A new coplanar waveguide (CPW) fed ultra-wideband (UWB) antenna with band notched characteristic is proposed in this paper. In order to achieve sharp and controllable notch-band characteristic, one pair of half-wave-length stubs and slits is introduced inside the tapered slot and circular patch, respectively, on the basis of a UWB antenna. Simulated and measured results show that the antenna has a reflection coefficient (S11) less than -10 dB in the range of 3.0 to 11 GHz, which can meet the requirements of a UWB communication system. It shows a good notch characteristic in 5.0~5.8 GHz, which can covers the operating band of wireless local area network (WLAN) well. The antenna has a stable gain and good radiation characteristics in the pass band. It is simple in structure and easy in fabrication. Moreover, it has broad application prospects.
There exist some problems that the water content of the test object cannot be reflected in real time. The detection time is too long, and the heating measurement method destroys the seed tissue for the traditional measurement of the water content of the seed. In this paper, a structure of single excitation coil to double receiving coils is proposed to measure the water content of the seed via electromagnetic induction. The relative permittivity of the seed can be obtained by the relationship between the amplitude ratio and the water content of the seed. First of all, according to the electromagnetic field theory, the functional relationship between the amplitude ratio of the electromotive force amplitude signals of the two receiving coils and the water content of the seed is established. Secondly, fifty sets of theoretical values of the mentioned model can be obtained through simulation analysis. Finally, comparative tests are carried out by using soybean seeds. The experimental results preliminarily verify the feasibility of the electromagnetic measurement method of the water content of the seed. The advantage of the proposed method is that the measurement of the water content of the seed is non-contacting.
Printed, circularly polarised, microstrip line fed antenna having asymmetric slotted structure is presented. Two antennas, antenna 1 (A1) and antenna 2 (A2), having the same design but radiating with opposite senses of circular polarisation are fabricated. The geometrical structure consists of uneven combination of elements fixed through parametric variations. The measurements yielded significant impedance bandwidth (IBW) and axial ratio bandwidth (ARBW) for axial ratio (AR) ≤ 3 dB. A1 offered IBW of 9.67 GHz (2.46-12.13 GHz, 132.6%), ARBW of 7 GHz (4-11 GHz, 93.33%) and a peak realised gain of 4.05 dBi. A2 offered IBW of 10.05 GHz (2.55-12.6 GHz, 132.7%), ARBW of 7.3 GHz (3.9-11.2 GHz, 96.7%) and a peak realised gain of 4.1 dBi. This constitutes a wide coverage of over 88% of the ultra-wideband (UWB) spectrum (3.1-10.6 GHz). Omnidirectional radiation patterns and marginal group delays are the other features of these antennas. The proposed design is validated through simulations and experimental investigations.
A medium-gain vertically polarized omnidirectional antenna array (VPOA) with wide bandwidth is proposed in this paper. Initially, a conventional printed dipole antenna with integrated balun (IB) is introduced to use as the wideband element. Then, four antenna elements are alternately arranged in the vertical direction to achieve high gain. Moreover, the four elements are excited by a shunt-fed feeding network which is utilized to provide uniform amplitude and phase for the elements. The feeding network has a common ground with the balun, and it can be easily integrated with the IB. Furthermore, two metallic cylinders placed in the normal direction of the substrate are used as two reflectors to improve the gain variation in the horizontal plane. In order to validate the design method, a prototype is fabricated and measured. The measured results indicate that the proposed antenna has an impedance bandwidth of 56% (1.12-2 GHz) for VSWR≤2 and a simple structure with lateral size of 0.45 λ0 (λ0 is the free-space wavelength at center frequency). In addition, stable omnidirectional radiation patterns are obtained with gains around 6.5 dB and the gain variations in the horizontal plane less than 2 dB across the operating band.
