The exponential increase of data traffic in next generation wireless communication attracts optimized design of antenna arrays (AAs) to be deployed in RANs. The traditional antenna array synthesis techniques have become exhaustive leading to the introduction of machine learning assisted new binary optimization algorithm. In this paper, three specific AA features are given particular attention: peak sidelobe level (PSLL), first null beam width (FNBW), and broad sector null in interference directions. These contrast each other, and a multi-objective new binary cat swarm optimization (MO-NBCSO) with a novel mutation probability is developed to derive the best-compromised solutions among them. The computational complexity is approximated as O(MN²) (here, M and N represent the number of objectives and population size, respectively). Hence, a 20×20 planar antenna array is considered for synthesis and pareto fronts are generated alongside state-of-the-art MO algorithms. A fuzzy-based decision approach is introduced to choose the best trade-off solutions. A detailed comparative performance study is carried out by the two-performance metrics, namely, I-metric and S-metric. Numerical results illustrate that MO-NBCSO is a better candidate to produce the best antenna arrays in terms of array characteristics over other algorithms.

Methods of manual analysis for infrared image and temperature detection of power transmission and transformation equipment typically have problems, such as low efficiency, strong subjectivity, easy to make mistakes and poor real-time feedback. In this paper, a high temperature anomaly detection method based on SegFormer in infrared image of power transmission and transformation equipment is proposed. Many infrared images of power transmission and transformation equipment are collected and preprocessed, and the temperature information of each infrared image is read out using the DJI sdk tool to construct the temperature data matrix. In the segmentation stage, the SegFormer network is used to segment the key parts of the power transmission and transformation equipment to obtain the mask for detection. The maximum values of the temperature data in the mask area are calculated, and the high temperature anomaly detection atthe key parts of the power transmission and transformation equipment is realized. The test results on the test set show that the overall performance of the method is the highest as compared to other methods such as FCN, UNet, SegNet, DeepLabV3+, and an automatic temperature recognition can be realized, which has important practical value for the detection of high temperature anomaly at the key parts of power transmission and transformation equipment.

This paper designs a miniaturized, wide stopband microstrip filtering coupler based on coupled resonators. Firstly, a short-stub loaded uniform-impedance resonator (SSLUIR) is proposed, , and the size of the SSLUIR is reduced by adjusting the impedance ratio of the stubs and bending them. Then, the resonance performance of SSLUIR during electrical and magnetic coupling is studied. By adjusting the electrical length of the short stubs, higher harmonics are suppressed, and the upper stopband is widened. Finally, a 3 dB 180° microstrip filtering coupler is designed based on SSLUIRs. The measurement results show that the center frequency of the filtering coupler is 2.43 GHz, with a relative bandwidth of 6.6%. It can suppress harmonics within the 8.2f₀ range by more than 18 dB and has a size of 0.23λ_g×0.33λ_g. The correctness of the design method for miniaturized and wide stopband filtering coupler has been verified.

Wireless communication systems have developed significantly over the last few decades. Due to the saturation of lower frequencies of microwave spectrum (3-30 GHz) and the increasing need for high speed, emerging systems for consumer or professional use are progressively shifting to upper microwave and millimeter waves. Our study proposes a methodology for evaluating and classifying losses on a vertically polarized millimeter wave link at 80 GHz. To achieve this, we simulated the link budget of a Nokia 80UBT millimeter wave link operating in its real propagation space (with overground) with Pathloss 5.1 Design tool. Then we built a 3.58 km full-scale link in the Tongo-Bassa watershed of the coastal city of Douala in Cameroon. Analysing data collected over the period from December 06, 2020 to December 16, 2021 under Power BI allowed us to characterize the response of the millimeter signal in free space, during dry and rainy seasons. We then challenge ITU-R P.837-7 and ITU-R.P.838-3 Recommendations on statistical models of rainfall for propagation modeling, especially for millimeter signals propagated in an equatorial climate with heavy rainfalls. The study estimated a rainfall rate for 0.01% of the time at 110.1 mm/h, with a millimeter link cut-off for a rainfall rate greater than 64.8 mm/h, with a specific attenuation due to rain of 6.5 dB/km.

Generalized Mie theory provides a theoretical solution to the extinction cross-section curve of an electromagnetic scattering event with a multiparticle aggregate, given the configurational information of the constituent particles. However, deducing the configuration of the aggregate from the extinction cross-section curve is a non-trivial inverse problem that can be cast as a global optimization problem. To address this challenge, we propose a computational scheme that combines global optimization search algorithms with a calculator known as the Generalized Multiparticle Mie-solution The scheme is tested using mock scattering cross-section curves based on randomly generated aggregate configurations. The scheme successfully reproduces the scattering curve by minimizing the discrepancy between the two scattering curves. However, the ground-truth configuration is not reproduced, as initially expected. This is due to the inability of the global optimization algorithm scheme used in the present work to correctly locate the global minimum in the high-dimensional parameter space.Nonetheless, the partial success of the proposed scheme to reconstruct the mock curves provides an instructive experience for future attempts to solve the inverse electromagnetic scattering problem by fine-tuning the present approach.

A wide band circularly polarized planar antenna of high radiation efficiency is proposed in the present work for future generations of wireless communications requiring circular polarization in the X-band of the microwave spectrum. The main radiating part of the antenna is a rectangular turn-shaped strip that is capacitively loaded by two corner-shaped parasitic elements. The antenna is fed through coplanar waveguide (CPW) region whose ground structure is defected by etching two rectangular annular slots. The purposes of both the corner-shaped parasitic elements and the rectangular annular slots of the CPW ground plane are to increase the impedance matching and the 3 dB axial ratio (AR) bandwidth, and to enhance the antenna efficiency. The design is achieved through complete parametric study to find the optimum dimensions of the antenna. A prototype of the proposed antenna is fabricated for experimental assessment of its performance. The results obtained by both simulation and experimental measurements show that the impedance matching bandwidth is about 5.3 GHz (8-13.3 GHz); the 3 dB AR bandwidth is about 3.1 GHz (8-11.1 GHz); the maximum gain ranges from 4.5 to 5.5 dBi; and the radiation efficiency is higher than 98% over the operational frequency band.

