Hamidreza Karami

Swiss Federal Institute of Technology in Lausanne | EPFL

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 s...

In this paper, a series of numerical simulations are conducted for various 2D and 3D configurations to demonstrate the performance of the Time Reversal MUltiple SIgnal Classification (TR‐MUSIC) method. The results reveal the excellent performance of TR‐MUSIC, taking into account the effects of noise, soil types (both homogeneous and layered), and t...

In this paper, we present a review and classification of the published works on the use of Electromagnetic Time Reversal (EMTR)‐based methods to locate landmines. Different approaches for landmine localization using EMTR are investigated. Specifically, the classical time‐domain EMTR, iterative EMTR, EMTR‐DORT (Décomposition de l’Opérateur du Retour...

This paper presents a rigorous assessment of natural frequencies associated with fault-originated travelling waves in power networks, factoring in the presence of multiple junctions and branches. The proposed assessment exploits the Baum-Liu-Tesche (BLT) equation. An enhanced fault location accuracy is consequently attained leveraging rectified nat...

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...

In this paper, three machine learning (ML)-based approaches-XGBoost, Artificial Neural Network (ANN), and Random Forest algorithms-are compared for the localization of lightning through the analysis of lightning-induced voltages on power transmission lines. Across all methods, two sensors are employed to capture lightning-induced voltages on power...

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...

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 EM...

We present a novel time-reversal spatial convergence metric, inspired by probability theory and the electromag- netic wave potential energy density, and apply it to sev- eral FDTD time-reversal simulations based on a modified Meep implementation. The proposed metric is a convex- quadratic function of time, attaining its minimum at a time and a valu...

Robotic or prosthetic organs are designed to have the maximum similarity to human organs. This paper aims to improve robotic hand control via an adaptive Fuzzy-PI controller using EMG signals. The data is collected from the FDS and FPL muscles of the forearm of five individuals who performed eight movements. Then, appropriate filters are used to el...

Gas-insulated switchgear (GIS) are some of the most reliable and most expensive equipment that are nowadays used in power systems. Condition monitoring of the power system equipment can help operators detect defects like partial discharges (PDs) early, prevent severe damage to the insulation of the apparatus and the related costs. Different techniq...

Robotic or prosthetic organs are designed to have the maximum similarity to human organs. This paper aims to improve robotic hand control via an adaptive Fuzzy-PI controller using EMG signals. The data is collected from the FDS and FPL muscles of the forearm of five individuals who performed eight movements. Then, appropriate filters are used to el...

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 int...

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 backw...

Utilizing electromagnetic mechanisms, energy harvesting from linear and non-linear lateral vibration of a rotating shaft is investigated in the present study. Moreover, the boundary condition of the shaft is simply supported, and the stretching for the given shaft is addressed for a non-linear mode. In this respect, rotary inertia and gyroscopic ef...

The localization of partial discharges (PD) is important to monitor the conditioning of high voltage insulator materials. One of the key components in power grids is the high power transformer. Localization of PDs in these pieces of equipment can increase the reliability of power networks. One of the most commonly used methods to localize PDs is th...

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 electro...

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 pres...

In this paper, a graphene-based metamaterial absorber is proposed and investigated numerically, in which the interaction between a split ring resonator (SRR) and graph -ene results in a high-Q absorption. To make a better understanding of the resonance mechanism, the electric and the magnetic fields, and the surface currents at the resonance freque...

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, whi...

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 circui...

In this paper, the time reversal (TR) technique is extended to localize a partial discharge (PD) source in the acoustic regime. The proposed acoustic TR method consists of three steps, a) the acoustic waves emitted by the PD source are recorded by at least one sensor, b) the recorded signal(s) are reversed in time and back injected into the conside...

This article presents for the first time an OpenACC (Open accelerators)-aided Graphics Processing Unit (GPU)-based approach adopting a 3D moving window finite difference time domain (MW-FDTD) method for calculating lightning electromagnetic fields over large-scale terrains. The efficacy and accuracy of the proposed method are evaluated by comparing...

In this study, first, a comparison on the application of electromagnetic time reversal (EMTR) and time difference of arrival (TDoA) in partial discharge localization in power transformers is presented. A two-dimensional finite-difference time-domain simulation is used to calculate the signal recorded by the sensors. Results show that, in a transfor...

In this article, direct characterization of the wide-band input impedance of grounding system buried in multilayer soil is presented. The problem is formulated by mixed-potential integral equations solved by the method of moments (MoM). The method accommodates both delta-gap voltage and impressed-current excitations. The input impedance is then dir...

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...

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...

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 mor...

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 equipm...

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 c...