In this study, the physical optics approximation (POA) algorithm is described for predicting the electromagnetic (EM) scattering of three dimensional (3D) two-layer rough surfaces. The POA is initially used to calculate the composite scattering of an object and single layer rough surface for two dimensional (2D) situations. We extend this method to the case of a rough layer with two rough interfaces. The multiple coupling interactions between the upper and lower layer are considered based on an iterative strategy. Because the coupling effect is considered, the 3D model is quite time-consuming. In order to obtain numerical results rapidly, a parallel technique based on the OpenMP is adopted to accelerate the coupling iterative calculation. The model is applicable for moderate to large surface roughness. However, the rough surface should have small to moderate slopes so as to meet the conditions of POA. In numerical results, the normalized radar cross section of two-layer rough surfaces model under different polarizations is calculated, and the model is validated by comparison with a numerical reference method based on the method of moment. In addition, the influence of roughness on the scattering model is analyzed and discussed.
The haze-prone areas are usually places with limited transmission line corridors and large power loads. The performance of transmission lines is under threat of haze. The haze particulates around the transmission lines would be charged and affect the electric field near high voltage direct current (HVDC) transmission lines. Accoring to the influence mechanism of haze on ionized field, the electric perfromance of HVDC transmission lines under haze weather is dicussed. In the paper, an improved meshless local Petrov-Galerkin method (MLPG) is proposed to investigate the distribution of ionized electric field, and example of an actual transmission line is studied to verify the validation of the proposed method at first. It is proved that the proposed method agrees well with the measurements. Then the ionized field distribution under different haze weather levels is discussed, as well as the influenced factor. Results indicate that the ionized electric field and ion current density on the ground would increase under haze weather, but with the similar trends to good weather condition. Meanwhile, the haze weather levels have greater influence on the ionized electric field than ion current density, where the increase of corona and space charge are the main reasons.
For wireless power transfer via magnetic resonant coupling (MRC-WPT), magnetic coupling between resonant coils can be greatly enhanced when a ferrite core is introduced inside the coils. Based on the equivalent circuit model of wireless power transfer system, transfer characteristics of the MRC-WPT system with air resonant coils and a ferrite core are respectively analyzed in this paper. The influence mechanism of the load on the power transfer efficiency is investigated. Also, the requirement of load for improving transfer efficiency is derived when adding the ferrite core to the system. The numerical simulation and experiment result indicate that the transmission efficiency in the MRC-WPT system with ferrite core is higher than that in the counterpart with air resonant coils in the whole transfer region when the load is larger than the maximal critical load. In addition, for different transfer distances, the system efficiency for the system using the ferrite core tends to become lower than that in the air coil system when the load is smaller than the critical load.
Recently, the introduction of surface phase in Snell's law and Huygens' phenomena leads to ultrathin phased surfaces which can tailor the transmission and scattering of the incident wavefront in many ways. In this article, a remodeled Jerusalem cross used as the meta-element whose geometrical parameters are varied to obtain 360° phase variation, and a 3-bit quantization is presented to design phase coded surfaces to manipulate (focusing and splitting) normally incident beam. Further, two 3-bit phase quantized supercells of approximately 2λ length and width are proposed and simulated (3x3 matrix arrangement) to test and compare the scattering properties with traditional chessboard type supercell. Obtained simulated results show diffused reflections for both the models and reduced intensity of four corner lobes in comparison to chessboard supercells (at θ=30˚ and ϕ=45˚). Experimentally recorded monostatic RCS of model-2 prototype has a close agreement with the simulated results and more than 10 dBsm RCS reduction observed from 9 GHz-11 GHz.
Torque ripple is the main cause of motor vibration and noise. In order to reduce the torque ripple of the switched reluctance motor(SRM), a new type of rotor tooth profile is studied, namely adding a semi-oval auxiliary core on both sides of the conventional parallel rotor tooth profile. Using a finite element method, a 12/8-pole SRM was modeled, and an optimal modified model was obtained through parameterized simulation. At the same time, in order to further reduce the torque ripple, the turn-on and turn-off angles of the power converter are optimized, and the torque jump caused by the commutation phase is alleviated. The combination of turn-on and turn-off angles is obtained through simulation calculation, and it can not only significantly reduce the torque ripple of the SRM, but also alleviate the local saturation caused by the double salient pole. This method can reduce the local saturation caused by the double salient structure and the large torque jump caused by the commutation phase. This method is of reference for other double salient motors. This method has implications for other double salient pole motors.
