Volumen 72 (2021): Edición 4 (August 2021)

The early fault identification in high-voltage power systems is a substantial aspect not only to minimize equipment failure but also to increase both the reliability and stability in power system. Subsequently, the aim of this paper is to propose the adaptive fault-identification scheme based on multi-resolution analysis technique. The proposed method is dependent on monitoring both voltages and currents from single-ended measuring system. The correlation among the reactive power computation and discrete wavelet transform is used to generate the significant criteria which are used to discriminate between short-circuit currents and energizing heavy loads behaviour. Different transmission network configurations are investigated to assess the dependability, security, and reliability of fault identification relay as well. The correlative protection scheme attains the accurate results under healthy disturbances, and therefore it is superior to other conventional approaches. In addition, a selective study is applied to different mother wavelets to find the best one. The response of the proposed scheme to the compensated transmission line is also verified at a wide range of compensation levels with faults before and after compensated bank. Simulation tests have been handled via ATP-EMTP to investigate the proper practicability and adaptability of the fault-identication relay.

This work proposes a novel frequency domain despeckling technique pertaining to the enhancement of the quality of medical ultrasound images. The results of the proposed method have been validated in comparison to both the time-domain and the frequency-domain projections of the schur decomposition as well as with several other benchmark schemes such as frost, lee, probabilistic non-local means (PNLM) and total variation filtering (TVF). The proposed algorithm has shown significant improvements in edge detection and signal to noise ratio (SNR) levels when compared with the performance of the other techniques. Both real and simulated medical ultrasound images have been used to evaluate the numerical and visual effects of each algorithm used in this work.

In this paper, a miniaturized implantable antenna system for biomedical applications is presented. The system consists of almost two similar patch antennas, named internal and external. The internal antenna is implanted inside the body at a depth of 2 mm, and the external antenna is to be attached to the body aligned with the internal one. The antenna system consists of implant-side antenna with dimensions are 10.25×10.25×1.27 mm³ , while the external antenna dimensions are 11.1×11.1×1.27 mm³. The proposed antennas designs showed dual resonant frequency on ISM bands (ie , 915 MHz and 2450 MHz ). The computed -10 dB bandwidth considering three-layer human phantom demonstrates that a bandwidth of 870 to 970 MHz and 2.38 to 2.47 GHz for internal and external antennas are achieved. The Specific Absorption Rate (SAR) has been considered for health care consideration. The measured and simulated scattering parameters are compared, and good agreements are achieved. The proposed antenna system is simulated and investigated for biomedical applications suitability.

In the operation of large-scale power systems for the long-distance transmission of large amounts of electricity, a number of cases have been reported in which anomalies in the Earth’s magnetosphere, referred to as geomagnetic storms, have caused a severe system collapse. Changes in the geomagnetic field cause a semi-saturating phenomenon, in which the high-voltage lines and especially the high-voltage windings of the power transformers of the system are overloaded with current and subsequently also thermally. The present article briefly explains the physical nature of magnetic storms and then describes a new device that either eliminates the possibility of a step-down power transformer accident or significantly reduces its effects on the system. The essence of this device are frequency filters, which are connected in parallel to the high-voltage windings of power transformers. At the beginning of a geomagnetic storm, the frequency filter is automatically connected to the system and is automatically disconnected when it subsides. The operation of frequency filters does not require human intervention, acquisition and operating costs are low and their integration into existing power systems is easy.

In this paper, disulfides WS₂ and MoS₂ were successfully prepared using thermal decomposition and utilised for fabrication of supercapacitor- and water splitting electrodes. Both, energy storage and conversion performances of these electrodes were compared with electrodes prepared with commercial MoS₂, WS₂, and activated carbon (AC). The electrochemical characterisation confirmed the pseudocapacitive character of disulfide-based supercapacitor electrodes. A strong influence of the scan rate on the specific capacitance was found, which is due to the diffusion of ions and the pseudocapacitive nature of charge storage. A specific capacitance of 405 mF/cm² at 10 mV/s scan rate was achieved on MoS₂ structures prepared by thermal decomposition. This value is 3.5-times greater than the capacitance achieved on commercial MoS₂ and 6.8-times greater than capacitance achieved on structures with activated carbon. A specific capacitance of 396 mF/cm² at 10 mV/s scan rate was achieved on WS₂ structures prepared by thermal decomposition, which was 2.2 and 6.7-times greater than the capacitance achieved on commercial WS₂ and AC based electrodes, respectively. Water-decomposition structures showed greater catalytic activity of thermally decomposed disulfides for HER compared to commercial materials and AC. The study showed a high perspective of MoS₂ and WS₂ prepared by thermal decomposition for energy storage applications by means of supercapacitors and energy conversion trough water electrolysis and hydrogen generation.

