The core structure of transformers and reactors is subject to stress and high-frequency excitation during operation. The core structure is made of laminated silicon steel sheets, which are subject to magnetostrictive strain under alternating magnetic fields. To investigate the comprehensive magnetic properties of oriented silicon steel sheets under the influence of harmonics and stress, this paper builds a magnetic property measurement system for electrical steel and investigates the magnetization and magnetostriction characteristics of oriented silicon steel sheets of type 30SQGD105 under working frequency, harmonic and applied stress conditions. The results show that the effects of harmonics and stress on the hysteresis characteristics of the silicon steel sheet are small, and the effects on the magnetostriction characteristics are large.
A general theory of a passive multi-port system is presented, incorporating an arbitrary number of feed and load ports. The result is a nonlinear equation system, in which the solution variables are the load admittances, connected to the load ports. The solution ensures impedance match at all feed ports at one particular frequency. It is also shown how this theory can be applied to adaptive and reconfigurable antennas, by using switches to include or exclude some of the load admittances. If, by open state of a switch, the corresponding load admittance is excluded, then the nonlinear equation system is simplified. In general, one load admittance per feed port is required to obtain complex conjugate impedance match. Then, the admittance has a real and an imaginary part, where the real part relates to a resistor, adding loss to the system. It is shown how loss-less matching can be obtained by using two, purely reactive admittances per feed port.
To address the problems of torque ripple, vibration, and noise generated by cogging torque in a dual-stator single-rotor axial magnetic field permanent magnet motor, this article adopts an unequal thickness pole structure to reduce cogging torque. At first, the process of cogging torque generation is analyzed, followed by an examination of the mathematical formulation of cogging torque using the energy technique and the Fourier decomposition method. Then, the impacts of several pole optimization approaches on cogging torque reduction are then compared, and the findings are investigated using the finite element method to demonstrate the efficiency of the optimization method. The results show that the optimization effect of unequal thickness pole structure is the best. Lastly, the optimized motor's air-gap flux density, counter-electromotive force, harmonic content, and rotor mechanical strength were compared and studied to demonstrate that the unequal-thickness structure used in this research can increase motor performance. Finally, based on the determined motor parameters, experimental study of the prototype was carried out to verify the correctness of the motor structure and analysis.
Advancement in radar component technology has led to a reduction in the size, weight, and power consumption of radar systems. Experimental radar systems can now be integrated onto smaller, maneuverable platforms, such as small unmanned aerial vehicles (sUAVs). Integration onto rotor-based sUAVs enables data collection over novel synthetic apertures which can be optimized for different scenarios. The design, simulation, and experimentation of a light-weight, ultra-wideband synthetic aperture radar (SAR) is presented here that will be used for the detection of obscured surface targets. The approach outlined herein uses 3-dimensional (3-D) imagery to vertically resolve clutter from the target. A vertical-grid aperture is presented which yields vertical resolution. Point spread functions are derived for both linear and vertical-grid apertures. The analytical expressions are verified using simulations. Finally, experimental data is used to form 3-D imagery and demonstrate the importance of vertical resolution in the discrimination between scatterers above the ground, as well as clutter mitigation.
The paper represents a rigorous solution to the problem of diffraction of a normally incident plane electromagnetic wave by a circular hole in a perfectly conducting screen of arbitrary thickness, obtained using the eigenmode technique with allowance for the presence of a plane dielectric layer on a thick substrate behind the screen, which can play a part of a radiation detector. The main goal of the work is to describe the effect of diffractionlensless focusing in circular apertures and to determine the conditions of its appearance in the near zone of small holes, when its radius, the thickness of a screen and a dielectric layer are of the order of the wavelength.
A new non-singular fast terminal Sensor-less sliding mode control algorithm (INFTSMC) for IPMSM based on an improved extended sliding mode disturbance observer (IESMDO) is constructed to address the problem of degraded control performance of IPMSM because of uncertainties. Firstly, a mathematical model of IPMSM under parametric ingestion is developed, and a new control law for the speed loop is designed. Then, an improved non-singular fast terminal sliding mode speed controller (INFTSMC) based on a novel extended sliding mode disturbance observer (IESMDO) is designed, where an improved super-twisting control law is designed to speed up convergence, while IESMDO can accurately observe the unknown perturbed part F of the system in real-time relative to the sliding mode disturbance observer (SMO). Finally, high-order square root cubature Kalman-filter (CKF) combined with an adaptive estimator is proposed to accurately estimate the speed and rotor position of the motor in real-time. Through simulations and semi-physical experiments with PI and traditional NFTSMC, it is verified that the algorithm has better transient steady-state performance when external disturbances and parameter perturbation are added externally to the motor, which is conducive to improve the control effect of IPMSM.
