore, the front-to-back ratio is found to exceed 22 dB. The antenna design achieves a maximum gain of 7.5 dBi while consistently maintaining a gain greater than 6.3 dBi across the wide frequency range. The antenna dimensions at the lowest functional frequency of 2.66 GHz are 0.372λ₀ × 0.355λ₀, facilitating its extension into an array component.

Building Integrated Photovoltaics (BIPV) technology has emerged as a significant trend in building low-carbon and energy-efficient structures. Exposure to rainwater erosion and immersion can cause its waterproofing failure, significantly shorten the service life of the roof, and considerably lower indoor comfort. To address this, we developed a construction method for waterproofing details of photovoltaic roofs with embedded bolts. This approach optimized the joint design, enhanced the continuity of the waterproofed layer, and improved the building efficiency. We propose a Multivariate Heterogeneous Accumulation Grey Model to quantify the performance and long-term degradation of PV roof waterproofing, which can fully exploit factors such as temperature change and water flow. The application of the new model for quantitative prediction not only demonstrates the effectiveness of the new process improvements, but also provides a novel theoretical tool for future research. Prediction results indicate that the total exudate volume under the new process is less than 2,000 mL (only 1/6 that of the control group). The experiments demonstrate that key waterproofing details with embedded bolts are superior to those of traditional methods in terms of impermeability and durability. The results provide a scientific and technical solution for improving the waterproofness of photovoltaic roofs.

A directional circularly polarized dielectric resonator antenna for different main-beam angles is designed using the Particle Swarm Optimization (PSO) method. It is a single-feed, single-layer structure. For demonstration, the main-beam angle θ is designed at 30° and a 5G frequency of 5.8 GHz. To verify our design, a prototype is fabricated using 3D-printing technology. Its reflection coefficient, radiation pattern, realized gain, and total antenna efficiency are measured. Measured results show good agreement with simulated ones. The prototype has a -10 dB impedance bandwidth of 37.24% (4.84-7 GHz), a 3-dB axial ratio bandwidth of 15.52% (5.3-6.2 GHz), a peak gain of 5.87 dBi, and a peak total antenna efficiency of 96%. It has a low profile of 0.2λ₀, where λ₀ is the free-space wavelength at 5.8 GHz.

To enhance the electromagnetic transient performance and torque dynamic response quality of permanent magnet synchronous motor vector control systems, this study proposes a novel adaptive sliding mode control strategy based on a state-dependent nonlinear approach law. This method first replaces the sign function in traditional sliding mode control with a sigmoid function, mechanistically achieving continuous construction of quasi-sliding mode dynamics and effectively eliminating high-frequency chattering in control signals. Building upon this foundation, the electromagnetic-mechanical state variables are dynamically incorporated into the approach law design to construct a state-dependent nonlinear approach law. This enables the controller to adaptively adjust based on the motor's operational state, thereby achieving dynamic optimization control of electromagnetic torque and speed without relying on precise models. Furthermore, a global fast terminal sliding surface is introduced to achieve rapid convergence of system states within finite time. For composite disturbances such as load transients, flux fluctuations, and unmodeled dynamics, a fuzzy logic-based gain adaptive mechanism for extended state observers is designed. This dynamically adjusts observer bandwidth to enable real-time, precise observation and feedforward compensation for total disturbances. Experimental results demonstrate that the proposed method exhibits significant advantages in improving torque dynamic response, enhancing steady-state accuracy, and strengthening system disturbance rejection capabilities, providing an effective solution for high-performance permanent magnet synchronous motor drive control.

Radar-based vital sensing methods have received significant attention due to their potential to provide continuous, non-contact measurements for heartbeat and respiration monitoring. Our original two-wave model extracts respiration and heartbeat data by formulating the estimation process as a minimization problem. Although the original method examines temporal changes in respiration and heartbeat signals in a different manner from existing methods, it remains sensitive to the slight body movements that often occur in laboratory experiments. In this study, we propose a modified two-wave model with improved robustness against such movements. Using experimental data collected with a millimeter-wave Multi-Input Multi-Output (MIMO) frequency-modulated continuous-wave (FM-CW) radar system, we demonstrate that the improved model can successfully measure both respiration and heartbeat signals even in cases where the original method fails, thereby improving the capability for non-contact vital signal detection.

