This paper presents a mechanically reconfigurable reflectarray with height adjustment for phase compensation. We designed, fabricated, and measured a prototype of 11×11 elements with microcontrollers to verify the feasibility of the proposed reflectarray. Simulated results show that the phase curve of the unit has good linearity and exhibit broadband characteristics. The maximum phase shift of the unit reaches about 200° at a center frequency of 16 GHz, which meets the requirement of a reflectarray with 1-bit phase quantization. Experimental results show that the gain of the proposed reflectarray is 17.7 dBi, with beam scanning range of ±50°. The proposed configurations can be used for a low-cost beam scanning antenna in wireless communication.

This article contains a digest of the theory of electromagnetism and a review of the transformation between inertial frames, especially under low speed limits. The covariant nature of the Maxwell's equations is explained using the conventional language. We show that even under low speed limits, the relativistic effects should not be neglected to get a self-consistent theory of the electromagnetic fields, unless the intrinsic dynamics of these fields has been omitted completely. The quasi-static limits, where the relativistic effects can be partly neglected are also reviewed, to clarify some common misunderstandings and imprecise use of the theory in presence of moving media and other related situations. The discussions presented in this paper provide a clear view of why classical electromagnetic theory is relativistic in its essence.

A compression algorithm for the T-matrix scattering solution from multiple objects and incident fields is derived and examined which we call the Compressed T-Matrix Algorithm (CTMA). The CTMA is derived by applying the SVD and Woodbury matrix-inverse identity to compress the original T-matrix system of equations and simultaneously compress the matrix of right-hand side incident field vectors. This is suited for scattering problems with many incident directions. We quantify the compression rates for different collections of dielectric spheres and draw comparisons to the Characteristic Basis Function Method (CBFM) with which the CTMA shares many structural similarities.

The basic climatic characteristic of the tropical areas is abundant precipitation throughout the year. For such precipitation the radio signal (RF) power of these areas gets diminished in communicating any signaling information from a sender to a receiver i.e. rain fading occurs in these areas. Rain fading is one of the major causes which decline the characteristics of radio system in tropical areas. To reduce excessive rain fading various fade reduction techniques such as diversification techniques, adaptive power control technique and adaptive waveform technique have been used. Frequency diversification technique is an effective technique for diminishing rain fading. In this work in order to diminish rain fading a suggested model has been implemented. Frequency diversification improvement factor is accepted to heighten the performance of this suggested model. Besides, by adopting an experimental data sheet a comparison of this suggested model with a number of various existing rain attenuation predicted models has been depicted for validation of the suggested model. The experiment was performed by accepting two mm-Wave connectors acting on two frequencies of 26 GHz and 38 GHz, respectively, for observing which model renders better result in the tropical region with respect of various distances, frequencies, and elevation angles.

This paper aims to develop a new 3D analytical model devoted to the study of nonlinear transient magneto-thermal coupled problems in permanent magnet transverse flux induction heating device (PMTFIHD). Firstly, a 3D analytical solution of magneto-dynamic field problem taking into account the transverse edge effect in the workpiece is derived using variables' separation technique. This transverse edge effect allows determining the exact resulting heating power density, which is the heat source of the transient thermal problem in the work-piece. Secondly, the 3D transient analytical solution of the temperature distribution is obtained by combining variables' separation technique and Green's function method. Then, the previous models are exploited in a transient simulations procedure of the magneto-thermal process allowing the nonlinear physical properties of the part to be taking into account. Finally, the performances of the studied PMTFIHD will be calculated, in order to validate the developed 3D coupled models. The simulation results from the developed models are validated with those obtained by the finite element method and the experimental results.

In this paper, wideband and high efficiency millimeter-wave circular Airy orbital angular momentum (OAM) beams, which have desired multiplexing OAM modes, directions and beam numbers, are generated by the proposed three metal layer transmission metasurfaces (TMSs) with size 12λ₀×12λ₀ based on the Airy-OAM phase superposition method. The measured results indicate non-diffracting propagation distance 31λ₀, autofocusing property, high aperture efficiency 13.1%, and wideband 16.8% (28 GHz-33 GHz). The design method can be used for circular Airy OAM beam generation in point-to-point, point-to-multipoint wireless power transmission (WPT), and OAM mode multiplexing communication systems.

This paper studies the optimal design of a double-sided linear flux switching permanent magnet motor (DLFSPM) to improve the average thrust generated by motor operation and reduce the fluctuation range of thrust applying the Response surface methodology (RSM) and Particle Swarm Optimization (PSO). An analytical mathematical model of the electromagnetic thrust force of the DLFSPMs is developed. The functional model of the optimization parameters and objectives based on the RSM is constructed. The finite element analysis (FEA) is used to carry out numerical experiments on the geometric structure design variables. PSO is applied to an optimization tool for optimizing the DLFSPMs' mover structure parameters. Finally, the FEA comparison and analysis of the optimization results with the initial results reveal a significant improvement in the electromagnetic characteristics of the DLFSPMs. The feasibility and effectiveness of the optimization method are verified by the FEA results.

