Air-gap magnetic energy variation with angular position produces cogging torque, which may results in mechanical vibration, acoustic noise, and torque ripple. Various cogging reduction methods of design modifications viz. skewed magnets, skewed slot, asymmetrical displacement of magnets/slots etc. are reported in the literature. All such methods adversely affect machine performance in terms of air-gap magnetic field, back emf, and induced voltage. This paper introduces the cogging torque reduction by skewing of slot opening. In order to obtain machine performance, the no load magnetic field of the proposed machine is determined using combined methods of two-dimensional subdomain analytical analysis method and multislice method. The machine is considered as a stack of slices along axial direction. The adjacent slices differ in relative location of slot openings. The analytical field solution of each slice is obtained by use of subdomain method, and algebraic summation of slices is taken as field solution of actual machine. The analytical analysis developed is compared with finite element analysis (FEA). The close agreement of analytical results with FEA results confirms the validation of analytical solution. Furthermore, the machine parameters viz. cogging torque, back emf, and induced voltage are evaluated analytically, and results are compared with FEA solution. To demonstrate the effect of skewed slot opening on machine's performance, a machine of same rating without skewing of slot opening is investigated, and their performances are compared.

In this paper the analysis and investigations are carried out on portable antennas for worldwide interoperability for microwave access (WiMAX) applications of flexible coplanar waveguide (CPW)-feed split-triangular shaped patch (STSP). The proposed STSP antenna is fabricated from polyimide substrate material having the dimension of 18×20×0.1 mm³ (volume is 36 mm³). It resonates at 3.55 GHz frequency of a reflection coefficient (S₁₁) of -24.45 dB and offers impedance bandwidth of 580 MHz (3.3-3.88 GHz) with a gain of 2.06 dBi. The STSP antenna has small size, light weight, low volume, and is flexible for WiMAX applications. Simulation and measured results of the proposed STSP antenna are in close agreement.

A flexible fully textile-integrated bandstop frequency selective surface working at a central frequency of 3.75 GHz and presenting a 0.6 GHz bandwidth has been designed, manufactured and experimentally characterised. The frequency selective surface consists of a multilayered woven fabric whose top layer presents periodic cross-shaped conductive resonators, and due to its symmetries, its performance is largely independent of polarisation and angle of incidence. These properties make the prototype very interesting for shielding applications. The designed frequency selective surface is based on a layer-to-layer angle interlock 3D woven fabric. This technology provides the prototype with flexibility, portability and the possibility of manufacturing it in a large scale production by the use of existing industrial weaving machinery, in contrast to conventional frequency selective surfaces manufactured using rigid substrates. The proposed textile frequency selective surface has been simulated and experimentally validated providing good agreement between the simulations and measurements. The measured maximum attenuation has been found to be higher than 25 dB under normal incidence conditions.

^nullA quasi-octave bandwidth arbitrary-angle compact waveguide twist using a single matching step is presented. The proposed twist, based on a single intermediate ridge waveguide section that broadens its mono-mode operation, exhibits a similar wave impedance to the rectangular waveguide connected to its ports thus facilitating the reflections minimization in an extended frequency range. An exemplary 45° twist has been manufactured in the 10 GHz to 19.3 GHz frequency range (~64%) for demonstration purposes. The measured data are in concordance with those predicted by the simulation. This result represents, to the authors' knowledge, today's state-of-the-art in terms of compactness and bandwidth performance.

In this paper, a compact, circularly polarized printed monopole antenna is proposed at ISM band (2.4-2.48 GHz) for biotelemetry and implantable applications. The proposed antenna possesses a small dimension (10×10×0.3 mm³) and simple microstrip feeding structure. The circular polarization is easily achieved by introducing an ``L'' shape stub at the ground plane in ISM. The simulated 10 dB impedance bandwidth is around 13.87%, and 3 dB AR bandwidth is around 5.3%. The effect of different body phantoms is discussed to evaluate the sensitivity of the proposed antenna. The simulated peak gain of the proposed antenna is about -7.79 dBi across the operating band. The SAR analysis of the antenna configuration has also been studied.

