In this paper, a dual-band modified multiple-input-multiple-output (MIMO) antenna with high isolation is presented and discussed. The proposed compact structure (35 × 25 mm²) consists of two monopole elements and defected ground planes to obtain high impedance bandwidth. Two elliptical-shaped patches are placed orthogonal to each other to obtain high isolation, and a neutralization slit is integrated into the ground plane of each element to further improve the isolation between the elements. The measurement results of the proposed structure show satisfactory agreement with the simulation results. The measured bandwidths are 47.05% (2.6-4.2 GHz) and 64.72% (5.11-10 GHz) at S₁₁ ≤ -10 dB which covers bandwidth requirements of WiMAX (3.4-3.6 GHz, 5.25-5.85 GHz), sub 6 GHz 5G band (3.4-3.8 GHz), WLAN (5.15-5.35 GHz, 5.725-5.825 GHz), and X band satellite communication systems (7.25–8.39 GHz). The designed antenna offers a peak gain of about 9.0 dBi and radiation efficiency of about 92%. The measured minimum isolation is greater than 27.3 dB across the dual band with a maximum value of 73.4 dB. The envelope correlation coefficient (ECC) is below 0.0035, channel capacity loss less than 0.37 bits/s/Hz, and peak diversity gain about 10 dBi.

An outer rotor coreless bearingless permanent magnet synchronous generator (ORC-BPMSG) has the characteristics of long service life, high efficiency, low noise, etc. However, the stability and reliability of the system and the output voltage are affected by the rotor vibration. In this paper, the step size and error of improved variable step least mean square (VSLMS) adaptive filter using improved simplified particle swarm optimization (ISPSO) is proposed, which suppresses the vibration of the rotor. The mathematical model and working principle of the ORC-BPMSG are introduced. The performances of improved VSLMS adaptive filter parameters are optimized by the improved SPSO algorithm, which generates a compensation signal to realize vibration compensation. The simulation system for the vibration compensation of the ORC-BPMSG is constructed, and dynamic suspension experiment and variable speed experiment of the rotor are carried out, which verify the robustness and stability of the proposed method.

A new approach to the bandwidth maximization of reconfigurable antenna arrays for monopulse radar applications is proposed and tested. The provided radiating systems allow switching the radiation behavior from sum to difference patterns (and vice versa) while sharing the excitation amplitudes of a user-decided set of radiating elements. Furthermore, the proposed design procedure guarantees the maximum possible bandwidth performance once the overall antenna size, the desired beamwidth, sidelobe level, and slope in the target direction of the generated power patterns are fixed. The synthesis problem is cast and solved as a sequence of convex programming optimizations, and hence the maximization of performances is attained with advantages in terms of computational times as well as convergence to the global optimum. The given theory is supported by numerical experiments including arrays with ultra-wideband performances.

A novel miniaturized bandpass filter (BPF) is proposed, which is based on a stepped-impedance resonator (SIR) and cross-coupling theory. This filter has the characteristics of small size and high out-of-band rejection. The filter consists of four 1/2 wavelength stepped-impedance resonators and two 1/4 wavelength short-circuit microstrip resonators. By designing a new kind of structure, the cross coupling is realized between the second and the fifth resonators, and two transmission zeros are introduced out of band. Zero-degree feeding is realized due to the symmetry of the structure and feeding position, which adds two other transmission zeros outside the band. Four transmission zeros are introduced outside the passband of the filter, which greatly increase the out-of-band rejection of the filter. The passband of the filter is 3.2 GHz~4.2 GHz, and the out-of-band rejection at 2.6 GHz and 4.8 GHz reaches -60 dB. The size of the filter is only 7.2 mm * 8 mm (0.21λ_g*0.24λ_g), which realizes the miniaturization of the filter.

