This article presents the design and optimization of multi-ring permanent magnet thrust bearing (PMTB) with an axial air gap between successive axial stacks. Larger air gap due to the inclusion of conductive materials needs to be critically analysed in permanent magnet bearings with eddy current damper. High conductivity materials can be filled in an axial air gap instead of a radial air gap to increase the required amount of damping. Three-dimensional (3D) mathematical model for load-carrying capacity for the said configuration is presented using the Coulombain model. The significance of an axial air gap between successive ring pairs in the configuration concerning maximization in the bearing characteristics is presented. Variables such as the number of axial stacks, an axial air gap between the successive rings, an inside radius of rotor ring magnets, and an inside radius of stator ring magnets are optimized at different air gap values for maximizing the load-carrying capacity and stiffness. A significant increase in the values of bearing characteristics is observed in the optimized configuration as compared to bearing with a single permanent magnet ring pair. Optimized PMTB with comparable load carrying capacity and stiffness values can be used to replace conventional bearings used in high-speed applications to improve system efficiency.

In this paper, a new cross section configuration of partially dielectric-filled rectangular waveguide (PDF-RW) is proposed and analyzed. It may beused when substrate integrated waveguides (SIWs) are designed such as to maximize the frequency bandwidth for insertion losses as low as possible. Imposing the boundary conditions for the electromagnetic field components, the equations for the cutoff frequencies and propagation constants are developed for the TE_m0 modes. It is shown that the cutoff frequency equations developed in this paper may also be used to analyze particular cases investigated by other authors. The ratio between the cutoff frequencies of the TE₂₀ and TE₁₀ modes is computed and represented graphically for different geometric dimensions of the proposed PDF-RW configuration. The conductor and dielectric losses for the TE₁₀ mode are computed as well, based on the results provided by the equations developed in this paper. The results obtained by using the proposed approach are compared to the HFSS (High-Frequency Structure Simulator) results, and very good agreement is observed between them.

This article discusses the effect of sectorization technique in hemispherical dielectric resonator antennas (HDRA) for the first time with its significant effects on electromagnetic modes and various antenna parameters. The sector angle (β) forms an additional framework for better optimization of HDRA. The resonance frequency, impedance bandwidth, co-cross polarization characteristics have been investigated in new sectored HDRA geometries excited at their TE₁₁₁ and TM₁₀₁ modes. Further, examination of circular polarization (CP) is carried out by detuning of degenerate orthogonal modes in HDRAs, and β = 180° has been particularly examined in details for CP. Based on the results, appropriate values of `β' and probe position (P_r) are chosen followed by modelling a prototype and experimental.

Vertically- and horizontally-polarized antennas were investigated for on-body to on-body (OB2OB), in-body to in-body (IB2IB), and on-body to in-body (OB2IB) wireless propagations at frequencies of 915 MHz and 2.45 GHz. Theoretical formulations, simulations, and measurements were employed to study the effect of source antenna orientation on the attenuation of the radio frequency (RF) wave as it propagates around, inside, and through the body near the torso region. The results show that the vertical polarization is preferred for OB2OB communication, and the horizontal polarization is better for IB2IB communication. Furthermore, the dominant propagation mechanism and optimum antenna excitation for OB2IB communication are identified to be distance-dependent. The horizontally-polarized dipole is preferred at a shorter distance while the vertically-polarized dipole is preferred at a larger distance away from the source. The observed results were explained using the estimated attenuation rates of the different propagation mechanisms.

