In order to improve the efficiency of transformer fault diagnosis and monitoring in power systems, and to realize fault diagnosis of unmanned remote adaptive transformer equipment, we present a method of multi-sensor and multi-direction optical image integrated monitoring in this paper. By monitoring and collecting transformer fault information combined with the changing characteristics of transformer temperature and electrical signals, we establish a transformer calculation model based on multi-level fault and multi-characteristic parameters. According to the characteristics of transformer faults, we use a deep belief network identification (DBNI) algorithm for the transformer and construct the training samples of the transformer diagnosis model using an optimum weight fusion algorithm. The experimental results show that the DBNI model can fully explore the characteristics of large samples, analyze multiple faults information, and extract the hidden features of fault samples. The DBNI model has higher fault diagnosis accuracy than a BP neural network and a single DBN without data fusion and SVM. The DBNI's fault diagnosis accuracy reaching 99.45%. The experimental results show that this model has good robustness of interference ability and can be used intuitively to carry out remote on-line unattended transformer fault diagnosis and information feedback.
Reconfigrable antennas that are able to provide a high spatial diversity are increasingly adopted in many wireless applications. An original design of a planar printed compact antenna that achieves an electronically controlled beam steering by using metamaterial hybridization is presented in this paper. The designed antenna, made of coupled split ring resonators, is able to switch between 8 radiation patterns steering in 8 different directions at the working frequency of 2.45 GHz. The spatial diversity is assessed from the analysis of the correlation matrix between the patterns. This concept would provide a promising and compact alternative for low power telecommunication systems.
It is well known that high refractive index contrast is essential to the formation of an omnidirectional Photonic Band Gap (PBG). It is generally cited also that the width of the omnidirectional PBG of a dielectric mirror is determined by the refractive-index contrast. But in this work, we show that this condition is not really general criteria. Dielectric mirror with higher refractive index contrast does not necessarily mean that it has the largest omnidirectional photonic band gap. So, we investigate the necessary conditions on the high and low refractive indices of the quarter wave layers to have the largest omnidirectional bandwidth in the visible range. We present a profound study of the omnidirectional band center wavelength and the bandwidth behaviors versus the layers refraction indices. It is shown therefore that one can modulate omnidirectional photonic band gap center by modulating the optical phase of the mirror.
The present paper investigates the propagation and dispersion of elastic surface waves in an asymmetric inhomogeneous isotropic three-layered plate in the presence of magnetic field and rotational effects. The skin layers are exposed to an external magnetic field force while the core layer is assumed to be in a rotational frame of reference, which are perfectly bounded together with free-ends conditions. The resultant displacements and shear stresses in the respective layers are derived analytically together with the general dispersion relation. Further, the general dispersion relation is analyzed for some physical cases of interest. Finally, the effects of the magnetic field, rotation and electric field on the propagation and dispersion of the present model are presented graphically.
In this paper, a new measurement method is proposed to estimate the complex permittivity for each layer in a multi-layer dielectric material using a Ku-band rectangular waveguide WR62. The Sij-parameters at the reference planes in the rectangular waveguide loaded by a multi-layer material sample are measured as a function of frequency using the E8634A Network Analyzer. Also, by applying the two dimensional finite difference in time domain (2D-FDTD), 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 Sij-parameters. This method has been validated by estimating, at the Ku-band, the complex permittivity of each layer of three bi-layer and one tri-layer dielectric materials. A comparison of estimated values of the complex permittivity obtained from multi-layer measurements and mono-layer measurements is presented.
This paper documents a novel design of dual-band dielectric resonator antenna exhibiting circular polarization at a high-frequency band of (7.85 GHz-7.93 GHz) in addition to linearly polarized lower frequency band of (5.12 GHz-5.49 GHz) using new materials, sapphire and TMM13i for antenna design. Sapphire and TMM13i being resistant to physical change, the novel design is suitable for weather radar application as circular polarization reduces signal attenuation in adverse climatic conditions. A four-layered structure with sapphire and TMM13i stacked alternatively with aperture coupled feed is presented. Additionally, the corners of the patch have been truncated, and a slot has been etched in order to obtain the dual-band resonance and circular polarization respectively. The design is simulated using Ansys HFSS and fabricated for measurements. The VSWR (Voltage standing wave ratio) is measured to be less than two for both the bands. The simulated and measured gains of the antenna are 5.2 dB and 4.9 dB, respectively.
This work presents a hybrid analytical-numerical approach to evaluate the integral representations for the time-harmonic electromagnetic (EM) field components produced in the air space by a vertical magnetic dipole (VMD) placed on a plane homogeneous conducting medium. Explicit expressions for the fields are derived by substituting a rational approximation, generated by the vector fitting algorithm, for the non-analytic part of the integrand of the electric vector potential. This permits to rewrite the representation for the electric vector potential as a combination of simple closed-contour integrals around the pole singularities of the rational approximation, which may be directly evaluated. As a result, each field component is given as a sum of cylindrical Hankel functions depending on the radial distance between source and field points, plus an exponential term that is a function of the total distance of the field point from the dipole.
