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    Inverse design of compact power divider with arbitrary outputs for 5G applications

    , Article Scientific Reports ; Volume 12, Issue 1 , 2022 ; 20452322 (ISSN) Shadi, M ; Tavakol, M. R ; Atlasbaf, Z ; Sharif University of Technology
    Nature Research  2022
    Abstract
    Since the recent on-demand applications need more sophisticated circuits and subsystems, components with configurable capabilities attract attention more than before in commercial systems, specifically the fifth generation (5G). Power dividers play a crucial role in 5G phased array systems, and their role becomes more significant if the output powers ratio is adjustable. Here, we suggest a design methodology by which planar power splitters with arbitrary output power levels can be designed in light of very simple perturbations, i.e., vias. Through our design procedure, we find an optimized pattern for hybrid vias-some of them are made of PEC, and others are dielectric, e.g., air,... 

    Foveated scanning: Dynamic monodimensional enlargement of resolved field of view in lenses of scanner systems

    , Article Applied Optics ; Volume 55, Issue 26 , 2016 , Pages 7314-7323 ; 1559128X (ISSN) Javaherian, F ; Rashidian, B ; Sharif University of Technology
    OSA - The Optical Society 
    Abstract
    An inconsistency between the circular symmetric geometry of conventional optical imagers and the geometry of long linear sensors used in today's line-scan cameras results in suboptimal separate design of optics and electronics of scanner systems. Based on the method of foveated optical imaging, a technique named foveated scanning (FS) is proposed in this paper. The FS technique is employed to enlarge the one-dimensional resolved field of view (RFOV) of conventional lenses and permits optimized performance on a line-of-interest in the image plane where the optoelectronic sensor is located. The achieved enlargement of RFOV is verified on a proof-of-concept basic telephoto lens. Both modulation... 

    Fine-grained access control for hybrid mobile applications in Android using restricted paths

    , Article 13th International ISC Conference on Information Security and Cryptology, 7 September 2016 through 8 September 2016 ; 2016 , Pages 85-90 ; 9781509039494 (ISBN) Pooryousef, S ; Amini, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc 
    Abstract
    Hybrid Mobile Applications are a new generation of mobile applications that have recently introduced new security challenges. In these applications, untrusted web content, such as an advertisement inside an embedded browser, has the same privileges as the entire application and can directly access the device resources. Unfortunately, existing access control mechanisms are very coarse-grained and do not provide adequate facilities for fine-grained access rule definition and enforcement in hybrid mobile applications. In this paper, we propose a fine-grained access control mechanism for privilege separation in hybrid mobile applications. Our proposed access control mechanism, called... 

    Reciprocal metasurfaces for on-axis reflective optical computing

    , Article IEEE Transactions on Antennas and Propagation ; Volume 69, Issue 11 , 2021 , Pages 7709-7719 ; 0018926X (ISSN) Momeni, A ; Rajabalipanah, H ; Rahmanzadeh, M ; Abdolali, A ; Achouri, K ; Asadchy, V. S ; Fleury, R ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2021
    Abstract
    Analog computing has emerged as a promising candidate for real-time and parallel continuous data processing. This article presents a reciprocal way for realizing asymmetric optical transfer functions (OTFs) in the reflection side of the on-axis processing channels. It is rigorously demonstrated that the presence of cross-polarization exciting normal polarizabilities (CPENPs) of a reciprocal metasurface circumvents the famous challenge of Green's function approach in implementation of on-axis reflective optical signal processing while providing dual computing channels under orthogonal polarizations. Following a comprehensive theoretical discussion and as a proof of concept, an all-dielectric... 

