This paper presents a novel variable leakage flux flux-intensifying motor (VLF-FIM) to improve flux-weakening ability. The innovation lies in the variable leakage flux property and the characteristic of Ld>Lq. The two characteristics can be achieved by the adoption of magnetic barriers and magnetic bridges. Consequently, the flux-weakening ability is enhanced. Then, the topology structure and operation principle of the proposed machine are introduced. Based on the two-dimensional finite element method (2DFEM), the electromagnetic performances of the proposed motor are analyzed and compared with the conventional interior permanent magnet motor (CIPMM) in detail. The performances mainly include torque, flux-weakening ability, constant power speed range (CPSR), irreversible demagnetization risk of the PM, structural strength, etc. Finally, the results show that the proposed motor has some advantages, such as good flux-weakening ability, a wide constant power range, and a large high-efficiency area. In addition, it verifies the effectiveness of the proposed method in improving the flux-weakening ability of the motor.
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.
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.
This paper presents a star-shaped compact dielectric resonator antenna for wideband and multiband wireless applications. The slots in the dielectric slab have been created to achieve wider bandwidth. The star-shaped alumina dielectric is placed on a low cost FR-4 substrate and fed using a microstrip line. The electrical dimensions of the proposed dielectric resonator antenna are 0.86λ0×0.86λ0×0.13λ0. The proposed design resonates at multiple frequency bands of 5.04-6.13 GHz, 6.87-7.97 GHz, and 8.58-9.63 GHz having the fractional bandwidths of 20.76%, 15.3%, and 11.4%, with peak gains of 3.71 dBi, 6.20 dBi, and 8.10 dBi, respectively. The design was fabricated to validate the simulation results. Good agreement can be seen between the measured and simulated results.
An efficient analysis and optimization method is proposed to compensate the influence of asymmetric radome on an antenna by correcting amplitude and phase of the excitations. The asymmetrical and heteromorphic radomes are inevitable for the radar on high-speed aircraft. Many previous researches focused on the optimization of the radome structure and thickness to reduce the influence of radomes. However, the influence of complex streamlined radome cannot be compensated by merely optimizing the structure and thickness of the radome. Therefore, an alternative optimization method, optimizing amplitude and phase of feeds, is used in this paper. This paper adopts the active element pattern (AEP) technique, utilizing full-wave simulation method to extract the AEP for each antenna element and computing radiation patterns of array antenna by using vector composition of AEP. In combination with hybrid genetic algorithm-particle swarm optimization (HGAPSO), the antenna radiation characteristics can be obtained by updating excitations, which avoid the repeated full-wave simulation in the optimization process. Furthermore, the speed updating formula of PSO algorithm is improved combined with prior information, and the convergence speed is further increased. Finally, a 64 elements array antenna-radome system was optimized as an example in the cases of continuously adjustable phase and digital discrete phase.
The electromagnetic characterization of layered materials is applicable to many different applications. In previous work it has been shown that reflection-only techniques - which vary the underlying structure of the sample stack to obtain two independent measurements - are a variation of a single unifying scheme such that there is a single set of closed-form unifying extraction equations for the electric permittivity and magnetic permeability. In this paper, the error propagation method is applied to this single set of closed-form extraction equations in order to derive an accompanying set of closed-form equations to predict the measurement uncertainty of electric permittivity and magnetic permeability. An error analysis is performed on the layer-shift method, and results are compared to a Monte Carlo simulation to prove the viability of the general error analysis equations.
This paper presents a dual-band polarization dependent phase gradient metasurface (PGMS) lens based on phase compesation method. The proposed metasurface (MTS) consists of a multi-layered unitcell with elliptical structures encircled by a square loop. Owing to the elliptical shape, the unitcell produces an independent phase control for different polarizations of incident wave at two operating frequencies. The present work is aimed to design a dual band gain enhancement MTS lens antenna in the broadside direction at 10 GHz and 12 GHz. The proposed MTS is designed by one-to-one spatial phase mapping with major and minor axes of the elliptical unitcell at 10 and 12 GHz for x- and y-polarized incident waves, respectively. The performance of the MTS is validated by placing two linearly polarized patch antennas operating at 10 GHz and 12 GHz at the focal distance. The simulation and measured results show a gain enhancement of 10 dB in the frequency range of [9.5-10.1] GHz and [11.6-12.1] GHz for x- and y-polarized waves, respectively.
