Mohamed Bakr

• McMaster University

Reservoir computing (RC) is a bio-inspired framework suited for temporal data processing. Here we propose an all optical coherent RC for the equalization of the impairments of fiber optic (FO) system based on coherent detection. We compare the performances of the RC systems based on semiconductor saturable absorber mirror (SESAM) and highly nonline...

Augmented Reality and Virtual Reality are one of the key advances in technology in the last decade. Their usage is rapidly increasing across various contexts. The COVID-19 pandemic and the pressing need for remote learning tools that imitate as close as possible real training environments motivated more research and investigation of AR/VR tools. We...

A novel, polarization-independent, wide-angle reception Chand-Bali nano-antenna is proposed. An adjoint-based optimization algorithm is used to create the same resonance at both linear polarizations of the incident radiation. The nano-antenna optimal parameters reveal that two hot spots with a strong field enhancement are created. These hot-spots c...

The switched reluctance machine is considered as the simplest machine in terms of the machine structure. The lack of permanent magnets on the rotating part enables the machine to operate at high speeds and reduces the thermal requirements of the machine. However, the double salient structure of the SRMs creates challenges such as high acoustic nois...

This work proposes an efficient and easy-to-implement single-layer artificial neural network (ANN)-based equalizer with improved compensation performance. The proposed equalizer is used for effectively mitigating the distortions induced in the short-haul fiber-optic communication systems based on intensity modulation and direct detection (IMDD). Th...

Non-invasive detection of biomarkers can help in the early screening of lethal diseases, such as cancer and Alzheimer's. In this paper, we present a numerical study of a high-quality resonant permittivity-asymmetric metasurface that offers tunability in the mid-infrared range by employing the phase change property of Germanium Antimony Telluride, G...

This article introduces a new technique for reducing the time of calculating radial and tangential force density waves of switched reluctance machines (SRMs). The method is based on the finite element (FE) simulation of a fraction of an electrical cycle. The new approach shows that a significant time reduction is achieved as compared to the time re...

Existing research on geometry optimization of switched reluctance motor (SRM) using machine learning algorithms has focused only on the machine’s static characteristics. The dynamic characteristics, however, are critical to improve the SRM performance, particularly at high speeds. This paper introduces an advanced optimization method utilizing a su...

A brief review of the applications of machine learning to the electromagnetic modeling and design optimization of high‐frequency structures is presented. The structure of artificial neural networks (ANNs), their training, and testing phases are discussed. The applications of ANNs to the forward and inverse modeling of electromagnetic structures are...

With the growing need for portable, compact, low-cost, and efficient biosensors, plasmonic materials hold the promise to meet this need owing to their label-free sensitivity and deep light–matter interaction that can go beyond the diffraction limit of light. In this review, we shed light on the main physical aspects of plasmonic interactions, highl...

This work proposes a novel and powerful adaptive digital back propagation (A-DBP) method with a fast adaption process. Given that the total transmission distance is known, the proposed A-DBP algorithm blindly compensates for the linear and nonlinear distortions of optical fiber transmission systems and networks, without knowing the launch power and...

Switched reluctance machines (SRMs) have recently attracted more interest in many applications due to the volatile prices of rare-earth permanent magnets (PMs) used in permanent magnet synchronous machines (PMSMs). They also have rugged construction and can operate at high speeds and high temperatures. However, acoustic noise and high torque ripple...

This work presents a comprehensive review of the developments in using Machine Learning (ML)-based algorithms for the modeling and design optimization of switched reluctance motors (SRMs). We reviewed Machine Learning-based numerical and analytical approaches used in modeling SRMs. We showed the difference between the supervised, unsupervised and r...

Switched reluctance machines (SRMs) are getting more popular due to their uncomplicated and rugged structure. However, acoustic noise and vibration resemble two main issues with this type of machine. Radial forces acting on the machine stator contribute significantly to acoustic noise generation. These forces can be reduced by optimizing the machin...

We investigate, for the first time, optimization of the responsivity of metal-insulator-insulator-metal (MIIM) diodes by carefully considering materials' properties. The diode's resistance is fixed at 100 Ω in order to match the nano antenna's impedance and to increase the total efficiency of the rectifying antenna (rectenna). The optimization is p...

