The thermal characteristic of a new out-rotor fault-tolerant permanent-magnet (FTPM) motor is modeled and predicted in this paper. Flow characteristics and thermal characteristics of this FTPM motor are calculated by using computational fluid dynamics method. The key is that an equivalent model is developed to replace the real motor, offering the merits of simplified meshing progress and convenient thermal calculation. Furthermore, the effectiveness of the developed equivalent model has been verified by simulation and experiment. In addition, the temperature distribution of the entire motor is given by using equivalent models. The results can be provided to improve motor thermal performance.
So far, several methods to reduce the cogging torque of permanent magnet motors have been introduced. Implementation and evaluation of these methods have usually been done on radial flux types of motors. Nowadays, as axial flux permanent magnet motors have more advantages over radial ones, they are more attractive. Therefore, in this paper analytical modeling and calculation of the most effective method impact in reducing the cogging torque in axial flux permanent magnet motors will be studied. In fact, in this method the radial edges of the magnets will be curved to have a significant impact on reducing this unwanted component. This paper introduces a new concept to model this method. Finally, the accuracy of the proposed method will be verified by finite element analysis.
The authors present an analysis of conditions on the boundary between layers having varied electromagnetic properties. The research is performed using consistent theoretical derivation of analytical formulas, and the underlying problem is considered also in view of multiple boundaries including the effect of the propagation of electromagnetic waves with different instantaneous speeds. The paper comprises a theoretical analysis and references to the generated algorithms. The algorithms were assembled to enable simple evaluation of all components of the electromagnetic field in relation to the wave propagation speed in a heterogeneous environment. The proposed algorithms are compared by means of different numerical methods for the modelling of electromagnetic waves on the boundary between materials; moreover, the electromagnetic field components in common points of the model were also subject to comparison. When in conjunction with tools facilitating the analysis of material response to the source of a continuous signal, the algorithms constitute a supplementary instrument for the design of a layered material. Such design allows us to realize, for example, a recoilless plane, recoilless transition between different types of environment, and filters for both optical and radio frequencies.
In this paper, through-wall detection problem using a data-driven model is addressed. The original problem is cast into a regression one and successively solved by means of the relevance vector machine (RVM). Multiple scattering is included in the nonlinear relationship between the feature vector extracted from the backscattered field and the position of the target obtained through a training phase using RVM; hence the nonlinearity inherent in the problem is considered. Besides, the presence of the wall is also contained in this relationship. The predictions obtained by RVM are probabilistic which capture uncertainty, and we can define error-bars for the predicted results. Therefore, the ill-posed nature of the problem is accounted for naturally, rather than using other regularization schemes. To access the effectiveness, accuracy and robustness of the proposed approach, numerical results related to a two-dimensional geometry are presented. This method is demonstrated efficient qualitatively and quantitatively.
In this paper, we propose a planar metamaterial particle that consists of two bright elements imprinted on a dielectric substrate in the microwave region. The two bright elements are a circular ring resonator (CRR) and an asymmetric single-split rectangular resonator (ASRR). The structure exhibits a narrow transparency band in a wide absorption/reflection band through coupling between the two bright modes. We study the proposed structure through numerical simulation and experiment. We also test different orientations of the structure for possible application as an efficient frequency selective-band obscurant.
Two finite-difference time-domain (FDTD) methods incorporated with memristor are presented. The update equations are derived based on Maxwell's equations, and the physical model is given by Hewlett-Packard (HP) lab. The first method is derived by calculating the memristance directly while the second method is derived by the relationship between electric charge and flux. Numerical results are given to discuss the accuracy, efficiency and stability of both proposed methods.
The number of composite insulators used in power transmission lines increases year by year. To detect and assess the aging status accurately concerns the security and stability of the power system. In order to achieve nondestructive testing of the sheds of composite insulators, a unilateral mini Nuclear Magnetic Resonance (NMR) sensor is proposed in this paper. The design of the magnet body and the optimization of the RF coil are presented. The Carr-Purcell-Meiboom-Gill (CPMG) sequence was employed to record the 1H relaxation curves of the sheds of three composite insulators from 110 kv lines with different service years. The curves were fitted to both single exponential function and inverse Laplace transformation functions. The results demonstrate that an increase of service year of the insulator results in a decrease of the effective transverse relaxation time (T2eff). It is indicated that the sensor has a potential to assess the aging status of the composite insulators.