A compact CPW-fed triple-band Multiple Input Multiple Output (MIMO) antenna is designed for WLAN, WiMAX, and 5G applications in this article. Three resonant frequencies, including 2.4 GHz, 3.5 GHz, and 5.5 GHz are generated by two branches and a rectangle radiation patch. The proposed antenna comprises two antenna elements placed side by side with a meandering neutralization line (NL) inserted between the elements to realize decoupling. To analyze the performance, it is fabricated and experimented. The measured results reveal that it has three impedance bandwidths: 2.38-2.52 GHz (5.7%), 3.28-3.62 GHz (10.1%), and 5.05-6.77 GHz (29.1%) with the measured isolation up to 16 dB. Furthermore, the parameters of diversity performance like envelope correlation coefficient (ECC), diversity gain (DG), efficiency, gain, channel capacity loss (CCL), mean effective gain (MEG), and total active reflection coefficient (TARC) are also analyzed, and the results indicate that the proposed antenna is desirable for integration in WLAN/WiMAX/5G devices.
The method of retarded potentials is used to derive the Biot-Savart law, taking into account the correction that describes the chaotic motion of charged particles in rectilinear currents. Then this method is used for circular currents, and the following theorem is proved: The magnetic field on the rotation axis of an axisymmetric charged body or charge distribution has only one component directed along the rotation axis, and the magnetic field is expressed through the surface integral, which does not require integration over the azimuthal angle φ. In the general case, for arbitrary charge distribution and for any location of the rotation axis, the magnetic field is expressed through the volume integral, in which the integrand does not depend on the angle φ. The obtained simple formulas in cylindrical and spherical coordinates allow us to quickly find the external and central magnetic field of rotating bodies on the rotation axis.
This paper presents an electrically small antenna (ka = 0.87) with ultra-low-profile 0.005λ0 and six reconfigurable endfire radiation patterns, which cover the entire 360° azimuth plane. An equivalent magnetic dipole and six switchable equivalent electric dipoles form the six reconfigurable endfire radiation patterns by switching the ON/OFF states of six PIN diodes. The designing bright point is the dual side printed loop, that is, an Alford loop and six loaded circular arc stubs, which form the equivalent magnetic dipole. This technique can reduce the size by 77% compared with single side printed loop, expand the bandwidth, and produce a strong and uniform near magnetic field, which leads to a high F/B ratio. Compared with published pattern-reconfigurable ESAs with endfire radiation characteristics, the proposed antenna has highet F/B ratio about 35.6 dB, more switchable states and expanded bandwidth. In addition, the measured peak realized gain and radiation efficiency at 1.5 GHz are 3.52 dBi and 77.6%, respectively.
Through-the-earth (TTE) communication systems are useful for post-disaster emergency communications due to their likelihood of surviving a mine disaster. The wireless channel and electromagnetic environment (EME) are two primary factors that affect the performance of a TTE system and have not been well understood in a mining environment. This paper reports our recent measurements conducted in an active coal mine to characterize the wireless channel and EME of a TTE system. TTE transmissions were successfully demonstrated in a mine location with a depth of 567 m (1,860 ft) by using ground rods installed on the surface and existing roof bolts in the underground. The results show that the EME in the mine is dominated by the 60-Hz signal and its harmonics for both surface and underground environments. The signal attenuation caused by the channel increases for frequencies greater than 90 Hz, which appears to be an optimum frequency point showing the smallest attenuation. An analytical path loss model for TTE channels is developed and validated using measurement results. This paper provides a measured data set as well as a model that an electric-field TTE system operator or system designer can reference when implementing TTE technologies in a mining environment.
Unconditionally stable approximate Crank-Nicolson (CN) perfectly matched layer (PML) implementation is proposed to treat open region problems for a bandpass rotational symmetric structure. To be more specific, this implementation is based upon the CN Douglas-Gunn (DG) procedure and the complex envelope (CE) method in body of revolution (BOR) finite-difference time-domain (FDTD) lattice. The proposed scheme inherits the advantages of the CNDG procedure, CE method, and BOR-FDTD algorithm which can improve the efficiency, enhance the absorption, and maintain the calculation accuracy. The effectiveness which includes accuracy, efficiency, occupied resources, and absorption is illustrated through a numerical example. The numerical results reveal that the proposed scheme provides considerable accuracy, creditable absorption and outstanding efficiency. Meanwhile, it can also verify that the proposed scheme is stable without the limitation of Courant-Friedrich- Levy (CFL) condition.
Steel-tower structure buildings are different from traditional buildings and lack of effective channel models. A ray-based channel model suitable for severe multipath effects is proposed in this paper. The calculation method of channel parameters is introduced in detail, and the statistical characteristics at different frequencies are also analyzed based on the ray tracing (RT) method. We compare the RT-based channel data at 800 MHz, 2.4 GHz, 6 GHz, and 28 GHz with different positions of transceivers, and obtain the corresponding characteristics of channel parameters. According to the probability density distribution of each parameter, it is shown that the angle offset, delay, and power attenuation can be well fitted by Laplace distribution, Gaussian distribution, and exponential distribution, respectively. On this basis, the power delay profile at different positions is analyzed. These results can be used to optimize the deployment of sensor networks and evaluate the performance of communication systems inside the tower structure buildings.