A single fed polarization reconfigurable antenna is presented. The antenna comprises of a circular ring-shaped radiating element along with reconfigurable feed network located at its center which eliminates the need for additional space for reconfigurable feed network. A separate biasing network is placed to bias the pin diodes in the feed network for polarization reconfiguration and achieves three polarization states (linear, left-hand and right-hand circularly polarization). The antenna is designed to operate at 2.4 GHz ISM band. The antenna parameters are simulated using Ansoft high-frequency structure simulator and are validated using Agilent network analyzer (N9925A) and antenna test systems. The antenna achieves a good -10 dB impedance bandwidth of 85 MHz (2.40-2.485) GHz in linear state and 85 MHz (2.41-2.495) GHz in the circularly polarization states along with better cross-polarization isolation (≥ 15 dB) in the operating bands and hence more suitable for modern wireless communications.
This paper is devoted to an engineering laser-based diagnostic technique which is able to extract the value of the temperature structure coefficient in a hot turbulent wind tunnel jet, by using a thin laser beam which is sent into the jet. Some experimental investigations are carried out to characterize the jet under study and the probabilities of the positions of the laser beam impact on a photocell are measured. The theoretical values of the same probabilities are computed by assuming that the laser beam direction is a Markov random process. By means of an optimization technique with constraints, based on the Golden Section algorithm, the temperature structure coefficient of the jet is determined. The validity of the result obtained is proved by a good agreement which is observed in the comparison between another parameter computed from that result and the previously published data.
A wideband planar linear-circular polarization converter comprised of periodic centrosymmetric dual-loop unit cells with wideband property is presented in this letter. Full wave simulation and parameter study are carried out to demonstrate the basic working principle of the converter. Also, the performances of the device under oblique and deflected incidence situations are considered and discussed. A prototype is manufactured and tested. The measured results show that its working band covers from 19.3 GHz to 31.8 GHz with less than 3 dB axial ratio, which agree well with the simulated ones and thus validate the design concept.
In this paper, a novel wideband dual-band dual-polarized magneto-electric (ME) dipole antenna is proposed. The proposed antenna consists of a folded double-layer magneto-electric dipole, a stair-shaped feeding line with a balun structure and a rectangular box-shaped reflector. The folded double-layer magneto-electric dipole is able to generate two resonant frequencies. The polygon balun structure can better match the antenna impedance. The rectangular box-shaped reflector not only can suppress antenna's back radiation but also can realize high gain over the operating frequencies. Both simulated and measured results show that the antenna can obtain two wide impedance bandwidths of 60% (1.54-2.87 GHz) in lower frequency band and 27% (4.62-6.10 GHz) in higher frequency band with the reflection coefficients lower than 10 dB for both input ports. The isolation between ports is greater than 25 dB in the corresponding frequency band. The gains of the measured antenna were 8.5-9.7 dBi in the low frequency band and 8.5-11.5 dBi in the high frequency band, respectively.
Substrate integrated waveguide (SIW) is widely used in filter design due to its advantages of high Q value, high power capacity, small size and easy integration. In this paper, a symmetric folded substrate integrated waveguide (SFSIW) miniaturization method is proposed. Through the comparison of the miniaturization degree of the resonant cavity before and after folding, the feasibility of this method is verified, and the miniaturization theory of SIW filter is further improved. Using a symmetrically folded SIW resonator, a two-cavity filter and a three-cascaded cross-coupling filter were designed. This structure achieves better miniaturization of the filter. The high Q value of the SFSIW resonator makes the filter's insertion loss smaller, the transmission characteristics better, and the simulation and measurement results are consistent.