In this paper, the effects of layer number on the electronic bandstructure and electron mobility of strained multi-layer MoS2 have been investigated. Ab initio simulations are utilized to investigate the bandstructure of multi-layer MoS2, and its low-field mobility has been calculated by the linearized Boltzmann transport equation. The results indi...

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...

Given that the effectiveness of interstitial hyperthermia for cancer treatment is related to the temperature achieved during the ablation process, there is a need for an accurate understanding of the required temperature distribution which is affected by the physical shape and form of tumours. Although a maximum peak temperature value and minimum b...

Because the effectiveness of interstitial hyperthermia is related to the temperature distribution achieved during the process, accurate understanding of energy transport within biological organs is necessary. This strongly depends on the complexity of the extended model. Herein, the coupled nonlinear set of transient equations for electromagnetic,...

A new microstrip Rotman lens with enhanced side lobe level (SLL) is proposed for X-band applications. A proper nonuniform distribution of the initial width of output ports is considered to improve the SLL. The benefit of SLL improvement is not based on using additional attenuators or amplifiers at the output ports. Moreover, an analytical backgroun...

The effects of biaxial strain on the direct-current (DC) performance of transition-metal dichalcogenide (TMD)-based double-gate field-effect transistors (DGFETs) were investigated. The TMDs used as the transistor channel were MoS\(_2\), MoSe\(_2\), WS\(_2\), and WSe\(_2\). The results indicated that tensile strain increased the DC performance of th...

Recently Controlling the electromagnetic wave, especially in terahertz range is highly demanded due to the development of practical devices and application systems. In this paper, we propose a scheme to design tunable abnormal reflection structure consisting of molybdenum disulfide (MoS2) array on a grounded SiO2 and a gold layer beneath them to re...

Presents a response to comments on the paper, "Direct characterization of grounding system wideband input impedance" (Grcev, L.), IEEE Trans. Electromagn. Compat., 2019, to be published, doi: 10.1109/TEMC.2018.2861799. This note aims at responding to the comments raised by Grcev on our paper. We are fully confident that our citation and description...

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 ground...

Zinc oxide (ZnO) thin film has in recent years emerged due to its unique physical, electrical and chemical properties. The microstructural and optical properties of nanocrystallite ZnO films fabricated using electrospinning and post-calcination, undoped and doped with aluminum, (AZO nanostructure films) were investigated in this study. The results...

The effect of a mixed propagation path on the ground-surface electromagnetic fields generated by an electrojet is evaluated. To this aim, the finite element method is used for two-dimensional modeling of the problem. Results are first obtained for the case of horizontally stratified ground and compared with those obtained by the use of the complex-...

Electromagnetic Time Reversal (EMTR) has been recently proposed as a lightning location method. The method is based on the recording of the full electric or magnetic field waveform at multiple stations, time-reversing the recorded fields, and back-propagating them using numerical simulations into the location domain. The back-propagated fields will...

Device-to-device (D2D) communication is a promising 5G technology, which helps to increase spectrum efficiency and sum-rate, as well as to decrease experienced latency. The main challenges of D2D communication are power consumption of paired devices, channel estimation between device pairs, and interference management between devices that use the s...

The effect of multilayer stratified ground on the harmonic impedance of grounding systems is evaluated. To this aim, the mixed-potential integral equation is used. The method is general as it allows taking into account 1) stratified soil structure with any number of layers and 2) grounding electrodes with arbitrary shapes. Moreover, the method has...

Direct characterization of grounding system wide-band input impedance is presented. The problem is formulated by mixed-potential integral equations solved by the method of moments (MoM). The method accommodates both delta-gap voltage and impressed-current excitations. The input impedance is then directly obtained from the MoM matrix. Contrary to th...

Recent developments in metamaterial designs have opened up the possibility of absorption in the terahertz frequency range. In this paper, a multi-resonant absorber is presented in which the resonance frequencies are theoretically organized by doping graphene ribbons with a ring-shaped gold on each ribbon per unit cell. This action allows the free e...

A robust, fast and simple scheme for calculation of potential integrals that encountered singular terms in time domain integral equation (TDIE) for planar PEC scatterers in free space is presented. In this method singular terms of the potential integrals, like other terms, calculated numerically by selecting some points in the source and observatio...

This paper presents an efficient time-domain approach to evaluate the effect of the metallic shield on enclosed multilayered structures. In the proposed method, using the surface equivalence theorem, the multilayered structure is divided into separate layers, which are coupled together by the assumed unknown magnetic currents on the nonmetallic int...

The paper presents a comprehensive approach for full-wave modeling of grounding systems buried in a multilayer stratified ground. The dyadic spectral domain Green's function associated with the multilayer stratified ground is first derived. This Green's function is then evaluated by numerical solution of Sommerfeld's integrals along the deformed pa...

