In Terahertz (THz) frequencies, using traditional phase delay components is extremely difficult and graphene has the potential to be used in THz. Graphene is typically used at less than λ/16 dimensions. However, it has the potential to change the properties of a unit cell in reflectarray and act as an electronic phase-shifting element at λ/2 dimensions. Therefore, this paper proposes the design and application of graphene in unit cells to develop reflectarray beam steering. A metal-graphene hybrid structure is proposed in this work for designing the reconfigurable reflectarray antenna (RRA). The unit cell operating at 1.025 THz frequency, consists of a thin graphene sheet as a phase-shifting element inside a golden ring, where graphene is used as the phase delay component. The variation in the chemical potential of graphene leads to changes in the reflection coefficient phase for each unit cell. A circular aperture array comprising a maximum of 489 elements shows a total of 80° beam-steering with side-lobe levels of less than -10 dB and a maximum gain of over 20 dBi. The -1 dB bandwidth of 12% was obtained at the centre frequency of 1025 GHz between 950 GHz and 1075 GHz. The aperture efficiency of the designed RRA is found to be 11%. This type of antenna could be an advent for the development of terahertz Reflecting Intelligent Surface (RIS).

Biomedical devices (BDs) monitor vital signs and diagnose illnesses to improve patients' lives. These BDs rely on battery power, which is often short-lasting. To address this limitation, wireless power transfer (WPT) has been proposed in research as a solution for wirelessly recharging BD batteries. This paper aims to enhance WPT in a nonradiative near-field system for implanted BDs by designing and fabricating a triple-layer receiver coil operating in the 13.56 MHz ISM band. First, three square coil models --- single-layer, double-layer, and triple-layer—were developed and simulated using HFSS ANSYS software. The coil models were tested at air gaps ranging from 2 to 40 mm between the transmitter and receiver coils. The single-layer and double-layer coils, each with a receiver coil size of 10×10×0.5 mm, achieved transfer efficiencies of 76.19% and 80.03%, respectively, at an air gap of 10 mm. In contrast, the triple-layer coil, designed with a receiver coil size of 10×10×1.5 mm, attained a transfer efficiency of 87.83% at the same air gap. Additionally, the study analyzed the specific absorption rate (SAR), which was measured at 0.1823 W/kg for 1 g of tissue. Second, the triple-layer square coil was validated through fabrication and experimental testing in different environments, including air, acrylic, and biological tissue (beef). The results demonstrated transfer efficiencies of 80%, 77%, and 63% in air, acrylic, and tissue, respectively. Moreover, the experimental results closely matched the simulation ones, confirming that the triple-layer square coil model accurately represents real-world performance.

The inherent volatility and uncertainty associated with photovoltaic (PV) power generation present significant challenges to maintaining grid stability. As the level of PV integration into the grid continues to rise, the importance of accurately predicting its power output becomes increasingly critical. This study presents a new PV power prediction model utilizing the K-means++-BiLSTM-Transformer framework. Initially, the Pearson correlation coefficient is computed to determine the key factors influencing the prediction of PV power significantly. Following this, the K-means++ clustering algorithm is applied to analyze historical power data, categorizing it into three distinct groups corresponding to different weather conditions. Finally, the BiLSTM-Transformer architecture is employed to develop a power output prediction model tailored for the three weather scenarios. The prediction model is subsequently optimized using Bayesian methods to determine the optimal model configuration for each specific weather condition. Experimental findings demonstrate that the proposed K-means++-BiLSTM-Transformer similar day PV power prediction model exhibits superior accuracy, enhanced generalization, and increased robustness compared to alternative prediction models.