In order to support 5G communication, this article suggests a small, four-port MIMO antenna with a G slot. This antenna has an electromagnetic band gap (EBG) in the shape of an S that is engraved on the substrate in the space between consecutive pairs of radiating patches. The recommended MIMO antenna is constructed from an FR4 substrate and measures 48x48x1.6 mm³. Between antenna elements 1 and 2, the integrated EBG structure of the MIMO antenna can reduce mutual coupling by 10.5 dB. The suggested four port G slot MIMO antenna with an S-shaped EBG structure displays the performance in terms of ECC less than 0.0002 and diversity gain larger than 9.99 with consistent frequency band extending from 3.3 GHz to 3.7 GHz. The proposed four port MIMO antenna is designed using HFSS software, and its simulation results are measured using anritsu combinational analyzer MS2037C vector network analyzer.

A compact and novel star shaped fractal microstrip patch conformal MIMO antenna suitable for WLAN, vehicular communications (5.855-5.925 GHz) and Fixed Satellite Services (FSS) applications is proposed in this paper. Analysis of planar and conformal single element and four element MIMO antennas is presented. Proposed star shaped fractal MIMO antenna is prototyped on Polyamide substrate of geometry 104 x 30 x 0.4 mm³. It achieved an impedance bandwidth (S₁₁ < -10 dB) of 3.7 GHz operating from 4.53-7.86 GHz. Radiation patterns and surface current distribution are investigated at 5.9 GHz and 7.3 GHz center frequencies. A peak gain of 5.42 dB and 4.86 dB are obtained at 5.9 GHz and 7.3 GHz respectively. Radiation efficiency is more than 98% and MIMO performance parameters are also analyzed. Proposed conformal MIMO antenna showsfine diversity performance for WLAN, vehicular and FSS communications.

A waveguide mode solver based on boundary integral equation (BIE) method and matrix compression is developed in this study. Using an accurate discretization based on a Nystrom method and a kernel-splitting technique, the BIE method gives rise to three different formulations of a nonlinear eigenvalue problem. H-matrices are used in order to accelerate and increase the precision of the subsequent computations. Results from these investigations on a canonical photonic crystal fiber (PCF) chosen as an example demonstrate that the data sparse representation of the BIE discretization reduces the memory storage, as well as the assembly and solution times.

A compact new dual band 4-port Vivaldi MIMO (Multiple-Input-Multiple-Output) antenna is designed for 5G mmWave applications. The proposed MIMO antenna resonates at two frequencies 28 GHz and 39 GHz, and it has dimensions 22x22x0.79 mm³. The Vivaldi structure etched on ground plane acts as a defected ground structure (DGS). The proposed antenna is fabricated on Rogers RT/duroid 5880 material having 0.79 mm thickness and 2.2 dielectric material. For high frequency and broad band applications RT/duroid material is suited to maintain low dielectric loss, and it works in high temperature places also. For the proposed four port Vivaldi MIMO antenna, the isolation between any two antenna elements is obtained below -21.59 dB. The bandwidths achieved for two bands are 4.64 GHz (26.31-30.95 GHz) at 28 GHz resonant frequency and 2.69 GHz (38.35-41.04 GHz) at 39 GHz resonant frequency for 4-port MIMO antenna. The gain achieved at 28 GHz is 5.65 dB and at 39 GHz is 5.53 dB. It is possible to achieve MIMO performance parameters such as ECC < 0.003, DG = 10, CCL < 0.4 (bits/s/Hz), TARC < -10 dB, and MEG ratio is 1.01. Simulated and measured results are compared, and the antenna is designed using ansys HFSS tool.

The deep flux weakening (FW) switching point of the interior permanent magnet synchronous motor (IPMSM) is difficult to track accurately. After entering the deep FW region, the current regulator is easily saturated, and the current following capability is poor. Aiming at these problems, a deep FW control of the IPMSM based on thed-axis current error integral regulator (DCEIR) is proposed. Firstly, the deep FW switching point is accurately calculated by using the maximum torque per volt (MPTV) as the limit of the d-axis current. Secondly, through the study of the voltage deviation, it is found that the q-axis regulating current is related to the DCEIR. On this basis, a new transformation relationship between d-axis current and q-axis current in the deep FW region is obtained. Finally, the simulation and experiment results are compared with the conventional negative d-axis current compensation method (NDCCM). It is verified that the proposed method can successfully restrain the saturation of the current regulator and enhance the current following capability in the deep FW region.

In this communication, a compact metasurface-based circularly polarized antenna with inverted L-shaped slots engraved in the ground is proposed for biomedical applications. The prospective antenna operates in the two frequency bands covering Medical Device Radio Service (Med Radio) and Industrial, Scientific, and Medicine (ISM) bands with center frequencies of 2.45 GHz and 4.1 GHz respectively. On mounting the prototype on the body, the impedance bandwidth of 14.4% and 42.5%, peak gain of 3.04 dB, and AR bandwidth of 0.3 GHz and 1.1 GHz in the two frequency bands (2.31-2.67 GHz and 3.28-5.04 GHz) are obtained respectively. For validating the prospective design, an antenna with the size of 0.264λ₀ × 0.264λ₀ × 0.014λ₀ was fabricated on a Rogers RT/Duroid 6002 substrate and measurements were done in different scenarios. Link budget analysis of the device was also done for ensuring its communication ability.