A novel coplanar waveguide fed compact dual-band antenna for 2.5/5.7 GHz applications is presented in this paper. The above characteristics are obtained by carefully optimizing the slotted ground planes and meander short placed between the signal strip and one of the lateral ground planes. The proposed antenna has been designed on a substrate with dielectric constant 4.4, thickness 1.6 mm, and it occupies a small area of 18.2×20 mm2. The experimental analysis shows 2:1 VSWR bandwidth up to 150 MHz and 370 MHz for 2.5 GHz and 5.7 GHz, respectively. Antenna radiation characteristics, including return loss, radiation pattern, radiation efficiency and gain are also validated with numerical simulation and experimental measurements.
Due to the spatial and temporal distribution of meteorological conditions along the transmission lines, the equivalent model with lumped parameters cannot accurately represent the line model with the actual parameters. In the paper, the nonuniform parameter model based on the dynamic thermal rating (DTR) technology of transmission lines is adopted to establish the power flow analysis model based on the conductor temperature. The algorithm presented in the paper is adopted to analyze the power flow of power networks with known load and meteorological parameters. And then cases with parameters of dierent seasons and spatial distribution in practical conditions are used to verify the feasibility of the algorithm. It is shown that the power flow analysis model established in this paper can realize the accurate analysis of the thermal load capacity of the transmission line in the power grid, which has great practical significance.
Design and development of a novel arrow headed modified cross slot array antenna with dual band characteristics and circular polarisation is reported. The proposed array configuration consists of an array of four arrow headed modified cross slot elements which are electromagnetically coupled by using a 1:4 corporate feed network. The slot elements are etched on the ground plane of the dielectric substrate with a feeding network on the other side. The proposed slot array shows dual band behaviour and enhanced gain characteristics compared to a single element arrow headed modified cross slot antenna. The slot array antenna shows resonance at two frequencies of 1.72 GHz (1.6912 GHz-1.7656 GHz) and 2.45 (2.3656 GHz-2.5568 GHz) GHz with circular polarisation in the upper band. This novel slot array configuration has a measured gain of 6.23 dBi at the lower resonant frequency and 7.01 dBi at the upper resonant frequency. The proposed slot array antenna exhibits bidirectional radiation patterns with improved gains. The simulated results are in good agreement with the experimental ones.
In this paper, the nonlinear single negative metamaterials (NLSNM) based on the microstrip loaded with varactor diodes are investigated. It is found that the NLSNM, including nonlinear epsilon-negative metamaterial (NLENM) and nonlinear mu-negative metamaterial (NLMNM) can be realized by loading varactor diodes and chip inductors onto the microstrip, and their transmission gaps can be controlled conveniently by the signal power. In addition, the nonlinear property of the heterostructure constructed of NLMNM and epsilon-negative metamaterial (ENM) is also studied, and the results show that the transmission property, especially the transmittance of the tunneling peak of the NLMNM-ENM heterostructure can also be regulated by the signal power. The NLSNM may have important potential applications in the microwave switch controlled by the signal power.
Accurate analysis of the thermal field in switched reluctance motor (SRM) is critical to the service life and safety performance of the SRM. According to the general structure of SRM, a two-dimensional (2D) finite element analysis (FEA) model was established, and the loss of each component, especially the iron loss, was analyzed by Orthogonal Fourier decomposition method, revealing the characteristics of the loss. A magnetic-thermal one-way coupling method is further used to model the temperature of the SRM, and basic assumptions and reasonable boundary conditions are set. Transient thermal analysis was carried out under natural cooling conditions and high vacuum conditions, respectively, and the results were compared and analyzed to understand the temperature distribution of the main components under two operating conditions.
This paper deals with the influence of steel non-linearity when calculating the induced current/voltage on a pipeline circuit with earth return under 50-60 Hz induction by power lines or electrified railway lines. By having at disposal the measured curves of the per unit length pipe internal impedance versus the current flowing in it, one can calculate induced voltage and current on the pipeline-earth circuit by means of the successive approximations method. The paper presents some comparison of the results when ignoring or not the steel pipe non-linearity. In certain cases, the differences can be significant.