In radar target detection, long-term coherent integration (LTCI) is widely employed to improve the signal-to-noise ratio (SNR) and enhance the detection capability for weak and small targets. Meanwhile, the airborne radar, with advantages of wide-area surveillance, high sensitivity, and strong maneuver ability, demonstrates significant superiority in detecting high-speed targets. However, during the flight of the airborne radar platform, motion errors and the relative motion of high-speed targets can cause significant range migration (RM) and Doppler frequency migration (DFM), degrading coherent integration performance. To this end, this paper proposes a coherent integration method for high-speed target in airborne radar based on the symmetric autocorrelation function, scaled Fourier transform, and sequence reversing autocorrelation function (SAF-SFT-SRAF). Detailed comparisons between SAF-SFT-SRAF and several typical methods demonstrate that the proposed method effectively balances computational complexity and detection performance.

Recently it was demonstrated that a new type of radio frequency surface electromagnetic wave appears on the surface of a lossy conductive medium in the presence of dielectric permittivity gradients. We present theoretical and experimental study of gradient surface electromagnetic wave (GSEW) excitation and propagation on such conductive surfaces as various metals, water, and human skin. The geometry of our experiments is designed to emulate various potential biosensing and bioimaging applications of GSEW. We demonstrate the capability of GSEW-based techniques to detect the presence of metallic and dielectric objects underwater in close proximity to the water surface. Since the dielectric properties of the human body are similar to those of water, we anticipate that the developed GSEW technique may supplement x-ray and ultrasound-based biosensing and bioimaging.

The Mode-Matching Method (MMM) is a numerical technique that can be used to calculate electromagnetic wave propagation through a stepped waveguide junction. We present a generalized approach to mode-matching that works by minimizing the mean-squared error (MSE) of electromagnetic boundary conditions. The process begins by expressing each component of the electromagnetic field profile as a finite summation of modes within each waveguide region. Given some arbitrary pair of mode profiles, we next calculate the squared-error of each boundary condition along the entire span of the junction. The squared error is then averaged across the junction, resulting in a single matrix-vector equation for MSE. That equation is finally differentiated with respect to the mode amplitudes, and the result is then set to zero. The solution is thus a field profile in each waveguide region that minimizes the MSE of electromagnetic boundary conditions.

A wideband quasi-isotropic planar biconical antenna with plano-concave lens is designed for IoT applications. The antenna is realized using a broadband planar biconical dipole and a pair of plano-concave lenses. The cones of biconical dipole are placed at 70˚ angular separation for least gain deviation (GD) across the radiating sphere. A pair of plano-concave lenses suppress GD in elevation plane and improve the impedance matching bandwidth (IBW). Different design parameters are analyzed for wide IBW and 7 dB gain deviation bandwidth (GBW). The designed antenna dimensions are 0.25λ_o × 0.3λ_o × 0.004λ_o at 2.35 GHz. The proposed antenna provides 71.6% (1.51-3.2 GHz) IBW and 73.6% (1.5-3.25 GHz) 7 dB GBW. Experimental results are in good agreement with the simulated ones. The proposed antenna is suitable for IoT based smart applications, energy harvesting and 5G cellular communication.

In this paper, a triple-band bandpass filter based on metamaterials and fractal geometry is proposed. The proposed filter is designed based on three concepts. First, Transmission Lines (TLs) function both as feed lines and as resonators at high frequencies. Second, metamaterials open loop 0th iteration Modified-Minkowski resonators are employed for the middle-frequency band. Third, at a lower frequency, in the 1st iteration, Modified-Minkowski resonators are introduced in the space between TLs to optimize space utilization. The proposed filter has been designed at center frequencies 11 GHz, 6 GHz, and 5 GHz by using Rogers RO 4003 substrate with a thickness of 1.5 mm and dielectric constant of 3.5 resulting in an overall size of 32.2 mm × 20.6 mm. The design simulation is performed using CST microwave studio. To validate the results, the proposed filter has been fabricated. A strong correlation between the measured and simulated results confirms the effectiveness of the design. The proposed filter has three bands at 5 GHz, 6 GHz, and 11 GHz with corresponding S₂₁ values of -0.39 dB, -1 dB, and -0.26 dB and a size reduction of 31% compared with conventional Dual-Band Bandpass Filter for wireless applications.

