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Karami Hamidreza

Chef de projet Ra&D HES

Main contract

Chef de projet Ra&D HES

Desktop: B21

Haute école d'Ingénierie et de Gestion du Canton de Vaud
Route de Cheseaux 1, 1400 Yverdon-les-Bains, CH

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2024

Partial discharge localization in power transformer tanks using machine learning methods

Scientific paper ArODES

Farzin Khodaveisi, Hamidreza Karami, Matin Zarei Karimpour, Marcos Rubinstein, Farhad Rachidi

Scientific Reports, 2024, 14, 1, 11785

Link to the publication

Summary:

This paper presents a comparison of machine learning (ML) methods used for three-dimensional localization of partial discharges (PD) in a power transformer tank. The study examines ML and deep learning (DL) methods, ranging from support vector machines (SVM) to more complex approaches like convolutional neural networks (CNN). Multiple case studies are considered, each with different attributes, including sensor position, frequency content of the PD signal, and size of the transformer tank. The paper focuses on predicting the PD location in three-dimensional space using single-sensor electric field measurements. Various aspects of each method are analyzed, such as the input signal, core methodology, correlation coefficient between the predicted location and the actual location, and root mean square error (RMSE). These features are discussed and compared across the different methods. The results indicate that the CNN model exhibits superior performance in terms of location accuracy among the methods considered.

Spatiotemporal energy-density distribution of time-reversed electromagnetic fields

Scientific paper ArODES

Elias Le Boudec, Hamidreza Karami, Nicolas Mora, Farhad Rachidi, Marcos Rubinstein, Felix Vega

IET Science, Measurement & Technology, To be published

Link to the publication

Summary:

Time reversal exploits the invariance of electromagnetic wave propagation in reciprocal and lossless media to localize radiating sources. Time-reversed measurements are back-propagated in a simulated domain and converge to the unknown source location. The focusing time (i.e. the simulation instant at which the fields converge to the source location) and the source location can be identified using field maxima, entropy, time kurtosis, and space kurtosis. This paper analyses the spatial energy-density distribution of time-reversed electromagnetic fields by introducing a convergence metric based on the spatial average and variance of the energy density. It is analytically proven that the proposed metric identifies the focusing time and the source location, with direct links to the source frequency content. The analytical results are verified in a free-space numerical simulation and the proposed metric is then compared to existing ones in a simulated inhomogeneous medium. Next, this metric is applied and compared in an experimental case study to localize electromagnetic interference sources. The proposed metric outperforms existing ones to identify the focusing time and can also be used to locate the source. Finally, because of its tensorial nature, it can handle anisotropic media, opening the door to quantitative analyses of time-reversal focusing in metamaterials.

2023

Assessment of the feasibility of applying the electromagnetic time reversal theory to locate defects in grounding electrodes

Scientific paper ArODES

Rafael Alipio, Naiara Duarte, Hamidreza Karami, Marcos Rubsinstein, Farhad Rachidi

Energies, 16, 13, 5104

Link to the publication

Summary:

In recent years, the electromagnetic time reversal (EMTR) theory has been successfully applied for locating various sources of disturbances, such as short-circuit faults, in power systems. In this paper, a theoretical analysis of the feasibility of applying EMTR to locate defects (corrosion and break points) in grounding systems is presented. An EMTR algorithm to locate faults in buried grounding wires is proposed and a comprehensive analysis with respect to some salient influencing parameters, for instance, the ground conductivity, medium losses, the defect location and type (soft or hard), is carried out. According to the obtained results, the proposed method appears to be very promising for real applications. The need for experimental validation to confirm the applicability of this method is emphasized.