Reconfigurable metasurface absorbers enable collecting or emitting radiation within selected frequency bands. It is thus necessary to decipher such behavior for many applications, including plasmonic energy harvesting, radiative cooling and thermal emitters. In this article, we propose a compact reconfigurable vanadium dioxide (VO2)-based metasurfa...

A general nonlinear adjoint sensitivity analysis (ASA) approach for the time-dependent nonlinear Schrodinger equation (NLSE) is presented. The proposed algorithm estimates the sensitivities of a desired objective function with respect to all design parameters using only one extra adjoint system simulation. The approach efficiency is shown here thro...

A plasmonic switchable polarization-insensitive metasurface absorber is proposed. The design provides two modes of operation by employing phase-change material in semiconductor and metallic phases. In this paper, we study the switchable absorption behavior of the metasurface operating in a dual-band and single-band modes targeting the mid-infrared...

We propose a wide-band metamaterial perfect absorber (MPA), using the coupling in the near-field of a quadruple split-ring resonator concentric with crossed ellipses. We designed the MPA with a metal-insulator-metal (MIM) structure for use in thermal energy harvesting. A gradient-based optimization approach was carried out to maximize the absorptio...

A novel time-domain adjoint sensitivity analysis (ASA) approach is proposed. Our FDTD-based approach accelerates wideband sensitivity calculations for high frequency structures with nonlinear media. The introduced approach supports simulated problems with current sources or incident field excitation. Using only one extra system simulation, the sens...

Energy harvesting rectennas require ultrafast rectifying diodes that are efficiently matched to the optical nanoantenna. These diodes should possess low on-resistance and high responsivity. Here, we introduce a metal-insulator-metal diode composed of a new material, Ti-TiO2-Al. This diode has a 1.0 nm ultrathin insulator layer fabricated using atom...

This Letter proposes a novel adjoint sensitivity analysis approach for the nonlinear Schrödinger equation, which describes the light wave propagation in optical fiber communication systems. Using only one extra adjoint system simulation, all the sensitivities of a general objective function with respect to all fiber design parameters are estimated....

The impedance mismatch between a rectenna's two components, the antenna and the rectifying diode, represents a serious impediment to improving the rectenna's efficiency. Also, the diode's capacitance and the device equivalent resistance determine the rectenna's cutoff frequency. For the detection of the terahertz-frequency signals, ultrafast rectif...

A plasmonic dual-band polarization-insensitive metasurface absorber is proposed. The design provides subwavelength and confined collection of the absorbed energy in the gaps of the structure. In this paper, we study the absorption behavior of the metasurface operating in a dual-band mode targeting the mid-infrared range suitable for energy harvesti...

We propose a wideband adjoint variable method for sensitivity analysis of structures comprised of dispersive and anisotropic magnetized ferrite. Our algorithm efficiently estimates the gradients of the desired response with respect to all the designable parameters using only one extra simulation regardless of the number of parameters.

We present a novel FDTD-based adjoint sensitivity analysis approach. Using only one extra FDTD simulation, the sensitivities of the desired objective function with respect to all parameters are estimated regardless of their numbers. Unlike previously published approaches, our technique does not utilize the wave equation and results in a much simple...

We propose an effective approach for optimal wideband cloaking of objects with arbitrary shapes exploiting adjoint sensitivity analysis. Our method optimizes the voxel-by-voxel constitutive parameters of an anisotropic cloak resulting in a large number of optimizable parameters. The associated sensitivities of a wideband cloaking objective function...

In this paper we present a novel nanoantenna (nantenna) design for energy harvesting. The nantenna has an “E” shape and is placed on a SiO2 substrate. Its operation is based on the excitation of surface plasmon polaritons through the gold arms of the E shape. By varying the lengths and widths of the arms, two overlapping working bandwidths can be a...

We present an adjoint-based technique for estimating second-order sensitivities of a generic wideband objective function using the finite-difference time-domain (FDTD) method. Our proposed algorithm estimates both the first- and the second-order sensitivities of the objective function with respect to all considered parameters using at most n+1 extr...

We propose an efficient adjoint variable method (AVM) for estimating wideband second-order response sensitivities using the finite-difference time-domain (FDTD) approach. Our AVM approach reduces the number of required simulations for computing the Hessian matrix of the desired objective function from O(n2) to only n + 1 where n is the number of de...

