This paper presents a single stage 2-way Wilkinson Power Divider (WPD) suitable for Internet of Things (IoT) low frequency applications in the band from 200 MHz to 1 GHz. It is realized using a meandered line, and an open shunt stub matching network is added to get a compact structure. Moreover, a Vertical Periodic Defected Ground Structure (VPDGS) is added below each arm in order to improve the performance at the center frequency without adding extra length to the divider. The size of the proposed power divider is 30 × 15.3 mm² (0.082λ_g × 0.041λ_g). The fabricated power divider achieves a fractional bandwidth of 107%, an input return loss of better than 10 dB, an output return loss of 20 dB, an isolation of better than -10 dB and maximum exceeded insertion loss of 0.9 dB. The proposed compact power divider is implemented on Rogers RT/ Duroid 5880 with thickness 0.254 mm in order to bend on any conformal surface.

In this paper, a novel all-metallic probe-fed antenna is proposed for L5, L1, and S bands for Navigation with Indian Constellation (NavIC) applications, and it can be used for tracking applications. The proposed antenna dimensions are 30 mm x 80 mm x 8 mm (0.11λ x 0.31λ x 0.03λ) electrical size calculated at 1176.45 MHz (L5). The radiating plane has a comb like structure where there are 8 slots which are of identical size 24 mm x 1 mm and a short slot with 6 mm x 1 mm. The ground plane is 30 mm offset with respect to the radiating plane (top plane). Usually, a high dielectric substrate antenna can resonate at lower frequencies keeping the size of the antenna electrically small, but without substrate the proposed antenna resonates at lower frequencies keeping the antenna size electrically small. The proposed design is electrically compact and economical, and the dielectric loss in the antenna is zero as the antenna is designed with copper alone, which gives a strong impression that a substrate free antenna can resonate at lower frequencies. So, from this method it can also make the antenna light weight.

Millimeter-wave (mmWave) frequencies are considered as candidate bands for 5G/6G mobile networks. Diffraction models are significant for predicting non-line-of-sight (NLOS) wireless channels while it is shown that the line of sight (LOS) path is usually blocked by buildings in urban area environments. A lot of investigations on the diffraction loss have been performed, and most of them just considered a one obscuring object and a short propagation distance. In this paper, we conduct a statistical analysis of the diffraction loss in the outdoor NLOS in Urban Micro Cell, considering a transmitter (TX) and a receiver (RX) which are located at an aggregation point on the roof of a building. We have focused on analyzing the diffraction loss suffered by mmWave signals when they hit one or two obscuring points located over rooftop of the buildings. The objects have different heights located at various distances between TX and RX. We have considered the bands: 28 GHz, 38 GHz, 60 GHz, 73 GHz and 100 GHz. The analysis is based on the diffraction model named the Knife Edge Diffraction (KED). We have strictly followed the ITU Recommendations ITU-R P.526-15 (10/2019). In this work, we use two schemes that characterize the KED model, namely Single KED (SKED) and Double Isolated KED (DIKED). Different scenarios are performed by varying different parameters of the channel between TX and RX. The results show that the diffraction loss is inversely proportional to the distance between the obscuring object and the transmitter, the wavelength, and the distance between the TX and RX.

It is commonly believed that electromagnetic waves cannot propagate in lossy conductive media and that they quickly decay inside such media over short length scales of the order of the so-called skin depth. Here we prove that this common belief is incorrect if the conductive medium is stratified. We demonstrate that electromagnetic waves in stratified lossy conductive media may have propagating character, and that the propagation length of such waves may be considerably larger than the skin depth in homogeneous media. Our findings have broad implications in many fields of science and engineering. They enable radio communication and imaging in such strongly lossy conductive media as seawater, various soils, plasma and biological tissues. They also enable novel electromagnetic metamaterial designs by mediating the effect of losses on electromagnetic signal propagation in metamaterials. Our results demonstrate a new class of inherently non-Hermitian electromagnetic media with high dissipation, no gain, and no PT-symmetry, which nevertheless have almost real eigenvalue spectrum.