Here we present the design of a low loss top metal silicon (Si) hybrid dielectric-loaded plasmonic waveguide (TM-SiHDLW) and a compact, high performance optical resonator by numerical simulation based on finite element method. The waveguide adopted a thick (200 nm) top metal stripe structure to yield optimal performance due to reduced Ohmic loss in conductor around the stripe edge/corner. Moreover, a relatively thick (150 nm) dielectric spacer between the Si ridge and the metal stripe was employed to achieve both long propagation length and good field confinement. The effect of a thin (10 nm) silicon nitride (SiNx) layer covering the waveguide which was added for minimizing uncertainties on optical properties of SiHDLW resulting from high density of dangling bonds on Si surface was also investigated. Simulation results show that there is no significant degradation on the performance of the TM-SiHDLW. For the proposed plasmonic waveguide, a propagation length of 0.35 mm and a mode area around 0.029 μm2 were demonstrated. The TM-SiHDLW waveguide was then used as the basis for anoptical resonator, which was designed to operate at the fundamental TE011 mode for yielding high quality factor at a relatively small footprint size. A metal enclosure was also adopted to reduce the radiation loss, and a high quality factor of ~1900 was obtained, more than double the results in other disk or ring resonators of comparable size. Compared to the resonatorsbased on a rounded top metal Si hybrid dielectric-loaded plasmonic waveguide (RTM-SiHDLW) which has a much longer propagation length than the TM-SiHDLW, as reported in our previous work, the performance is essentially the same. This is simply because, for the resonators, the radiation loss is the dominate loss mechanism and the dissipation in the waveguide structure itself, thus, contribute little to the final quality factor of the plasmonic resonators.
As we know, a moving target's azimuth shift in SAR image is proportional to the projected velocity of its across-track velocity in the slant-range plane. Therefore, we can relocate the moving target in SAR image after estimating its velocity. However, when Doppler ambiguity occurs due to the limitation of the SAR system's pulse repetition frequency (PRF), this relationship will not hold any more, in this case, we cannot relocate the moving target to the right position. The Doppler spectrum of a moving target with arbitrary velocity may entirely situate in a PRF band or spans in two neighboring PRF bands. In this paper, we conduct a detailed theoretical analysis on the moving target's azimuth shift for these two scenarios. According to the derived formulas, one can relocate a moving target with arbitrary velocity to the right position no matter Doppler ambiguity occurs or not. Simulated data are processed to validate the analysis.
Satellites are the most important link in today's battle field, and with the advancement of anti-satellite technologies like anti-satellite missiles and directed energy weapons, satellites are becoming vulnerable to attack. The vulnerability of satellite depends highly on its probability of being detected and tracked, and optics or radars are the two major means of detection. To avoid detection, several suggestions have been made in the past to deflect ambient light and decrease the RCS (radar cross section) to avoid detection. The most notable RF stealth suggestion among them is the proposal of using an inflatable polymer cone to change its shape and reduce satellite's RCS. In this study we examine the RCS of this so-called stealth satellite in S-band with FDTD simulations, and analyze its frequency and radar incident angle dependence. Results indicate this shape is advantageous in bore sight monostatic backscatter RCS reduction, but in other directions the RCS increases due to sheer size effect, which makes it even more vulnerable to bi-static radar tracking. When it is slant illuminated, the RCS of the stealth satellite shows no RCS reduction effects. Such inflated device is susceptible to space debris damage and cumbersome to operate, and may interfere with the original mission of the satellite. Best strategy for satellite self-defense is orbit change.
The inevitable increase in radio interference within microwave systems continue to be of major concern as more of radio communication services compete with bandwidth assigned to the fixed service, fixed satellite service and broadcasting satellite service. Interference hampers coverage and capacity of these services often lead to the reduction in the signal to noise ratio at the receiving terminals. The existing global hydrometeor scatter model proposed by the International Telecommunication Union, when applied to the tropical and subtropical location often leads to considerable inaccuracies due to the wide range of intense climatic and geographical nature of this region. In this study, the bistatic intersystem interference due to hydrometeors between satellite systems and terrestrial downlink receiver terminal systems in a subtropical station computation is based on the Awaka and Capsoni cell models. For the attenuation of both wanted and unwanted paths to the receiver, the existing model based on the specific attenuation has been modified to include the equivalent path length through rain in the estimation of the attenuation. Results obtained show that the Capsoni model exhibits the normal trend under a moist atmosphere with a gaseous attenuation more pronounced at frequencies greater than or equal to 30 GHz. Also at high rain rates greater than 70 mm/h and considering the rain with melting layer, up to about 70 dB difference was observed between transmission losses estimated using Awaka and Capsoni models at link probabilities ranging between 1-10-3% unavailability of the time.
A time domain hybrid method is presented for efficiently solving the electromagnetic coupling problems of transmission lines in cavity. The proposed method is based on the finite-difference time-domain (FDTD) method and transmission line (TL) equations (FDTD-TL), which can achieve a strong synergism on the computations of field and circuit. The FDTD method with an auto mesh generation technique is employed to obtain the electric fields of transmission lines excited by an incident wave from the outside of the cavity. The electric fields are introduced into the TL equations as additional voltage sources at each time step of FDTD method. The current and voltage responses of terminal loads can be obtained by the TL equations. Two examples are presented to demonstrate the correctness of this method. The high efficiency of this hybrid method is verified by comparing the computation time with the traditional method.
The matrix method for the calculation of antenna far-field using irregularly distributed near-field measurement data is presented. The matrix method is based on the determination of the plane wave expansion (PWE) coefficients from the irregular near-field samples using a matrix form that connects the radiated field with the corresponding plane wave spectrum. The plane wave spectrum is used to determine the far-field of the antenna under test (AUT). The matrix method has been implemented, and its potentialities are presented. The validations using analytical radiating model (dipoles array) and experimental measurement (X band standard gain horn antenna) results have demonstrated the efficiency and stability of the proposed method.