The continuous and discrete radiation spectrum of a highly dielectric constant structure with extremely high losses is revisited herein. This work is motivated by the need of efficient electromagnetic power extraction from antenna-sources implanted into the human body. As the dielectric constant of biological tissues varies between 35 and 80 with a conductivity increasing from 0.5 to 2 S/m with frequency, the involved propagation and particularly radiation phenomena cannot be described by the current state of the art published research. Since the scope of the biomedical applications refers to the communication or energy transfer between an implanted device and an external one, the problem to be addressed involves primarily the near field and secondary the far-radiated field. Many of human body parts as the hands, legs, torso and neck can be modeled as cylinders. Indicatively, a non-magnetic infinite cylinder with an average dielectric constant ε_r1 = 58.1 and conductivity σ = 1.69 S/m is considered, with focus on the hand with average radius 2.75 cm. Although a plethora of excellent publications elaborates both analytically and numerically on the radiation from dielectric cylinders including losses, there is not any work studying rods with so high dielectric constants and extremely high losses, (loss tangents around unity or higher), while most of them are dealing with the far field rather than the near field. Classical works reveal radiation due to the discrete surface and leaky modes as well as a continuous spectrum, while complex modes appearing as quadruplets are found responsible for only energy storage. These are indications of discrete modes transitions as dielectric losses are increased. It is herein proved that indeed increasing losses are causing not only mode transition but also a change in their nature as surface or leaky, while the complex mode quadruplet breaks resulting in radiation in both the near and far fields, while losses have significant effects in the continuous spectrum (sky or space wave). These phenomena are exploited to serve the main purpose of this paper aiming to devise a physical mechanism supporting efficient energy and signal transferring inwards or outwards a highly lossy, high dielectric constant cylinder. The novelty of the proposed methodology stems from a Wiener-Hopf based non-meromorphic Kernel factorization resulting in a field product representation. This is composed of well defined individual terms with each one of them building on a specific pole-mode. The proposed formulation is found to be equivalent to the generalized ``multiplicative'' and ``additive'' steepest descent methods regarding the far field evaluation, but additionally is capable of providing the near field as well. The latter feature supports important biomedical applications. Due to the huge extent of the subject and in order to facilitate the continuous spectrum the analysis is restricted to the excitation by an infinitesimal electric dipole positioned at the origin and oriented along the axis of the cylinder. Studying this structure, a low attenuation low order mode is encountered which is mainly responsible for the energy transferring. This is in accordance with Frezza et al. findings for a ``deeply penetrating'' mode into highly lossy media.

In recent years, permanent magnet synchronous linear motor (PMSLM) has gained tremendous momentum in industry, especially in the high-precision field. This is mainly because it has the advantages of small size, high control precision, reliable operation. However, due to the special structure of linear motor, the control strategy of rotating motor cannot be directly applied to PMSLM. Three control strategies for reducing loss and improving efficiency of PMSLM are proposed in this paper. Firstly, the mathematical model of PMSLM is established and the loss model and efficiency equation are established. Secondly, we adopt the loss model control strategies of i_d=0, maximum thrust current ratio and direct thrust are used to optimize the efficiency of the motor. Finally, simulation experiments are carried out for the three proposed optimization strategies, and the effects of initial speed and load on motor efficiency are analyzed. The effectiveness of the three loss model control strategies proposed in this paper is fully verified by the simulation results, and it is found that the loss model control strategy of i_d=0 has the most obvious efficiency improvement.

Micro-nano opto-electronic devices are demanded to be highly efficient and capable of multiple working wavelengths in several light-matter interaction applications, which is a challenge to surface plasmonics owing to the relatively higher intrinsic loss and larger dispersion. To cross the barriers, a plasmonic metasurface combining both high Q-factors (highest Q > 800) and multiple resonant wavelengths is proposed by arranging step-staged pyramid units in lattice modes. Different numerical relations for nonlinear frequency conversions have been constructed because of its strong tunability. Also, characteristics of high radiation efficiency (> 50%) and largelocalized optical density of state (> 10⁴) have been proved through the numerical simulation. Such tunable high-Q metasurface can be implemented to quantum nonlinear process and enable the strong light-matter interaction devices into reality.

In this paper, a potential-based partial-differential formulation, called the all-frequency stable formulation, is presented for the accurate and robust simulation of electromagnetic problems at all frequencies. Due to its stability from (near) dc to microwave frequencies, this formulation can be applied to simulate wide-band and multiscale problems without encountering the infamous low-frequency breakdown issue or applying basis function decompositions such as the tree-cotree splitting technique. To provide both efficient and flexible numerical solutions to the electromagnetic formulation, a mixed continuous-discontinuous Galerkin (CDG) method is proposed and implemented. In regions with homogeneous media, the continuous Galerkin method is employed to avoid the introduction of duplicated degrees of freedom (DoFs) on the elemental interfaces, while on the interfaces of two different media, the discontinuous Galerkin method is applied to permit the jump of the normal components of the electromagnetic fields. Numerical examples are provided to validate and demonstrate the proposed numerical solver for problems in a wide electromagnetic spectrum.