    A 10-W X-Band class-f high-power amplifier in a 0.25-μm GaAs pHEMT technology

    , Article IEEE Transactions on Microwave Theory and Techniques ; Volume 69, Issue 1 , 2021 , Pages 157-169 ; 00189480 (ISSN) Alizadeh, A ; Yaghoobi, M ; Meghdadi, M ; Medi, A ; Kiaei, S ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2021
    Abstract
    In this article, a design methodology is presented to realize integrated class-F high-power amplifiers (HPAs). A harmonic-control network (HCN) is proposed to present short- and open-circuit impedances to each transistor employed in the output stage of the HPA at {2}f {0} and {3}f {0} frequencies. The HCN absorbs the parasitic capacitance of the transistor and lends itself to be absorbed in the matching and power combiner networks, reducing the die area of the HPA. A proof-of-concept 9.7-10.3-GHz class-F HPA was designed and implemented in a 0.25- μ ext{m} GaAs pHEMT technology with V {DD} of 6 V. The designed HPA consists of two amplifying stages, and its output stage includes 16... 

    A 10-W X-band class-F high-power amplifier in a 0.25-μm GaAs pHEMT technology

    , Article IEEE Transactions on Microwave Theory and Techniques ; Volume 69, Issue 1 , 2021 , Pages 157-169 ; 00189480 (ISSN) Alizadeh, A ; Yaghoobi, M ; Meghdadi, M ; Medi, A ; Kiaei, S ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2021
    Abstract
    In this article, a design methodology is presented to realize integrated class-F high-power amplifiers (HPAs). A harmonic-control network (HCN) is proposed to present short- and open-circuit impedances to each transistor employed in the output stage of the HPA at {2}f {0} and {3}f {0} frequencies. The HCN absorbs the parasitic capacitance of the transistor and lends itself to be absorbed in the matching and power combiner networks, reducing the die area of the HPA. A proof-of-concept 9.7-10.3-GHz class-F HPA was designed and implemented in a 0.25- μ ext{m} GaAs pHEMT technology with V {DD} of 6 V. The designed HPA consists of two amplifying stages, and its output stage includes 16... 

    Investigation of a class-j mode power amplifier in presence of a second-harmonic voltage at the gate node of the transistor

    , Article IEEE Transactions on Microwave Theory and Techniques ; Volume 65, Issue 8 , 2017 , Pages 3024-3033 ; 00189480 (ISSN) Alizadeh, A ; Medi, A ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2017
    Abstract
    In this paper, performance of class-J mode power amplifiers (PAs) is studied when a second-harmonic voltage component is added to the input node of the device. Theoretical formulations for the optimum load impedances, output power, and drain efficiency are developed for this case, and it is shown that the inclusion of a proper second-harmonic voltage at the gate node of the transistor improves the drain efficiency and output power. To check the accuracy of the theoretical analyses and the simulation results, a proof-of-concept 1-GHz 0.65-W class-J PA is fabricated in a 0.25-μm AlGaAs-InGaAs pHEMT technology. The nonlinear gate-source capacitor (CGS) of the transistor is employed to generate... 

    Dual-band design of integrated class-J power amplifiers in gaAs pHEMT technology

    , Article IEEE Transactions on Microwave Theory and Techniques ; Volume 65, Issue 8 , 2017 , Pages 3034-3045 ; 00189480 (ISSN) Alizadeh, A ; Frounchi, M ; Medi, A ; Sharif University of Technology
    Abstract
    This paper presents two integrated concurrent dual-band class-J power amplifiers (PAs) in AlGaAs-InGaAs pHEMT technology. Design flexibility of class-J space is employed to explore the availability of a dual-band PA where the center frequency of the second band is twice the center frequency of the first band (f2=2f1). The theoretical formulations are developed for f2=2f1 case, for which it is not feasible to obtain high efficiencies using class-F-1, class-F, and other high-efficiency modes. A proof of concept 5/10-GHz class-J PA is manufactured in a 0.1- μm GaAs pHEMT technology. The proposed PA delivers 26.9- and 26-dBm output power with peak power added efficiencies (PAEs) of 49% and 46%... 