To meet 5G requirements, designing an optimal antenna is challenging due to numerous design factors. Conventional electromagnetic modeling simulators require excessive time and processing power during the antenna design process. Machine learning (ML), an innovative technology, can be used in the domain of antenna design with favorable performance and can resolve problems that the previous conventional methods cannot. The main goal of this work is to create an antenna that operates at 28 GHz, which is a significant 5G band for the 5G futuristic infrastructure revolution, and to predict the return loss of an antenna using some machine learning models like K-Nearest Neighbor (KNN), Extreme Gradient Boosting (XG-Boost), Decision Tree (DT) and Random Forest (RF). On comparing results, all models perform well with over 83% accuracy. However, the Random Forest model predicts return loss with higher accuracy at 90% and lower MSE and MAE values of 1.99 and 0.827, respectively. Moreover, this antenna holds potential for 5G applications and can be efficiently optimized using a machine learning approach, saving valuable time.

Quartz-enhanced photothermal spectroscopy (QEPTS) technique is suitable for simultaneous measurement of multi-gas in near-infrared (NIR) and mid-infrared (MIR) bands with advantages of wide spectral response and high sensitivity. Here, we report a multi-gas sensing system based on QEPTS using NIR and MIR Lasers. A quartz tuning fork (QTF) with a resonant frequency f₀ of 32.742 kHz was employed as a photothermal detector. A continuous wave distributed feedback (CW-DFB) fiber-coupled diode laser with a center wavelength of 1.58 µm and an interband cascade laser (ICL) with a center wavelength of 4.47 μm were used as the light sources to simultaneously irradiate on different surfaces of QTF for scanning the absorption lines of carbon dioxide (CO₂) and nitrous oxide (N₂O). A multi-pass cell with an effective optical path of 40 m and a 40 cm absorption cell were selected for the measurements of CO₂ and NO₂, respectively. The developed sensor was validated by the detection of mixtures containing 3000 ppm CO₂ and 20 ppm N₂O. The relationships between the second harmonic (2f) amplitude of the QEPTS signal and the CO₂ and N₂O concentrations were investigated. Allan deviation analysis shows that this sensor had excellent stability and high sensitivity with a minimum detection limit (MDL) of 2.729 ppm for CO₂ in an integration time of 195 s and 0.038 ppb for N₂O in an integration time of 90 s, respectively.

A brand-new four-channel mux system built entirely out of multicore photonic crystal fiber (PCF) structures, which permit wavelength multiplexing at 0.85, 1.19, 1.1, and 1.35 µm, has been confirmed. The multiplexer is a device that sends multiple messages or signals simultaneously via one communication channel. PCF is a category of optical fiber primarily according to the characteristics of photonic crystals, and it is an effective waveguide based on the interaction of microstructured materials with various refractive indices. Silica substance was used to fill up a few air-hole places to optimize the PCF mux structure along with coupling light between more nearby ports (cores) over the PCF axis. The low-index portions are air holes that may be found anywhere along the length of the fiber, and the background material is often natural silica.

Composite materials are being widely used in the automotive industry where they are progressively replacing metallic materials as structural parts for being robust and lightweight. Their complexity, often leading to lots of unknown behavioral effects when placed near the electronic systems present in vehicles, should be studied and treated. In the automotive industry, the shielding effectiveness of these materials should be considered as the most important parameter to be known in advance. Faurecia, one of the world's largest leading automotive suppliers, sought to assess the shielding effectiveness of their product such as dashboards and door trims. Their objective was to enhance the shielding effectiveness, thereby ensuring superior isolation and protection of electronic systems against electromagnetic interferences (EMI). Thus, this paper presents a novel method for characterizing the shielding effectiveness of various composites using two electromagnetic methods to cover a wide frequency range, starting from 10 Hz up to 8 GHz. The first method, based on loop antennas, was used to cover the low frequency range starting from 10 Hz up to 120 MHz. Frequencies between 100 KHz and 1.5 GHz were not discussed in this paper because of the many studies that already exist at this frequency range, using the coaxial transmission cell. The second method used for frequencies higher than 1.5 GHz, consists of ultra-wide band antennas (Vivaldi).

In this paper, a pioneering and innovative approach for multiple-band ridge gap waveguide (MB-RGW) based narrowband bandpass filter for satellite applications is presented. The MB-RGW represents a significant and emerging technological advancement within the domain of microwave and millimeter-wave engineering. It comprises a periodic structure that enables the propagation of electromagnetic waves along its axis. We have provided a detailed analysis of the MB-RGW, which includes its design, simulation, and experimental results. A prototype filter, designed according to specifications, was successfully produced with a fabricated circuit area measuring 42.25 mm × 76.25 mm × 8.8 mm. We demonstrate that the MB-RGW can achieve multiple bands with a single structure, making it a versatile and efficient device for a wide range of applications. We also present a detailed analysis of the factors that affect the performance of the MB-RGW, including the geometry of the ridge and the spacing between ridges. Our experimental results show that the MB-RGW can achieve high levels of attenuation and isolation, making it a promising candidate for use in microwave and millimeter-wave circuits and systems. The experimental results show S₁₁ smaller than -20 dB over relative bandwidths, and S₂₁ has a maximum of -0.6 dB. The proposed filter demonstrates four resonances at frequencies of 10.6 GHz, 12.6 GHz, 14.7 GHz, and 17.1 GHz, catering to mobile and fixed radio locations as well as satellite applications. It exhibits a fractional bandwidth of 0.44% at 3 dB in the X-Band and approximately 0.57% to 0.61% at 3 dB bandwidth in the Ku-band. The filter offers a compact, cost-effective, and easily implementable solution for satellite communication systems, including space operations, earth exploration, satellite TV broadcasting, and fixed satellite services (FSS). Overall, this paper provides a comprehensive overview of the MB-RGW and its potential for the use in a range of applications.