In this paper, a novel mechanical variable flux interior permanent magnet synchronous motor (MVF-IPMSM) is proposed. Based on the basic topology and operating principle of MVF-IPMSM, the effect of the special PMs structure in the new rotor topology on the air gap magnetic field and the design of the mechanical magnetic adjustment device of the proposed motor are analyzed, in which the finite element analysis (FEA) method is adopted. The electromagnetic characteristics of the MVF-IPMSM are analyzed including internal magnetic field distribution, air gap flux density, and torque characteristics. Furthermore, the ability of magnetic field regulation is also analyzed which can be reflected by the torque-speed and power-speed envelopes. Finally, a prototype is manufactured and tested. The measured results are compared with the FEA results, and the prototype experiments verify the effectiveness and feasibility of the design of the proposed MVF-IPMSM.

To aid with the design, evaluation, and optimisation of charged particle instrumentation, computer modelling is often used. It is therefore of interest to obtain accurate predictions for trajectories of charged species with the help of simulation. Particularly for solenoids and coils, which are often used for guiding, deflecting or focusing particle beams, knowledge of the magnetic field is required, especially in the fringing field regions. A novel model, which is based on a direct-line-of-action force between interacting charges, is described in this paper which accurately predicts the deflection of an electron beam trajectory traversing through a coil and the fringe field region. The model is further compared with a standard field model and a commercially available software package. Additionally, a relatively straightforward experiment has been designed and implemented to verify the simulation results, where it is found that the presented direct-action model is equally as accurate as field-based simulations compared with the experimental results. Furthermore, the magnetic field of a solenoid is visualised and analysed in terms of its radial, axial, and total field strength and compared to a force map obtained from the direct-interaction model. This representation allows for further comparison of the field and force interaction models and it is found that they are qualitatively the same.

To reduce the calculation time of traditional model predictive torque control (MPTC), lower torque ripple, and improve the dynamic characteristics of predictive control, a model predictive torque control strategy applied in permanent magnet synchronous motor (PMSM) based on fast predictive switching table is proposed. This paper presents the 12-sector division method first. Then, based on sector division MPTC, a fast predictive switching table is proposed to reduce the 14 candidate voltage vectors of the sector division MPTC to 5. In addition, the the Proportional Integral (PI)-based adjustable weight coefficient is designed, so that the two physical quantities in the cost function have different weights under different working conditions, which improves the dynamic response of the system. As the experiment shows, PMSM uses the control strategy of this paper to output smaller torque steady-state fluctuation and faster dynamic response.

To improve the control accuracy of the model prediction current (MPC) loop of a permanent magnet synchronous motor (PMSM), a new high-order super-twisting sliding-mode controller combined with a sliding-mode disturbance observer is proposed as a speed control strategy. Firstly, the linear term is added to the scaling term based on the original algorithm, which enhances robustness while weakening jitter. In addition, load perturbations and parameter uptake in the system are considered. The perturbation observation error is introduced into the switching gain function, and an improved sliding-mode disturbance observer is designed as feedforward compensation. The disturbance immunity of the system is effectively enhanced. Simulated and experimental results verify the correctness and effectiveness of this control strategy.

In this paper, the spatial impedance of the wireless power transfer (WPT) system is analyzed, and a resistance tunnel is found. First, the definitions of the spatial impedance in the near field are discussed, and one definition is chosen. By using this definition, the concept of the resistance and the reactance are extended from a scaler form into a vector form. Under this definition and this concept, the spatial impedance is analyzed, and a resistance tunnel is found. The tunnel possesses an obvious direction which is from the receive coil to the transmit coil, and possesses a concave phenomenon on the resistance's magnitude curves. The reason for the forming of the tunnel is also analyzed by discussing the x- and z-components of the resistance. Second, the influences on the resistance tunnel by four factors are discussed. Only the current phase difference determines the existence of the resistance tunnel. The other factors only influence the magnitude and the distribution of the resistance. The correctness of the theoretical calculation is verified by implementing an electromagnetic simulation via FEM. Since the WPT system is one of the typical coupling systems in the near field, one can infer that the resistance tunnel not only exists in the WPT system, but also exists in other coupling coil systems in the near field.

