A dual band flexible antenna for applications at 900 and 2450 MHz is proposed in this paper. The antenna offers a compact size of 0.23λ_o × 0.120λ_o × 0.0007λ_o, where λ_o is the wavelength at the lower resonance. The antenna comprises a simple geometrical structure consisting of a W-shaped serpentine structure fed by a microstrip line, while a Defected Ground Structure (DGS) technique was utilized with a partial ground plane to achieve wide operational bandwidth. An additional capacitor was loaded in between the slots to achieve a higher resonance, thus resulting in a compact dual band antenna. Various performance parameters were analyzed, and results were compared with the measured ones. The antenna offers good performance in terms of size, bandwidth, gain, and radiation pattern and thus increases the potential of the proposed antenna for both rigid and flexible devices.

Exceptional points are spectral singularities in non-Hermitian systems at which two or more eigenvalues and their corresponding eigenvectors simultaneously coalesce. Originating from quantum theory, exceptional points have attracted significant attention in optics and photonics because their emergence in systems with nonconservative gain and loss elements can give rise to many counterintuitive phenomena. Metasurfaces - two-dimensional artificial electromagnetic materials structured at the subwavelength scale - can provide a versatile platform for exploring such non-Hermitian phenomena through the addition of dissipation and amplification within their unit cells. These concepts enable a wide range of exotic phenomena, including unidirectional propagation, adiabatic mode conversion, and ultrasensitive measurements, which can be harnessed for technological applications. In this article, we review the recent advances in exceptional-point and non-Hermitian metasurfaces. We introduce the basic theory of exceptional point and non-Hermiticity in metasurfaces, highlight important achievements and applications, and discuss the future opportunities of non-Hermitian metasurfaces from basic science to emerging technologies.

When particle swarm optimization (PSO) is used to identify the parameters of permanent magnet synchronous motor (PMSM), the movement of particles is not selective, which makes the algorithm easy to fall into the local optimum, and the accuracy is poor. The simulated annealing particle swarm optimization (SAPSO) improves the accuracy and evolution speed, but SAPSO has redundant iteration problems. To solve these problems, a motor parameter identification method based on fast backfire double anneal particle swarm optimization (FBDAPSO) is proposed. By reducing the optimization time and quickly tempering and annealing the "misunderstood" difference, the motor adjustable model and fitness function are designed, and the number of iterations is constantly reset to achieve the effect of online identification. Under different working conditions, simulated and experimental results show that the proposed method can quickly and accurately identify the four parameters of the motor's stator, winding resistance, stator winding d-axis inductance, stator winding q-axis inductance and permanent magnet flux linkage at the same time, compared with the traditional method of parameter identification, and it has better accuracy, rapidity, and robustness.

In this letter, a compact dual-band patch antenna based on ball grid array (BGA) packaging for 5G mmWave is proposed. The patch antenna adopts a U-slot and a shorting pin to achieve dual-band operation of 28 GHz and 37 GHz. A single-layer FR4 substrate provides cost-effective features for the massive application. The BGA packaging not only reduces the size but also enables the antenna to be surface-mounted with other components in the same package, which improves the integration. The antenna has been fabricated and measured, and an acceptable agreement was obtained between the simulation and measurement results.

A novel coplanar waveguide (CPW) fed wide slot antenna for broadband circular polarization (CP) operation is proposed in this letter. Utilizing an asymmetrical ground plane and an open slot, broadband axial ratio and good impedance characteristics can be obtained in the middle and low bands. The perturbation patch on the right side of the wide slot excites the upper-band CP mode. By adjusting the upper-part feedline and the wide slot structure, the axial ratio performance can be optimized to a wideband axial ratio bandwidth (ARBW). Compared with wide slot antennas of similar size, the proposed antenna has a simpler structure while achieving a wider ARBW. The proposed antenna has been fabricated and tested. The measured results show that the -10 dB impedance bandwidth (ZBW) is 2.40-7.55 GHz (103.5%); 3-dB ARBW is 2.47-6.2 GHz (86.0%); and the peak gain is about 4 dBic. Right-hand circular polarization (RHCP) radiation pattern is achieved in +z direction. The proposed antenna can be used in WLAN/WiMAX applications and various wireless communication systems which require broadband ZBW and ARBW.