This study proposes a dual-band MIMO antenna with high element isolation for 5G smartphones. The antenna unit consists of stacked F-shaped radiators, perpendicular to the motherboard, printed on the outer side frames. The antenna feeder is shaped like the Chinese character ``正'' and is printed on the inner surface of the side substrate. Based on this design, eight F-shaped antenna units are placed at the ends of two long side panels, forming an 8-element MIMO antenna system. High isolation in the operating bands is achieved using ground stubs and defective ground structures (DGSs). All radiating elements are etched on a low-cost FR4 substrate with a total size of 150×75×6.8 mm³. The antenna system is modeled and measured to operate in the N78 (3.3-3.8 GHz), N79 (4.4-5.0 GHz), and WLAN 5 GHz bands (5.15-5.85 GHz). The isolation between neighboring antenna units is greater than 15 dB, with total efficiencies ranging from 62% to 79%, and a measured envelope correlation coefficient (ECC) of less than 0.01. Additionally, the antenna performance in one-handed and two-handed holding scenarios has been evaluated, showing favorable results. These findings demonstrate that the proposed antenna system is well suited for MIMO applications in 5G smartphones.

This article presents a compact multi-band microstrip patch antenna designed for 5G, Ku, and K-band applications. The antenna operates at 3.5 GHz and 15.6 GHz, supporting 5G communications (3.3-3.6 GHz) and satellite applications (15.6-20 GHz). Fabricated on an FR4 substrate (ε_r = 4.3, tanδ = 0.025) with dimensions of 13 × 10 × 1.6 mm³ (0.15λ_o × 0.12λ_o × 0.02λ_o), where λ_o represents the wavelength at the lower frequency of 3.5 GHz, the antenna achieves return losses of -19 dB and -39 dB at the respective frequencies, with peak gains of -2.8 dBi and 3.7 dBi. The design's consistency is validated through a comparative analysis with recent studies. The antenna was placed near the ear and mouth area of a human head phantom model to perform a comprehensive SAR analysis. SAR analysis confirms compliance with safety standards, maintaining SAR levels below 2 W/kg. The proposed design demonstrates promising performance for modern communication systems.

This paper presents a comparative study of electromagnetic interference (EMI) shielding properties of PVDF-PVP composite film with VGCNF as a conducting filler. The films were fabricated using solvent casting and further tested for their mechanical and thermal properties. The process was followed by a comparative analysis of shielding effectiveness calculated via dielectric parameters against the shielding measured through scattering parameters with the help of a network analyzer. Scanning Electron Microscopy was also done to better understand the morphological structure of the films. The film, with a thickness of around 0.18 mm, showcased shielding effectiveness within 25 dB-34 dB across a frequency band of 12 GHz to 18 GHz while being flexible and mechanically durable.

To improve the requirements of stopband rejection in ultra-wideband (UWB) filters, a modified T-shaped resonator is proposed and optimized based on multimode resonator theory. The conventional resonator is enhanced by loading open-circuit branches and introducing circular slots to create transmission zeros, while asymmetric coupling lines and a ``ram's horn'' structure are employed to realize dual trapping at 6.3 GHz and 6.8 GHz. Additionally, a defective ground structure is incorporated to further improve the filter's performance. The proposed filter exhibits a passband range of 4.1 GHz to 10.7 GHz, with a minimum insertion loss of -0.2 dB and a return loss greater than 10 dB. The filter demonstrates excellent out-of-band rejection, with trap depths of -28.4 dB and -50 dB at the trapped frequencies of 6.3 GHz and 6.8 GHz, respectively.