Axial flux Permanent Magnet (AFPM) machines, due to its high torque capability, high power density and compact size, are the most suitable candidates for in-wheel Electric Vehicle application. However, the presence of cogging torque in AFPM machines, resulting from the interaction of PMs and stator slots, introduces torque ripples, noise and vibrations which deteriorates the performance of the machine. To overcome this, several techniques for cogging reduction are utilized. Out of various techniques, rotor magnet shape variation is most commonly utilized. This paper investigates the effect of some preferred magnet shaping techniques in AFPM machines on several performance parameters such as magnetic flux density distribution in air gap, cogging torque, flux linkage, no load-induced emf, emf harmonics, electromagnetic torque and torque ripple. These parameters were analyzed using 3-D Finite Element Method (FEM) based simulations. It was found that a maximum cogging reduction by 62.49% and output torque ripple by 63.25% were obtained by using short-pitched and skewed rotor magnets. This also resulted in a reduction of induced emf by 14.18% and electromagnetic torque by 15.17%.

In this paper, the effects of the locations of four dual-band antennas on a mobile terminal chassis are investigated in the vicinity of user's hand. To perform this study, a dual band four-port mobile terminal antenna for 5G is designed for operation in between 3.34 and 3.84 GHz (lower band, LB) and 5.15 and 6.52 GHz (upper band, UB), respectively. Due to the symmetry of the antenna elements (AEs), a right hand standard phantom is placed at a fixed position. Meanwhile, the antenna elements are placed at seven different locations across the chassis, with the best possible locations chosen based on the maximum efficiency in data mode. The influence of the human hand on the antenna performance is assessed based on two aspects: 1) in terms of matching (impedance mismatch (IM) and impedance bandwidth (IB)); and 2) in terms of efficiency (radiation efficiency (RE) and total efficiency (TE)). To validate its performance, the proposed antenna has been fabricated and measured. Results showed good agreement between simulations and measurements. Based on the results, a general design guideline for future 5G antennas operating in the sub-6 GHz bands considering user's hand effects can be outlined. The observed maximum variation for the proposed antenna with user's hand in terms of IM is -8 dB and -5 dB, respectively, and 57% and 37% in TE, respectively.

The reliable detection of geometrically-based stealth targets using a conventional single sensor radar system may be extremely difficult. This is because low Radar Cross Section (RCS) from certain angles results in a low Signal to Noise Ratio (SNR). In the present work, multi-target tracking of stealth targets is investigated in a multi-static radar with passive receivers. The Directions of Arrival (DOA) of targets are estimated by the receivers without knowing the number of targets, and their positions are obtained based on the transmitter beam direction. The B2 bomber aircraft model has been used as a stealth target. The RCS of the model has been simulated for all collection of incident and reflected angles from an oblique impinging plane wave. Probability of Detection (Pd) is modeled using a Toeplitz-based method for different SNRs due to different RCS patterns and is fed to an Iterated Corrected Probability Hypothesis Density (IC-PHD) filter. In spite of considering the transmitter and receivers resolution in our input data generation, the proposed algorithm is able to track the targets individually when they are much close to or even cross each other. Simulation results show the improved performance of the proposed method compared to other existing approaches.

A circularly polarized (CP) antenna with simple feeding network for ultra-high-frequency (UHF) radio-frequency identification (RFID) reader application is presented in this letter. The proposed antenna consists of a slot loop etched on the ground and a simple feeding network using bended microstrip lines. And the two parts of the antenna are printed on either sides of a thin substrate, thus a low-profile antenna is obtained. The slot loop is meandered based on the first-order Minkowski fractal technique for antenna size reduction. To generate circularly polarized radiation, two branches of the feeding network are designed to be orthorhombic with 90° phase difference. The antenna is simulated and practically fabricated with a compact size of 80×80×1.6 mm³. The 10-dB impedance bandwidth and 3-dB axial-ratio (AR) bandwidth are measured to be 50 MHz (0.896-0.946 GHz) and 12 MHz (0.916-0.928 GHz), respectively. The measured peak gain exhibits stable value of 3 dBi over the impedance bandwidth. Furthermore, a wide 3-dB beamwidth of 120° is achieved for the proposed antenna. Based on the above, this antenna is well suited for applications in UHF RFID handheld readers.

This paper presents a distributed estimation strategy called alternation diffusion LMS estimation (AD-LMS) to estimate an unknown parameter of interests from noisy measurement over wireless sensor network. It is useful in the wireless sensor networks where robustness and low consumption are desired features. Diffusion LMS is introduced in this estimation strategy to improve the performance and reduce the communication burden. With the proposed strategy, whether each node distributes its estimation depends on an alternative parameter. The node only exchanges its estimation when the instant time meets some conditions. Next, each node combines the estimations of neighbors with its own estimation using combination coefficients upon the topology of the network. At last, the nodes update their estimations with a normalized LMS algorithm. The proposed AD-LMS strategy is compared to standard diffusion strategy. The results show that they achieve exactly the same coverage rate and nearly the network performance (network MSD and steady-state MSD) of standard diffusion strategy while reducing the communication burden significantly.