    Class-J2 Power Amplifiers

    , Article IEEE Transactions on Circuits and Systems I: Regular Papers ; Volume 64, Issue 8 , 2017 , Pages 1989-2002 ; 15498328 (ISSN) Alizadeh, A ; Yaghoobi, M ; Medi, A ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2017
    Abstract
    This paper presents the theoretical introduction and experimental validation of the "Class-J2 Mode Power Amplifier," which provides higher efficiency and output power compared with conventional class-J mode counterpart. This mode of operation is realized by injection of the second-harmonic current to drain node of a class-J power amplifier (PA) to reduce the 45° phase shift between drain current and voltage signals. Similar to class-J PAs, the second-harmonic impedance of class-J2 PAs is purely reactive to simplify the design of the output matching network. The auxiliary second-harmonic injection circuit comprises a transistor biased in class-B mode followed by a class-C biased amplifier to... 

    Waveform engineering at gate node of class-j power amplifiers

    , Article IEEE Transactions on Microwave Theory and Techniques ; Volume 65, Issue 7 , 2017 , Pages 2409-2417 ; 00189480 (ISSN) Alizadeh, A ; Frounchi, M ; Medi, A ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2017
    Abstract
    In this paper, the class-J mode of operation is investigated when sinusoidal, half-sinusoidal (HS), triangle, pulse, and reduced conduction angle voltage waveforms are shaped at the gate node of the transistor. Output power, maximum power-added efficiency (PAE), large signal gain (LSG), and load-pull contours are presented and compared for each input signal. It is shown that PAE of a class-J power amplifier (PA) is improved when an HS voltage is realized at the gate node of the transistor. This enhancement can also be observed for a pulse input with 20% duty cycle, however, at the expense of reduced output power and LSG. A proof-of-concept, two-stage class-J PA is designed and fabricated in... 

    Integrated output matching networks for class-J/J-1 power amplifiers

    , Article IEEE Transactions on Circuits and Systems I: Regular Papers ; Volume 66, Issue 8 , 2019 , Pages 2921-2934 ; 15498328 (ISSN) Alizadeh, A ; Hassanzadehyamchi, S ; Medi, A ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2019
    Abstract
    In this paper, two output matching networks (OMNs) are proposed for integrated class-J and class-J-1 mode power amplifiers (PAs). The first MN provides the required load impedances of the class-J mode (i.e., Z(f0) = Ropt + j Ropt and Z(2 f0) = -j (3π/8)Ropt), where as the second MN realizes the optimal impedances of class-J-1 PAs (i.e., Z(f0) = Ropt - j Ropt and Z(2 f0) = j (3π/8)Ropt ). Detailed theoretical analyses are presented for each MN, and the values of matching components (i.e., inductors and capacitors) are obtained in terms of Ropt. Analytical derivations are verified by simulation results, while bandwidth and loss performances of each MN are also characterized. Two... 

    An X-Band Class-J Power Amplifier with Active Load Modulation to Boost Drain Efficiency

    , Article IEEE Transactions on Circuits and Systems I: Regular Papers ; Volume 67, Issue 10 , 2020 , Pages 3364-3377 Alizadeh, A ; Hassanzadehyamchi, S ; Medi, A ; Kiaei, S ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2020
    Abstract
    In this paper, the performance of the class-J mode power amplifier (PA) is studied when an auxiliary network performs active load modulation on the main transistor. Load modulation is realized by injecting an additional class-C like current with conduction angle of $alpha $ to the drain node of the main transistor. The injected current employs a phase shift of $phi $ with respect to the half-sinusoidal current of the main transistor, and its maximum value is tuned with the size of the transistor used in the auxiliary network. Detailed theoretical formulations are presented for the optimal load impedances of the PA at the fundamental and second-harmonic frequencies. Furthermore, the output... 

