A compact asymmetrically fed U shape slot antenna for 5G smartphone application is presented. The antenna consists of two major components that are responsible for generating broadband circular polarization (CP) (i) the microstrip patch feed structure employed at the top plane and (ii) U shape slot mechanism employed at the ground plane. The U shape ground radiator is approximately half wavelength slot mode which is responsible for lower band CP operation. The planar monopole structure is formed by the microstrip line feed. This planar monopole is a quarter wavelength mode used for achieving higher band CP operation. By combining these two CP modes generated by U shape slot and port-line structure, a broadband CP antenna is designed. The circular polarization is achieved with lesser complexity in the design structure. To get the practical validation of the simulated design, it is then fabricated and tested for measured results without using power divider. The measured axial ratio bandwidth covers from 2.00 GHz to 6.50 GHz (4.50 GHz) and the -10 dB Impedance Bandwidth (IBW) covers from 1.66 GHz to 8.10 GHz (6.44 GHz) respectively. The isolation between two asymmetric port-lines is greater than 14.5 dB within 3-dB axial ratio bandwidth.

In this paper, a numerical electromagnetic model of a low-cost detection modality for red palm weevil pests in palm trees using resonant-based microwave sensors is presented. The developed sensor is based on the complementary split-ring resonator concept. The complementary resonator is easily modeled using printed circuit board technology, where the transmission response from two ports at ends of 50 Ω-matched transmission line is recorded. The microwave sensor has been designed to work at the 2.45 GHz ISM-band and is placed underneath a finite size 3D model of a palm tree trunk infested with the red palm weevil pest. For comparison purposes, the numerical simulation results are compared against a reference case of a healthy palm trunk. The results show the capability of the proposed numerical electromagnetic model in detecting presence of the red palm weevil in palm trees.

An equivalent source model based on neural network is proposed to rapidly estimate the magnetic radiation characteristics of linear synchronous motor (LSM) in electromagnetic suspension (EMS) maglev system. The equivalent source is composed of electric dipoles and a closed three-dimensional (3-D) surface, and is developed in terms of source reconstruction method. A few sampling data of magnetic field simulation results serve as the input information to determine the unknown current distribution on equivalent source model. To solve the inverse radiation problem and characterize the whole radiation pattern with high efficiency, the current distribution signature of equivalent model is fitted into artificial neural network models. Separate neural network models are fitted under different phases of winding excitation, which enables the low-frequency magnetic field estimation under both 3-phase balanced operation and unbalanced operation. The equivalent source model is extended to estimate LSM radiation in multi-source environment, and the comparison with numerical simulation verifies its accuracy and efficiency.

In this paper, a novel behavioral model for the receiver front-end is presented. This model allows the accurate prediction of the nonlinear effects of the receiver front-end including the in-band distortion, intermodulation and harmonic generation. The behavioral model is a block-oriented model that consists of three blocks, the frequency conversion block, nonlinear block， and memory linear block. The nonlinear block and memory linear block are represented by the polynomials in time domain respectively, which can characterize the high-order nonlinearities and the strong memory effects by the appropriate adjustment of the polynomial order. An original model parameter identification procedure that can efficiently estimate the model parameters by using the specific input-output data is also proposed. Moreover, the presented behavioral model and identification procedure are assessed by the experiment with the excitation of single-tone signals, multitone signals and WCDMA signals, respectively. The comparison between the measurement and model simulation suggests that the behavioral model has good accuracy of the prediction of the nonlinear effects of the receiver front-end.

This paper proposes an absorption-transmission-absorption (A-T-A) type frequency-selective rasorber (FSR) with high selectivity that is loaded above a polarization conversion structure (PCS) and applied to a circular polarization (CP) slot antenna array for ultra-wideband radar cross section (RCS) reduction. Outside the operational frequency band (out-of-band) of the antenna, the energy of the incident electromagnetic (EM) wave is directly absorbed by the FSR, whereas from within the operational frequency band (in-band) of the antenna, the incident EM wave penetrates the FSR and irradiates it on the PCS placed on the lower layer of the FSR structure, which meets the phase cancellation condition and is diffused at the same time, thereby realizing the in-band RCS reduction. Due to the lower insertion loss in the passband, higher quality factor (Q value) in the transmission band, and wider absorption band, the proposed FSR can minimize the gain loss (only 0.2 dB) of the CP slot antenna array and widen the RCS reduction bandwidth to 135.5% (5-26 GHz). In addition, due to the central symmetry of the FSR and PCS structures, the CP slot antenna array has monostatic RCS reduction performance for both horizontally polarized (HP) and vertically polarized (VP) incoming waves.

