Volume 71 (2020): Edizione 4 (August 2020)

Reflection and transmission (refraction) of a homogeneous plane wave at the planar boundary of two dielectric media is a well known phenomenon commonly treated in nearly all standard textbooks. Here the analysis of reflection and refraction of evanescent plane waves on the planar boundary between various combinations of lossy, gainy and lossless media is performed. It is shown that by the appropriate choice of the profile of evanescence various effects can take place.

A new approach is proposed to design the sliding mode (SM) controller for the unstable second-order plus dead-time (SOPDT) processes. The sliding mode control consists of two control laws ie continuous control law and discontinuous control law. The continuous control law parameters have been derived in terms of unstable SOPDT process parameters using the root locus technique. On the other hand, the parameters of discontinuous control law are tuned by optimizing a performance index using a recently developed metaheuristic search algorithm, namely the grasshopper optimization technique. The performance index is framed to achieve a good trade-off between performance and control efforts. Finally, simulations are conducted to validate the effectiveness of the proposed approach over the other existing techniques. It is observed that the proposed approach is able to deliver better disturbance rejection, minimal control efforts and good setpoint tracking.

The paper is devoted to obtain original equivalent subsystem method to design of decentralized controller for linear large scale systems. On the theoretical example a new robust decentralized PID switched controller design procedure is obtained for linear time-varying (gain scheduled plant model) uncertain complex system with decentralized output and input structure. Controller design procedure to decentralized controller design performs on the subsystem level. The designed decentralized switched controller ensures the robust stability of closed-loop complex polytopic system with performance H₂ quadratic cost function (QSR). The proposed practical examples with ideal or non-ideal switch of switching parameters show the effectiveness of equivalent subsystem approach.

Detection and analysis of partial discharge (PD) have been regard as the most effective method for condition monitoring and asset management of gas-insulated structures (GIS) in the power system. However, PD detection sensitivity and accuracy are greatly influenced by on-site noise and interference, resulting in failures in PD severity assessment, defect identification or localization. Although de-noising of PD signal under AC was well studied, related investigations under DC have not been carried out. With the rapid development of HVDC technology, it is a new challenge to eliminate noise from PD signal under DC for diagnosis of related power facilities. Therefore, this paper dealt with the discrimination of PD signal based on wavelet transform (WT) techniques for HVDC GIS, aiming to improve the sensitivity and accuracy of insulation diagnosis. Experimental setup was configured to generate PD signal under DC and four types of artificial defects were fabricated to simulate typical insulation defects in GIS. The WT techniques were used to discriminate PD pulse sequences from background noise, amplitude modulation radio interference, non-sinusoidal noise, and switching impulse and the effectiveness was compared with a high-pass filter.

In this paper the properties of handover traffic are analyzed in the system with channel reservation. The reservation of several traffic channels only for handover calls leads to probability of handover calls congestion decrease to the level of per mill or even lower. The congestion of all traffic channels in the neighbouring cells is the cause that handover traffic process deviates from the Poissonian distribution and this deviation is negligible, because handover calls congestion probability is very low. This low handover calls probability is also the reason why implementation of one equivalent cell instead of 6 neighbouring cells surrounding the central cell does not model satisfactory the traffic flow in the mobile network. The randomness of handover calls arrival to the central cell is tested by our originally developed simulation program. Coefficient of variation of time between handover calls arrival to the central cell is calculated as the result of simulation. We introduced the ratio of the coefficient of variation of the time between new handover calls appearance in the central cell to the value of this coefficient for surrounding cell as the measure of handover calls randomness: the nearer this ration to 1, the more random is handover calls arrival to the central cell.

To improve the sensitive and reliability of condition monitoring in gas insulated switchgear (GIS), discharge perception system applied to GIS insulators protrusion discharge based on single ultraviolet photon is built. Step method is used to inspire the discharges of different severity, based on which, the regression relationship of ultraviolet (UV) signal and electrical signal are studied, and the perception mechanism of UV signal in different severity of discharges is analyzed. The study indicates that, the development of protrusion discharge in GIS can be divided into four stages, and there is no positive correlation between the number of ultraviolet photons caused by discharge radiation and insulation deterioration level, but related to the diffusion, migration and recombination of charged particles, then UV optical method for quantitative monitoring of discharge in each stage is provided, which provide a new method for quantitative measurement of GIS insulator discharge.

The design and implementation of planar multi-way differential power dividers remain a challenge in terms of the compactness and especially, for the achievable characteristic impedance of the quarter-wavelength transformer when considering large number of outputs. In this work, the double-sided parallel stripline is recommended to realize such a power divider with out-of-phase outputs, and explicit design methods are provided. The proposed multi-way power divider was developed without the use of lump elements on a single substrate. For system applications, a prototype operating at 41.6 MHz with 12 pairs of out-of-phase outputs that utilize the microstrip line as the output interfaces was fabricated and examined. At the center frequency of 41.6MHz, the developed prototype measured insertion losses akin to 14.3 dB as compared with the theoretical data of 13.8 dB. The attainable impedance bandwidth ranges from 10 MHz to 80 MHz under a magnitude imbalance of ±0.3 dB. The isolations of the adjacent outputs are about 13.1 dB as compared with the theoretical values of 14.428 dB, and are better than 34 dB for more distant ones. Parameter measurements are in good agreement with the numerical predications, thus demonstrating the realization of the proposed multi-way power divider.

JSON is probably one of the most popular data formats in the Internet of Things (IoT). It has gained popularity among developers due to its easy readability. The disadvantage of this format is the size of the resulting document and the associated bandwidth requirements. In order for us to be able to transfer such data securely, it is necessary to secure it before transferring it. Often, this data is compressed before it is encrypted. This article deals with a non-standard method of data compression, which reduces the computational demands on the device side. It should be noted that many of these devices are powered by batteries with limited capacity.

Resonant coaxial SMA microwave permittivity sensor is introduced. It is constructed using only commercially available SMA connectors. The sensor is tested in two different frequency ranges for two different dielectric constant ranges, from 1 to 10 and from 10 to 80. Presented sensor is designed, fabricated, simulated, and tested. Good agreement between simulations and measurements is shown. The sensor is also applicable for differential permittivity measurements.

As 5G technology is advancing towards its final phase of development and the deployment of 5G networks is underway, academic, development and industrial communities are already moving towards the research and development of 6G wireless networks. While 5G technologies had been hauled as an enabler for Internet of Everything, many limitations of such cellular systems are coming to light as they are being deployed. These drawbacks of 5G networks have motivated worldwide interest on developing the next generation wireless system, 6G, with the capability to fully incorporate wide-ranging applications from virtual reality to autonomous systems. In this paper, an overview of the first five generations of wireless systems has been shown, followed by a survey on 6G wireless network along with a discussion on the possible requirements and challenges of 6G.