A novel compact (20 × 22 mm2) triple band eliminated monopole antenna for ultra-wideband (UWB) applications is presented. A novel radiating patch with reduced ground plane is utilized for achieving a -10 dB impedance bandwidth of 3.28-13.28 GHz. An upper inverted U-shaped slot is introduced into the radiating patch to notch C-band (3.68-4.19 GHz), and a lower inverted U-structured slot is utilized to eliminate WLAN band (5.18-5.82 GHz) interference. The interference due to down link of X-band (7.27-7.87 GHz) is rejected by via hole connected between patch and rectangular strip printed above the defected ground structure. The proposed antenna has nearly stable radiation patterns, and realized gain over UWB frequency range makes it suitable for recent portable wireless communication applications.
This paper presents a technique based on time domain reflectometry (TDR) to determine the dielectric and magnetic properties of lossless materials fitted inside a transmission line section. The proposed method involves three different line terminations namely open, short, and matched load. The described technique involves placing a sample of material under test (MUT) inside a terminated transmission line and exciting this with a vector network analyser from the other end to measure the reflection coefficient. Results achieved from a transmission line model were compared with numerical simulations obtained using CST Microwave Studio. The comparison shows that the electric and magnetic properties of a material may be determined precisely with this technique. Experimental results are also presented to validate the proposed method. Estimates of measurement errors, resulting from sample length uncertainty, vector network analyser uncertainty, and open-end inaccuracy are discussed.
This paper presents a method for calculating the air-cored coil impedance with the employment of a mathematical model of an ideal filamentary coil. The proposed algorithm enables assigning, in a very quick way, each cylindrical air-cored coil to the corresponding filamentary coil using only two equivalent parameters. The first of them is the radius of the coil, whereas the second one is the distance between the coil and the surface of the tested material. The changes both in the parameters of the system under consideration and in the tested material bring about the same change in the impedance of the air-cored coil and the corresponding filamentary coil. This property brings a lot of advantages, since it allows using simpler final formulas for the filamentary coil and performing the calculations in a much shorter time, while obtaining the same results as in the case of the air-cored coil. At the same time, the creation of the scale of the measuring instrument and its calibration becomes far simpler since it is based on only two equivalent parameters.
The electromagnetic circumstance of the small-room of substation turns to be more complex with the increase of the voltage level of the power grid. In this paper, a physical model for protective small-room of substation on the basis of the random plane wave hypothesis and wave-chaotic approach is constructed to get the scattering parameters, combining the Random Coupling Model (RCM) to deduce inducted voltage of coaxial cable terminal and making statistical analysis and prediction for electromagnetic quantity coupled to the cable terminal. The results of simulation by FEKO show the validity of the method introduced in this paper, which provides a guidance for the electromagnetic protection in the protective small-room.
Beam-steering antennas especially with Butler matrix feed network are an effective remedy for wireless communications systems troubles such as disruptive effects in mm-wave frequency. In this work, a novel 4×4 Butler matrix feed beam steering antenna is designed at 35 GHz. A zeroth order resonance antenna element is used for bandwidth and radiation efficiency increment. To increase the gain of the antenna a novel mm-wave Fabry Perot layer which is composed of a partially reﬂective surface is designed. All designing steps are presented.
To make a truly compact size system on-chip (SoC) device for wireless bio-telemetry application, the design of a miniaturized on-chip antenna (OCA) with enhanced gain becomes a prime challenge in recent time. Unsuitable Si (Silicon) substrate and relatively larger antenna size at lower microwave frequencies make it even more challenging for the researchers. In this work, an OCA is designed on a low resistive (ρ = 10 ohm.cm) Si substrate by using standard CMOS technology process. The top metal layer of CMOS layout has been used for designing the antenna to reduce fabrication complexity. By using slot miniaturization technique, the proposed antenna size of λ0/22 x λ0/21.4 mm2 is achieved and operable at ISM 915 MHz band for biotelemetry applications. A gain enhancement technique for OCA is proposed by introducing a 0.2 μm thin film of Cobalt Zirconium Oxide (CoZrO) ferrite material, and the gain is enhanced by +12.28 dB with the bandwidth and fractional bandwidth (FBW) of 1.14 GHz and 124%, respectively. The simulation results of the proposed antenna with coating of bio-compatible material show its potential applicability for implantable bio-telemetry applications. An equivalent circuit of the proposed OCA is presented and verified by ADS circuit simulator.