This paper presents a set of statistical channel models based on 60 GHz radio measurements in a server room. The channel models are developed for possible use-cases, corresponding to potential deployment scenarios in wireless data centers (WDCs). A simple parametric channel model is used to model both the deterministic and stochastic channel parameters in the delay domain, within the 57-64 GHz unlicensed band. A simulation framework is accordingly provided to generate channel realizations for WDC use cases. The accuracy of the simulation framework is verified using the delay spread as a validation metric. The reported models are useful for practical system design and evaluation of WDCs millimeter-wave systems.
In order to improve the performance of decoupling control for an interior permanent magnet synchronous motor (IPMSM), a recursive least square algorithm with fuzzy forgetting factor is proposed to identify IPMSM parameters. Firstly, the problems of coupling and parameter identification of IPMSM are analyzed. Secondly, the identification process of resistance and flux linkage is analyzed, and the static parameters are identified as the initial value or constant value. Thirdly, fuzzy control is used to dynamically adjust the forgetting factor in the recursive least square algorithm to make the identification of direct axis and quadrature axis inductance parameters more accurate. Finally, the effectiveness and accuracy of the proposed parameter identification algorithm are verified on the platform, and the good performance of the proposed algorithm in decoupling control is verified. The experimental results show that the identification method can accurately identify the motor parameters in static state and dynamic state. At the same time, the forgetting factor is dynamically adjusted to improve the parameter identification effect and decoupling control performance of the motor.
A conformal metamaterial absorber operating at the quad band is analyzed in this paper. The proposed structure is fabricated on a 0.5 mm thick, flexible polyester dielectric substrate. The proposed structure works at the chosen frequencies 4.11 GHz, 5.37 GHz, 7.39 GHz and 8.4 GHz with the absorptivities of 96%, 95%, 90% and 94%, respectively. The structure has essential novelty of miniaturization of λ/146 in the thickness, which is an exceptionally flexible material for Radar applications. Quad band excitation can also be analyzed by the iteration of the proposed structure as well as circuit analysis. The flexible polyester material is etched with silver coating for the development of the fabricated structure. The simulated results can also be associated with the measured ones from the planar as well as a cylindrical surface to realize flexibility for stealth technology. It can be accomplished by the free space measurement technique in an anechoic chamber.
In this paper, eigen analysis of the correlation matrix for an 8-element singly curved conformal antenna array with plane wave(s) incident at different angles is presented. The signal eigenvectors derived from the correlation matrix are used as the array weights to generate peak beams toward the directions of the signals, and the noise eigenvectors derived from the correlation matrix are used as the array weights to generate nulls in the directions of the signals. A 1 x 8 microstrip patch antenna array is embedded on an anhedral corner type structure with different amount of surface deformation to analyse the array pattern. The patch antenna elements in the conformal array are excited with attenuators (for amplitude control) and phase shifters (for phase control) to implement the complex signal eigenvectors practically. The simulated eigenbeams using conformal antenna array are in good agreement with the measurement results. Furthermore, the effects of surface deformation on gain and beamwidth of array main beam is discussed. The proposed eigenbeam conformal antenna array can be used in smart and adaptive array applications.
In this article we give an analytical formula for calculating the self-inductance for circular coils of rectangular cross-section which has a non-uniform current density. Recently, the formula for calculating this important electromagnetic quantity was published in the form of the single integral whose kernel function was asum of elementary functions. However, a new formula is obtained in the form of elementary functions, single integrals, and the complete elliptic integral of the first, second and third kind. Although its development looks tedious, we obtain a rather user-friendly expression for the calculation. From the general case, the self-inductance of the thin disk coil (pancake coil) with the nonuniform current is obtained in a remarkably simple form. The results of this work are compared with different known methods, and all results are in the excellent agreement. Our approach has not been found in the literature.
Monitoring the prestress of prestressed steel strands is important but difficult. The magnetoelastic inductance (MI) method is used to monitor the prestress. A coupling model was established to describe the correlation among stress, magnetism, and inductance. A prestress monitoring system based on the MI effect was proposed. To verify the feasibility of the method, experiments were carried out. The results showed that influenced by the hydration heat of the grouting materials, the fluctuation range of the inductance was 1.033%. When the hydration came to an end, the inductance approached the initial inductance. For internal steel strands, the obtained inductance-prestress relationship was similar to the relationship of external steel strands. Thus, the prestress of the internal steel strands could be monitored by the MI method.