This work proposes a design of rectenna for Wi-Fi energy harvesting application at 2.42 GHz. The proposed antenna includes a modified rectangular patch and two circular radiating elements with partial ground, and adopts a total area of 80 × 80 mm². With the partial ground structure, the proposed antenna shows a better reflection coefficient (S₁₁) at 2.42 GHz. The proposed antenna is a modified conventional patch antenna that shows its improved suitability for Wi-Fi energy harvesting at the targeted band. For rectenna, an impedance matching circuit based on microstrip transmission lines, radial stubs, and enhanced Greinacher voltage doubler rectifier circuits are designed. The rectifier circuit occupies a total area of 25 × 25 mm². The antenna part of the rectenna exhibits quite good S₁₁ < -10 dB and 3.94 dB peak gain. To validate the design experimentally, a prototype of the proposed rectenna is also fabricated. The measured result indicates that at the resonant frequency the rectenna achieves the peak efficiency of 78.53%, and the output voltage is 4.7 V at 0 dBm input power.

Doppler-based techniques for ocean current measurement have been demonstrated in the past years. The Doppler shift of the ocean backscattering from space-borne microwave instruments not only includes the contributions from ocean current but also includes satellite movement and the wind-wave induced. Geometrical Doppler shift induced by satellite movement is highly dependent on the accuracies of satellite attitude determinations and speed. In this study, we derive the detailed formulas to investigate how satellite attitude determination and speed errors affect ocean current retrieval for a Doppler scatterometer through the spatial correlation coefficient phase and the transformation between orbital coordinate system and satellite-carried local level frame (LLF). Our results show that ocean current speed retrieval accuracy is sensitive to the accuracies of satellite attitude determination and speed, and compared with the satellite speed error, satellite attitude error has a larger impact on ocean current retrieval. By comparisons, with the same attitude accuracy for satellite roll, pitch, and yaw, ocean current speed error induced by the roll error is found to be the smallest. With an accuracy of 0.001° satellite attitude determination and 0.01 m/s for satellite speed accuracy, the total ocean current speed retrieval error induced by satellite attitude determinations (including roll, pitch, and yaw) and speed errors reaches a maximum value of 16.37 cm/s at side-looking direction and a minimum value of 11.05 cm/s at forward and backward-looking directions. Our results confirm the importance of satellite attitude determination accuracy for future ocean current mission and will also be useful to motivate the design of future Doppler measurement instruments.

This paper addresses the design and fabrication of an embroidered textile RFID tag antenna. The main feature of this design is that we have embroidered an RFID chip on the textile support which avoids the use of metallic wires or soldering. The modeled equivalent circuit of the tag is presented to get physical insight into RFID tag antenna design. The detailed results given in this paper include the effect of the bending and the human body proximity on the antenna performance. It is shown that the bending does not introduce a conspicuous effect on the tags read range while the dissipative characteristics of the human body cause a gain and read range reduction. The proposed design may find applications in wearable devices dedicated to health monitoring applications.

Topological refractions created by valley sonic crystals (VSCs) have attracted great attentions in the communities of physics and engineering owing to the advantage of zero reflection of sound and the potential for designing advanced acoustic devices. In previous works, topological refractions of valley edge states are demonstrated to be determined by the projections of the valleys K and K′, and two types of topological refractions generally exist at opposite terminals or different frequency bands. However, the realization of tunable topological refractions at the fixed frequency band and terminal still poses great challenge. To overcome this, we report the realization of tunable topological refractions by VSCs with triple valley Hall phase transitions. By simply rotating rods, we realize 3 types of topological waveguides (T1, T2 and T3) composed of two VSCs, in which the projections of the observed valley edge states can be modulated between K and K′. Additionally, based on the measured transmittance spectra, we experimentally demonstrate that these valleyedge states are almost immune to backscattering against sharp bends. More importantly, we realize tunable topological refractions at the fixed frequency band and terminal, and experimentally observe the coexistence of positive and negative refractions for T1 and T3, and negative refractions for T2. The proposed tunable topological refractions have potential applications in designing multi-functional sound antennas and advanced communication devices.

In this paper, a second-order tri-band balanced bandpass filter (BPF) with multiple transmission zeros (TZs) and compact size is presented. The structure consists of novel stepped impedance square ring loaded resonators (SI-SRLRs), which can excite six resonance modes. For design of SI-SRLR, we analysed the odd-mode equivalent circuit and obtained the electrical lengths from the design graph. Meanwhile, the wider frequency distances between differential modes (DMs) and common modes (CMs) are realized by selecting the proper admittance ratio of SI-SRLR. Then for design of BPF, six TZs are introduced by source-load coupling, which lead to band-to-band isolation of 23 dB. Additional T-shaped stubs and open stubs are loaded on the symmetric plane of SI-SRLR, which result in high CM suppressions of 43 dB, 25 dB and 37 dB at three DM centre frequencies. Finally, a tri-band differential BPF operating at 1.46 GHz, 4.45 GHz and 5.48 GHz is fabricated and measured. The measured 3-dB fractional bandwidths of three passbands are 6.8%, 7.4% and 5.6%. A wide DM and CM stopband suppression of 20 dB is achieved to 14.6 GHz (10f₀). The measurements verify well the proposed structure and the design method.