In this paper, we present a dual-polarized, pattern reconfigurable, liquid metal dipole antenna. The proposed design consists of a pair of ±45° polarized reconfigurable dipole antennas, two vertically placed feeding structures with filtering branches, and a resin frame for injecting liquid metal to adjust pattern. By introducing the U-shaped structure, a better impedance matching performance is achieved in two bands. The polarization can be switched by injecting liquid metal into different dipole microfluidic channels. By controlling the liquid metal reflector around the magnetic dipole, the reconfigurable pattern of +45° polarized antenna can be realized at 0°, 180° and 90° on the plane of phi=90°, and the reconfigurable pattern of -45° magnetic dipole antenna can be achieved at 0°, 90° and 270° on the plane of phi= 0°. The basic antenna operates with linear polarization around 4.8 GHz. The VSWR is less than 1.5. In the radiation pattern of the antenna, the port isolations of the two crossing ports are S₁₂ and S₂₁. S₂₁ port isolation is more than 35 dB. The antenna has good pattern reconfigurable characteristics, and the simulation results of the antenna indicate good radiation directivity. Moreover, the height of the proposed antenna is 0.625λ at 4.8 GHz. The good performance of the antenna makes it a candidate for base station systems below 5G sub-6 GHz.

A quasi-isotropic dielectric resonator antenna (DRA) is proposed under the 5.8 GHz industrial, scientific, and medical (ISM) standard. The antenna consists of a hollow cylinder and and a coaxial probe which feeds electricity. By digging a large hole in the cylindrical dielectric resonator, the HEM_11δ mode and the TM₁₀ mode of the floor are excited, the two modes are orthogonal, and the radiation characteristics are equivalent to orthogonal magnetic dipoles and electric dipoles, so as to achieve quasi-isotropic radiation characteristics. The large hole can also reserve space for other electronic components for Bluetooth devices with small space, such as capsule endoscope, mobile phone and Bluetooth headset. The characteristics of the antenna are simulated and analyzed by HFSS, and the optimized antenna structure parameters are obtained. The antenna is made for experimental testing. The measured results demonstrate that the antenna exhibits a good -10 dB-impedance bandwidth at 5.38-5.68 GHz and has the characteristics of miniaturization, quasi-isotropy, and high gain.

A circularly polarized (CP) patch antenna with a fractal structure that can be applied to the BeiDou navigation satellite system (BDS) is proposed. Etching two incomplete rings of different sizes with the antenna center as the center on the radiation patch generates CP. By adding a periodic structure based on the Sierpinski Carpet fractal around it, the size can be reduced while the gain is further improved. The dimension of the antenna is 0.35λ_o × 0.35λ_o × 0.03λ_o. Measured results manifest that the impedance bandwidth (S₁₁ < -10 dB) is wider than 40 MHz at 1.561 GHz; the gain in 3-dB axial ratio (AR) bandwidth can reach 3.33 dBi; the beamwidth exceeds 140° in the 3-dB AR bandwidth.

