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.

A filter with good impedance matching for both in-band and a wide range of out-of-band is reported in this paper. Thus, the proposed filter offers low reflection for a wide range of frequencies, and it can be called as quasi-reflectionless filter. Also, the proposed filter improves the passband flatness significantly. The quasi-reflectionless filter consists of n-pole conventional U-shaped bandpass filters with absorptive stubs (ABSs) placed at the input and output ports. Each part in the whole filter is individually investigated. The U-shaped resonator is studied first, and then the ABSs are analyzed mathematically and simulated to optimize the attenuation rejection. Several parameters that have an influence on the overall performance are investigated. Different n-pole filters are simulated to simply enhance the out-of-band rejection without affecting the passband response. The filter response is furthermore improved by introducing two transmission zeros using the cross-coupling between the two ABSs. To validate the proposed idea, the 3-pole U-shaped quasi-reflectionless BPF is fabricated on an FR4 substrate at the operating frequency of 3.5 GHz. The filter has measured responses very close to the simulated ones.

The defective array elements which are unavoidable due to the long full-time antenna system operation directly affect its radiation pattern, sidelobe level (SLL), directivity, and the system performance. Therefore, reducing these undesirable effects is a main interest in designing such arrays in practice. In this paper, a partially compensating method based on the genetic optimization algorithm (GA) is proposed to mainly reduce those undesirable effects of the defected elements. Unlike the existing fully compensating methods where all of their active elements were optimized to compensate for the effects of the defected elements, the proposed method optimizes the excitation weights of some optimally selected active-elements. Thus, the whole array elements do not need to be redesigned again as in the case of the fully compensating methods. This greatly simplifies the design implementation of these arrays. Moreover, a very large defective percentage ranging from 5% up to 50% has been considered to demonstrate the effectiveness of the proposed method. Furthermore, the drawback effects of the randomly failing elements at the array center have been highlighted, and some suggestions have been provided.

A compact and broadband stub-loaded dual-mode dipole antenna is proposed. In this paper, the first- and third-order modes are combined to achieve broadband frequency response. To do so, the third-order mode is compressed close to the first-order mode by loading two pairs of identical stubs at an optimal distance from the dipole-centre. Stubs are symmetrically loaded to both the arms of the dipole. Stub parameters such as length, width, and location play a critical role in decreasing the third-order mode frequency. Therefore, a parametric analysis is also carried out to see the effects of variation in the stub parameters. The proposed antenna is fabricated, and measurements are performed to verify the simulation results. A good agreement between the simulated and measured results is obtained.

A novel high performance four-port multiple input multiple output antenna is suggested for 5G application functioning at 3.4 GHz band. The antenna design measures an inclusive volume of 32 mm x 32 mm x 0.8 mm³. The broad frequency bandwidth, excellent gain, decreased interelement gap, and effective isolation within the MIMO components of the proposed system are clearly novel. Each antenna in the four-element MIMO system has been situated orthogonally to the others while maintaining a small size and good result. The antenna has exceptional average total efficiency in the 5G Sub-6 GHz spectrum and is in good agreement with the measured results. It also offers a high realized gain compared to prior MIMO antennas. The antenna has a high impedance matching whose isolation is about -28 dB, computed envelope correlation coefficient smaller than 0.10, channel capacity loss average value less than 0.2\,bits per second per hertz, and the diversity gain about 10 dB. The typical peak realized antenna gain of the offered MIMO antenna is also delivered with a high radiation efficiency at the frequency of 3.4 GHz. The reflection coefficient, mutual coupling, radiation pattern, current distribution, and gain of antennas are all measured and explained. The design has a compact high volume and adequate bandwidth with good accomplished gain making the antenna very strong for 5G application.

A reconfigurable filter integrated single-pole double-throw (SPDT) switch (FIS) based on capacitor loaded ring resonators is presented in this paper. The design incorporates two PIN diodes between two symmetric square ring resonators. The ring resonators can be switched between allstop and bandpass responses, by adjusting the state of the PIN diodes, allowing the corresponding signal path to be in OFF-state with high isolation or ON-state with bandpass filter response. For demonstration, filtering switch is fabricated and measured for 2.4 GHz applications. The measurement results feature an ON-state low insertion loss of -2.1 dB and port-to-port isolation of -50 dB at the band of interest, and good consistency is achieved between simulated and measured results.

In active phased arrays, T/R module performance drifts due to active components' aging and thermal effect. Hence periodic online field calibration is required during the deployment of a radar system. This paper presents an innovative design of a precise and consistent calibration network consisting of a buried leaky coaxial cable (LCX) and a calibration switch network (CSN) for fast periodic field calibration of an active phased array. In the antenna plate, leaky coaxial cables are buried within the wall of the cavity-backed antenna to realize calibration lines. A 1:30 way Wilkinson power divider/combiner is realized as a calibration switching network for simultaneous excitation of multiple calibration lines to characterize multiple radiating elements in the active array. An S-Band (3.3 GHz ± 200 MHz) experimental active array with 64T/R modules is configured and tested in the near-field test range (NFTR) to demonstrate the performance of the proposed calibration network. Simultaneous excitation of multiple radiating elements significantly reduces array calibration time and provides more flexibility to other multifunction radar functions. The availability of multiple receivers and non-overlapping RF beam forming networks in the radar system limits the improvement factor in array calibration time mentioned in this paper.

A Metamaterial Terahertz perfect absorber is proposed in this letter. The structure comprises Vanadium oxide (VO2) resonator hexagonal rings placed on top of a silicon dioxide (SiO2) substrate in a concentric pattern on a metal ground layer, with 1 THz and 6 THz operating frequency. Numerical studies are done by an electromagnetic solver. The results show almost perfect absorption, with 112% average absorption at different incident polarization angles, in the range of 1.64 to 6.1 THz. The optimization is carried out on physical dimensions for maximum absorption results. The proposed design can be used as a highly efficient absorber in applications like solar energy harvesting, cloaking, sensing, imaging technology, and EMC projects.