This article reports a single layer tri-band bandpass, polarization insensitive Frequency Selective Surface (FSS). The unit cell is designed by considering different square loop elements and cross dipole element to pass Wi-Max and WLAN frequency range with low loss. Three different shapes of loops and one cross dipole are arranged in a way that gives a triple-band-pass characteristic from the proposed structure. These loops and dipole are designed to pass Wi-MAX (2.5-2.7 GHz, 3.4-3.6 GHz) and WLAN (center frequency, 5.5 GHz) bands. The structure performance is independent of incidence angle of wave due to its symmetrical geometry which makes the design polarization insensitive and achieves good angular stability. A 14x14 array of proposed unit cell is realized and measured. The proposed FSS achieves a 3 dB transmission bandwidth of 25% at 2.6 GHz, 65.6% at 3.5 GHz and 65.6% at 5.5 GHz. The advantage of the proposed design is that it has a simple and compact geometry fabricated on a low-cost substrate and achieved tri-band band pass response with a wide angular stability.

To address the problems of large volume, heavy weight, and inconvenient installation of the shield board of a wireless charging coil (WCC) installed on the body of an electric vehicle (EV), a new shielding method is proposed in this paper. From the perspective of engineering practice, according to the principle of passive shielding, and in line with the vertical direction of WCC with ferromagnetic material shielding, this novel shielding method involves only a low permeability metal shielding ring set around the transmitting coil in the horizontal direction. Using the finite element simulation software COMSOL Multiphysics, the EV model, the magnetic coupling resonance (MCR) WCC model, and the pedestrian body model at the observation point are designed. The influence of the metal shielding ring on the self-inductance and mutual inductance of WCC is calculated. The magnetic induction strength (B) and electric field strength (E) of pedestrian body at observation points before and after adding a metal shielding in the horizontal direction are evaluated, and the electromagnetic exposure safety of a pedestrian body in this electromagnetic environment is analyzed. Compared with the shielding method of only adding ferromagnetic material in the vertical direction and after using new shielding, the maximum B of a human trunk is reduced by 43%, the maximum E reduced by 44%, the maximum B of human head reduced by 44%, and the maximum E reduced by 39%. After adding the metal shielding ring, the maximum B and E of human trunk decreased from 8.56 × 10^-1 times and 2.28 × 10^-1 times of the International Commission on Non-Ionizing Radiation Protection (ICNIRP) exposure limit to 4.89 × 10^-1 times and 1.27 × 10^-1 times, respectively, and the maximum B and E of human head decreased from 1.62 × 10^-3 times and 8.58 × 10^-4 times of the ICNIRP exposure limit to 9.18 × 10^-4 and 5.25 × 10^-4 times, respectively. The simulation results show that the new shielding method can significantly reduce the electromagnetic radiation of the pedestrian's trunk and head central nervous system (CNS) at the observation point. The effectiveness of the shielding method is proven, and this work provides a certain guidance for the engineering design of WCCs.

This paper proposes a Yagi-Uda antenna array realized on a Silicon substrate and supported by a substrate integrated waveguide for multi-band operation in the K and Ka bands. The structure of the dipole and the first director of the Yagi-Uda antenna were modified and tuned for multi-band response, making it completely novel in comparison to the existing Yagi-Uda structures supporting multi-band operation. As the feed, a substrate integrated waveguide was designed to assist with multi-band operation and to overcome the challenges presented by the Silicon substrate. An array is implemented to improve the gain. The antenna array's prototype was constructed and tested to back up the claims. The proposed array operates at frequencies of 23.7, 26.3, 27.5-28.3, and 29.4 GHz. The array exhibits good end-fire radiation patterns for the resonant frequencies, with a peak gain of 19.65 dBi and an efficiency of 89.8% at 23.7 GHz. This is the first report of an antenna fed by a substrate integrated waveguide and realized on Silicon with a high gain and applications in the K and Ka bands.

The aim of this paper is to develop a hybrid modeling approach based on direct coupling between the finite element method (FEM) and the partial element equivalent circuits method (PEEC). Through this FEM-PEEC approach, we can efficiently compute the three-dimensional eddy current distribution created by a rectangular coil (exciting coil) in conductive and magnetic structures having heterogeneous dimensions. Magnetic field created by the rectangular coil is given by calculating quasi-static Green's function integrals. In goal to construct rectangular coil, the calculation is made for elementary parallelepipedic conductors oriented respectively in x and y directions. By this manner, three possible configurations are proposed and compared to show errors, especially in corners. By only meshing the active parts of the domain (without air region), we confirm through the issued results that the proposed methodology contributes to accelerate the execution time while maintaining the precision. The obtained results are validated with the numerical ones by 3D FEM (Flux 3D Software).