This paper mainly deals with the channel diversity and the effect of spatial consistency parameters for different millimeter wave (mmWave) bands (28, 38 and 73 GHz) according to the channel parameters of the NYUSIM model. Statistical analyses are performed for various spatial consistency scenarios in an urban microcell (UMi) environment. Most of the recent analyses ignored the effect of adjusting the spatial consistency parameters on the 5G mmWave channel characteristics, including path loss (PL), received power, and path loss exponent (PLE). As a result, we have analyzed the effect of each parameter mentioned above for both directional power delay profile (DPDP) and omnidirectional power delay profile (OPDP). Numerical results illustrate how the characteristics of mmWave channels communication can be affected by changing the spatial consistency parameters.

This paper deals with analyzing a novel eddy current damper for an axially magnetized multi-ring permanent magnet thrust bearing (MPMTB). Initially, the bearing is optimized for maximum axial force by selecting three general parameters (air gap, outer diameter of stator, and length) using a generalized optimization procedure. Then, the axial force of an optimized bearing is validated with the mathematical model results. Finally, the novel and conventional eddy current dampers (ECDs) for an optimized MPMTB are analyzed for damping forces and coefficients using three-dimensional (3D) finite element transient analysis in ANSYS. Based on the analysis results, the proposed novel structure could be selected to replace the conventional one for providing damping to MPMTB effectively without affecting the radial air gap between the rotor and stator rings.

This paper proposes two low divergence angle orbital angular momentum (OAM) Fabry-Perot (F-P) antennas with nonuniform superstrates. There are two steps to design the proposed two F-P antennas. First, two primary array antennas (a slot array antenna and a patch array antenna) are designed. Both antennas can generate OAM vortex beams with a mode of -1. Second, two F-P resonator cavity antennas are formed by loading a nonuniform partially reflective surfaces (PRS) superstrates above the two primary antennas in order to increase the antenna gain and reduce the divergence angle. The PRS is designed non-uniform for increasing the aperture efficiency. The measured results indicate that the F-P OAM antennas can obviously improve the performance of primary OAM antennas: (1) for the slot array antenna, the divergence angle reduces from 27° to 18°, and the maximum gain increases from 5.2 dBi to 7.5 dBi; (2) for the patch array antenna, the divergence angle decreases from 30° to 18°, and the peak gain increases from 3.4 dBi to 7.2 dBi.

In this paper, a novel mechanical-flux-weakening interior permanent magnet (MFW-IPM) machine is proposed to improve flux-weakening ability. The key of the proposed machine is that the permanent magnet is rotatable, and a mechanical device is equipped on both sides of the rotor. The mechanical device can regulate the air-gap magnetic field by rotating PM to change the leakage flux and magnetization direction of PM. As a result, the flux-weakening ability is improved. The flux-weakening principle of the MFW-IPM machine is investigated in detail. In addition, a multi-objective optimization method is adopted to improve the performance of the proposed machine. Then, the electromagnetic performances of the original machine and optimized machine are compared by finite element analysis. Finally, both simulation results and experimental tests verify the effectiveness of the flux-weakening enhancement design and optimization method.

The engine of a fighter plane is one of the largest scattering centers of the entire aircraft. One possible way of reducing the radar cross section (RCS) of the engine is to use an S-shaped bending air inlet to avoid direct radar wave illumination and reflection. We evaluate the efficacy of an S-shaped air inlet on RCS reduction by simulating the boresight and ±15˚ bistatic RCS for a digital model of an engine located behind an S-shaped inlet, using a multi-level fast multipole method (MLFMM) code in the S and X bands. The results show that a curved S-type air inlet can reduce the engine boresight bistatic RCS by ~10-12 dBsm at 3 GHz, and ~16 dBsm at 10 GHz when radar wave is incident from boresight, but not to the level required by RF stealth standards. When the radar waves are incident from θ=105˚ φ=90˚ or θ=90˚ φ=345˚, the RCS reduction is less effective, which is the results of the bend direction of the S-type air inlet.