This paper presents the temperature-dependent design of streamlined constant and variable thickness ablatable radomes for hypersonic applications. An optimized three-layer radome wall configuration is proposed, consisting of a radome shell sandwiched between an outer ablative layer and an inner matching layer. The outer ablative layer offers protection against temperatures up to 1600˚F, while the inner matching layer effectively prevents total internal reflections. The radome shell is designed using the inhomogeneous planar layer model to account for the temperature gradient existing across its thickness. The numerical analysis of the radome wall is done using the 3D ray tracing method with aperture integration. Power transmission and boresight error characteristics of the radomes remain stable over a thermal operating range of 250˚F to 1600˚F. The performance of the radomes in dynamic flight conditions is analyzed using the time step analysis. Post ablation, the power transmission of constant thickness and variable thickness radomes remains well above -0.6 dB and -0.5 dB, respectively. The broadband performance of both radomes is analyzed over the X-band. Except for the boresight direction, the power transmission over the X-band remains above -1 dB for all incidence angles. The maximum boresight error is observed to be less than 4.29 mrad over the X-band.

This paper presents a novel absorption-scattering integrated multi-layer metasurface (ASIMMS) designed to effectively control the propagation and absorption of electromagnetic waves. Special attention is paid to the efficient suppression of abnormal reflection and parasitic reflection under oblique incidence conditions. The research achieved high efficient beam coupling in the desired direction by precise impedance modulation and excitation of an appropriate set of evanescent wave patterns. The high conductivity of multi-walled carbon nanotube films (MWCNTFs) is used to enhance the localization of electromagnetic field inside the metasurface, thereby improving the absorption efficiency. The experimental results show that the designed ASIMMS achieves 86.8% electromagnetic wave absorption, 11.1% expected directional reflection efficiency, and 97.9% absorption-scattering efficiency at the operating frequency of 10 GHz under 15° oblique incidence. This method proficiently controls both direction and magnitude of scattering while effectively utilizing any diffraction order, paving the way for innovative applications in beam manipulation, stealth technology, and electromagnetic shielding.

A novel position-free control strategy for permanent magnet synchronous motors (PMSMs) based on an improved fuzzy sliding mode observer (FSMO) is proposed to enhance the accuracy of rotor position estimation across different speeds. Traditional sliding mode observers (SMOs) employ a single sliding mode control rate, limiting their precision under varying speed conditions. To address this, the proposed FSMO adaptively adjusts the boundary layer thickness based on system stability and speed, effectively suppressing sliding mode chattering under diverse operating conditions. Additionally, a complex coefficient filter is integrated to mitigate the adverse effects of abrupt boundary layer changes on system stability by filtering the back electromotive force (EMF). Furthermore, a phase-locked loop (PLL) is employed to precisely extract and estimate rotor position and speed. Experimental results demonstrate that the proposed FSMO outperforms conventional SMOs and fixed-boundary-layer SMOs, achieving more accurate rotor position and speed estimation across different operating speeds.

The microphysical structure of rain has a significant impact on the quality of radio signal transmission in the upcoming deployment of 5G millimetre-wave wireless communications in South Africa. To address this, mitigation techniques that integrate rain attenuation prediction models into network management systems are essential. This study uses a machine learning technique, symbolic regression coupled with differential evolution, to predict the rain attenuation in urban and rural 5G scenarios. Symbolic regression derives the mathematical models characterizing the attenuation, while differential evolution optimizes the model coefficients. The models' accuracies are validated through predictive performance metrics, including Mean Absolute Error (MAE) and Mean Squared Error (MSE). The urban model showed excellent accuracy, and the rural model improved significantly after optimization. The interpretability of the models provides valuable insights into rain-induced attenuation and supports better design and optimization of 5G mmWave communication systems.