2022

EMC impact of disturbances generated by multiple sources

Scientific paper ArODES

Hamidreza Karami, Marcos Rubinstein, Farhad Rachidi, Christophe Perrenoud, Emmanuel de Raemy, Pascal Kraehenbuehl, Arturo Mediano

Electronics, 2022, vol. 11, no. 21, article no. 3530

Link to the publication

Summary:

In this paper, the impact of an increasing number of arbitrary electrical/electronic devices on the overall radiated emissions is investigated. Understanding and quantifying such an impact are prerequisites to the proper evaluation of electromagnetic compatibility (EMC) of various electronic systems and devices and, if needed, to revisiting the international standards. To evaluate the radiated emissions from multiple electronic devices, each arbitrary electronic device is characterized using an equivalent Huygens’s surface, in which the tangential components of electric and magnetic near fields are calculated (or measured). The radiated emission from the arbitrary electronic device can be calculated using the electric and magnetic near fields for an arbitrary phase (correlated or uncorrelated), position, and orientation. The influence of several parameters affecting the radiated emissions from multiple arbitrary electronic devices, including the number of disturbance sources, the polarization of each device, the radiation pattern of each device, the location and orientation of each device, and the phase shifts between devices, are analyzed. The numerical results show that the mentioned parameters have a significant effect on the radiated emissions, and cannot be neglected in EMC considerations. In general, increasing the number of electronic devices leads to an increase in the level of radiated emissions. However, the increase depends on other parameters such as the arrangement (the radiation pattern for each device, the distance between the devices, and the orientation and/or polarization of each device). The proposed method can be straightforwardly applied to devices characterized by near-field measurements or multimodular large equipment with long cables.

An inverse-filter-based method to locate partial discharge sources in power transformers

Scientific paper ArODES

Hamidreza Karami, Farzane Askari, Farhad Rachidi, Marcos Rubinstein, Wojciech Sikorski

Energies, 2022, vol. 15, no. 6, article no. 1988

Link to the publication

Summary:

Partial discharge (PD) occurrence in power transformers can lead to irreparable damage to the power network. In this paper, the inverse filter (IF) method to localize PDs in power transformers is proposed. To the best of the authors’ knowledge, this is the first time that the inverse filter method has been used to localize PD sources in the electromagnetic regime. The method comprises two phases: the forward phase and the backward or backpropagation phase. In the forward phase, the waveform emitted from the PD source is recorded with one or several sensors. In the backward phase, the recorded signal is transformed into the frequency domain, inverted, transformed back into the time domain, and then back injected into the medium. Finally, a suitable criterion is used to localize the PD source. The efficiency of the proposed IF method is assessed considering different scenarios. It is shown that, for the considered configurations, the proposed IF method outperforms the classical time-reversal technique.

2021

Single-sensor EMI source localization using time reversal :

Scientific paper ArODES

an experimental validation

Hamidreza Karami, Mohammad Azadifar, Zhaoyang Wang, Marcos Rubinstein, Farhad Rachidi

Electronics, 2021, vol. 10, no. 19, article no. 2448

Link to the publication

Summary:

The localization of electromagnetic interference (EMI) sources is of high importance in electromagnetic compatibility applications. Recently, a novel localization technique based on the time-reversal cavity (TRC) concept was proposed using only one sensor, and its application to localize EMI sources was validated numerically. In this paper, we present a validation of the proposed time-reversal process in which the forward step of the time-reversal process is performed experimentally and the backward step is carried out via numerical simulations, a realistic scenario which is applicable to practical source localization problems. To the best of the authors’ knowledge, this is the first implementation of a three-dimensional electromagnetic time-reversal process in which the forward signal is provided experimentally while the backward propagation step is carried out numerically. The considered experimental setup is formed by a partially open cavity and two monopole antennas to emulate the EMI source and the sensor (receiving antenna), respectively. Assuming that the location of the source is the feed point of the monopole antenna, the resulting three-dimensional location error in the experimental validation was only 1.49 cm, which is about one-third the length of the monopole antenna, corresponding to about λmin/2 (diffraction limit).