This paper presents a new integro-differential coupling between partial equivalent electrical circuits (PEEC) and finite difference method (FDM) taking into account the magnetization effect. This coupling is intended for thin plates having simultaneously significant conductive and magnetic properties in presence of exciting coils of complex topologies. These cases exist in eddy current nondestructive testing (ECNDT), eddy current separation, induction or levitation melting devices and more other applications. The choice of FDM, is in relation with rectangular surfaces generated by numerical meshes leading to mathematical integrations of magnetic and electrical quantities with independent variables, unlike more complicated forms of surfaces generated by finite element method (FEM) or others. Fully successful analytical expressions have been realized and implemented in overall coupling process. The PEEC method is mainly used to calculate the magnetic field applied to the nodes of the plate from different inclined polygonal coils. The results of magnetic field and eddy current distributions on thin plates are presented, and parts of them are compared with those realized by Flux 3D software.

Due to low power density, it is difficult for a single-band rectenna to harvest enough power for IoT devices like wireless sensors. Thus to supply these consuming devices, harvesting RF energy from multiple frequencies is a solution to enhance the amount of harvested DC power. In this work, we introduce a triple-band rectenna, working at 900 MHz, 1.8 GHz and 2.1 GHz, three readily available bands in the ambience, for energy harvesting application. The proposed rectenna consists of three monoband rectifiers connected to a multi-band receiving antenna via a highly efficient triplexer. The antenna is made by superposing two concentric rings and manipulating their radii to achieve the desirable operating frequencies, with antenna gains of respectively 2.5 dBi, 4.5 dBi, and 4 dBi. The contiguous triplexer is made by connecting open stubs band-reject filters and optimizing their positions, resulting in the triplexing efficiency higher than 75%. The measured RF-DC efficiency under -10 dBm triple-tone input power is 40%.

This paper explores the effects of extended exposure to salt water fog on the microwave absorption properties of unidirectional carbon-fiber reinforced polymer (CFRP) circuit analog absorbers (CAA). Single-layer CFRP CAAs were fabricated using a wet-layup technique and were then subjected to a controlled salt water fog chamber following B117 standards. A total of ten samples using 305 g/m² areal-weight unidirectional CFRP were fabricated. Three samples were withdrawn from the salt water environment at ten-day intervals and tested, with the final samples being withdrawn after 30 days. The mass of each sample was measured immediately after removal to measure mass-accumulation and after a five-day interval to measure mass-loss. A free-space microwave reflection measurement system was implemented to track and quantify changes to the absorption capabilities of the CAA. A physically-based electromagnetic model was developed to characterize the changes caused by salt water absorption, and good agreement was observed with measured data.

This paper proposes a zero-forcing beamforming design for the energy efficiency optimization of the magnetic resonance based wireless power transfer system with multiple transmitter coils, which aims to secure energy transfer control. A scheme based on beamforming technology is proposed to prevent unauthorized users from accessing the system, which builds a beamforming model consisting of multiple transmitter coils, a target receiver, and a non-target receiver to simulate the actual system. Then to optimize the proposed system's energy efficiency while constraining the target receiver's energy, spectral efficiency, and transmitter's power, the proposed beamforming model is constructed as an optimization problem. To solve this non-convex nonlinear fractional programming problem, the Dinkelbach algorithm is used for fractional conversion, and then the zero-forcing constraints are equivalently replaced. Finally, two solutions of the nonlinear solution and closed-form solution are derived. The simulation results show that the energy efficiency optimization strategies of zero-forcing beamforming with the two derived solutions can satisfy the design requirements.

A dual-band two port MIMO antenna with very high isolation is proposed for 5G/WLAN application. The overall size of the MIMO antenna is (18 × 44× 0.8) mm³. The unequal arm of the Inverted-F Antenna (IFA) is the reason for the dual bands. Bending and extending one of the arms with the staircase shape is responsible for the proposed dual-bands having resonant frequency at 3.45 GHz (3.3 GHz-3.65 GHz) and 5.1 GHz (4.8 GHz-5.5 GHz) respectively with percentage impedance bandwidth of 10% and 13.6% respectively. The proposed antenna uses a simple decoupling structure based on a wide inverted T-shaped slot to achieve good isolation (better than 18 dB and 34 dB respectively for the dual-bands) between the ports. The envelope correlation coefficient (ECC) and channel capacity loss (CCL) are within the acceptable limits.