    A 10-W X-Band Class-F High-Power Amplifier in a 0.25-μm GaAs pHEMT Technology

    , Article IEEE Transactions on Microwave Theory and Techniques ; 2020 Alizadeh, A ; Yaghoobi, M ; Meghdadi, M ; Medi, A ; Kiaei, S ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2020
    Abstract
    In this article, a design methodology is presented to realize integrated class-F high-power amplifiers (HPAs). A harmonic-control network (HCN) is proposed to present short- and open-circuit impedances to each transistor employed in the output stage of the HPA at 2f_0 and 3f_0 frequencies. The HCN absorbs the parasitic capacitance of the transistor and lends itself to be absorbed in the matching and power combiner networks, reducing the die area of the HPA. A proof-of-concept 9.7-10.3-GHz class-F HPA was designed and implemented in a 0.25-μm GaAs pHEMT technology with VDD of 6 V. The designed HPA consists of two amplifying stages, and its output stage includes 16 transistors in parallel to... 

    Performance analysis of EEG seizure detection features

    , Article Epilepsy Research ; Volume 167 , 2020 Niknazar, H ; Mousavi, S. R ; Niknazar, M ; Mardanlou, V ; Coelho, B. N ; Sharif University of Technology
    Elsevier B.V  2020
    Abstract
    Automatic detection of epileptic seizures can serve as a valuable clinical tool which involves a more objective and computationally efficient method for the analysis of EEG data in order to generate increasingly accurate and reliable results. Automatic seizure detection is also an important component of closed-loop responsive cortical stimulation systems. The goal of this study is to evaluate EEG-based features recently proposed for seizure detection to discover the optimum ones for a reliable seizure detection system. We extracted seizure detection features from intracranial EEG signals that were recorded during invasive pre-surgical epilepsy monitoring of people with drug resistant focal... 

    3D Bioprinting of oxygenated cell-laden gelatin methacryloyl constructs

    , Article Advanced Healthcare Materials ; Volume 9, Issue 15 , 2020 Erdem, A ; Darabi, M. A ; Nasiri, R ; Sangabathuni, S ; Ertas, Y. N ; Alem, H ; Hosseini, V ; Shamloo, A ; Nasr, A. S ; Ahadian, S ; Dokmeci, M. R ; Khademhosseini, A ; Ashammakhi, N ; Sharif University of Technology
    Wiley-VCH Verlag  2020
    Abstract
    Cell survival during the early stages of transplantation and before new blood vessels formation is a major challenge in translational applications of 3D bioprinted tissues. Supplementing oxygen (O2) to transplanted cells via an O2 generating source such as calcium peroxide (CPO) is an attractive approach to ensure cell viability. Calcium peroxide also produces calcium hydroxide that reduces the viscosity of bioinks, which is a limiting factor for bioprinting. Therefore, adapting this solution into 3D bioprinting is of significant importance. In this study, a gelatin methacryloyl (GelMA) bioink that is optimized in terms of pH and viscosity is developed. The improved rheological properties... 

    A distributed topology control algorithm for P2P based simulations

    , Article 11th IEEE International Symposium on Distributed Simulation and Real-Time Applications, DS-RT 2007, Chania, 22 October 2007 through 24 October 2007 ; November , 2007 , Pages 68-71 ; 15506525 (ISSN); 0769530117 (ISBN); 9780769530116 (ISBN) Hariri, B ; Shirmohammadi, S ; Pakravan, M. R ; Sharif University of Technology
    2007
    Abstract
    Although collaborative distributed simulations and virtual environments (VE) have been an active area of research in the past few years, they have recently gained even more attention due to the emergence of online gaming, emergency simulation and planning systems, and disaster management applications. Such environments combine graphics, haptics, animations and networking to create interactive multimodal worlds that allows participants to collaborate in real-time. Massively Multiplayer Online Gaming (MMOG), perhaps the most widely deployed practical application of distributed virtual environments, allows players to act together concurrently in a virtual world over the Internet. IP...