Metamaterials are artificially configured composite materials exhibiting unique characteristics such as negative effective permittivity and permeability. Due to these distinctive characteristics, metamaterials have drawn special attention in designing novel antenna structures and improving antenna performances. The application of metamaterial in antenna technology significantly brings miniaturization to the antenna structure, enhances the impedance bandwidth, gain, and efficiency of the antenna as well as improves isolation between the MIMO antenna elements. The substrate integrated waveguide (SIW) reduces the conductor and dielectric loss, and surface waεve excitations in the antennas. Although an overview of the performance enhancement of microstrip patch antennas under the influence of metamaterial has been incorporated in this article, the authors have put more effort in presenting a detailed study on working mechanism of metamaterial-based SIW antennas. Thus, a detailed review of the novel designs of metamaterial-inspired SIW cavity-backed slot antennas (CBSA), leaky-wave antennas (LWA), aperture antennas, and H-plane horn antennas has been included. The theoretical background of the metamaterials characteristics has been presented. Moreover, the working principles of metamaterial-based SIW CBSAs, SIW LWAs, SIW aperture antennas, and SIW H-plane horn antennas have been thoroughly outlined in obtaining antenna miniaturization, gain enhancement, beam steering through frequency scanning, polarization flexibility, bandwidth broadening, and isolation improvement. Besides this, a study has also been included in eliminating the limitations of SIW on-chip antennas such as narrow bandwidth, low gain, and efficiency by including metamaterial/metasurface in the antenna designs. Although the emphasis has been given to elaborating the attractive antenna performances, some design limitations have also been identified, and those need further investigation. This survey brings up not only the conceptual framework of the attractive characteristics of metamaterial, the design methodology of the non-resonant type metamaterial in the SIW environment, and the working principles of metamaterial-inspired SIW antennas but also the design limitations. Thus, consideration can be given to this article as the potential design guidelines of the metamaterial-based SIW antennas, and possible ideas can be obtained for doing further advanced research on the identified research gaps.

This paper describes the concept and implementation of a compact dual-band microstrip slot antenna and its four-unit multiple-input–multiple-output (MIMO) implementation for sub-6 GHz utilizations. The proposed structure comprises a 50 ohm microstrip monopole on the top side with a defective ground structure (DGS) having semicircular and rectangular slots. This quad-element MIMO antenna has a size of 60 × 60 × 1.6 mm³. The proposed antenna provides wide impedance bandwidths of 23.7% (2.42 GHz to 3.07 GHz) for the first band and 42.2% (4.14 GHz to 6.37 GHz) for the second band with a mutual coupling value less than -34 dB for the two bands. The antenna also provides a low envelope correlation coefficient, good antenna gain, and acceptable radiation efficiency across the frequency ranges.

Aiming at the problem of motor speed decrease in direct-drive permanent magnet synchronous generator (D-PMSG) wind power generation system after permanent magnet (PM) demagnetization faults, a demagnetization fault-tolerant control strategy in D-PMSG wind power generation system is proposed. Firstly, the D-PMSG mathematical model is described in normal and demagnetization. Secondly, an extended Kalman filter (EKF) observer is designed to observe the PM flux online. Then, flux linkage parameters are introduced into the two-vector model predictive fault-tolerant control so that the increase of stator current is controlled within the limit range. Meanwhile, the motor speed can follow the change of the given speed. In addition, the improved Luenberger mechanical torque observer is designed in the speed outer ring to deal with the vibration caused by unstable wind speed. Finally, compared with the dual-closed-loop Proportional Integral (PI) control, the experimental results show that the demagnetization fault-tolerant control strategy has smaller speed overshoot and smaller speed fluctuation when the mechanical torque changes. The method can maintain the speed balance when the PM demagnetization faults occur and have stronger fault tolerance and anti-interference ability.