Magnetoacoustic concentration tomograghy of magnetic nanoparticles (MNPs) with magnetic induction (MACT-MI) is a multi-physics field imaging method based on the coupling effect of magnetic field and acoustic field. In order to generate a gradient magnetic field with higher uniformity by using lower current excitation, this paper takes the magnetic field gradient of 0.3 T/m as the design objective and utilizes the Beetle Antennae Search Algorithm to optimize the parameters of the excitation current of multiple coils. The uniformity of gradient magnetic field generated by four typical six-coils structures with different radii and distances was compared with that generated by the Maxwell coil, and then the optimal structure of six-coils was determined. By using the finite element method, the physical process of MACT-MI was numerically solved according to the optimization results, and we obtained the one-dimensional and two-dimensional distribution images of magnetic force and sound pressure. The results show that compared with the Maxwell coil, the multi-coil structure can effectively reduce the current excitation and provide a higher uniform gradient magnetic field, which makes the magnetic force of MNPs more uniform and promotes the complete reconstruction of the sound source. These research results can provide research ideas for the optimization of MACT-MI system and lay a foundation for subsequent experiments and even clinical practice.

Shale oil and gas are unconventional oil and gas resources that can be used as alternative energy sources in the future. Shale reservoirs are the new growth point for the exploitation of oil and gas and development of China's oil and gas industry. The heterogeneity of the shale stratum determines the complexity of its mining. Accurate identification and detection of its oil-bearing characteristics are principal tasks in the oil shale deposit evaluation and economically exploitable interval division. Dielectric logging cannot rely on traditional resistivity logging curves, and it is not affected by the formation water salinity, which can provide the formation water porosity. Combined with other types of logging, it can effectively evaluate the formation oil saturation. In this study, we applied a new type of high-frequency dielectric logging tool in the production of shale oil, developed by the 22nd Institute of China Electronics Technology Group Corporation, based on different dielectric constants of oil, rock matrix, and water. We first introduced the principle of dielectric logging and the major advantages of the dielectric logging tool, and further proposed a new complex refractive index model with clay correction and explained the processing methods, which improved the accuracy of calculating the formation water saturation. Furthermore, the developed technology was applied and evaluated in the Songliao Basin.

A simple design configuration of a broadband polarization-insensitive double-layered microwave absorber is presented here. The proposed absorber is designed using indium tin oxide (ITO) based on thin resistive film. The novelty of structure is to achieve large absorption bandwidth with more than 99% absorption. The proposed structure is modeled for 20 dB absorption bandwidth at normal incidence from 6.3 GHz to 14.2 GHz spanning over C-band, X-band, and Ku-band. Under oblique incidence the proposed structure is stable up to 60˚ for TE polarization and 45˚ for TM polarization. To understand the operating principle of absorption of proposed structure, an equivalent circuit is derived, and surface current distribution is also studied. A fabricated sample is measured, which validates our simulation.

As the explicit finite-difference time-domain (FDTD) method is restricted by the well-known Courant-Friedruchs-Lewy (CFL) stability condition and is inefficient for solving numerical tasks with fine structures, various implicit methods have been proposed to tackle the problem, while many of them adopt time-splitting schemes that generally need at least two sub-steps to finish update at a full time step, and the strategies used seem to be an unnatural habit of computation compared with the most widely-used one-step methods. The procedure of splitting time step also reduces computational efficiency and makes implementation of these algorithms complex. In the present paper, two novel one-step absolutely stable FDTD methods including one-step alternating-direction-implicit (ADI) and one-step locally-one-dimensional (LOD) methods are proposed. The two proposed methods are derived from the original ADI-FDTD method and LOD-FDTD method through some linear operations applied to the original methods and are algebraically equivalent to the original methods respectively, but they both avoid the appearance of intermediate fields and are one-step method just like the conventional FDTD method. Numerical experiments are carried out for validation of the two proposed methods, and from the numerical results it can be concluded that the proposed methods can solve equation correctly and are simpler than the original methods, and their computation efficiency is close to that of the existing one-step leapfrog ADI-FDTD method.

This paper discusses the design of a 6-m Cassegrain optics based multiband reflector antenna integrated with beam waveguide (BWG) optics, which consists of an ellipsoidal mirror and three plane mirrors. The presented antenna has been simulated, and 75.8% and 76.8% aperture efficiencies have been achieved at 0.225 THz and 0.338 THz, respectively. The initial design parameters of elements of BWG network are computed using fundamental Gaussian beam parameters. The simulated results of the antenna including aperture efficiency have been presented and discussed in detail. The antenna has been designed for the ground based THz telescope for radio astronomy.