This paper presents a metamaterial loaded interdigital capacitor antenna having fractal geometry. The antenna consists of multiple split ring resonators (MSRR) with shorted ground. The metamaterial loading is achieved by MSRR that enhances the gain. Furthermore, multiband characteristics is obtained by two L-shaped rings providing the fractal geometry. The antenna has the physical dimension of 27 × 39.20 mm for the outer ring and in terms of wavelength has the dimension of 0.486 × 0.707λ. This antenna structure is designed and simulated on an FR-4 epoxy substrate of thickness h = 1.56 mm and dielectric constant ε_r = 4.4. The antenna resonates at multiple frequencies i.e. 1.5 GHz, 2.2 GHz, 2.70 GHz, 4.20 GHz, 4.9 GHz, 5.3 GHz, 7.2 GHz, 7.5 GHz and 8.8 GHz respectively at different matching values with gains of 9.5 dB, 14.5 dB, 11.9 dB, 3.6 dB, 4 dB, 1.5 dB, 3.8 dB and 6.5 dB. The comparison of the simulated and measured return losses shows a good agreement. The antenna finds its applications in GPS, space and satellite communication, radar, body area network (BAN) communication system.

Random arrays have been typically studied by considering real uniform excitations. This is suited for single-beam radiation patterns but does not allow for more sophisticated patterns. Indeed, only even patterns, with respect to the steering angle, can be achieved. To overcome this limitation, we recently proposed a new model whereby the excitation coefficients are not uniform and are determined by means of two random variable transformations. In this paper, we deal more extensively with the properties of this model, highlighting things that have not been pointed out previously. In order to get analytical results, we just consider symmetric random arrays. For such a case, we determine the design error, that is the cumulative distribution function of the supremum of the the difference between the actual and desired array factors. It is shown that general shaped beams can be actually achieved but at the cost of an increase of the design error as compared to the single-beam case. Numerical analysis validates the presented theory.

Wireless power transfer (WPT) via coupled magnetic resonances has been in development for over a decade. Frequency splitting occurs in the over-coupled region. In addition, the vibration of the receiver and relay coils is observed in the over-coupled region. The vibration mechanism of the relay coil is investigated in this study. First, the circuit model of a three-coil WPT system is established, and the transfer characteristics of the system are examined by applying circuit theories. Second, the transfer characteristics of the three-coil WPT system are analyzed using simulation software. Third, the energy equation of state of the three-coil WPT system is established with the introduction of entropy variable. Lastly, the experimental circuit of the three-coil WPT system is designed. The experimental results are consistent with the theoretical analysis. The vibration of the relay coil is clearly explained. The transfer characteristics of the three-coil WPT system, particularly the relay coil, may provide ideas to achieve the maximum output power and transmission efficiency under various operating conditions.

In this paper, a new measurement method is proposed to estimate the complex permittivity for each layer in a bi-layer dielectric material using a Ku-band rectangular waveguide WR62. The S_ij-parameters at the reference planes in the rectangular waveguide loaded by a bi-layer material sample are measured as a function of frequency using the E8634A Network Analyzer. Also, by applying the transmission lines theory, the expressions for these parameters as a function of complex permittivity of each layer are calculated. The Nelder-Mead algorithm is then used to estimate the complex permittivity of each layer by matching the measured and calculated the S_ij-parameters. This method has been validated by estimating, at the Ku-band, the complex permittivity of each layer of three bi-layer dielectric materials. A comparison of estimated values of the complex permittivity obtained from bi-layer measurements and mono-layer measurements is presented.

Efficiency of high frequency surface wave radars may be improved by inserting a metamaterial in the vicinity of transmitting antennas that will reinforce the propagation of surface waves. This paper deals with the first and second order derivations of the surface impedance boundary conditions (IBC) applied to model such a metamaterial, which is equivalent to a bounded ground with a low negative permittivity. The goal of this paper is to extend an approach previously based on the classical Leontovich IBC which is usually restrained to high permittivity grounds. As shown here, a simplification in the expression of the surface impedance is possible in the case of a planar and homogeneous surface. That allows to have a first order impedance boundary condition substituted for the required second order impedance boundary condition.