In this work, a Tri-Band frequency reconfigurable antenna for LTE (Long Term Evolution)/WiFi (Wireless Fidelity)/ITS (Intelligent Transportation Systems) applications is presented. The proposed design consists of a wine glass shaped slotted radiating patch along with a switchable rectangular ring type slot on the ground plane. This structure operates in three different states viz. state-1, state-2, and state-3 at 4.5 GHz (LTE band), 5.9 GHz (ITS band), and 3.8 GHz (LTE band)/5 GHz (Wi-Fi band), respectively, with an overall compact size of 30 × 30 × 0.762 mm3. Multi-band resonances are obtained by incorporating slots in the main radiating element and ground plane. Moreover, switching among these bands is achieved by placing two PIN diodes at optimized positions on the rectangular ring slot in the ground plane. For the proposed design, good agreement between simulated and measured results is obtained in all the three operating states of the design, which makes it suitable for compact reconfigurable systems.
Accomplishing high efficiency with acceptable output load power is a formidable design challenge in resonant wireless power transfer (WPT) system employed for charging Electric Vehicle (EV). This necessitates a trade-off among the assorted parameters like coil quality factor, coupling coefficient and electric load for performance enrichment of resonant WPT system. It is realized that the high value of quality factor does not ensure higher power transfer efficiency but it is largely influenced by the electric load. For each coupling coefficient there exists an optimum load for which maximum power can be delivered. It is also perceived that for a fixed vertical separation gap of the coils, increasing receiver coil quality factor has no profound effect on the output load power as well as efficiency. The circuit model based analytical results agree well with the comprehensive experimental results and elucidate the strategic design guidelines for a competent wireless electric vehicle charging system.
Modeling wave propagation often requires a truncation of the computational domain to a smaller subdomain to keep computational cost reasonable. The mere volume of papers on absorbing boundary conditions indicates that a perfect solution is not available. A method is proposed that is exact, at least in the case of a time-domain finite-difference scheme for the scalar wave equation. The word `exact' is used in the sense that there is no difference between a computation on the truncated domain with this method and one on an enlarged domain with reflecting boundaries that are placed so far away that their reflections cannot reach the original domain within the modeled time span. Numerical tests in 1D produce stable results with central difference schemes from order 2 to 24 for the spatial discretization. The difference with a reference solution computed on an enlarged domain with the boundary moved sufficiently far away only contains accumulated numerical round-off errors. Generalization to more than one space dimension is feasible if there is a single non-reflecting boundary on one side of a rectangular domain or two non-reflecting boundaries at opposing sides, but not for a corner connecting non-reflecting boundaries. The reason is that the method involves recursion based on translation invariance in the direction perpendicular to the boundary, which does not hold in the last case. This limits the applicability of the method to, for instance, modeling waveguides.
We analyzed the effect of loss and coupling to EIT metamaterials using circuit approach, giving the effect of two parameters: coupling and loss on the resonant property of the EIT metamaterials. To verify the results of the circuit analysis, simulations and experiments were performed. The structures were fabricated with superconducting NbN and varied temperature to verify the effect of loss. The distances were adjusted to observe the effect of the coupling strength. The results of simulations and experiments were consistent with the circuit analysis.
A two port multi-input-multi-output (MIMO) dielectric resonator (DR) antenna (DRA) is proposed with circularly polarized radiation. The antenna geometry allows to find circular polarization and improved impedance bandwidth by reducing the separation between the DR elements. The isolation between the ports of the antenna remains more than 15 dB in the operating passband even after reducing the separation between the radiating elements. The antenna provides the 10-dB impedance and 3-dB axial ratio bandwidth of 34.85% and 4.55%, respectively. The MIMO performance of the proposed antenna is confirmed by calculating the parameters like envelop correlation coefficient, diversity gain, mean effective gain, channel capacity loss, and the total active reflection coefficient. The proposed antenna can be utilized for C-band applications.
Results of the study of magnetic properties of nanocomposite samples (CoFeZr)x(CaF2)(100 - x) (31 at.% ≤ x ≤ 47 at.%) produced in argon (Ar) and argon with oxygen (Ar with O2) sputtering atmosphere are presented in this paper. The magnetic resonance spectroscopy at room temperature using continuous wave X-band electron spin resonance (ESR) was used for analysis of samples magnetic properties. After analysis it is established that in the case of samples produced in argon sputtering atmosphere the value of g increases with the rise of metal content and for samples produced in argon with oxygen atmosphere the value g decrease with the rise of x. Such a behavior of g(x) is explained by the presence of core-shell structure of NPs represented by ferromagnetic core and antiferromagnetic core that results in quenching of orbital motion of electrons.
In this article, the diffraction of plane electromagnetic waves by double half-planes with fractional boundary conditions is considered. As particular cases, the diffractions by wedges and corners are considered for different values of fractional orders. The results are compared to the analytical ones. The interesting properties of wedge diffraction are outlined for intermediate fractional orders.