With the increasing maturity of marine energy development technology, the application ratio of submarine cable in marine engineering is climbing. The connection of submarine cable between offshore wind farms and mainland power grids is of great significance, and temperature is an important indicator for evaluating the safe operation status, which affects the stability and reliability of the cable directly. When the cable load exceeds the rated range, it will lead to a sharp rise in temperature, which will not only shorten its service life, but also may trigger an electrical fault. At lower loads, the cable fails to make full use of its transmission capacity under the rated load, thus affecting the economy of power supply. Therefore, the control of temperature rise of transmission lines during long-term operation is particularly critical, which is related to the stable operation of the power grid and the safety of power supply directly. This study conducted a detailed calculation of the current carrying capacity of submarine cable in accordance with the IEC60287 standard, and simulated the temperature field distribution of HYJQF41-F-26/35 kV 3 × 70 mm² three core AC submarine cable in different laying environments using COMSOL simulation software, providing a scientific basis for the structural design and material selection of three core submarine cable.

In this paper, a broadband vertical rectangular waveguide (RWG)-to-microstrip line (MSL) transition structure for millimeter-wave solid-state circuits is proposed. The planar circuit in this transition is composed of a V-shaped probe and tapered fin-line ground, and the probe is inserted into the waveguide through a slot on the narrow side of the RWG. To facilitate energy coupling from RWG to MSL, a back-short with a length of a quarter-wavelength is designed on the bottom side of the probe to achieve effective electric coupling. A back-to-back prototype module has been designed to verify the performance of the transition. The measurement results show that the return loss of the back-to-back transition structure is better than 13 dB across the entire Ka-band, with the insertion loss (IL) of a single transition better than 0.55 dB. The measurement results agree well with simulation ones, validating the feasibility of the proposed transition circuit. A tolerance analysis is performed through simulations to verify the reliability of this transition design.

This research introduces a new, compact, absorptive frequency-selective reflector, or notched absorber (AFSR), which is low-profile and polarization-insensitive. The objective of the proposed study is to create a miniaturized FSS-based notched absorber that exhibits a high level of angular stability and a robust operational bandwidth of 110% (4.1 to 14.1 GHz). It consists of a reflecting band situated between two absorption bands. The absorption bands are 4.1 to 5.7 GHz and 9.0 to 14.1 GHz, respectively. A low insertion loss of 0.40 dB is achieved at approximately 6.8 GHz, and a wide reflection window with a -3 dB band is extended from 5.8 GHz to 8.0 GHz. The proposed notched absorber comprises three layers with a metal sheet at the bottom. The intermediate layer serves as a bandpass filter, which passes the in-band signal while working as a ground plane for out-of-band absorption. In contrast, the top layer is responsible for broad out-of-band absorption. The total thickness of the band notch absorber is 0.36λ (where λ stands for the wavelength associated with the lowest operating frequency). The equivalent circuit model of the proposed structure has been developed to understand better how band-notch absorbers work at their most basic level. In addition, we examined the distribution of surface current. The notched absorber that was designed is fabricated, and measurements have been done in a semi-anechoic chamber. The measured results are in excellent agreement with the simulated ones. The proposed notched absorber can be employed in radomes, to reduce electromagnetic interference and protect sensitive equipment from unwanted electromagnetic radiation, superstratum on an antenna, RCS reduction and stealth characteristics.

This paper introduces a novel asymmetric design for spoof surface plasmon polariton (SSPP) transmission line-based endfire antenna. It utilizes the phase reversal condition in an asymmetric SSPP transmission line to achieve high gain endfire radiation. The antenna design uses mono-planar fabrication using the CPW concept. Achieving asymmetry in the SSPP transmission line involves simply bending a straight SSPP transmission line containing H-shaped unit cells. Successive upward and downward bending of the transmission line introduces the phase reversal condition and increases the antenna's gain. Notably, there are no limitations on the length over which bending occurs to achieve the phase reversal condition. Simple design principles, a single-layer configuration, and high gain are the advantages of the antenna. Results from the fabricated prototype closely match simulation results. Within the 7.7-8.3 GHz operating band, the antenna exhibits a 7.5% bandwidth and a peak gain of 13.6 dBi. It can find applications in various wireless communication systems requiring high gain and endfire radiations.