An experimental validation of partial discharge localization using electromagnetic time reversal

Scientific paper ArODES

Hamidreza Karami, Mohammad Azadifar, Marcos Rubinstein, Farhad Rachidi

Scientific Reports, 2021, vol. 11, article no. 220 (2021)

Link to the publication

Summary:

The localization of partial discharge (PD) sources is of importance for the monitoring and maintenance of power transformers. Time difference of arrival (TDoA) based methods are widely adopted in the literature for the localization of PDs. Recently, time reversal (TR) was suggested as an efficient means to locate PD sources. As opposed to TDoA, which needs at least 4 sensors, TR is able to locate PD sources in power transformers with only one sensor. Moreover, it needs neither line-of-sight wave propagation from the PD sources to the sensor nor time synchronization. In this study, we present for the first time an experimental demonstration of the ability of the TR process to locate PD sources. A typical TR process includes three steps: (1) recording the PD-emitted field by a sensor, (2) time reversing and back injecting the signal into the medium, (3) using a proper criterion to obtain the focusing point which corresponds to the location of the PD source. In this work, we present a laboratory setup in which steps one and two are performed experimentally, both in the frequency and in the time domain. The obtained peak electric field value is used as a criterion in the third step. It is found that the accuracy of the proposed method is better than 2.5 cm in a transformer tank model with dimensions 73 × 73 × 103 cm3. The effects of the presence of scatterers such as transformer windings are also investigated experimentally and found not to affect the location accuracy of the method.

2020

A compressive sensing framework for EMI source localization using a metalens structure :

Scientific paper ArODES

localization beyond the diffraction limit

Mohammad Azadifar, Hamidreza Karami, Farhad Rachidi, Marcos Rubinstein

IEEE Transactions on Electromagnetic Compatibility,

Link to the publication

Summary:

In this article, we propose a novel approach for the localization of electromagnetic interference (EMI) sources based on the concept of compressive sensing and metalenses. We show that using the spatial and frequency dispersion offered by the metalens, we can create a scanning beam to provide an image of the current distribution in a printed circuit board. We deployed a computational imaging framework to extract the information in the observation plane of the imaging system and thus obtain the location of the EMI source. To use mode diversity offered by the metalens, we suggest using the compressive sensing platform. To the authors’ best knowledge, this is the first utilization of metalenses, computational imaging, and compressive sensing to locate EMI sources. Numerical simulation is used to implement and investigate the ability of the proposed approach to localized EMI sources. The obtained results show a very accurate localization skill. The proposed approach overcomes the diffraction limit and provides λ/17 superresolution. Moreover, the proposed approach uses a single stationary antenna to collect data and does not need either mechanical scanning, which is time consuming, or a beamforming array, which is expensive.

Grounding Resistance of a Hemispheric Electrode Located on the Top of a Finite-Height, Cone-Shaped Mountain

Scientific paper ArODES

Antonio Sunjerga, Marcos Rubinstein, Dragan Poljak, Hamidreza Karami, Farhad Rachidi

IEEE Transactions on Electromagnetic Compatibility, 2020, vol. 62, no. 5, pp. 1889-1892

Link to the publication

Summary:

In this letter, we present an analytical solution for the resistance of a hemispheric grounding electrode located on the top of a mountain. The mountain is modeled as a truncated cone with a finite height. Recently, a closed-form solution for the grounding resistance was derived first for a hemispheric electrode on top of a cone and later for a more realistic case of a truncated cone with a flat region at its top. The height of the cone was considered infinite in those studies. Here, we extend these studies for the case of a truncated cone with finite height. The analytical solution is compared with numerical simulations and the results agree reasonably well.

Machine learning-based lightning localization algorithm using lightning-induced voltages on transmission lines

Scientific paper ArODES

Hamidreza Karami, Amirhossein Mostajabi, Mohammad Azadifar, Marcos Rubinstein, Chijie Zhuang, Farhad Rachidi

IEEE Transactions on Electromagnetic Compatibility, 2020, vol. 62, no 6, pp. 2512 - 2519

Link to the publication

Summary:

In this article, we present a machine learning-based method to locate lightning flashes using calculations of lightning-induced voltages on a transmission line. The proposed approach takes advantage of the preinstalled voltage measurement systems on power transmission lines to get the data. Hence, it does not require the installation of additional sensors such as extremely low frequency, very low frequency, or very high frequency. The proposed model is shown to yield reasonable accuracy in estimating two-dimensional geolocations for lightning strike points for different grid sizes up to 100 × 100 km2. The algorithm is shown to be robust against the distance between the voltage sensors, lightning peak current, lightning current rise time, and signal to noise ratio of the input signals.