The present paper proposes a novel technique to reduce the peak side lobe ratio (PSLR) in the time waveform of the synthetic aperture radar (SAR) pulse. The dependence of the instantaneous frequency on the time over the SAR pulse duration is formulated as an arbitrarily shaped piecewise linear (PWL) curve. The slopes of the linear segments of this curve are optimized to get the minimum PSLR of the received radar echo at the output of the SAR receiver. The particle swarm optimization (PSO) method is used to optimize the shape of the time-frequency curve to achieve the dual-objective of minimizing the PSLR of the received SAR echo and to realize the required pulse compression ratio (PCR). The slopes of the linear segments of the time-frequency curve are the control parameters that determine the position of each particle in the swarm. The proposed method can be considered as an optimized form of non-linear frequency modulation (NLFM) for SAR pulse compression. It is known that the conventional NLFM using second-order time-frequency curve results in a PSLR of -18 dB. The proposed method results in a PSLR of -45.6 dB and achieves a range resolution of 1.4 m. The developed PSO algorithm is shown to be computationally efficient and its iterations are fastly convergent such that a few iterations are enough to arrive at the steady state of the cost function. Finally, a SAR transceiver is proposed as a software-defined radio (SDR) in which the proposed SAR pulse compression technique is employed in the transmitter to generate the transmitted pulse and in the receiver to construct the transfer function of the matched filter (MF).
This article demonstrates the design development, fabrication, and testing of an off-set edge-fed monopole hybrid fractal antenna for ultra-wideband (UWB) applications at a design frequency of 3.2 GHz. The proposed monopole antenna is compact 38.12 mm × 38.42 mm, slotted, and uses a combination of two numbers of Koch plus Minkowski hybrid fractal technology. Antenna resonates at four frequencies i.e. quad tuned (3.2 GHz, 4.94 GHz, 7.21 GHz, and 10.10 GHz). The reflection coefficient, S_{11} < -10 dB obtained for the excellent UWB fractional bandwidth 119.55% (2.85 GHz to 11.32 GHz) is more than the standard FCC bandwidth (3.1 GHz-10.6 GHz). The antenna has gained 6.73 dBi at 3.49 GHz, 5.91 dBi at 5.52 GHz, 8.26 dBi at 6.81 GHz, and 8.02 dBi at 10 GHz with a maximum radiation efficiency of 89.81%. The main feature of the proposed work is that the antenna is circularly polarized in frequency bands 3.14 GHz-3.30 GHz (Axial ratio: 1.61 dB) and 9.07 GHz-9.45 GHz (Axial ratio: 2 dB) and elsewhere linearly polarized. A total of 16.37% antenna size miniaturization has been achieved with excellent UWB and S_{11} performance. The measured and simulated reflection coefficients are found in good agreement. Therefore the fabricated and tested antenna is well suitable for Wi-Max (3.3/3.5/5.5 GHz), ISM (5.725-5.875 GHz), WLAN (3.6/4.9/5.0/5.9 GHz), military band applications (radio location, fixed-satellite and mobile-satellite, S-band, C-band and X-band satellite communications, etc.), aeronautical radio navigation, radio astronomy, ITU-8, Sub-6 GHz band, and Radar applications.
This work examines the effects of high frequency radio transmission on the human body. A magnetic point source is used to generate a signal that is transmitted through the human body at a specified distance. The study was conducted to evaluate the health effects of exposure to high frequency radiation, in relation to current density, induced electric field and specific absorption rate at frequencies of 6.78 MHz and 13.56 MHz. The results for both an equivalent cylinder and a realistic human body model were compared. The analytical method presumes a sinusoidal current distribution along the cylinder and introduces the approximations of field integrals. The numerical simulations by the commercial software FEKO confirmed the analytical results depicted in the paper. The study shows that maximum differences between the results of the proposed analytical model and human model (regardless being realistic or cylinder) are less than 10%. This is convenient because analytical methods can ensure fast estimations of the exposure standard limitations.
Parallel computing for the three-dimensional spatial spectral volume integral equation method is presented for the computation of electromagnetic scattering by finite dielectric scatterers in a layered medium. The first part exploits the Gabor-frame expansion to compute the Gabor coefficients of scatterers in a parellel manner. The second part concerns the decomposition and restructuring of the matrix-vector product of this spatial spectral volume integral equation into (partially) independent components to enable parallel computing. Both capitalize on the hardware to reduce the computation time by shared-memory parallelism. Numerical experiments in the form of solving electrically large scattering problems, namely volumes up to 1300 cubic wavelengths, in combination with a large number of finite scatterers show a significant reduction in wall-clock time owing to parallel computing, while maintaining accuracy.