Orbital angular momentum (OAM) is a fundamental characteristic of electromagnetic waves and has gained significant attention in recent years because of its potential applications in various fields of radio and optics. Furthermore, the OAM has been proposed as a means to increase the spectral efficiency of wireless communication systems. By encoding multiple independent data streams on different OAM modes of electromagnetic waves, OAM communication systems can increase the amount of information that can be transmitted over a single radio frequency channel. In this paper, we developed a new method for steering the OAM wave using an intelligent reflective surface (IRS) that is suitable for the far field. Specifically, we designed the IRS coefficients to reflect and steer different multiplexed orders between different users based on OAM waves by controlling the IRS impedance, which can be fluctuated depending on the beam steering direction. Moreover, we investigated the physical limitations of the IRS by noting the relations between the number of transmitted modes, the IRS size, and the impedance values in the IRS. Each impedance element in the IRS consists of real and imaginary values, and the negative values in the real part are used as an indication for reaching the physical limit. One suggestion to decrease the negative real values is by using windowing to decrease the beam waist. The proposed method may enable the extended coverage of OAM wireless communication.

This study focuses on the utilization of a slotted patch MIMO antenna to enhance isolation and gain. The MIMO antenna configuration includes two radiators integrated with an array of Frequency Selective Surfaces (FSSs). These antenna components are implemented on an FR-4 substrate and encompassed by FSS units that are optimized for X-band frequencies. The proposed MIMO antenna possesses dimensions of 65 mm (width) × 45 mm (length) × 1.6 mm (height). The primary objective of incorporating FSSs is to not only enhance isolation but also achieve high gain. The proposed FSS design features a circular ring structure with a rectangular loop at its center. The FSS unit cells exhibit excellent stability across various polarization incidence angles and operate within the frequency range of 7 to 9 GHz. The FSS loaded antenna offers a bandwidth ranging from 8.0 to 8.55 GHz, with a peak gain of 6.5 dB and isolation exceeding -20 dB among the MIMO elements. Furthermore, the study explores the MIMO antenna's performance in terms of diversity gain (DG), efficiency, and Envelope Correlation Coefficient (ECC), demonstrating superior results compared to existing state-of-the-art approaches. The proposed findings are validated by fabricating a sample prototype and conducting a comprehensive comparison between simulated and measured results.

Enhancing the capacity of wireless communications systems is necessary to manage growing networks. Thus, this work presents an analytical model for describing the deterioration in orbital angular momentum (OAM). The proposed model is based on a uniform circular array, which can be applied in OAM generation to obtain the desired beam properties. First, the side-lobe problem in OAM applications is examined and resolved by optimizing the beam synthetization. Then, comparisons between the two window techniques are used to evaluate their impacts. Finally, the effects of selecting the optimal window technique and width on the solutions are investigated. Numerical results and the comparisons between derived formulas and those obtained via full-wave numerical simulations are shown.

An efficient time domain hybrid method, consisting of the finite-difference time-domain (FDTD) method, Norton's theorem, transmission line (TL) equations, and some interpolation techniques, is presented to realize the fast coupling simulation of branched lines (BLs) radiated by ambient wave. Firstly, the branched lines are decomposed into multiple independent multi-conductor transmission lines (MTLs) according to the branched nodes. Then the TL equations with interpolation techniques are employed to build the coupling model of each MTL. The transient responses on these MTLs are solved by the FDTD method, which are employed to extract the Norton circuits of these MTLs acting on the branched nodes according to the Norton's theorem. Finally, the correlation matrix of the voltages and currents at the ports of the branched nodes is derived and solved. Meanwhile, these voltages are fed back to the corresponding MTLs as boundaries to realize the interference signal transmission among the BLs. Numerical examples about the coupling of branched lines contributed by five wires in free space and complex environment are simulated and compared with that of traditional FDTD to verify the correctness and efficiency of this proposed method.

At present, numerical methods suitable for the electromagnetic interference (EMI) analysis of the transmission line (TL) excited by the leakage electromagnetic (EM) fields generated by the integrated circuit (IC) of the electronic device are still rare. An efficient time domain hybrid method, consisting of the dynamic differential evolution (DDE) algorithm, transmission line equations, finite difference time domain (FDTD) method and non-uniform grid technique, is presented to realize the fast simulation of the leakage EM fields to the TL. Firstly, a source reconstruction method based on the DDE algorithm is employed to extract the equivalent dipole array to represent the leakage EM radiation from the IC of the device. Then, the coupling model of the TL excited by the leakage EM fields is constructed by the TL equations and non-uniform grid technique, and solved by the FDTD method to realize the synchronous calculation of the leakage EM field radiation and the transient responses on the TL. Finally, the correctness of the source reconstruction method has been tested, and the accuracy and efficiency of the proposed method have been verified via two simulation cases of the transmission line excited by leakage EM fields arising from IC in free space and shielded enclosure by comparing with that of the MOM method.

Optically transparent antennas have attracted increasing interest in recent years. However, the inherent ohmic loss of transparent conductor used in antennas will always introduce degradation of radiation efficiency. It is of most importance to find the optimization between the material loss and radiation efficiency. In this paper, we design and experimentally demonstrate a high-performance optically transparent dual-polarized cross dipole antenna over 3.4-3.8 GHz for 5G wireless communication based on the characteristic analysis of surface current distribution. By making current distribution uniform on the radiators and reducing the current on the ground, the mutual coupling between the elements is alleviated, and the radiation efficiency can be optimized. The proposed antenna is fabricated with 0.118-Ohm/sq meshed metal, and the optical transparency of antenna is 81%. The proposed antenna achieves a voltage standing wave ratio (VSWR) of less than 1.3, radiation efficiency of 72% (84% of pure copper) and a peak gain of 4.5 dBi (5.1 dBi of pure copper). Compared to current state-of-arts, the proposed antenna exhibits better performance of the figure of merit (FOM) in terms of the bandwidth, optical transparency and radiation efficiency. Our work paves the way to diverse application of beyond-5G wireless communication.