This study explores the anisotropic electromagnetic properties of carbon nanotube (CNT)/polylactic acid (PLA) nanocomposites, fabricated in-house and shaped using traditional compression molding and advanced 3D printing techniques. By examining the effects of CNT content (ranging over 1-4 wt.% (weight percent)) and 3D printing path orientation, this research investigates how these factors influence shielding effectiveness (SE) and the corresponding nanocomposite complex dielectric permittivity tensor. Notably, a significant variation in SE was observed between the different printing path orientations, with a difference of over 20 dB at 4 wt.% CNT. Experimental measurements were used to develop an anisotropic model for the complex dielectric permittivity, with the permittivity components for samples at 4 wt.% CNT extracted to be 36.5-j44.5 along the printing direction (ε_||) and 8.3-j3.1 in the perpendicular direction (ε_⊥) over the X-band frequency range (8.2-12.4 GHz). These findings demonstrate that CNT alignment during 3D printing induces highly directional electromagnetic properties. Furthermore, we demonstrate that anisotropic simulation models provide a more accurate prediction of the electromagnetic response of 3D-printed nanocomposite structures than isotropic models. In brief, this study emphasizes the necessity of considering anisotropic properties in the design and simulation of 3D-printed nanocomposites for electromagnetic shielding and other applications.

To improve the position detection accuracy of sensorless control for permanent magnet synchronous motors (PMSM) and address issues such as significant chattering amplitude in traditional Sliding Mode Observers (SMOs), a Novel Adaptive Nonlinear Super-Twisting Sliding Mode Observer (NANSTSMO) combined with a Higher-order Gain Compensation Phase-Locked Loop (HGCPLL) is designed in this study. First, a multimodal nonlinear function is designed to replace the sign switching function, and this multimodal nonlinear function is then integrated with both the NANSTSMO and the HGCPLL. Second, a compensation mechanism is introduced to precisely estimate the rotor position. Finally, simulations are conducted using MATLAB/Simulink, and a motor test platform is constructed. Compared with the traditional sliding mode control and referenced sliding mode control strategies, the proposed method demonstrates superior effectiveness.

In this study, we describe a circular ring slot antenna with three circular holes, which is supplied by a CPW-fed split ring resonator metamaterial. This proposed antenna covers sophisticated satellite communication applications for wireless devices, including 5G, military, and aerial radar, and resonates between 2.4 GHz and 10.4 GHz, with a center frequency of 3.542 GHz and an S₁₁ of -37.7 dB, and a center frequency of 7.5 GHz and an S₁₁ of -30.4 dB, respectively. The produced antenna satisfactorily validates the specified antenna metrics. The suggested antenna is built on an affordable FR4 substrate and has physical dimensions of 38 × 38 × 1.6 mm³. The proposed simulated design antenna is validated by the measured data. The results show a good correlation between the measured data and the simulation. The operational impedance range of the proposed antenna is less than -10 dB. The circular ring slot antenna has proven to be remarkably capable of reaching multiband frequencies of 3.54 GHz and 7.5 GHz. The proposed antenna may have an effect on radiation characteristics and gain, resulting in a good contender. Each component of the circle-shaped ring slot antenna design is essential to achieving the important and encouraging results.

This article presents a miniaturized wideband planar inverted-F antenna (PIFA) for deep biomedical implant applications at 915 MHz. Compactness and wide impedance bandwidth are achieved using a shorting pin, a circular radiating patch, and open-ended slots etched in the ground plane. The antenna occupies an ultra-small volume of 63.5 mm³ and is designed and analyzed inside a four-layer cylindrical human tissue phantom. Simulated and measured results show stable impedance matching over the ISM band, with a measured -10 dB bandwidth of 481 MHz (44.02%) and a peak realized gain of -28 dBi. Specific absorption rate (SAR) analysis confirms compliance with IEEE safety limits. In-vitro measurements using minced pork exhibit close agreement with simulations, validating the antenna's performance and suitability for reliable deep biomedical implant communication systems.