When a high voltage direct current (HVDC) system works at single line operation mode, a big current will flow into the earth through the grounding system directly. Then the large current can cause damage to surrounding equipment and the environment. Therefore, it is significant to study the current dispersion characteristics of HVDC grounding system. Firstly, a ±800 kV HVDC model operated at single line mode is built. The grounding current can be seen as the equivalent current source injecting to the grounding system. Secondly, the current dispersion characteristics of horizontal, cross and ring electrodes are investigated. It proves that the ring grounding electrode shows better current dispersion characteristic. And the double-ring grounding electrode whose ratio of inner and outer rings is controlled at 0.7 to 0.75 can get a better current dispersion characteristic. In addition, a dynamic seasonal frozen soil resistivity changing model is built to study the effects of season on the grounding electrodes. The frozen soil would not only increase the ESP, the resistance to ground, and step voltage, but also reduce the current density and electrical field. When the frozen soil is melting, the current dispersion characteristics are the best. The results provide meaningful reference for the design of the grounding system in extremely cold regions.

The aim of this research is to propose a new efficient and reliable approach on the field of Non Destructive Testing (NDT), for the characterization of cracks in non-ferromagnetic material by Electromagnetic Acoustic Transducer (EMAT). EMAT is an ultrasonic technique that generates and detects ultrasonic waves in the conductive material without physical contact. The research goes through two principal phases. The first, which is a forward model, is based on Finite Element Method (FEM). The FEM is applied to simulate the EMAT response (output voltage) to the material under test in order to build a database for the inversion tool. The second is the inverse model and depends on the Partial Least Square Regression (PLSR) method, as it is a fast, simple, and accurate inversion tool, in order to estimate the depth and width of the cracks on the surface of non-ferromagnetic materials. PLSR is a dimensionality reduction method which aims to model the relationship between the matrix of independent variables (predictors) (X) and the matrix of dependent variables (response) (Y). The purpose of PLSR is to find the Latent Variables (LV) that have a higher ability of prediction by projecting original predictors into a new space of reduced dimensions.

In general, a single beam reflection can be realized by 2-bit coding metasurfaces. In order to obtain multi-beam reflection, a design method for coding sequence based on 2-bit coding metasurfaces is proposed, which can manipulate the direction of reflected beams by 2-bit addition rule and control the number of reflected beams by addition theorem on complex codes. This method simplifies the design process of coding sequence, and the direction and number of multi-beams can be flexibly designed. In this paper, the design of dual-beam reflection is taken as an example to illustrate the design process of coding sequence. Both simulation and measurement results show that the designed metasurface realizes the dual-beam reflection, and the direction of reflected beams is consistent with expectations. The proposed method is of great significance for the design of multi-beam reflection based on coding metasurfaces.

In this work, the design of an ultra-wideband (UWB) fork monopole antenna based on a surface impedance substrate integrated waveguide (SIW) resonator has been proposed. The SIW resonator not only improves the antenna bandwidth and its performances, but also permits to reduce the antenna size and weight. An antenna prototype has been designed, fabricated, and experimentally assessed. The obtained results are quite satisfactory, and they demonstrate the potentialities of the proposed geometry.

In this paper, an S band, 300 MHz bandwidth, and 20 kW average power klystron was developed in the Aerospace Information Research Institute, Chinese Academy of Sciences. The klystron operates at 72 kV beam voltage and 41 A beam current with peak powers of over 850 kW and efficiency of over 30% at a 2.47% RF duty cycle. The results, including simulations, design, technologies and performances of the klystron, are presented. Some problems, such as gain dip, high order mode oscillation, output window cracking, and startup time, were also discussed.

We exploit the properties of differential geometry of minimal surfaces to introduce a novel approach for characterizing wavefronts. Since Gaussian and mean curvatures describe global and local properties of any differentiable surface, a method for characterizing wavefronts endowed with non--trivial topological features has been introduced. We provide experimental evidence that the wavefront of an l = 1 radio-vortex at 30 GHz can be fully characterized by exploiting the wavefront phase in the far field of the source, accessing a small portion of the beam only. A particular care is dedicated to distinguish diffraction effects from the intrinsic curvature of the helicoidal wavefront. Results are applicable to the local measurement of the topological charge and to the local detection of orbital angular momentum radiation at the millimetric wavelengths.