A novel time-domain adjoint variable method (AVM) algorithm for general 3D anisotropic and inhomogeneous materials based on the transmission line modeling (TLM) is proposed. The developed algorithm enables sensitivity analysis of an arbitrary lossless anisotropic material with possibly non diagonal material tensors. The anisotropic material propert...

We present an adjoint variable method for estimating the sensitivities of arbitrary responses with respect to the parameters of dispersive discontinuities in nanoplasmonic devices. Our theory is formulated in terms of the electric field components at the vicinity of perturbed discontinuities. The adjoint sensitivities are computed using at most one...

We propose a wideband adjoint variable method for sensitivity analysis of dispersive structures utilizing finite difference time domain (FDTD). Using only one extra FDTD simulation, the sensitivities of the desired response are estimated over the frequency band of interest with respect to all the design parameters. The presented theory is based on...

In this paper, we propose a theory for wideband adjoint sensitivity analysis of problems with nonlinear media. We show that the sensitivities of the desired response with respect to all shape and material parameters are obtained through one extra adjoint simulation. Unlike linear problems, the system matrices of this adjoint simulation are time var...

We present, for the first time, an efficient adjoint variable method (AVM) for estimating second-order sensitivities exploiting time-domain transmission-line modeling. For a structure with ${mbi n}$ designable parameters, the complete Hessian matrix of any desired objective function is estimated using ${mbi n}$ extra simulations as compared to $O({...

Nanoplasmonic optical interconnects is proposed to mitigate challenges facing electronics integration. It provides fast and miniaturized data channel that overcome the diffraction limit. We present a three dimensional plasmonic coupler that vertically bends the light to multilevel circuit configurations. It exploits light guiding in nanoscale plasm...

We propose an integrated power divider/combiner at the interface between silicon nanowire and plasmonic slot waveguide (PSW). The proposed configuration facilitates light access and manipulation in planar nano-plasmonic circuits. The light is incident from a standard silicon nanowire to be accessed by a nano-plasmonic circuit providing subwavelengt...

We present a novel technique for vertical coupling of light guided by nanoscale plasmonic slot waveguides (PSWs). A triangularly-shaped plasmonic slot waveguide rotator is exploited to attain such coupling with a good efficiency over a wide bandwidth. Using this approach, light propagating in a horizontal direction is efficiently coupled to propaga...

In this paper, we propose to extend the adjoint variable method (AVM) to the sensitivity analysis of dispersive materials. In the optical range, most common materials are frequency dependent. The complexity of the modeling approaches of these materials delayed the development of simulation-based AVM techniques. We circumvent the mathematical diffic...

This article proposes a new trust region‐based optimization technique for Radio Frequency (RF)/microwave devices. The proposed approach is apt for modeling scenarios, where standard ANN multilayer perceptron (MLP) and Prior Knowledge Input (PKI) models fail to deliver a satisfactory model. This approach feeds output of standard ANN model as knowled...

We propose a wide-band power divider/combiner configuration to facilitate light access and manipulation in planar nano-plasmonic devices. Light is incident from a standard silicon nanowire (negligible propagation losses) to be accessed by a nano-plasmonic circuit providing subwavelength confinement. The structure circumvents the inherent losses ass...

The authors present a new approach for evolutionary antenna design. Through exploiting efficient adjoint sensitivity analysis techniques, the antenna structure evolves to better satisfy the design constraints. The coordinates of a selected number of control vertices are chosen as optimisation parameters thus enabling evolution to arbitrary shapes....

We discuss a novel finite element method-based technique for estimating accurate sensitivities of the desired response. Our technique utilizes the central adjoint variable method (CAVM) for estimating the response sensitivities. This approach features accuracy comparable to that of the central finite difference (CFD) approximation at the response l...

We propose an adjoint variable method (AVM) for efficient wideband sensitivity analysis of the dispersive plasmonic structures. Transmission Line Modeling (TLM) is exploited for calculation of the structure sensitivities. The theory is developed for general dispersive materials modeled by Drude or Lorentz model. Utilizing the dispersive AVM, sensit...

We propose a surface plasmon multilevel coupler based on the orthogonal junction coupling technique between silicon nanowires and plasmonic slot waveguides (PSWs). It couples light of different polarizations from a silicon nanowire into multilevel plasmonic networks. Two orthogonal PSWs are employed to guide each polarization to its respective port...