Metamaterials are emerging as a key enabler for 6G wireless communications, attracting growing attention from industry due to their engineered electromagnetic properties that enable control over wave propagation. Metamaterials have shown promise across diverse applications; however, the desire to achieve 1 TBPS data rates in 6G communications is partially constrained by a major fundamental challenge in metamaterials: achieving gigahertz of instantaneous bandwidth (IBW) values. To address the IBW issue, we designed, fabricated, and tested a fundamental component of metamaterial, i.e., a modified split ring resonator (MSRR), achieving 90% of the targeted 1 GHz IBW and an effective permeability (μ_eff) close to 25 within the IBW. In addition, the gain-bandwidth product (GBWP) is over 1.5× greater than that of commercial 5G antennas, while maintaining the same aperture size of 1.59λ_c. We studied and reported the effect of MSRR frequency-dependent μ_eff on the IBW and GBWP and proposed an optimized MSRR design that achieves 3× the bandwidth of a conventional SRR. Finally, we integrated the proposed MSRR atop a wideband patch antenna, enhancing peak realized gain by 6 dBi.

A low sidelobe dual-beam reflectarray antenna is proposed based on the sparse array principle. The reflected dual beams achieve high gain through optimized phase compensation, in which the transmissive elements act as dummy elements to suppress sidelobes. A global search optimization technique based on genetic algorithm (GA) is adopted to improve the arrangement of transmissive and reflection elements. Since all the reflective and transmissive elements operating in the same wide frequency band are non-uniformly distributed on the aperture, both the backward radiation and cross polarization levels are effectively suppressed. The measurement results show that the sidelobe level of the dual-beams is less than -19 dB. The peak gain and peak aperture efficiency of the designed antenna are 26.0 dBi and 38.9%, respectively. The 3-dB gain bandwidth is 13.8%. The front to back ratio at 30 GHz is 27 dB. This dual-beam antenna has the advantages of high gain, low sidelobes, and wide beam radiation range, which make it suitable for millimeter-wave multi-target radar detection systems.

Traditional side-lobe suppression techniques such as Chebyshev and Taylor tapering provide limited adaptability to hardware constraints and fixed array geometries. Existing Genetic Algorithm applications predominantly focus on planar arrays with variable spacing, leaving linear arrays with fixed element spacing underexplored. This work presents a genetic algorithm-based amplitude tapering framework for optimizing side-lobe levels in 8­element linear phased arrays with fixed 0.48λ spacing. The approach incorporates hardware quantization constraints and validates performance through experimental implementation. Experimental validation uses the Analog Devices CN0566 Phaser kit operating at 10.25 GHz (centre frequency) with 0.5 dB gain resolution and 2.8125˚ phase quantization. Genetic algorithm parameters including population size, mutation rate, and fitness function were held constant while the convergence rate and side-lobe suppression are evaluated. This research work demonstrates practical genetic algorithm implementation for linear phased array optimization under real-world hardware constraints, providing design guidelines for X-­band radar and communication systems.

The traditional microstrip-fed Vivaldi antenna has the disadvantage of a high cross-polarization level owing to the nonparallelism between the electric field and the antenna plane. Based on the balanced E-field distribution property of the grounded coplanar waveguide (GCPW) structure, this paper proposes a planar ultrawideband Vivaldi antenna with low cross-polarization. The measured results confirm that an enhanced impedance bandwidth of 159.54% is achieved in the range of 2.01-17.86 GHz (|S₁₁| < -10 dB) with a 4-6 dB improvement in cross-polarization over traditional Vivaldi antenna. In addition, the proposed antenna has a maximum gain of 9.9 dBi within the size of 88.2 mm × 107.3 mm × 1 mm. Owing to the advantages of ultra-wideband, low cross-polarization ratio, stable radiation patterns and high gain, the proposed method can be widely applied in UWB communication and multifunctional integrated RF systems.