Free-electron radiation results from the interaction between swift electrons and the local electromagnetic environment. Recent advances inmaterial technologies provide powerful tools to control light emission from free electrons and may facilitate many intriguing applications of free-electron radiation in particle detections, lasers, quantum information processing, etc. Here, we provide a brief overview on the recent theoretical developments and experimental observations of spontaneous free-electron radiation in various structured environments, including two-dimensional materials, metasurfaces, metamaterials, and photonic crystals. We also report the research progresses on the stimulated free-electron radiation that results from the interaction between free electrons and photonic quasi-particles induced by the external field. Moreover, we provide an outlook of potential research directions for this vigorous realm of free-electron radiation.

This paper proposes an efficient and accurate scattered field prediction method based on Kirchhoff Approximation called `Mirror Kirchhoff Approximation' (MKA) which is suitable for evaluating the shadowing effect by a metal cuboid. The disadvantages of conventional methods, such as low accuracy of Kirchhoff Approximation (KA) for metal cuboid and high computational complexity of Method of Moment (MoM) for a shadowing object at millimeter wave (mmWave), have motivated the establishment of an efficient and accurate prediction method for a metal cuboid at mmWave. The proposed method solves the previous issues by introducing the ray-based reflection into conventional KA. The idea and detail formulations of the proposed method are presented. The proposed method is validated by comparing with MoM and KA in terms of complexity and accuracy. The results imply that the proposed method presents good accuracy with low calculation time. The MKA has a maximum 8.3 dB improvement compared with conventional KA. Calculating time is improved by 392-915 times compared with MoM.

A co-planar waveguide-fed symmetrical staircase-shaped ultra-wideband antenna is proposed in this work. This antenna consists of three pairs of rectangular notches, two symmetrical C-shaped slots and two pairs of quarter-circular-ring-slits which are etched on the rectangular radiator and ground plane, respectively. By sequentially inserting three pairs of rectangular notches with proper positions, an excellent impedance bandwidth of 1.55-16.95 GHz (166.51%), i.e., a 10.94:1 ratio bandwidth is obtained. The total volume of the prototype is merely 0.239×0.224×0.004λ_l³, λ_l wavelength of the free space at the lowest operating frequency (i.e., 1.55 GHz). As a result, wider impedance bandwidth, fair gain and better impedance matching of the proposed antenna are obtained. It is observed that the simulation results are in good agreement with the measurement results. The transmission line model (TLM) of the proposed antenna is presented, and it shows the antenna behavior based on the effect of each element. It is observed that the characteristics of the TLM model are close to the simulation result using the CST simulator. The prototype is successfully implemented, fabricated, and compared with the experimental results.

This letter proposes a 2×2 surface-mount dipole antenna array based on via fence for 5G millimeter-wave applications. The dipole antenna element was first proposed, which has a compact size and low cost. Then the via fences are introduced to reduce coupling between adjacent elements and enhance isolation. In this way, compared with a 1×2 antenna array without the via fence, the isolation of a 1×2 antenna array with a via fence is improved by 12 dB at 26 GHz. The elements are extended into 2×2 arrays with and without the via fence, and their performance is evaluated by the evaluation board. The measurement results show that the -10-dB impedance bandwidth of the antenna array is 19% (24.7-29.9 GHz), and the peak gain is 9.5 dBi at 25 GHz. The proposed 2×2 array can be used in the N257 (26.5-29.5 GHz), N258 (24.25-27.5 GHz), and N261 (27.5-28.35 GHz) frequency bands. Low cost, small size, and high isolation characteristics make it one of the candidates for 5G millimeter-wave applications.

This paper presents crosstalk analysis of E-plane multichannel waveguide joints for high frequency. The multi-cavity modeling technique and method of moment are used to analyze the crosstalk. Waveguide has many practical uses in high powered RF systems. When two channel waveguides are joined, the phenomenon of crosstalk will certainly appear, and the reason behind is poor workmanship. The gap appearing at the flange joint causes power coupling to the neighboring ports. In this paper two channel E-plane waveguide joints for frequency range 15 GHz to 18 GHz have been analyzed. Scattering parameters data obtained from cavity model analysis have been verified and compared with CST microwave studio simulated and measured data.

