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.

Ground Penetrating Radar (GPR) systems work with the help of highly efficient antennas that work in the desired frequency ranges for effective subsurface imaging. For applications that require ultra-wideband operation, a robust antenna design is crucial to achieving both deep penetration and high-resolution imaging, but the main challenge is to design an antenna that works in the desired range while also maintaining optimum performance, like gain, directivity, etc. The objective of this work is to develop a microstrip patch antenna capable of operating efficiently in the frequency span of 1.5 GHz to 4 GHz for GPR applications in the CST Microwave Studio platform. Further, the design is optimized to ensure that the antenna structure will exhibit desired characteristics. Once the desired performance has been simulated, the antenna is fabricated using chemical etching technique. Chemical etching is quite precise as it provides the very precise dimensions that are required by a microstrip patch antenna, and it is easy to prototype within a laboratory-controlled environment. The practical test results are compared with simulated design results, to validate the antenna design for GPR applications. It was observed that the fabricated antenna performs successfully as expected since the simulated and practical results are close.

This paper introduces a deep neural network (DNN) training framework to tackle the general power pattern synthesis problem. Compared to the iterative solving method, the DNN-based approach offers a shorter response time, which is significant in adaptive scenarios. In contrast to the widely adopted supervised learning framework, the encoder-decoder network structure utilized in this paper does not necessitate the pre-synthesized results as the training label. The issue of difficult convergence in training caused by the non-uniqueness of the solution is well solved in our method.

This paper presents a novel technique to detect tumors in human breasts using a single high-gain antenna and metasurface (MTS) layer. This design is realized to educate artificial neural networks (ANNs) and deliver productive output. We employ an ANN algorithm to classify detected tumors as healthy, benign, or malignant, based on the permittivity of the detected tissues. The method for finding and sorting things uses the fact of normal and abnormal biological tissues having different dielectric properties, which are based on the tissue's actual permittivity. The study focuses on demonstrating the effectiveness of the proposed technique for the detection and localization of malignant tumors within human breasts. The proposed Vivaldi antenna is made to work over 5 GHz to 9 GHz with a gain of 17.7 dBi at 6.5 GHz and a half-power beamwidth of 10°. The electromagnetic analysis is done using voxel datasets from human models. For this, we located the breast tissue with tumor inside phantom between the antenna structure and the MTS layer. The obtained numerical results from CST MWS are validated experimentally to be used to realize the training of the considered ANNs for tumor detection. The obtained results from the considered ANNs show minimal average errors and high-performance indices for fat thickness, tumor size, and tumor type. The achieved results are found to realize minimum error percentage rate below 2%. The adopted method is found to be very suitable for tumor detection and localization.

This paper presents a simple and innovative approach to the design of multibeam scalar metasurface antennas. The proposed method, based on the equivalent currents on the antenna aperture, allows beams to be radiated in arbitrary directions with the desired polarization. Unlike other solutions available in the literature, this approach uses scalar metasurfaces, which are much simpler to implement than tensor ones, and also do not require optimizations through ad hoc developed numerical analysis tools. Analytical design equations based on the physics are introduced, and a block diagram for the designs of such antennas is presented. Two antenna designs are presented, and the corresponding numerical results demonstrate the flexibility of the presented method. A prototype of a two-beam antenna with orthogonal circular polarizations, operating at 20 GHz, was fabricated and measured. These results confirm the effectiveness of scalar metasurfaces in creating multibeam patterns, paving the way for various applications in advanced communication systems.