This paper presents a design study of a shark-fin antenna for future railway communications. Three specific bands are considered here as LTE-R (700 MHz), LTE (2100 MHz), and Lower 5G Band (3500 MHz). A 3-D metallic structure using the 3D printing technique has been designed and fabricated for the consideration of the required bands. The size (volume) of the antenna element is 163 × 61.9 × 10 mm³. The multi-physical simulations in terms of the smooth air flow and lower drag coefficient are performed for analyzing the need of shark-fin radome cover. More than 70 MHz bandwidth was observed for the LTE-R band and also a wide band response was observed that cover the required bands well i.e. the LTE, and lower 5G band. The proposed shark-fin antenna results the expected ideal radiation performance with an omnidirectional behavior in the horizontal plane.

In this paper, an absorptive filter-integrated switch (FIS) using switchable T-shape resonators is presented. The FIS was made up of two absorptive T-shape resonators and integrated with single pole double throw (SPDT) switch. A simple mathematical analysis of isolation and insertion loss of filter-integrated SPDT switch is discussed. PIN diodes were used as the switching elements for the SPDT switch and to reconfigure between the band-stop and bandpass responses. The proposed absorptive FIS design could be used for internet of things (IoT) applications such as Zigbee and Bluetooth at an operation frequency of 2.45 GHz. As a result, the proposed FIS exhibited low magnitude of insertion loss and high isolation. Therefore, the key advantages of the proposed FIS design are low insertion loss, high isolation, and good return loss at both ON- and OFF-state ports.

A six-element circular antenna array with Yagi-Uda corner reflector elements is proposed in order to achieve 360° beam-steering capability, high gain and cost-effective design objectives. The array element is mainly composed by a Yagi-Uda antenna, a corner reflector and a Wilkinson balun. For steering the main beam, instead of classical RF switching techniques, a virtual switching technique is offered. For this aim, each antenna element is connected to an affordable RF transceiver managed by a microcontroller. A USB hub is also used so that a computer operates all microcontrollers as peripheral devices. In this way, the switching operation can be performed in the software level. Furthermore, if every transceiver in the separate chain is set to a different frequency channel, a simultaneous communication is also possible with the help of the multithreading facility of the computer. In order to show the antenna array performance, the main antenna characteristics and test results are given. As a proof of concept, a wireless image collector scenario is also realized for a camera trap application. The results show that the circular antenna array design and switching technique work successfully.

A coplanar waveguide (CPW) fed uniplanar all-metallic antenna is proposed for mmWave 5G access points. The antenna has an impedance bandwidth from 26 to 30 GHz with a corresponding end-fire gain of 8 dBi at 28 GHz. The effective radiating volume is 0.0031 λ₀³ indicating a high gain yield for minimal physical footprint. The radiation efficiency is 99.5%, and the losses are primarily due to finite conductivity of copper. The pattern integrity is high across the band with cross-polarization level below 30 dB, due to lack of electrically thick dielectric substrate. Industry standard low-cost chemical etching technique is used for fabrication of the prototype. A compact, co-polarized stacked beam switching module is also proposed for wide angular coverage with three-ports. This module houses the proposed all-metallic antennas for beam switchability. A customized 3D-printed scaffolding using polylactic acide (PLA) is designed to house the proposed antennas. The antenna module has a wide angular coverage of ±50º. Since the proposed antenna has high radiation efficiency with high gain for minimal physical footprint, it could be a potential solution for mmWave 5G access points. Detailed simulated and measured results are presented.

In this study, plane wave diffraction by a perfect electromagnetic wedge which is lying between isorefractive media is investigated. The diffracted waves are constructed by using the relation between initial geometric optics waves and scattered waves at the transition boundaries. The uniform theory of diffraction method is used for derivation of the uniform wave expressions. Thus, obtained uniform expressions are analyzed numerically for different set of parameters.