The response of a uniformly moving metallic slab to an electromagnetic plane wave, at normal incidence, is studied. The analysis is based on the application of boundary conditions to Maxwell's equations as a function of time. The Doppler effect and amplitude of the obtained reflected wave agree with the literature. Moreover, a transferred wave which has not been analyzed in the literature is demonstrated. The frequency shift and the amplitude of this wave are studied analytically with the same technique used for the reflected wave. The transfer of electromagnetic wave through the metallic slab is made possible by the presence of a static magnetic field inside the moving metallic slab, if the motion of the slab is opposite to the direction of propagation of the incident wave. The amplitude of the transferred wave is approximately 2v/c times the amplitude of the incidence wave, with v being the speed of motion and c the speed of light in vacuum. This amplitude is thus very small for non-relativistic speeds. The analytical results are validated by full-wave simulations based on the Finite Difference Time Domain method, where both reflected and transferred waves are demonstrated. Furthermore, numerical electric field and magnetic field distributions are presented at different time instants.

A four-port ultra-wideband (UWB) multi-input multi-output (MIMO) Vivaldi antenna loaded with resistance and rectangular radiation patch is designed and fabricated. The compact antenna consists of an improved ground and four microstrip feeders, with an overall size of 26 mm × 52 mm × 0.8 mm. The antenna adopts the resistance loading technology to absorb the excess electromagnetic waves in the low-frequency band and broaden the low-frequency bandwidth of the antenna. The rectangular radiation patch loading technique optimizes the main radiation direction and broadens the high-frequency bandwidth of the antenna. Meanwhile, T-slots and fence-type structures are etched on the ground plane, and I-stubs are added between microstrip feeders to reduce the antenna coupling and increase the isolation degree between the antenna ports. Simulation and experiments show that the impedance bandwidth of the MIMO antenna is 3.0~12.3 GHz; the isolation degree of the whole working bandwidth is higher than 15 dB; the envelope correlation coefficient (ECC) is smaller than 0.0125; and the increased diversity gain (DG) is more significant than 9.98 dBi. The antenna has good radiation performance and stable gain, which is suitable for applying the UWB MIMO system. This antenna has a particular reference significance for the research of the MIMO Vivaldi antenna.

To solve the problem of single working frequency of traditional reflective focused metasurface, a dual-band reflective focused metasurface is proposed, which can realize independent focusing characteristics at 7.25 GHz and 20.5 GHz. The metasurface unit is composed of metal elements combined by a split-ring resonant structure working at 7.25 GHz and an elliptical resonant structure working at 20.5 GHz in the same plane, dielectric substrate and ground. Dual-band independent control and 360° phase coverage are achieved by adjusting the dimensions of unit. The surface current distribution also verifies the rationality of the designed metasurface element. Based on the principle of quasi-optical path, a dual-band reflective focused metasurface with independent focusing characteristics is designed. Through full-wave simulation, the focusing efficiency at 7.25 GHz and 20.5 GHz is calculated by Poynting theorem, which are 56.9% and 57.5%, respectively. The proposed dual-band metasurface has the characteristics of simple structure and low profile without multi-layer stacking and metal through-holes.

The growing demand for natural fibers in dielectric composite production has accelerated research into plant-based materials, particularly those derived from agricultural waste. Hence, this study attempts to evaluate the effect of processing factors and their elemental composition on the permittivity value of pineapple fiber-based dielectric composites. The dielectric composite was prepared following the randomized experimental conditions of two-level factorial analysis, and the permittivity value was measured using a G-band rectangular waveguide. The most significant factors affecting the permittivity value of the dielectric composites and the best condition were determined. The elemental composition of the dielectric composite was analyzed through an energy dispersive X-ray (EDX) analysis. The best conditions were obtained at a 1:10 ratio of pineapple leaves to distilled water, 50 minutes pulping times with a heating effect, and 5 g of pineapple leaf powder. The highest permittivity value of the composite was recorded at 3.31, with the heating effect as the most significant factor. The elemental analysis of the composite with the highest permittivity value presents that carbon was the dominant element in the composite at 78.05%. The obtained permittivity value exhibited by the composites shows that the pineapple leaf fiber-based dielectric composite could be a potential alternative as an antenna substrate.

This article presents the design and implementation of a beam-steering antenna array using a 4x4 Butler matrix feed network (BMN) for 5G applications. The proposed antenna array can achieve a gain of 14 dBi and a steering range of (+16º, -47º, +46.5º, -15.7º) to cover angular range extending from 45º to 135º. To achieve that, a simple, 4x4 Butler matrix etched on a single-layer microstrip structure is designed, optimized, and fabricated. The proposed design incorporates phase shifters, 3-dB couplers, and cross-over couplers. The proposed matrix is employed as a feeding network for 4-element wideband LPDA antenna array. The fabrication results of the feeding matrix and antenna array show very good agreement with the simulated results.

A design method of compact dual-band multi-beam antennas is proposed by integrating a dual-band metasurface lens with a dual-band planar antenna array in this paper. The dual-band multi-beam antenna designed through this method has a compact configuration, low cost, and is easy to integrate with other devices for communication. The dual-band multi-beam function of the antenna by this method has been verified through a double-layer dual-band metasurface lens and a five-element dual-bandplanar antenna array. A dual-band meta-cell with relatively independent performance at 13 GHz and 23.5 GHz is designed to form the metasurface lens. Dual-band magnetoelectric (ME) dipole antenna is used as the feed antenna element. The simulated and tested results indicate that the lens antenna generates five independent beams at both 13 GHz and 23.5 GHz. Considering practical applications, solutions to improve antenna performance and reduce losses have also been proposed.