Artificial material has the feature to realize a controllable effective permittivity, which leads to many potential applications in the RF and optical fields. In this study, an artificial material is proposed for a Resonant Cavity antenna (RCA) to enhance the gain of patch antenna. The artificial material is made of a lot of circular conducting patches in a uniform size hosted in an FR-4 substrate. The fabricated artificial material is in a square shape with a length and width of 52 mm × 52 mm and a thickness of 1.2 mm. The artificial material is set in front of a patch antenna to construct an RCA, and the gain property of the proposed RCA is evaluated with the simulation and measurement methods. The results by both the simulation and measurement methods prove that the gain is enhanced by the proposed artificial material. The maximum gains are 14.5 dBi in simulation and 12.8 dBi in measurement at 15 GHz for the RCA with on slab of the artificial material. The gain is improved compared to the gain of a patch antenna without the artificial material.

Multilayer grid polarizers for millimeter waves produced with photolithographic technology have been simulated. Polarizers have spectral bands of enhanced performance where polarization extinction ratio in decibels grows in proportion to the number of layers. Full-wave modeling is compared with three asymptotic models for subwavelength gratings using adjusted grating parameters. Random variations of interlayer spacings reduce the enhancement of polarizing performance, yet the latter continues to grow in proportion to the number of layers. Broadband signal detection is also considered.

A package-board co-design method was applied for a Narrowband Internet-of-Things (NB-IoT) SiP module. The electromagnetic interference (EMI) generated by the module was studied by improving the transmission quality of radio frequency (RF) signal. The SiP models of the initial design and the optimized design were simulated separately to show that the optimized design significantly increased effective transmission power of the RF signal and suppressed near-field electromagnetic radiation intensity to a certain extent. In addition, the optimized design model was verified by measurement. The measured results show good agreement with the simulated ones and demonstrate that the package-board co-design method can improve the electromagnetic compatibility (EMC) of NB-IoT applications.

A low-profile half-mode substrate integrated waveguide (HMSIW) filtering antenna with high frequency selectivity is proposed in this letter. The proposed antenna with a height of 0.014λ₀ (λ₀ is the free-space wavelength) consists of a slot-loaded HMSIW cavity, two parasitic patches, and five shorting pins. An upper-edge radiation null is generated by the interaction between the HMSIW cavity and parasitic patches. A rectangular slot etched on the HMSIW cavity is adopted to generate another null to improve the filtering performances at the upper stopband. Besides, the radiation in the lower stopband is suppressed by two nulls which emerge due to placing shorting pins under two parasitic patches. Thus, four radiation nulls can be obtained to enhance the frequency selectivity. The measured results illustrate that the proposed antenna provides an impedance bandwidth of 4.3% ranging from 2.74 to 2.86 GHz and a peak gain of 6.76 dBi during the operating frequency band. Moreover, four radiation nulls appear at 2.34, 2.56, 3, and 3.24 GHz in the lower and upper stopbands.

This paper proposes a novel bandpass filter for L-band based on CRLH TL, which is mainly formed by coupling a high-pass characteristic module with a low-pass characteristic module in a cascade. The high-pass module consists of an interdigitated coupled line and a grounding via, owning to its singular characteristics, which the miniaturization is realized. The low-pass module is composed of a C-type resonator with high-low impedance lines, which can realize great sideband attenuation characteristics. To further improve its out-of-band rejection characteristics, a complementary split-ring resonator (CSRR) defective ground structure with single-pole attenuation characteristics is loaded, and a transmission zero is introduced at 2.5f₀ out-of-band. The test results are in great agreement with the simulation ones, and the dimensions are only 0.20λ_g*0.22λ_g. Compared with other similar types, the filter proposed in this paper has miniaturization, great passband selection characteristics, stopband characteristics, and the advantage of low insertion loss.