A novel integrated compact antenna with photonic band gap (PBG) structure, having switching capability between lower and upper bands of 5G cellular communication is proposed. The proposed antenna can operate in the lower band (3.1 GHz to 3.5 GHz) as well as in the upper band (24 GHz to 27 GHz) of 5G cellular communication. Two radiating patches for the aforementioned frequency bands are developed in the same structure. A small patch for the upper-frequency band is inserted into a rectangular slot made in a large patch of the lower-frequency band. Both patches radiate at different times with the same ground. Two PIN diodes have been used to excite both patches at different times. The results indicate that the antenna has higher gain and wider bandwidth than the conventional antenna without a PBG structure.

This paper presents a 90° broadband compact phase shifter which employs loade λ/2 transmission line. By adding an H shaped open stub loaded transmission line, the bandwidth of the phase shifter is broadened. Detailed theoretical analysis and circuit configuration are presented to explain the mechanism. The proposed phase shifter is fabricated and measured to validate the design principle. The simulated and measured results show that the proposed phase shifter achieves 6.6 to 19.4 GHz bandwidth with low phase instability ±5°, very low insertion loss (0.3 dB in 7.5-15.2GHz), high return loss (10 dB), and a compact size (5.8cm*6.1cm). Good agreements are observed between the measured and simulated results with small phase deviation. Moreover, the configuration of the proposed phase shifter is simple in both design and fabrication which makes the design suitable for actual applications.

The study of the electromagnetic field, taking into account eddy currents in the conductive half-space, is based on the exact analytical solution of the general three-dimensional quasi-stationary problem. The mathematical model includes an approximate solution using asymptotic expansion in the case of strong skin effect. Analytical expressions are obtained for the electric and magnetic fields at a flat interface in the form of limited asymptotic series, each term of which is expressed through a known field of external sources. The expressions take into account the nonuniformity of the field near the surface, since they contain its derivatives with respect to the coordinate. The series expansion was carried out according to a small parameter, which is proportional to the ratio of the field penetration depth to the distance between the interface and the sources of the external field. The found expressions generalize the approximate boundary impedance condition for the case of the penetration of nonuniform electromagnetic field into conductive medium.

A time domain hybrid method is presented to solve the coupling problem of non-parallel transmission lines (NPTLs) excited by ambient wave efficiently, which consists of transmission line (TL) equations, finite-difference time-domain (FDTD) method, and interpolation techniques. In this method, NPTLs are firstly divided into multiple independent transmission line segments according to the FDTD grids. Then the TL equations are applied to build the coupling models of these TL segments, which rely on the calculation precisions of per unit length (p.u.l) distribution parameters of NPTLs and equivalent sources of TL equations. Thus, the p.u.l parameters of NPTLs are derived from empirical formulas, and the equivalent sources are obtained by some linear interpolation schemes of electric fields on the edges of FDTD grids. Finally, the difference scheme of FDTD is utilized to discretize the TL equations to obtain the voltages and currents on NPTLs and terminal loads. The significant feature of this hybrid method is embodied by its synchronous calculations of space electromagnetic fields and transient responses on NPTLs in time domain. The accuracy of this presented method is testified by the numerical simulations of plane wave coupling to NPTLs on the ground and in the shielded cavity by comparing with FDTD-SPICE method and CST software.

In this paper, a joint two dimensional (2D) direction of departure (DOD) and 2D direction of arrival (DOA) strictly noncircular (NC) unitary estimation of signal parameters via rotational invariance techniques (ESPRIT) method is proposed for an L-shaped bistatic multiple input multiple output (MIMO) radar. In the case that the incident signals are NC signals, we first utilize the received data vector and its conjugate counterparts to construct a new data vector, and then the unitary ESPRIT method is adopted to estimate the 2D-DODs and 2D-DOAs, which can automatically pair the four dimensional (4D) angle parameters. Simulation results are included to verify the effectiveness of the proposed algorithm.