This paper presents a structural optimization method for microstrip components based on topology optimization method. Topology optimization method optimizes structures via characteristic function that indicates the presence of materials at any point. In the proposed method, microstrips are modeled using an appropriate boundary condition of the util...

We present a memory efficient algorithm for the estimation of adjoint sensitivities with the transmission line modeling (TLM) method. Our algorithm manipulates the local scattering matrices to drastically reduce the required storage for problems with lossy dielectric discontinuities. Only one impulse per cell is stored for two dimensional simulatio...

The increasing complexity of high-frequency electromagnetic (EM) structures motivates research for efficient modeling approaches. There are two main targets for developing such structures. The first is to use these models to optimize the original time-intensive "fine" EM structure. In other words, a "surrogate" model is used as a substitute of the...

Simple and efficient approaches for filter design at optical frequencies using a large number of coupled microcavities are proposed. The design problem is formulated as an optimization problem with a unique global solution. Various efficient filter designs are obtained at both the drop and through ports. Our approaches are illustrated through a num...

We introduce a memory efficient approach for the reduction of the required memory storage in time domain transmission line modeling (TLM)-based adjoint variable method (AVM). The proposed approach is based on manipulating the TLM scattering matrices to remove all redundant calculations. The required memory overhead for our approach is drastically r...

We propose a novel approach for efficient design of large number of coupled microcavities. This approach is based on formulating the design problem as an convex optimization problem. This formulation allows for fast, efficient solution of the desing problem. A filter design using 150 coupled microcavities has been achieved in less than one second o...

We present the first time-domain adjoint variable method (AVM) algorithm for materials with dispersive constitutive parameters. We develop our algorithm based on transmission-line modeling techniques for electromagnetic problems. The developed theory is based on utilizing the $Z$-domain representation of the dispersive materials, which can model ar...

The electromagnetic inverse source problem (ISP) for homogeneous background medium is investigated numerically using the transmission-line matrix (TLM) method. By transforming all electromagnetic sources and fields into their equivalent link impulses within a TLM computational domain, a discrete linear inversion formulation is developed. Our formul...

We present, for the first time, an adjoint variable method (AVM) for wideband sensitivity analysis of dispersive materials. The time domain transmission line modeling technique is exploited to calculate the response and its sensitivities with respect to all the designable parameters using at most one extra simulation. A -domain representation of di...

This paper presents an approach for reducing the size of multi-input multi-output (MIMO) system antennas. In this approach, we minimize the spacing between elements such that both the return loss of each element and the coupling between any two elements are less than -10 dB. To reduce the spacing, the shape of individual antenna elements is allowed...

We present an accurate technique for efficiently estimating the gradient of time-varying responses at each time step. Using only one extra simulation, the sensitivities of a transient field response with respect to all the system parameters are evaluated regardless of their number at all time steps. A step function excitation is used to generate th...

A novel adjoint variable method (AVM) for estimating second-order sensitivities with time-domain TLM is introduced. For a structure with n designable parameters, the complete Hessian matrix is estimated using O(n) extra simulations as compared to O(n2) using traditional finite difference approaches. Our approach is illustrated through estimating th...

Computing the derivatives of the scattering parameters of microwave devices with respect to shape and material parameters is a problem of significant interest in high-frequency computer-aided design. The pioneering work of Bandler, Monaco, Tiberio and others in the late 1960s and the early 1970s brought about the circuit-based sensitivity analysis...

We present a memory efficient implementation of transmission line modeling (TLM)-based adjoint sensitivities. In the original theory, all the transmission line voltage impulses are stored for all the perturbed cells at each time step for both the original and adjoint simulations. This storage can be extensive especially for problems with dielectric...

Over the years, Transmission Line Modeling (TLM) of high frequency structures has seen great advances. The pioneering work of Johns, Hoefer, Vahdlieck, and others have helped in making TLM a robust modeling approach. This paved the way for the most recent developments in TLM-based adjoint sensitivity analysis which is reviewed in this work. We show...

We propose a surface plasmon polarization-controlled beam splitter based on plasmonic slot waveguides (PSWs). It couples light of different polarizations from a silicon nanowire into multilevel plasmonic networks. Two orthogonal PSWs are utilized as the guiding waveguides for each polarization. The proposed structure overcomes inherent polarization...