According to the characteristic mode basis function method (CMBFM) in analyzing electrically large problems, blocking and extending lead to the problem of slow convergence in the iterative solution of a reduced matrix equation, and the characteristic mode basis function method combined with principal component analysis (CMBFM-PCA) is proposed in this study. The characteristic modes (CMs), calculated from each extended block, are subjected to PCA to enhance the orthogonality between them and improve the reduced matrix's condition number to facilitate its quick convergence through an iterative solution. The corresponding numerical calculations demonstrate that significant efficiency and accuracy are achieved by the proposed method.

In this research article, we propose a split ring resonator (SRR) based metasurface absorber based on graphene material. The performance of the graphene-based absorber at terahertz frequencies can be altered by varying the chemical potential of graphene material. Because of its excellent tunability and optical responsiveness at terahertz frequency, graphene-based metamaterials have been widely used in optoelectronic devices, sensors, filters, and many more. The proposed structure contains three layers namely graphene-based patch as a conductive layer, lossy silicon as a dielectric layer, and finally gold as a bottom conductive layer. The proposed unit cell resonates at three different absorption peak frequencies of 2.91 THz, 8.1 THz, and 9.61 THz with operating frequency bands at (2.66 THz to 3.12 THz), (7.71 THz-8.47 THz), and (9.57 THz-9.63 THz), respectively. The purpose of this research is to present a thorough investigation of graphene-based THz metamaterial absorbers, including modeling and verification of the structure through an equivalent circuit approach. It is very much beneficial to understand the conductive phenomenon of graphene material by tuning the Fermi chemical potential and achieve a high percent level of absorption for the corresponding absorption frequency bands.

This paper presents a design of high-performance parallel-connected filters using the Chained filtering function. The filtering functions enable the placement of multiple return loss zeros at the same frequency, resulting in reduced sensitivity to fabrication tolerance and design complexity compared to traditional Chebyshev counterparts. To demonstrate the feasibility of this technique, a new filtering function (F_N) based on Chained filtering function is derived, and prototypes of fourth and sixth-degree Chained function filters in a parallel-connected topology are designed and fabricated. The overall size of the filters is 2.5 cm x 4 cm (fourth degree) and 2.5 cm x 5 cm (sixth degree). The measured insertion and return losses are 2.833 dB and 16.150 dB (fourth degree), and 2.674 dB and 18.074 dB (sixth degree). The achievable selectivity of the filters is 78.17 (fourth degree) and 89.68 (sixth degree). This design technique can serve as a useful tool for filter design engineers in terms of implementation.

Optical nano-antenna offers a new scheme for solar energy collection by breaking through the band-gap limitation of semiconductor materials. However, complex structure, low efficiency, and narrow bandwidth remain major issues. To address these problems, we propose a novel helical optical nano-antenna based on the bridge structure. The antenna structure consists of two coplanar Archimedes spiral arms and a base layer. We analyze the influence mechanism of structural factors on its radiation efficiency and polarization characteristics. Our results show that the antenna structure achieves a total radiation efficiency of 83.13% in the wide wavelength range of 400 to 1600 nm, which is significantly higher than that of the previously proposed dipole nano-antenna. For different linearly polarized incident waves, the antenna structure obtains the same order electric field at the spiral gap, which indicates that the antenna structure can fully consider the polarization characteristics of sunlight. It fundamentally solves the problem that the linearly polarized antenna can only receive half of the solar energy, improving the absorption efficiency.

In this paper, we propose a new physical model to accurately estimate the absorption characteristics in Metamaterial Perfect Absorbers (MPAs). The proposed model, relying on the reflection and refraction theory of microwaves, explains the physical mechanism of absorption and how unit-cell constitutive parameters can contribute to control the absorption characteristics. By considering Floquet modes (TE and TM) as two incident cross-polarized waves, analytical expressions have been established to estimate the absorption at normal and oblique incidences from the extracted constitutive parameters of the unit-cell. Analytical predictions are in excellent agreement with numerical results, proving the validity of our model. Furthermore, it can give an idea behind the absorption characteristics of MPA unit-cells without passing through full-wave simulation which usually takes time. Compared to previous works reported in the literature, the proposed method is efficient and does not require time-consuming tests and processing steps. Finally, analytical findings in this work hold for the general shapes of MPA resonators.

A dual-band metasurface antenna is designed consisting of three-layer metal patches and two-layer dielectric substrates. To facilitate the modal analysis of the metasurface, Characteristic Mode Analysis (CMA) is used to analyze the metasurface antenna with 4×4 rectangular patches, and the performance of the antenna is optimized based on the Modal Significance (MS) curves. In order to excite the current of different characteristic modes at certain frequencies, the symmetric resonant arms and cross-shaped impedance matching converters are used in the feeding structure. The measured results are consistent with the simulated values, and the designed antenna can yield the gains of 7.67 dBi at 3.5 GHz and 7.28 dBi at 4.9 GHz, which provides the potential applications in 5G and other wireless communications.

This paper presents a new process for additive manufacturing of purely metallic antennas based on Fused Deposition Modeling (FDM), with a filament composed by a mix between rounded shape copper powders with particle size in the range from 20 to 80 μm embedded in a polymeric matrix, to accomplish the desired antenna shape, followed by a post-processing involving de-binding to remove the base polymer and a further sintering process for obtaining a purely metallic component. This new process is validated by means of a prototype antenna consisting on a modified tri-band cactus monopole that is manufactured and measured demonstrating results in accordance with standard and alternative additive manufacturing techniques reported in literature.