Partial discharge localization using time reversal :

Scientific paper ArODES

application to power transformers

Hamidreza Karami, Mohammad Azadifar, Amirhossein Mostajabi, Marcos Rubinstein, Hossein Karami, Gevork B. Gharehpetian, Farhad Rachidi

Sensors, 2020, vol. 20, no. 5, article no. 1419

Link to the publication

Summary:

In this work, we present a novel technique to locate partial discharge (PD) sources based on the concept of time reversal. The localization of the PD sources is of interest for numerous applications, including the monitoring of power transformers, Gas Insulated Substations, electric motors, super capacitors, or any other device or system that can suffer from PDs. To the best of the authors’ knowledge, this is the first time that the concept of time reversal is applied to localize PD sources. Partial discharges emit both electromagnetic and acoustic waves. The proposed method can be used to localize PD sources using either electromagnetic or acoustic waves. As a proof of concept, we present only the results for the electromagnetic case. The proposed method consists of three general steps: (1) recording of the waves from the PD source(s) via proper sensor(s), (2) the time-reversal and back-propagation of the recorded signal(s) into the medium using numerical simulations, and (3) the localization of focal spots. We demonstrate that, unlike the conventional techniques based on the time difference of arrival, the proposed time reversal method can accurately localize PD sources using only one sensor. As a result, the proposed method is much more cost effective compared to existing techniques. The performance of the proposed method is tested considering practical scenarios in which none of the former developed methods can provide reasonable results. Moreover, the proposed method has the unique advantage of being able to locate multiple simultaneous PD sources and doing so with a single sensor. The efficiency of the method against the variation in the polarization of the PDs, their length, and against environmental noise is also investigated. Finally, the validity of the proposed procedure is tested against experimental observations.

On the efficiency of OpenACC-aided GPU-Based FDTD approach :

Scientific paper ArODES

application to lightning electromagnetic fields

Sajad Mohammadi, Hamidreza Karami, Mohammad Azadifar, Farhad Rachidi

Applied Sciences, 2020, vol. 10, no. 7

Link to the publication

Summary:

An open accelerator (OpenACC)-aided graphics processing unit (GPU)-based finite difference time domain (FDTD) method is presented for the first time for the 3D evaluation of lightning radiated electromagnetic fields along a complex terrain with arbitrary topography. The OpenACC directive-based programming model is used to enhance the computational performance, and the results are compared with those obtained by using a CPU-based model. It is shown that OpenACC GPUs can provide very accurate results, and they are more than 20 times faster than CPUs. The presented results support the use of OpenACC not only in relation to lightning electromagnetics problems, but also to large-scale realistic electromagnetic compatibility (EMC) applications in which computation time efficiency is a critical factor.

Localization of electromagnetic interference sources using a time reversal cavity

Scientific paper ArODES

Hamidreza Karami, Mohammad Azadifar, Amirhossein Mostajabi, Pierre Favrat, Marcos Rubinstein, Farhad Rachidi

IEEE Transactions on Industrial Electronics, 2021, vol. 68, no. 1, pp. 654-662

Link to the publication

Summary:

In this paper, we propose and implement a novel technique to locate Electromagnetic Interference (EMI) sources using the concept of time reversal cavity. We show in an intuitive manner that reflections from the surfaces of a cavity can emulate an infinite number of sensors in the Time Reversal (TR) method. In order to locate EMI sources, the equipment under test (EUT) is placed in a rectangular metallic cavity, of suitable dimensions according to the considered frequency band and the EUT size, equipped with a simple monopole or dipole antenna. We demonstrate that, by using only one sensor, we are able to locate EMI sources by taking advantage of the focusing properties of a time reversal cavity. The entropy criterion is applied to obtain the focusing time slice in which the maximum electric field determines the location of the EMI source. Both two- and three-dimensional numerical simulation schemes are deployed to demonstrate the ability of the proposed technique. The validity of numerical simulations is tested against frequency domain measurements. Compared to conventional EMI tests in anechoic chambers and scanning methods, the proposed technique represents a simpler and cost-effective test method requiring only one sensor (a monopole or dipole antenna).