Pneumothorax is the medical condition caused by the air concentration inside the pleural cavity, the space between the lung and the chest wall. Apart from traditional diagnostic methods, it can be detected by using microwave sensors that capture variations in reflected electromagnetic field (EMF). Sex and obesity, related to the internal composition of the biological tissues, can influence the reflected EMF and therefore the sensor diagnostic ability. This paper investigates the effect on the performance of a proposed on-body dual-patch antenna sensor for pneumothorax diagnosis, due to inter-subject variability in underlying tissue structure. The sensor operates at frequency range of 1-4 GHz. The challenge of the paper is to propose frequency bands for robust and safe sensor operation. S12 parameter alternation versus frequency is assessed for healthy and pathological cases. Implemented thorax numerical models include modified (i) closed rectangular multilayered and (ii) MRI-based anatomical ones. In rectangular models, thickness and configuration of muscle, fat and bone tissues are varied, according to literature. Additionally, sex-related anatomical differences are taken into account in MRI-based models. All scenarios are solved using Finite Difference Time Domain method. Results revealed that the proposed frequency bands lie within 1-2.7 and 2.9-3.5 GHz, for muscle, 1.4-3.5 GHz for fat and 1-2.2 and 2.8-3.5 GHz, for bone variations. Numerical evaluations for accurate anatomical models verify the findings.
This paper gives a comprehensive study on the modeling and design challenges of Through Silicon Vias (TSVs) in high speed three dimensional (3D) system integration. To investigate the propagation characteristics incurred by operations within the ultra-broad band frequency range, we propose an equivalent circuit model which accounts for rough sidewall effect and high frequency effect. A closed-form expression for TSV metal oxide semiconductor (MOS) capacitance in both depletion and accumulation regions is proposed. The coupling of TSV arrays and near and far field effect on crosstalk analysis are performed using 3D EM field solver. Based on the TSV circuit model, we optimize the TSVs' architecture and manufacturing process parameters and develop effective design guidelines for TSVs which could be used to resolve the signal integrity issues arising at high frequency data transmission in 3D ICs.
The electromagnetic field equations are solved to give the 4-potential in Hermite-Gaussian beams as a function of both the 4-positions of the beam waist and each point in the field. These solutions are the sums of products of position-dependent complex 4-vectors and modified Bateman-Hillion functions. It is assumed that the time difference between the beam waist and each other point is equal to the distance between the points divided by the speed of light. This method is shown to generate solutions that preserve their forms under Lorentz transformations that also correspond to the well known paraxial solutions for the case of nearly parallel beams.
Graphene is increasingly being used in the design of electromagnetic devices. The resistivity of graphene can be adjusted via chemical potential tuning, which truly benefits the implementation of tunable and reconfigurable devices. This paper investigates the switch-like attribute of parasitic graphene surface used in a dipole operating at 0.39 THz. Further, a novel orbital angular moment (OAM) generator with radiation reconfiguration is proposed. Spiral beams carrying variety of OAM modes can be produced easily using the generator.
In order to reduce the higher harmonic component of the magnetic field in magnetically levitated permanent-magnet planar motors (PMPMs), a sinusoidal index for 2-dimensional (2D) wave is proposed and verified by calculating the average total harmonic distortion (THD) of the discrete waveform. Based on this, a novel optimal design method using THD for 2-dimensional wave (THD2D) and fundamental amplitude is proposed for PMPMs. The finite element analysis and experimental results show that the higher harmonic component of magnetic field is reduced with average fundamental amplitude invariant, and the back-EMF is better. So the optimal design method can improve the electromagnetic performance of magnetically levitated PMPMs.
To avoid the spatial variation of scattering characteristic effect, a three-dimensional synthetic aperture radar (3-D SAR) imaging based radar cross section (RCS) extraction technique with fixed transmitter is developed. The 3-D SAR image is used to extract targets' RCS, so it can spatially distinguish different parts of a complex object, or the targets' RCS from environment. With the abilities of outdoor measurement, it can greatly reduce the cost of measurement. Two simulations of three squares and a 3-D complex-shaped electric-large flight model demonstrate the accurate prediction of RCS.
Biomedical imaging has played an important role in identifying and monitoring the effectiveness of the current state of the art treatments for many diseases. The authors recently proposed a novel single-transmitter-multiple-receiver holographic microwave imaging (HMI) technique for imaging small inclusion embedded in a dielectric object which has potential application in medical diagnostics. HMI image quality depends highly on the antenna baseline difference, in order words, the antenna array configuration. Different antenna arrays produce different quality of dielectric images by using HMI imaging algorithm. This paper investigates the antenna array configurations effect on image quality by using HMI imaging approach. Three configurations including spiral, random and regularly spaced arrays are presented in this paper. Both simulated and experimental results are obtained and compared to fully demonstrate the effectiveness of antenna arrays to the HMI technique. The results show that the proposed spiral and random array configurations have an ability to produce high-resolution images at significantly lower costs than regularly spaced arrays.