This paper presents the design and fabrication of an antenna based on Substrate Integrated Waveguide (SIW) for intersatellite crosslinks in C-band. The entire antenna consists of two elements of SIW slots array that is fed by a hybrid 3 dB directional coupler. The entire SIW slot array antenna is circularly polarized (CP), and each element has four longitudinal slots. The element's effective field matching is realized with a microstrip to SIW transition. The antenna design has been evaluated with its return loss, gain plot, and radiation pattern characteristics to validate the fabricated antenna. The fabricated prototype antenna radiates a left-handed circularly polarized (LHCP) electromagnetic wave with the peak gain of 5 dB and offers approximately 2% AR bandwidth around 5 GHz.

Radial flux Dual Stator Dual Rotor Permanent Magnet (DSDRPM) machine can be considered as an exterior rotor PM machine kept over an interior rotor PM machine. This facilitates with a scope for optimization of the relative placement of inner and outer stator slots of the machines to achieve cogging torque minimization. This paper deals with the analytical prediction of flux density distribution in an internal and external rotor PM machines with semi-closed slots and further utilizes it to calculate the cogging torque in DSDRPM machine. An optimal angle of shift between the stator slots of the two machines has been determined to obtain a reduction in the resultant cogging torque of DSDRPM machine. The analytical results are verified with the Finite Element Analysis (FEA) results and found to be in close agreement with each other.

In this paper a compact antipodal Vivaldi antenna with dimensions of 40×85 mm² for Ka band is presented. To enhance the antenna gain, epsilon near zero metamaterial (ENZ) unit cells are embedded at the same plane of the Vivaldi flare aperture. These ENZ unit cells have the advantage of confining the radiated fields with additional compact size. The obtained antenna exhibits an ultra-wide bandwidth from 23 GHz to 40 GHz with a reflection coefficient less than -10 dB. This is suitable for 5G applications at both 28 and 38 GHz. The antenna gain in this frequency band is found in the range from 14 to 17.2 dBi. The proposed antenna is designed by using CST-MW Studio, and the results are verified with experimental measurements.

For the first time, the concept of combinational use of subwavelength metasurfaces and plasma media is introduced in this paper for being utilized in practical radio frequency (RF) shielding applications. Using an equivalent circuit model, it is demonstrated that the simultaneous use of the lossy characteristic and special dispersion of plasma in low-frequency regime and the transmission zeros provided by spatially homogeneous metasurfaces in the upper frequency band results in superior shielding performances. The designed coating layer has an ultra-thin profile while exhibiting a super wide reject band ranging from 1 to 20 GHz (|S₂₁|<-10 dB). A fair comparison is also performed to elucidate that the proposed plasma-metasurface composite (PMC) shield outperforms the previously reported RF shielding FSSs in both bandwidth and thickness. The numerical results show that while maintaining a low profile, the shielding bandwidth of the designed PMC can be set to surprisingly include all the UHF, L, S, C, X, Ku, and K bands. Moreover, the designed coating layer provides a stable and polarization-insensitive reject band for different incident wave angles up to 45°. These superior performances, as well as the shielding tunability enabled by plasma, confirm the promising capabilities of PMC structures for various applications.

In order to have the required accuracies in method of moments (MoM) for numerical simulations of ocean scattering at microwave frequencies, we need to account for the much larger wavenumber of sea water relative to that of air. This paper presents simulation results of 2D ocean surface scattering with the required accuracies and that energy conservation is obeyed to 0.01%. A dense grid is required to discretize the MoM dual surface integral equation with up to 240 surface unknowns (120 surface electric field unknowns and 120 surface magnetic field unknowns) per free space wavelength. To solve the matrix equation efficiently, we develop a neighborhood impedance boundary condition (NIBC) technique to solve the matrix equation. We next calculate the emissivities of ocean surfaces using NIBC on surface integral equations using pulse basis/point matching and the Nystrom method. Results are illustrated for L-band and show that emissivities using NIBC combined with Nystrom are accurate to 2×10^-4 for vertical polarization and 10^-4 for the horizontal polarization. This means that our method can meet the accuracy goal of 0.2 psu salinity retrieval for the NASA Aquarius mission. Results of surface fields and emissivities are also compared to that of impedance boundary condition (IBC) which requires only 10 unknowns per free space wavelength.