2019

Numerical and experimental validation of electromagnetic time reversal for geolocation of lightning strikes

Scientific paper ArODES

Hamidreza Karami, Mohammad Azadifar, Amirhossein Mostajaba, Marcos Rubinstein, Farhad Rachidi

IEEE Transactions on Electromagnetic Compatibility, 2020, vol. 62, no. 5, p. 2156-2163

Link to the publication

Summary:

We implement an electromagnetic time reversal technique (EMTR) to locate lightning return strokes. The two-dimensional finite difference time domain is employed to simulate the EMTR process in both, the forward-time and the backward-time phases. Scatterers are included in the computational domain to emulate the presence of objects. Three possible criteria to find the optimum time slice of the EMTR process that includes the maximum peak field, maximum peak energy, and last local minimum of entropy are tested and it is found that only the entropy criterion can successfully locate the lightning discharge. Our analysis shows that the EMTR process in both, using an unchanged and a simplified medium for the backward time works reasonably well even with only two sensors. Furthermore, we validated the proposed method via experimental results using waveforms recorded at two sensors at distances of 14.7 and 380 km from the Säntis Tower. The results demonstrate that the EMTR back-propagation process leads to a refocusing of the radiated energy at the location of the Säntis Tower. The ambiguity in the obtained location when only two sensors are used can be resolved either by using an additional sensor or through a more accurate modeling of the terrain.

Single-sensor source localization using electromagnetic time reversal and deep transfer learning: application to lightning

Scientific paper ArODES

Amirhossein Mostajabi, Hamidreza Karami, Mohammad Azadifar, Alireza Ghasemi, Marcos Rubinstein, Farhad Rachidi

Scientific Reports, 2019, vol. 9, article no. 17372

Link to the publication

Summary:

Electromagnetic Time Reversal (EMTR) has been used to locate different types of electromagnetic sources. We propose a novel technique based on the combination of EMTR and Machine Learning (ML) for source localization. We show for the first time that ML techniques can be used in conjunction with EMTR to reduce the required number of sensors to only one for the localization of electromagnetic sources in the presence of scatterers. In the EMTR part, we use 2D-FDTD method to generate 2D profiles of the vertical electric field as RGB images. Next, in the ML part, we take advantage of transfer learning techniques by using the pretrained VGG-19 Convolutional Neural Network (CNN) as the feature extractor tool. To the best of our knowledge, this is the first time that the knowledge of pretrained CNNs is applied to simulation-generated images. We demonstrate the skill of the developed methodology in localizing two kinds of electromagnetic sources, namely RF sources with a bandwidth of 0.1–10 MHz and lightning impulses. For the localization of lightning, based on the experimental recordings in the Säntis region, the new approach enables accurate 2D lightning localization using only one sensor, as opposed to current lightning location systems that need at least two sensors to operate.

2018

Tower and path-dependent voltage effects on the measurement of grounding impedance for lightning studies

Scientific paper ArODES

Antonio Sunjerga, Daniel S. Gazzana, Dragan Poljak, Hamidreza Karami, Keyhan Sheshyekani, Marcos Rubinstein, Farhad Rachidi

IEEE Transactions on electromagnetic compatiblity, 2019, vol. 61, no. 2, pp. 409-418

Link to the publication

Summary:

We present an analysis aimed at evaluating the effect of the presence of the tower on the measurement of the grounding impedance. The Numerical Electromagnetics Code NEC-4 is used for the full-wave modeling of the structure including the tower and its footing grounding system, as well as the experimental setup used for the measurement of the grounding impedance. First, the effect of possible path-dependence in the evaluation of the integral of the electric field is investigated. It is shown that, up to a frequency of about 100 kHz or so, the voltage, and consequently the evaluated impedance are independent of the path of integration. At higher frequencies, differences appear, which might be significant especially for poor conducting ground. The effect of the distance to the reference remote earth on the evaluated voltage is also analyzed and it is shown that a distance of 100 m to the remote earth is appropriate to evaluate the grounding impedance potential rise. The simulation results show that at low frequencies (up to about 200 kHz or so for the considered 140-m tall tower), the effect of the presence of the tower can be disregarded. At higher frequencies, the evaluated impedance is affected by the presence of the tower. The poorer the ground conductivity, the more significant the effect of the presence of the tower on the evaluated impedance. Two injected current waveforms, representative of typical first and subsequent return strokes, are considered for the time-domain analysis. The effect of the presence of the tower can be significant for subsequent return stroke excitation, which has a wider frequency spectrum compared to first return strokes. It is shown that in the early-time region, part of the injected current flows into the tower. For a ground conductivity of 0.001 S/m, the tower peak current increases to about 10% of the exciting current, for the case of a subsequent strokes. It is also shown that the presence of the tower would cause a decrease in the peak potential rise leading therefore to an underestimation of the so-called impulsive grounding impedance.

2016

On practical implementation of electromagnetic models of lightning return-strokes

Scientific paper ArODES

Hamidreza Karami, Farhad Rachidi, Marcos Rubinstein

Atmosphere, 2016, vol. 7, no. 10, article no 135

Link to the publication

Summary:

In electromagnetic models, the return-stroke channel is represented as an antenna excited at its base by either a voltage or a current source. To adjust the speed of the current pulse propagating in the channel to available optical observations, different representations for the return-stroke channel have been proposed in the literature using different techniques to artificially reduce the propagation speed of the current pulse to values consistent with observations. In this paper, we present an analysis of the available electromagnetic models in terms of their practical implementation. Criteria used for the analysis are the ease of implementation of the models, the numerical accuracy and the needed computer resources, as well as their ability to reproduce a desired value for the speed of the return stroke current pulse. Using the CST-MWS software, which is based on the time-domain finite-integration technique, different electromagnetic models were analyzed, namely (A) a wire embedded in a fictitious half-space dielectric medium (other than air), (B) a wire embedded in a fictitious coating with permittivity (εr) and permeability (μr), and (C) a wire in free-space loaded by distributed series inductance and resistance. It is shown that, by adjusting the parameters of each model, it is possible to reproduce a desired value for the speed of the current pulse. For each of the considered models, we determined the values for the adjustable parameters that allow obtaining the desired value of the return speed. Model A is the least expensive in terms of computing resources. However, it requires two simulation runs to obtain the electromagnetic fields. A variant of Model B that includes a fictitious dielectric/ferromagnetic coating is found to be more efficient to control the current speed along the channel than using only a dielectric coating. On the other hand, this model requires an increased number of mesh cells, resulting in higher memory and computational time. The presence of an inhomogeneous medium generates, in addition, unphysical fluctuations on the resulting current distributions. These fluctuations, which strongly depend on the size of the coating as well as on its electric and magnetic properties, can be attenuated by considering conductive losses in the coating. Considering the efficiency in terms of the required computer resources and ease of implementation, we recommend the use of Model C (wire loaded by distributed inductance and resistance).

2023

Lightning localization using three-dimensional Time Reversal MUltiple SIgnal Classification (TR-MUSIC) algorithm

Conference ArODES

Siavash Rajabi, Hamidreza Karami, Marcos Rubinstein, Farhad Rachidi

Proceedings of the 2023 XXXVth General Assembly and Scientific Symposium of the International Union of Radio Science (URSI GASS)

Link to the conference

Summary:

In this paper a three-dimensional (3D) Time Reversal MUltiple SIgnal Classification (TR-MUSIC) algorithm is proposed to localize lightning discharges. The performance of the proposed algorithm was evaluated considering different scenarios and taking into account the presence of noise.