Transcranial magnetic stimulation (TMS) has been widely used in the treatment of varied physical and neuropsychiatric disorders, especially in major depression. The intracranial electromagnetic field is generated by the the time-varying current in the stimulation coil to change the potential of targeted neurons during the treatment. Since different mental disorders correspond to specific stimulation targets and broad stimulation range might raise serious side effects, stimulation focalization is very important in TMS. To achieve focalized stimulation, a novel magnetic stimulation coil with the field shaper and the crescent ferromagnetic core (the FSMC coil) is proposed and optimized in this study. The Finite-Element Method (FEM) is adopted to analyze the relationships between the design parameters of the field shaper and crescent ferromagnetic core and the characteristics of the intracranial electromagnetic field. Compared to traditional single circular coil, the focalization of the intracranial electromagnetic field generated by the optimized FSMC coil can be significantly improved both from 2D and 3D levels. To verify our method, an anatomically realistic human head model with different electrical properties assigned to each tissue of the brain is employed in this paper. We also checked the maximum induced charge density on the targeted plane generated by the optimized coil to make sure that it will not cause any induced neurologic damage.

This article proposes a new type of variable-leakage-flux flux-intensifying permanent magnet (VLF-FIPM) machine and performs optimization and multi-physical field analysis on it. By designing leakage flux bypass and various magnetic barriers, the proposed machine has the variable-leakage-flux characteristic and reverse saliency characteristic of L_d>L_q. Firstly, the evolution process from the conventional interior permanent magnet (IPM) machine to the proposed machine is explained. Secondly, the output torque, torque ripple, core loss and reverse saliency ratio of the proposed machine are optimized by multi-objective comprehensive optimization method. Then the electromagnetic performance of the optimal machine is compared with that of the initial machine and conventional IPM machine. Finally, the temperature field and stress field of the optimal machine in different states are analyzed in detail. Both theoretical results and simulation analysis verify the effectiveness of the proposed design idea and optimization of the VLF-FIPM machine.

Assis predicted that based on Weber's electrodynamics, an alternative direct-action model formulated before Maxwell, a charge accelerating inside a sphere at constant electric potential, should have a measureable effective mass. Although initially some experiments appeared in the literature that indeed claimed such an effect, all recent studies found no evidence. All experiments so far used either discharges or electrons with non-constant accelerations that could mask the existence of Assis's prediction. We performed an experiment using a Perrin tube, which produces a beam of electrons with a constant velocity that can be deflected by Helmholtz coils to hit a Faraday cup. The tube assembly was put inside a spherical shell, which could be charged up to 20 kV. Any effective mass of the electrons would have changed their position on the Faraday cup. We found no variation of the electron position within our experimental accuracy, which rules out Assis's effect by two orders of magnitude. This confirms Maxwell's theory and the fact that electrostatic potential energy cannot be localized to individual charges.

A Negative Group Delay (NGD) filter prototype design based on cascaded identical 2nd-order baseband stages is presented. The prototype design achieves an NGD-bandwidth product that in the upper asymptotic limit for a distributed design is a function of out-of-band gain in decibels raised to the power 3/4. This is an improvement of previous cascaded first-order designs that have an NGD-bandwidth functional dependency of out-of-band gain in decibels to the power of 1/2. The bandwidth is taken as the 3 dB amplitude response bandwidth. The corresponding NGD design upshifted to a non-zero center frequency, i.e. a Band-Stop Filter (BSF) design, is shown to be possible to implement with Sallen-Key topology, and an example is presented for a 500 MHz center frequency and a 100 MHz (20%) 3 dB bandwidth. The filter shows a 4.05 ns negative group delay with a 1.28 ns in-band variation and a 3-dB amplitude response over the bandwidth of 100 MHz, achieving an NGD-bandwidth product of 0.405. An in-band distortion metric is presented, which can be evaluated for any specified time-domain input waveform. It is shown that the bandwidth, order of filter and desired distortion for a particular input waveform are interrelated. Therefore, the proposed in-band distortion metric constitutes another trade-off quantity to be checked for any type of NGD design.

Single patch designs of a microstrip antenna with a U-slot or a pair of rectangular slots (E-shape) provide a single band circularly polarized response, and hence they are not useful in frequency and polarization agile applications. In this paper, a modified design of a Ψ-shape microstrip antenna is proposed for dual band and dual sense circularly polarized response. Use of unequal length rectangular slots in the modified patch, optimizes the inter-spacing between the modified TM21 and TM22 resonant modes, surface current distributions and impedance levels at them to yield dual band circularly polarized response. An impedance bandwidth of 1992 MHz (37.05%) is obtained which completely covers the axial ratio bandwidth of 11.84 and 5.67%, in the two bands with frequency ratio of 1.3 in between them, thereby satisfying the requirements of frequency agile systems. Over the impedance and axial ratio bandwidth, the antenna exhibits nearly broadside radiation pattern with a gain of around 7 dBi. A design methodology based on the simple parametric formulation is presented, which helps in realizing a similar antenna in the specific frequency band. The proposed antenna can find applications in frequency and polarization agile systems where the signal loss due to the interference and jamming can be reduced.