Carr-Purcell-Meiboom-Gill (CPMG) is generally used as the measurement sequence of unilateral NMR (UMR) sensors, and the NMR signals collected by the sequence are composed of a series of echo signals. In the traditional CPMG measurement signal, each echo peak value is first taken and then denoised, which would lead to the inaccuracy of the peak point taken, resulting in deviation. To ensure the measurement result more accurate, this paper proposes to employ wavelet technology to denoise the echo signal first, and then take the peak point to analyze the data. Firstly, a simplified model of the spin-echo signal without the influence of gradient magnetic field was established, and white noise was applied to a certain extent. Then, Signal to Noise Ratio (SNR) and Root Mean Square Error (RMSE) were used as evaluation indexes. The denoising effects under different wavelet bases and thresholds were compared. Finally, the Matlab simulation result showed that wavelet analysis had a good effect on the denoising of unilateral NMR spin echo signal.

A problem of scattering of electromagnetic waves by thin impedance biconical vibrators in а free space and in a rectangular waveguide is solved by an asymptotic averaging method and a generalized method of induced electromotive forces (EMF). An influence of the change of vibrator radius upon energy and spatial characteristics is numerically studied. Theoretical results are compared with the experimental data.

We introduce the concept of gap Zak or Chern topological invariants for photonic crystals of various dimensionalities. Specifically, we consider a case where Tamm states are formed at an interface of two semi-infinite Bragg mirrors and derive the formulism for gap Zak phases of two constituent Bragg mirrors. We demonstrate that gap topological numbers are instrumental in studies of interface states both in conventional and photonic crystals.

This paper presents a single element ultra-wideband (UWB) microstrip patch antenna with high directivity. In this work, techniques like partial ground and modification of the patch have been used to achieve the UWB. The designed antenna consists of a modified U-shaped radiating patch with a microstrip feed attached directly to it. The initial U-shaped radiating patch is modified by attaching an inverted trapezium on both sides of the feed line. Two parasitic patches are introduced near the feed structure of the antenna after etching away two rectangular slots with appropriate dimensions. Moreover, the proposed structure consists of a partial ground plane which contributes to the UWB nature. Modifications in the form of square and triangular slot etching are carried out in this part of the proposed structure. The proposed antenna is compact with dimensions of 16 mm × 19 mm × 1.6 mm. Finally, gain enhancement of the proposed structure is done by placing a Frequency Selective Surface (FSS) behind the proposed antenna with an air spacer in between the structures. A novel FSS unit cell is proposed, and its performances are checked experimentally. Later, FSS is combined with the antenna, and measured peak gain of 9.7 dBi is obtained experimentally. The overall size of the structure is 62.5 mm × 52 mm × 24.9 mm.

A broadband phase shifter (PS) with a constant phase based on a negative group delay (NGD) microwave circuit is proposed. The presented broadband PS is composed of distributed microstrip lines and two resistors, which is based on the positive group delay compensation principle. By tuning the electrical length of the phase shift transmission line, the constant phase can be obtained in the range of -360° ~ 0°. For verification, three broadband PSs with the phase shift of -90°, -180°, and -270° (90°) are designed, fabricated, and measured at the center frequency of 1.0 GHz. The measurements show that the -90° PS can achieve a constant phase of -90°±3.0° with a fractional bandwidth (FBW) of 73.1%; the -180° PS can achieve a constant phase of -180°±5.0° with an FBW of 51.1%; and the -270° PS can achieve a constant phase of -270°±4.0° with an FBW of 40.4%. Besides, the return loss is greater than 13.6 dB in the flat-phase bands.

In this paper, an AgileDARN (Agile Dual Auroral Radar Network) radar echo classification method based on support vector machine is proposed. AgileDARN radar echo includes ionospheric backscattering echo, meteor echo, noise interference, etc. With the continuous operation of AgileDARN radar, the amount of data increases rapidly, requiring efficient and reliable classification methods. In order to efficiently classify the echoes of AgileDARN radar, this paper proposes an echo classification method based on support vector machine. By analyzing the characteristics of the autocorrelation function (ACF) of the sampled data and extracting the features, the support vector machine(SVM) classification method is adopted to classify AgileDARN echo into ionospheric backscattering echo, meteor echo and noise interference. The data analysis shows that the classification accuracy of training data set is more than 99%, and that of test data set is more than 95%. Using this classification model to classify 1800 echo data of AgileDARN radar, the classification accuracy is more than 91% compared with the result of manual interpretation.

In this paper, a novel miniaturized dual-band embedded near-zero index (NZI) metasurface-based patch antenna is presented. A new methodology based on loading a narrowband microstrip patch antenna (resonating at 4.6 GHz) by a metasurface embedded in the middle of the antenna's substrate is introduced. The loaded antenna has a dual-band resonance of bandwidth of 15% and 43% at 2 GHz and 4.6 GHz, respectively. The metasurface layer is an array of square holes such that there is no hole below the patch. The metasurface layer is designed as a near-zero-refractive-index material (NZRIM). By controlling the phase reflection properties of the structure, the antenna gain is increased by 5.5\,dB, original bandwidth increased ten times and the front-to-back ratio improved from 7 to 187. Also, footprint miniaturization of 56.5% with a maximum size of (1.9λ₀)² is obtained. To the best of the authors' knowledge, such enhancement is the largest to date.