2022

Landmine detection using electromagnetic time reversal based methods

Conference ArODES

Hamidreza Karami, André Koch, Carlos Romero, Marcos Rubinstein, Farhad Rachidi

Proceedings of Global EM 2022, Global Electromagnetics Conference

Link to the conference

Summary:

In this paper, the interaction between a measurement system, the landmine, and the soil is investigated to detect an unknown buried object. In particular, the performance of different approaches for landmine localization using electromagnetic time reversal (EMTR) methods is investigated in terms of their detection efficiency and computational efficiency. The considered methods include the classical time-domain EMTR, iterative EMTR, EMTR-DORT (decomposition of the time reversal operator), and EMTR-MUSIC (Multiple signal classification). The obtained simulation results show that EMTR is a promising technique for landmine detection and localization.

An efficient computer code for the analysis of grounding systems using the method of moments

Conference ArODES

Hamidreza Karami, Carlos Romero, André Koch, Marcos Rubinstein, Farhad Rachidi

Proceedings of Global EM 2022, Global Electromagnetics Conference

Link to the conference

Summary:

We present an efficient computer code based on the method of moments (MoM) for the analysis of arbitrary grounding systems embedded in a lossy soil.

A time-reversal cavity for electromagnetic waves in transmission line networks with arbitrary topology

Conference ArODES

Zhaoyang Wang, Hamidreza Karami, Elias Le Boudec, Farhad Rachidi, Marcos Rubinstein

Proceedings of Global EM 2022, Global Electromagnetics Conference, 13-17 November 2022, Abu Dhabi, United Arab Emirates

Link to the conference

Summary:

This paper describes the realization of a time-reversal cavity for electromagnetic waves in transmission line networks. A frequency-domain analysis of the two-stage wave processes that pertain to the time-reversal cavity is presented for a multi-terminal and multi-node transmission line network characterized by arbitrary topology.

Source reconstruction method using phase-less magnetic near-field measurements :

Conference ArODES

application of the method of moment with roof-top basis functions

Hamidreza Karami, Marcos Rubinstein, Christophe Perrenoud, Emmanuel deRaemy, Pascal Kraehenbuehl, Arturo Mediano Heredia

Proceedings of 2022 International Symposium on Electromagnetic Compatibility – EMC Europe

Link to the conference

Summary:

Source reconstruction methods have many applications such as antenna diagnosis, calculating far-field radiated emissions, and identifying incompatible sources on integrated circuits or printed circuit boards. In this paper, the Gerchberg—Saxton algorithm is used to retrieve the phase of the transverse magnetic near-field data measured on two parallel plates above the equipment under test (EUT). Then, the method of moments using roof-top basis functions is applied to reconstruct the horizontal electric current densities for the EUT. The proposed method is validated by comparing its results to full-wave simulations obtained using the CST-MWS software.

A frequency-domain analysis of a time-reversal cavity for electromagnetic waves in transmission line networks

Conference ArODES

Zhaoyang Wang, Hamidreza Karami, Elias Le Boudec, Marcos Rubinstein, Farhad Rachidi

Proceedings of the 3rd URSI Atlantic and Asia Pacific Radio Science Meeting (AT-AP-RASC) 2022, 30 May - 4 June 2022, Gran Canaria, Spain

Link to the conference

Summary:

Recently, a closed time-reversal cavity for electromagnetic waves was demonstrated and experimentally realized using a network of transmission lines. This paper presents an analysis in the frequency domain of the wave propagation characteristics that pertain to the time-reversal cavity. The study illustrates, in the frequency domain, that the backward-propagation wave consists of the converging and diverging components, and only the converging wave constitutes a time-reversed counterpart of the forward-propagation wave. Moreover, it is found that the interfering effect of the diverging wave can exist for any of the observation points along the transmission line network. Finally, the analysis demonstrates that an active time-reversal sink remains effective in the frequency domain to overcome the interfering effect.

Achievements

PEOPLE@HES-SO Directory and Skills inventory

Karami Hamidreza

Chef de projet Ra&D HES

Chef de projet Ra&D HES

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