This article focuses on the low-frequency magnetic shielding of double-layer conducting plates with periodic circular apertures. The shielding effectiveness (SE) is measured as the insertion loss of the plates when they are placed between a pair of coaxial loops, one for magnetic field emission and the other for receiving. Our experimental results show that the SE sharply increases with the layer-to-layer spacing increasing from zero to the aperture diameter. For aluminum plates with 1 mm thickness, 20 mm unit cell and 10 mm aperture diameter, the enhancement is approximately 10 dB and 20 dB for 3 mm and 9 mm spacing, respectively. In addition, the effect of the lateral deviation on the SE is evident only if the spacing is smaller than the aperture diameter.

High resolution Synthetic Aperture Radar (SAR) images are affected by speckle noise, which considerably reduces their visibility and complicates the target identification. In this paper, a new Compressive Sensing (CS) method is proposed to reduce the speckle noise effects of complex valued SAR images. The sparsity of the SAR images allows solving the CS problem using Multiple Measurements Vector (MMV) configuration. Therefore, a special weighted norm is constructed to solve the optimization problem, so that the Variance-Based Joint Sparsity (VBJS) model is used to calculate the weights. An efficient Alternating Direction Method of Multipliers (ADMM) is developed to solve the optimization problem. The obtained results using raw complex-valued measurements with ground truth demonstrate the effectiveness of the proposed despeckling method in terms of both image quality and computational cost.

Studies of soil moisture with Global Navigation Satellite System (GNSS) have gained the attention of several researchers. Multipath amplitude, multipath phase, and multipath frequency are multipath observables that are utilized in the study of soil moisture. However, an inter-comparison of the performance of these parameters for soil moisture under different roughness and vegetation conditions is very much required to have a better insight so that more robust inversion algorithm for soil moisture retrieval with multipath observables can be designed. Therefore, this paper analyses the performance of these multipath observables for soil moisture over bare smooth soil, rough surface, and vegetated soil. Two different fields have been investigated to include the location variability. Navigation with Indian constellation (NavIC) multipath signal has been used in this study. Statistical parameters such as correlation coefficient (R), Root Mean Square Error (RMSE), and sensitivity have been determined to study the performance of multipath observable for soil moisture under different surface roughness and vegetation conditions.

An asymmetric coplanar waveguide (CPW) fed wideband circularly polarized monopole antenna with a slot structure is proposed in this article. Phase gradient metasurface (PGM) is placed beneath the monopole to improve the gain. Circular polarization (CP) is achieved over wide bandwidth by combining the monopole and slot modes. The asymmetric CPW-fed monopole antenna provides CP at lower frequencies, and slot mode provides CP at higher frequencies. The asymmetric ground plane in the monopole and asymmetric strips in the slot are combined to produce wide axial ratio bandwidth. The proposed design's detailed construction and operation are discussed with experimental validation. The proposed wideband CP antenna provides an impedance bandwidth of 95.46% and axial ratio bandwidth of 67.61%. The peak gain of 5.2 dBic is obtained at 2.35 GHz with 2 dB variation over operating bandwidth. The obtained radiation patterns provide good broadside radiation with better cross-polarization levels than co-polarization.

Carbon fiber wound hydrogen tanks are widely used in the field of new energy, but their complex multilayer structure makes it difficult to conduct nondestructive testing/structural health monitoring (NDT/SHM). In this paper, electromagnetic tomography (EMT) is used for noncontact in situ defect detection on a carbon fiber wound hydrogen tank. According to its structural characteristics, an open U-shaped sensor array that fits the curvature of the tank body is designed. To improve the quality of reconstructed images, an iterative image reconstruction algorithm based on a composite sensitivity matrix (CSM) is proposed. To verify the performance of the method, the method in this paper is compared with linear back projection (LBP), the Landweber iterative algorithm and the Tikhonov regularization algorithm, and the image quality is evaluated by comparing the image relative error and correlation coefficient. Both simulated and experimental results show that the method proposed in this paper is more accurate in defect localization and higher in quality than traditional image reconstruction algorithms.

The safety of the electromagnetic environment of wireless power transfer (WPT) systems is one of the prerequisites for the application of wireless charging technology for electric vehicles (EVs). The electromagnetic characteristics of a wireless charging EV with a new 7.7 kW WPT system were modeled and analyzed in this paper. Firstly, a complete model of the magnetic coupler was built as a source of electromagnetic radiation, and an external excitation source was added by coupling the resonant coils to the double inductor-capacitor-capacitor (LCC-LCC) topology circuit model. Secondly, the finite element analysis software COMSOL Multiphysics was used to solve for the magneto-quasi-static values to verify the electromagnetic safety of the wireless charging process. Then, two charging scenarios were investigated when the GA and VA aligned and misaligned, involving lateral offset and longitudinal offset cases. Finally, the simulation results were compared and analyzed, showing that the values of electromagnetic fields become higher as the offset distance increases. In worst-case scenarios, the highest magnetic flux density (1.1 μT) is observed in the virtual plane of the test on the left side of the vehicle, which occupies only 17.6% of the limits specified in ICNIRP 1998 (6.25 μT), indicating a good EMF safety performance of the wireless charging system.

A novel approach is presented to achieve improved sensing performance using a one-dimensional (1D) hyperbolic graded photonic crystal (PC). The graded structure achieves refractive index modulation that varies hyperbolically with layer depth, due to its graded index geometry. Porous materials are employed to facilitate analyte infiltration. The reflectivity and sensing performance of the proposed graded and non-graded geometry is evaluated using the transfer matrix method (TMM). The Sensing capability of the graded structure is evaluated analytically by infusing different analytes within the cavity, considering various cavity widths and incidence angles. At a 40-degree angle of incidence, the analytical results demonstrate that the suggested graded structure exhibits a maximum sensitivity of 469 nm/RIU, along with a detection limit and FOM of 9.1×10^-3 and 125 RIU^-1, respectively. The detailed electric field confinement of the graded geometry is also carried out at the interface. The proposed structure outperforms conventional non-graded structures with a 114% higher sensitivity. The bio-photonic design can easily be implemented and provides high performance compared to previous works that employ exponentially graded structures. The suggested biosensor can detect even minor fluctuations in the refractive index of blood serum samples with different cholesterol concentrations.