چکیده تشخیص پلاك خودرو یکی از مهمترین زمینههاي کاربرد تکنیکهاي کامپیوتري در سیستمهاي حمل و نقل هوشمند میباشد. عموما سیستمهای تشخیص پلاک خودرو شامل سه مرحله هستند: الف- مکان یابی پلاک، ب- جداسازی کاراکترهای پلاک، ج- تشخیص کاراکترها. تشخیص پلاک به علت تنوع پلاک‌ها و تغییر شرایط نوری در حین تصویربرداری یک کار بسیار مهم و چالشی است. بسیاری از تکنیک‌های...

چکیده تشخیص پلاك خودرو یکی از مهمترین زمینه‌هاي کاربرد تکنیکهاي کامپیوتري در سیستمهاي حمل و نقل هوشمند می‌باشد. عموما سیستم های تشخیص پلاک خودرو شامل سه مرحله هستند: الف- مکان یابی پلاک، ب- جداسازی کاراکترهای پلاک، ج- تشخیص کاراکترها. عدم موفقیت در انجام صحیح هر مرحله منجر به شکست قطعی مرحله بعدی می‌گردد. برای مثال؛ در صورت عدم جداسازی صحیح کاراکتر...

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 diffe...

The general form of 3-D static Green's function for a general structure consisting of N arbitrary adjacent dielectric wedges is derived using the Kontorovich-Lebedev and Fourier transforms. It consists of several point sources in physical space and a line image source in complex space for each region of the problem geometry. While the point sources...

Recent developments in metamaterial designs have opened up the possibility of the absorption in the terahertz frequency range. In this paper we present a multi-resonant perfect absorber that can be tuned to produce either single wideband or multi-band resonance in order to suit any special requirements. We demonstrate that the proposed structure le...

This paper proposes an efficient time-domain mixed potential integral equation (TD-MPIE) technique to analyze the penetrated transient electromagnetic field into a perforated rectangular metallic enclosure loaded with conducting objects. To this end, the surface equivalent principle is applied, and the fields in the interior and the exterior region...

Metamaterial-based perfect absorbers are used in many applications like photo-detectors, sensors, special light modulators, wireless communications and photovoltaic. The mechanism of absorption is based on the complete suppression of reflection and transmission of incident wave. Here we present a multi resonances perfect absorber made of Graphene m...

In this study, we introduce an indirect adaptive fuzzy wavelet neural controller (IAFWNC) as a power system stabilizer to damp inter-area modes of oscillations in a multi-machine power system. Quantum computing is an efficient method for improving the computational efficiency of neural networks, so we developed an identifier based on a quantum neur...

Lightning is one the major sources of electromagnetic interferences. Multisensor networks known as lightning location systems (LLS) are widely used to detect and locate different types of lightning discharges (see, e.g., Cummins and Murphy, IEEE Trans. EMC, 51 (3), pp. 499–518, 2009). Modern LLS use different detection techniques such as the Time-o...

This paper proposes an efficient modeling technique for time-domain electromagnetic analysis of a multilayered structure, using the surface equivalent principle and mixed-potential integral equations (MPIEs). First, the surface equivalent principle is used to replace the nonmetallic parts in each layer interface of the structure by prefect electric...

This paper proposes an efficient modeling technique for transient electromagnetic analysis of a rectangular metallic enclosure with multiple apertures, using the surface equivalent principle (SEP) and integral equations. The SEP is used to replace the apertures by perfect electric conductor surfaces while introducing appropriate magnetic current de...

In this paper, susceptibility of a Microstrip Transmission Line (MTL) as a simple Printed Circuit Board (PCB) against a normal incident plane wave is studied. Here, the induced voltage on the open port of the MTL is considered as the susceptibility criterion for the MTL. Two different approaches are applied: the Method of Moments (MoM) and the Fini...

This paper presents a general methodology based on the matrix pencil method (MPM) for the fitting of frequency-domain responses in order to be properly represented in time-domain analysis. By virtue of the proposed method, a rational fitting of the frequency-domain responses can be inferred, which, in turn, helps with their inclusion into time-doma...

This paper proposes an entirely frequency-domain technique for the transient analysis of electromagnetic systems involving nonlinearly loaded wire antennas over a lossy dielectric half-space. The analysis involves two stages. In the first stage, the problem is transformed into a nonlinear microwave equivalent circuit with the circuit parameters of...

A novel method for the preparation of radio frequency (RF) wave absorber polyurethane foam (PU) has been developed by impregnation of PU foam in n-hexane solution of room temperature vulcanizing (RTV) silicone rubber (SR) hybridized with graphite nanosheets (GNs) called doping solution. Extent of the GNs dispersion was optimized by the incorporatio...