Over the years, Transmission Line Modeling (TLM) has evolved into a robust numerical modeling technique through the pioneering work of P. B. Johns, Wolfgang Hoefer, and others. Using this technique, the electromagnetic (EM) phenomenon is modeled through the propagation of voltages and currents over a network of transmission lines. We review in this...

The conference program for the 2012 International Microwave Symposium (IMS2012) will include 13 Focus and four Special Sessions. Focus Sessions will include terahertz imaging, unprecedented microwave devices based on nanomaterials, advances in silicon-based millimeter-wave and terahertz integrated circuits and systems, and microwave components for...

The IEEE 2012 International Microwave Symposium (IMS2012), to be held in Montréal, Canada, on June 17-19, 2012, will include various interesting panel sessions and rump sessions. The subjects covered in this year's panels include terahertz-integrated circuits, RF scaling, RF MEMs, LDMOS devices, and MIMO systems. This year's rump session will addre...

We present a memory efficient algorithm for the estimation of adjoint sensitivities with the 2D transmission line modeling (TLM) method. The algorithm is based on manipulating the local scattering matrices to reduce the required storage for the original structure simulation associated with lossy dielectric discontinuities. Only one value per cell i...

We propose a simple and accurate technique for the design optimization of coupled resonator optical waveguides (CROWs). The technique is based on tapering the coupling coefficients at the CROWs stages to achieve arbitrary realizable filter response. A perturbation theory is developed for the linearization of the design problem. The coupling coeffic...

Thesis (Ph. D.)--McMaster University, 2000. Includes bibliographical references (leaves 171-177).

In this work, a computationally efficient antenna modeling technique. Our methodology is a two-stage approach is present. In the first stage, a Cauchy-based approximation model is constructed using coarsely discretized full-wave simulation. The accuracy of this model is improved using a space mapping (SM) approach. A limited number of high-fidelity...

In this article, we introduce an effective approach for dynamic impedance tuning of antenna matching circuits in both the transmitting and receiving modes. The tuning problem is described mathematically by a system of two nonlinear equations. These nonlinear equations are constructed by perturbing the tunable components of the matching circuit. We...

We review work relevant to the area covered by the transmission line matrix (TLM) method, including certain historical TLM developments and design parameter sensitivity analysis for time-domain simulations. We consider exact TLM sensitivity analysis, compare it with the finite difference approach, and demonstrate its use in accelerating design opti...

We present a novel approach for extending the bandwidth of narrow band antennas exploiting geometry evolution. The geometry of the antenna is allowed to evolve subject to constraints on the shape feasibility. The sensitivities of the objective function with respect to the coordinates of a number of control vertices are utilized to determine how the...

We demonstrate the application of the time domain transmission line method (TLM) to accurate modeling of surface plasmon polariton (SPP) structures. The constructed TLM allows for modeling of dispersive materials and perfect absorbing boundaries.

We propose a novel and efficient approach for filter design using multiple microcavities. This approach is suitable of large number of coupled cavities and can be exploited to get wide range of responses.

We propose a procedure for accelerating the space mapping optimization process. Exploiting both fine- and surro- gate-model sensitivity information, a good mapping between the two model spaces is efficiently obtained. This results in a signifi- cant speed-up over direct gradient-based optimization of the orig- inal fine model and enhanced performan...

We present the details and characteristics of graded index multimode mode interference (GIMMI) and its applications in optical communication components. This structure has unique features that allow for less sensitive wavelength dependant than the step Index case. This feature allows for wideband applications. In this paper, we present the applicat...

The Characterization of the material optical properties with terahertz time domain spectroscopy is usually formulated as an optimization problem with an objective function representing the deviation of the theoretical scattering parameters from the measured ones. Both the magnitude and phase of the scattering parameters are utilized. For samples of...

Direct nanobonding of p-Si/n-GaAs wafers based on surface activation that uses an Argon (Ar)-fast atom beam at room temperature has been investigated. The bonding strength of the interface was 14.4 MPa at room temperature, and remained nearly constant after annealing up to 600 °C. An amorphous layer with a thickness of 11.5 nm was found across the...

Computationally efficient simulation-driven design of ultra-wideband planar antennas is presented using Cauchy-based surrogate models of the coarsely-discretized antenna electromagnetic models.Verification of the proposed methodology is performed with satisfactory designs obtained at a computational cost of a few evaluations of high-fidelity antenn...