In this study, a novel, low-profile, polarization-insensitive, and compact band-notched absorber is presented. The objective of the proposed work is to design a miniaturized FSS-based band-notch absorber with high angular stability exhibiting strong operational bandwidth of 130.5% (1.7 GHz to 8.09 GHz). The absorber consists of a reflecting band sandwiched between two absorption bands. The absorption bands lie in between 1.7 GHz to 3.75 GHz and 5.65 GHz to 8.09 GHz respectively. The strong reflection band with 1 dB insertion loss lies in the frequency range from 4.25 GHz to 5.12 GHz. The proposed absorber structure comprises multiple layers with a metal sheet at the bottom. Total thickness of the band notch absorber is only 0.064λ_L (where λ_L is the wavelength corresponding to the lowest frequency of operation). The top layer comprises a modified swastika frame metallic structure loaded with lumped resistors placed on a dielectric substrate. Two air layers, one below the top layer and the other above the bottom metal, are inserted. In between two air layers a dielectric layer with a metallic rectangular ring pattern is positioned. The four-fold symmetrical structure results in polarization insensitive response. The equivalent circuit of the proposed structure is developed for understanding the underlying working principle of band notch absorbers. The surface current distribution has also been studied. The designed absorber is fabricated, and measurements are done in an anechoic chamber. The measured results show good agreement with the simulated ones.

Metamaterials offer a chance to design films that could achieve optical differentiation due to their special properties. Layered film would be the simplest case considering the easy-fabrication and compactness. Instead of performing the optical differentiation at the Fourier plane, Green-function based multi-layers are used to achieve optical differentiation. In this work, epsilon-near-zero (ENZ) material is utilized to realize the optical differentiation owning to the special optical properties that the reflection increases with the increase of incident angle, which fits the characteristics of optical differentiation. In addition, deep learning is also used in this work to simplify the design of ENZ layers to achieve the optical differentiation, and further realize the optical edge detection. Simulations based on the Fresnel diffraction are carried out to verify that our films designed by this method could realize the optical detection under different cases.

This paper proposes computing the mutual impedance of a multi-layer patch fed by a slotted waveguide using the combined equivalent electric and magnetic dipole-moment method and conventional moment method (EDM-MOM) as an efficient technique. The slot, PEC, and dielectric regions are substituted with equivalent currents. The unknown currents are expanded using the Rao-Wilton-Glisson and Schaubert-Wilton-Glisson basis functions. The matrix equations are then extracted from the boundary conditions. Using the EDM, each RWG or SWG of the PEC and dielectric is equivalent to an infinitesimal electric dipole, and that of the slot is equivalent to a magnetic dipole. The element matrix related to the waveguide excitation is calculated using the conventional moment method due to simple integration and accuracy. Further, the superposition of the mutual coupling between each equivalent electric or magnetic dipole in the first element and each dipole in the second element is used to obtain the mutual impedance of the two elements of the waveguide slot-fed patch array. The proposed method shows good agreement with CST software simulation results.

This paper aims to test the concentration of dissolved particles such as salt and sugar in a water sample and also test the quality of water. Ultra-Wide Band (UWB) antenna has been designed and used to test the water sample. The proposed UWB antenna has been resonated from 3.2 GHz to 10.6 GHz. The fractional bandwidth of the UWB antenna is 1.15. The measured antenna's characteristics were in good agreement with the simulated results. Then, the designed UWB antenna was used as a sensor on the water samples such as distilled water, rainwater, pond water, seawater, and Reverse Osmosis (RO) water. Hence, this paper explains the concentration of dissolved particles and testing of the quality of the water sample by using the return loss characteristics of the antenna when it is immersed in the water sample. This technique can be further extended for testing the quality of any other liquids.

Magnetic coupling based Wireless Power Transfer (WPT) systems for charging no doubt have emerged as an eye catching alternative charging methodology in recent years. However, a rigorous assessment between magnetic coupling based traditional WPT system and magnetic resonant coupling based WPT system is essential in order to characterize and decide the best suited technology corresponding to their applicability. The effectiveness of both the technologies and their power transfer characteristics have been demonstrated in perception of consumed input power, delivered load power for different coupling coefficient over varying operating frequency and electric load condition. The theoretical and analytical study supported with the simulation and bench set up experiments have been carried out in order to disclose the viability of both the technologies in the device charging. In addition, an inclusive correlation between the performance parameters of the WPT systems is established through the analysis, and justification regarding the RIC-WPT system as an alternative viable solution in the charging field has been outlined.