This paper, using the distributed parameter line model, presents an accurate fault location method based on fundamental frequency positive sequence fault components for EHV transmission line. The method based on positive sequence fault components Extra-High Voltage (EHV) electric transmission line. The method based on the positive sequence fault component is robust to the operating state of the prefault system and fault path resistance. The technique proposed in the paper does not require the fault type, fault phase, and the zero-sequence parameter to be obtained in advance. In addition, due to the use of fault component protection theory, the algorithm itself is not aected by the previous operating state of the system. The method uses a distributed parameter model, which is more accurate in positioning and smaller in error than a lumped parameter model by a large number of simulations. Accurate fault location is important for shortening the fault time and reducing the loss of the fault, so the positioning method proposed can improve the power supply quality and safety. This paper describes the characteristics of the proposed technique and assesses its performance by using Power Systems Computer Aided Design/Electromagnetic Transients including DC (PSCAD/EMTDC).

Integrated time delays are important for self-forced oscillation techniques in opto-electronic oscillators (OEO). Add-drop filters (ADFs) resonators using optical waveguide coupled to micro-ring resonators (MRR) are suitable for integrated optical time delays but suffer from a limited expected delay. 2-dimensional (2-D) photonic crystals (PhCs) with line defect are employed as confined optical waveguide to realize ADF resonators where longer optical delays than standard homogenous resonators are achieved by leveraging the slow-light effect. Moreover, achieving time delay up to microseconds (μs) is envisioned by cascading multiple identical ADF based on dispersive 2-D PhC micro-resonators. The focus of this paper is to devise a hybrid modeling procedure for accurate calculations of achieved time delays in various complex structures, while a combined electromagnetic modeling and analytical calculation technique overcomes a substantial computational resources and long computation times for a brute forced full-wave design and modeling. This innovative hybrid modeling for time delay estimation of cascaded ADFs is proposed for the first time to optimize physical design within short time period. First, transfer function performance of a homogenous ADF resonator is simulated using finite-difference-time-domain (FDTD) for both the full structure and structures with bi-fold symmetry and compared against proven analytical solutions to demonstrate accuracy of bi-fold symmetry while the computational resources are economized. The same modeling procedure is then extended to predicting performance of 2-D PhC based ADF resonator by quantifying key physical parameters of coupling factor, complex optical propagation constant, and optical transfer function for ADF resonator for the ring radius of curvature about 1.5 μm with various coupling gaps between feed waveguide and resonator guide. These parameters and the effective group index calculated by OptiFDTD software are applied to the analytical expressions to estimate single 2-D PhC ADF and attain a simulated time delay of 200 ps. The estimated time delay of 70 cascaded 2-D PhC based ADF resonators with R of 100 μm is estimated to be about 925 ns for the on-resonance frequency of 1534 nm.

Due to the optical diffraction limit, the resolution of a wide-field (WF) microscope cannot easily go below a few hundred nanometers. Super-resolution microscopy has the disadvantages of high cost, complex optical equipment, and high experimental environment requirements. Deep-learning-based super-resolution (DLSR) has the advantages of simple operation and low cost, and has attracted much attention recently. Here we propose a novel DLSR model named Modified Hybrid Task Cascade U-Net (MHTCUN) for image super-resolution in optical microscopy using the public biological image dataset BioSR. The MHTCUN has three stages, and we introduce a novel module named Feature Refinement Module (FRM) to extract deeper features in each stage. In each FRM, a U-Net is introduced to refine the features, and the Fourier Channel Attention Block (FCAB) is introduced in the U-Net to learn the high-level representation of the high-frequency information of different feature maps. Compared with six state-of-the-art DLSR models used for single-image super-resolution (SISR), our MHTCUN achieves the highest signal-to-noise ratio (PSNR) of 26.87 and structural similarity (SSIM) of 0.746, demonstrating that our MHTCUN has achieved the state-of-the-art in DLSR. Compared with the DLSR model DFCAN used for image super-resolution in optical microscopy specially, MHTCUN has a significant improvement in PSNR and a slight improvement in SSIM on BioSR. Finally, we fine-tune the trained MHTCUN on the other biological images. MHTCUN also shows good performance on denoising, contrast enhancement, and resolution enhancement.