A physics-based hybrid implicit-explicit finite-difference time domain (HIE-FDTD) method is developed for electromagnetic modeling of multi-passband frequency selective surfaces (FSSs). Using this self-developed HIE-FDTD simulator, several dual- and tri-passband FSSs are designed and further fabricated. The measurement results are in good agreement with the simulation ones, which prove high accuracy of the self-developed HIE-FDTD algorithm. In addition, the resonant frequencies of the designed FSSs can be effectively adjusted by changing their geometric parameters. This work provides electromagnetic guides of structure and parameter selections for designing multi-passband FSS.

In this article, we present the design and production of a miniaturized adjustable coupler with optimized dimensions of 48 mm in length and 31 mm in width. This coupler offers the possibility of covering all phases [0, 45°, 90°, 120° and 180°]. To be able to achieve this, the proposed coupler can be adjusted through the implementation of six SMV2019-079LF diodes which allow shifting from one phase to another. This new flexibility, in terms of phase shifting, can greatly improve the multifunctional use of this small and efficient coupler, in particular, in comparison with previously improved phase shifting couplers which are limited to one or two phases. The high performance and efficiency have been verified by the results obtained by simulation and measurement.

In this article, a miniaturized, dual-polarized corner-fed microstrip antenna is designed and fabricated at 1.43 GHz for Low Earth Orbit (LEO) Satellite applications. The antenna adopts a Complementary Split-Ring Resonator (CSRR)-inspired structure and slotted patch to achieve miniaturization. This reduces the patch size by 39.4%. Meandered impedance-transforming lines are placed for impedance tuning, and its benefit is demonstrated by both simulated and measured S₁₁ curves reaching lower than -20 dB. Feeding at corner increases its isolation to -25 dB over the whole bandwidth of 40 MHz and reaches lower than -33 dB at the resonant frequency. The antenna is fabricated and tested. Measured results are generally in good agreement with simulations.

In this paper, we present a gain-enhancement technique for reflectarray applications with compact aperture size and a low profile. To increase antenna gain, reflectarrays are constructed as an electrically large aperture, and the feed is required to be of high directivity, which is accompanied by a longer focal length. This increases the dimensions in two aspects, including the physical aperture size and the profile of the overall structure. To obtain high gain with compact dimensions, we develop a reflectarray that uses an active-integrated feeding antenna. This feeding antenna is connected to a microwave power amplifier, which enhances the gain without reducing the half-power beam widths (HPBWs) of the patterns. Accordingly, the feed can be arranged with a shorter focal length, whereas the spillover efficiency is still high. Moreover, the power amplifier contributes additional gain of 20.6 dB, and thus the proposed structure can achieve realized gain as high as 44.5 dB with dimensions of 9.2 × 6.7 square wavelengths. Such a high-gain and compact antenna is particularly suitable for satellite applications.

Metamaterials offer great promise for engineering electromagnetic properties beyond the limits of natural materials. A typical example is the so-called spoof surface plasmons (SPs), which mimic features of optical SPs without penetrating metal at lower frequencies. Spoof SPs inherit most of the properties of natural SPs, including dispersion characteristics, field confinement, localized resonance, and subwavelength resolution, and therefore are highly expected to offer a new solution for low-frequency applications. With the development of spoof SPs, three different theories have been introduced. The first one is the description of subwavelength corrugated metal surfaces by a metamaterial that hosts an effective plasma frequency. The second one is developed with high-index contrast grating, which can realize propagation with ultra low loss and localization with ultrahigh Q-factor resonance. The last one is structural dispersion induced SPs, a perfect low-frequency analogue of optical SPs, realized by exploiting the well-known structural dispersion waveguide modes only with positive-ɛ materials. Here, the developments of these three theories including propagation and localized SPs are reviewed, focusing primarily on the fundamental and representative applications.

The study of outer-rotor coreless bearingless permanent magnet synchronous generator (ORC-BPMSG) is intended to pave the way for the future of high-speed flywheel energy storage systems. A multi-objective parameter optimization method is proposed for the outer-rotor coreless bearingless permanent magnet synchronous generator with the aim of improving the fundamental wave content of the generator's output voltage, reducing harmonics and optimizing the suspension force at the same time. Firstly, the basic parameters and operating principle of the generator are described. Then, the response surface (RS) method is used to obtain the objective functions for the total harmonics distortion (THD), the mean value of the suspension force and the suspension force pulsation. The optimal optimizations of the ORC-BPMSG are selected by establishing the pareto solution set through the improved multi-objective particle swarm optimization (MOPSO) algorithm. Finally, the optimal ORC-BPMSG prototype is fabricated, and the performance of the prototype is verified. The experiments show that the optimized generator output voltage has fewer harmonics and operates reliably.