In this paper, we propose a noninvasive blood glucose monitoring system that can be easily integrated into smartwatches. This system makes use of dielectric properties of blood-flow in human blood vessels as well as frequency dependency of blood glucose. To prove the proposed design principle, authors have verified the system working with vector network analyser and a directional coupler. The entire system design is explained in this paper. At the time of final system integration, the vector network analyser and directional coupler can be replaced with other on-chip sensors. Authors have also compared the obtained results with finger pricking based blood-glucose measurement. The results agree and have been tabulated. Clarke error grid was also used to evaluate proposed system accuracy.

Terahertz era is becoming a more prominent and expanding platform for a variety of applications. In this paper, we propose a triband absorber with a hexagon-shaped radiating patch for THz applications. The proposed structure has three layers: a hexagonal patch made of graphene as a radiating patch, a silicon layer as a dielectric substrate, and a bottom conductive layer made of gold to prevent EM wave transmission. The proposed structure operates at three resonant frequencies 0.38 THz, 1.23 THz, and 1.77 THz respectively. We may accomplish maximum absorption level (above 90%) and maximum absorption bandwidth by setting relevant chemical potential and relaxation times to 0.2 ev and 0.2 ps respectively. The proposed structure contains a lossy silicon substrate, which has a dielectric constant of 11.9 and a loss tangent of 2.5e-004. The proposed structure reveals a larger absorption [above 90%] for the operating frequencies, and the effect on absorbance for different modes is illustrated.

Solid State Transformers (SSTs) are emerging as the major component of smart grid system. High Frequency Transformer (HFT) is the key element of SST. The optimum design of SST is a critical task due to the complex design of magnetic, electric and dielectric circuits of high frequency transformer and due to the design of power electronic circuits used at either sides of HFT. The most significant among above is the design of magnetic circuit and the possibility of using different magnetic materials for high frequency application. This paper discusses the performance analysis of HFT for different magnetic materials used for core construction. The magnetic materials considered in this analysis are amorphous, nanocrystalline and si-steel. Optimum HFT design is selected from a set of designs using an iterative algorithm, considering each core material separately. Validation of the design is done in Finite Element Method (FEM) analysis software. The design of a high frequency transformer, which is integrated in 1000 kVA 11 kV/415 V SST, is investigated both analytically and numerically, with optimum designs developed using three core materials.

In this work we show a novel method based on a local two-port interferometer to distinguish the topological charge of radio-vortices at 30 GHz by using a small portion of the entire wavefront only. The experimental investigation of the amplitude and phase properties of the interference pattern with a pure Gaussian beam (l = 0) and a l = 1 radio vortex is carried out, and results are compared with the theory based on Laguerre-Gauss modes. Experiments were performed both with the interferometer and with single antenna to highlight the effective benefits of the interferometric approach, sensitive to the azimuthal phase of the vortex field. Method is also extendable at higher topological charges for applications to high-density millimetric communications.

Prediction in the transition region between lit and shadowed regions is important for maintaining stable mobile communication for the beyond 5th generation. In this paper, as the difference between the reflection and diffraction from a dielectric circular cylinder and an absorber screen, respectively, a novel additional term is derived by a uniform theory of diffraction (UTD) in the lit side of the transition region. The proposed model is validated by the UTD and exact solutions of a dielectric circular cylinder. Through the proposal, we can separate the contribution of the shadowed Fresnel zone (FZ) number and boundary conditions (i.e., the surface impedance and the polarization) to the total field. The frequency characteristics of the shadowed FZ and boundary conditions are theoretically analyzed. The analyzed results show that the contributions of the boundary conditions are weaker than the shadowed FZ in the lit region at a high frequency.

Planar and conformal log periodic dipole array (LPDA) antennas are proposed in this paper with circular patch and hexagonal patch top loadings for multiband applications. Due to these top loadings, the size of the antennas is reduced, and the total dimensions of the two antennas are 44 mm x 40 mm. These antennas are fabricated on polyimide material with a dielectric constant of 3.3 and thickness of 0.1 mm. These two antennas resonate at 3.5 GHz, 5.7 GHz, 7.5 GHz and 9.3 GHz frequencies in both planar and conformal modes. The antenna characteristics of the proposed antenna models such as reflection coefficient, VSWR, radiation pattern, and gain are analyzed, and the measured results are in good agreement with simulation ones.

In this study, a compact, reconfigurable, and high-efficiency Long Range (LoRa) patch antenna, which is novel, is presented for Internet of Things (IoT) applications. The antenna is designed to operate at the three major frequencies used for LoRa communication, namely 915 MHz, 868 MHz, and 433 MHz, which are widely employed for global LoRa connectivity. The compact size and impedance matching of the antenna are achieved through the use of meandered radiating patches, a partial ground plane, and a ground plane stub. The antenna is prototyped on a commercially available and cost-effective FR-4 material and measures 80 mm x 50 mm x 1.6 mm (0.12λ x 0.07λ at the lowest resonant frequency), which is smaller than the size of a standard credit card. The antenna utilizes three RF PIN diodes (SW1, SW2, and SW3) for frequency reconfiguration, which are characterized by low insertion loss and fast switching time. The RLC equivalent circuit of the antenna was validated through simulations and measurements, yielding the peak gain and radiation efficiency of 2.1 dBi and >90%, respectively. These results prove that the antenna is a promising solution for LoRa IoT applications in terms of size, cost, and performance, filling a gap in the existing literature of LoRa MPAs that are typically large, non-reconfigurable, low-gain, and single-band.