It is a research hotspot of electric propulsion system that a high energy density permanent magnet machine is used as its main power. In general, the power system of electric propulsion consists of batteries, inverters and high energy density permanent magnet machines and loads. Based on harmonic effect of PWM sine alternating current generated by inverter, iron loss model of high energy density permanent magnet machine is established under inverter power harmonic, and iron loss calculation flow chart of high energy density permanent magnet machine for electric propulsion system is shown. The influences of different stator outer diameter and rotor inner diameter on iron loss are analyzed by using the finite element method. Through the above analysis, a 30 kW high energy density permanent magnet machine was designed. Then the noload test and iron loss separation test were carried out, verifying that the machine has very low core loss.

A wideband printed monopole antenna with two rejection bands is proposed in this article. The antenna provides a wideband from 5.4 GHz to 17.2 GHz with two rejection bands covering 6.9 to 7.4 GHz and 8.3 to 9.2 GHz with two peak notch frequencies of 7.2 GHz and 8.6 GHz respectively. Tested peak gain at two peak notch frequencies of 7.2 GHz and 8.6 GHz are 2.5 dBi and −1.5 dBi respectively. These two rejection bands are effectively used to avoid undesired intrusion from the C band and the X band. The lower rejection band has been realized by cutting an open ring circular slot on the metal patch whereas U like slot has been inserted on the ground plane just beneath the feed line to achieve the upper rejection band. Simulated and tested S₁₁ parameter, gain, radiation efficiency, E-H radiation patterns, and surface currents of the antenna are presented here. The antenna uses small dimensions and it is very simple to design. The proposed antenna confirms that it is useful for short-range and fast data communication systems.

A design of experiment (DoE) study is presented based on an investigation of the influences of the chosen geometric parameters of an Inverted Square Split Ring Resonator on its resonance frequency. A statistical software was used to determine DoE steps and the values of chosen geometrical parameters for the experiments. The determined experiments were carried out by making simulations with electromagnetic design software. The resonator simulation outputs were analyzed by using normality tests and tools of the statistical software. By using these analyses, mainly a 2-level full factorial DoE approach, the effects of the geometrical parameters (input factors), and their interactions on the resonance frequency (response factor) were presented. In the light of our findings, this study proposes a promising path for microwave studies with several advantages such as being able to understand the dynamics of an optimized RF resonator device system, designing these kinds of devices with a few experiments, and increasing the time efficiency via reducing the number of attempts.

This work deals with the possibilities of contemporary automatic identification of objects. Automatic object identification can be done by two computational procedures, namely object detection and object recognition. This work deals with the automatic buildings detection, specifically. Presented detection is performed using the edge detectors, namely Prewwitt, Roberts, Canny and Sobel. The main goal of our work was to automate the device for the detection of hazardous substances in the air, as the detection of hazardous substances is realized by laser-based CBRN (Chemical, Biological, Radiological and Nuclear) stand-off detectors, which evaluate the measured data from the reflected laser beam. In this case, buildings are the most reflective surfaces. In order to detect a building, it is necessary to find a suitable edge detector to be used in further research and serve as a basis for software solution of automatic identification.

The discrete time signal processing requires an anti-aliasing filter at the input and a reconstruction filter at output. Some filters of biquads structure are characterized by a decreasing of the attenuation at high frequencies, caused by the final value of the output resistance of the operational amplifier. In this paper we discuss a design of combined BP filter without mentioned decrease. The proposed filter structure was verified by SPICE simulation.