Misagh Khosronejad

Bio: Misagh Khosronejad is an academic researcher from Polytechnic University of Milan. The author has contributed to research in topics: Finite element method & Transformation optics. The author has an hindex of 3, co-authored 12 publications receiving 24 citations.

Design of an Archimedean spiral UHF antenna for pulse monitoring application

Abstract: In recent years, various research works have been carried out in the UHF partial discharge monitoring of power transformers. The proper design of decoupling UHF sensors is very important in this application. This paper presents a two-arm Archimedean spiral antenna with a ground plane and a double sided parallel feeding network as a sensor for the mentioned application. Due to some existing limitations in this context, the antenna design process is somewhat unique as compared to previous works in the general telecommunication area. The measured ‘10 dB’ return loss bandwidth is more than 3.8 GHz starting from 220 MHz. Finally, simulations and measurements results demonstrate the successful principle of operation of the proposed antenna.

An Efficient 2.5-D Finite-Element Approach Based on Transformation Optics for the Analysis of Elliptical Horns

Abstract: This paper describes a new method to analyze elliptical horns. The method is based on a coordinate transformation, which maps the elliptical shape to a circular shape, allowing to use the 2.5-D body-of-revolution finite-element method formulation with a greatly improved efficiency over 3-D methods. Applications are shown to the analysis and design of shaped arbitrary axial ratio horns.

Analysis of elliptical structures with constant axial ratio by Body-of-Revolution Finite Element Method and Transformation Optics

Abstract: This paper describes a method to analyze open or closed elliptical structures with constant axial ratio by a Body-of-Revolution (BoR) Finite Element Method (FEM). The method is based on Transformation Optics, a coordinate transformation that maps the elliptical shape to a circular shape, for which BoR-FEM represents a greatly efficient tool for the analysis.

Multilayer Full Polarization Conversion Transpolarizing Structures

Abstract: In this paper, we propose the design of two perfect multilayered linear transpolarization structures working in transmission. These linear polarization converters are capable to rotate the polarization 90° independently from the direction of the input linear polarization. Results show an excellent conversion ratio.

Controlling the Polarization State of Light with a Dispersion-Free Metastructure

Abstract: Metamaterials, artificial structures with unexpected properties, only function over a limited spectral window. Scientists have recently determined that the technique of combining a metallic metamaterial with a dielectric interlayer creates a device that modulates light over a wide range of frequencies.

Application of UHF Sensors in Power System Equipment for Partial Discharge Detection: A Review

Abstract: Condition monitoring of an operating apparatus is essential for lifespan assessment and maintenance planning in a power system. Electrical insulation is a critical aspect to be monitored, since it is susceptible to failure under high electrical stress. To avoid unexpected breakdowns, the level of partial discharge (PD) activity should be continuously monitored because PD occurrence can accelerate the aging process of insulation in high voltage equipment and result in catastrophic failure if the associated defects are not treated at an early stage. For on-site PD detection, the ultra-high frequency (UHF) method was employed in the field and showed its effectiveness as a detection technique. The main advantage of the UHF method is its immunity to external electromagnetic interference with a high signal-to-noise ratio, which is necessary for on-site monitoring. Considering the detection process, sensors play a critical role in capturing signals from PD sources and transmitting them onto the measurement system. In this paper, UHF sensors applied in PD detection were comprehensively reviewed. In particular, for power transformers, the effects of the physical structure on UHF signals and practical applications of UHF sensors including PD localization techniques were discussed. The aim of this review was to present state-of-the-art UHF sensors in PD detection and facilitate future improvements in the UHF method.

Optimisation of a sensor for onsite detection of partial discharges in power transformers by the UHF method

Abstract: Among the different solutions which allow onsite partial discharge measurement in energized power transformers, the UHF technique is gaining general interest. In order to apply this method in existing transformers, it is considered advantageous to design a UHF sensor to be fitted inside the transformer tank. This paper describes the constraints affecting the development of such sensor and the process followed to optimize its design. During this process, different solutions for broadband UHF antennas were analysed. The selection was based on computer simulation and experimental results. Computer simulation was used to evaluate differences in radiation pattern, antenna impedance, gain and effective area. Measurements of the antenna response to different partial discharge sources in oil were performed using an oil dielectric breakdown test set in an electromagnetic shielded laboratory. A group of selected antennas were then tested in a power transformer simulating the broadband signals generated by partial discharges by injecting controlled voltage pulses in the transformer. Finally, a sensor based on a conical monopole antenna structure was built and attached to a specially designed housing to be fitted inside the transformer tank through the drain valve. This final prototype was benchmarked during a high voltage factory test of a power transformer which showed a significant partial discharge activity.