Publications
150 results found
Wang J, Serb A, Papavassiliou C, et al., 2021, Analysing and measuring the performance of memristive integrating amplifiers, INTERNATIONAL JOURNAL OF CIRCUIT THEORY AND APPLICATIONS, Vol: 49, Pages: 3507-3525, ISSN: 0098-9886
Wang J, Serb A, Papavassiliou C, et al., 2021, Accounting for Memristor I-V Non-Linearity in Low Power Memristive Amplifiers, 2021 IEEE International Symposium on Circuits and Systems (ISCAS), Publisher: IEEE
Maheshwari S, Serb A, Papavassiliou C, et al., 2021, An Adiabatic Regenerative Capacitive Artificial Neuron, 2021 IEEE International Symposium on Circuits and Systems (ISCAS), Publisher: IEEE
Shen J, Stathopoulos S, Prodromakis T, et al., 2021, A reconfigurable CMOS-memristor active inductor, ISCAS 2020, ISSN: 0271-4310
A methodology is introduced here to exploit the programmability of the memristors in order to realize reconfigurable monolithic analogue circuit elements. Classical network synthesis methods are used to synthesize adjustable active inductors with inductance values exceeding those of on-chip passives by several orders of magnitude. In this paper, a wide range of active inductance values are obtained by employing memristor to control the biasing current of operational transconductance amplifiers used to implement gyrators. The gyration constant of the proposed gyrator will be linearly controlled by memristance state. The implementation of the designed circuit is realized in 0.18µm commercially available complementary metal-oxide-semiconductor (CMOS) technology from TSMC. Circuit performance is simulated using Cadence Virtuoso. The utilized off-chip memristor is a metal-oxide bi-layer memristor which exhibits a non-volatile memristance range of 4.7kΩ to 170kΩ. The active inductance range achieved is from approximately 95µH to 1.55mH with an inductive bandwidth of 69MHz and 18MHz respectively. The total power consumption is between 0.21mW to 1.95mW depending on the memristance and equivalent inductance.
Wang C, Xie L, Jiang X, et al., 2021, Design of a Multi-State Memristive Memory, 28th IEEE International Conference on Electronics, Circuits, and Systems (IEEE ICECS), Publisher: IEEE
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Malik A, Papavassiliou C, Stathopoulos S, 2021, A Stochastic Compact Model Describing Memristor Plasticity and Volatility, 28th IEEE International Conference on Electronics, Circuits, and Systems (IEEE ICECS), Publisher: IEEE
Foster P, Huang J, Serb A, et al., 2020, An FPGA based system for interfacing with crossbar arrays, IEEE International Symposium on Circuits and Systems (ISCAS), Publisher: IEEE, ISSN: 0271-4302
Foster P, Huang J, Serb A, et al., 2020, Live Demonstration: Electroforming of TiO2-x memristor devices using high speed pulses, IEEE International Symposium on Circuits and Systems (ISCAS), Publisher: IEEE, ISSN: 0271-4302
Szypicyn J, Papavassiliou C, Papandroulidakis G, et al., 2020, Memristor-Enabled Reconfigurable Integrated Circuits, 19th International Conference on Electronics, Information, and Communication (ICEIC), Publisher: IEEE
Fobelets K, Thielemans K, Mathivanan A, et al., 2019, Characterization of nnitted coils for e-textiles, IEEE Sensors Journal, Vol: 19, Pages: 7835-7840, ISSN: 1530-437X
Inductor coils are integrated in many wearable garments for EM wave screening, heating and health monitoring. This paper presents a critical evaluation of the inductor characteristics of circular weft knitted coils for applications in e-textiles. Inductors are knitted using circular needles with thin insulated metal wire and yarn knitted together. The resulting helical coils are characterized as a function of number of turns, coil diameter, needle size, and insulated metal wire material. The results are compared to wound coils. Simulations of the knitted and wound coils show close agreement with the experimental results and confirm a higher inductance for the knits compared to the wound coils with the same pitch between turns. The parasitic coil capacitance is higher in the knit due to the vertical legs of the stitches, absent in wound coils. Knits with thin Cu and Litz wires result in flexible and wearable textile coils.
Zhang L, Zhang L, Liu S, et al., 2019, Low-level control technology of micro autonomous underwater vehicle based on intelligent computing, CLUSTER COMPUTING-THE JOURNAL OF NETWORKS SOFTWARE TOOLS AND APPLICATIONS, Vol: 22, Pages: S8569-S8580, ISSN: 1386-7857
Lanyong Z, Lei Z, Bing L, et al., 2018, High-frequency modeling of common-mode chokes based on the identification of frequency-varying parameters, Pages: 779-784
To overcome the disadvantage of impedance measurement which is influenced by parasitic parameters and non-ideal characters of conductor lines as well as cannot perform the frequency-varying parameters. This paper presents a high-frequency modeling method of common-mode chokes based on frequency-varying parameters. A high-frequency lumped parameter model was built, which included winding inductances, leakage inductances, parasitic capacitances between and in the windings, equivalent resistances of magnetic cores and copper losses. Using traditional least-square method, the forgetting factor and rectangular window was introduced to estimate the frequency-varying parameters. The mean square convergence of this method is proved. The modeling method proposed in this paper is proven accurately by comparing the experimental result with simulation result between 150 kHz - 30 MHz. The restraining effects are best at the resonance frequency of the common-mode choke. In addition, an experiment is conducted to verify the conclusion by restraining the electromagnetic interference produced by a switching circuit.
Zhang L, Zhang L, Papavassiliou C, et al., 2018, Intelligent Computing for Extended Kalman Filtering SOC Algorithm of Lithium-Ion Battery, WIRELESS PERSONAL COMMUNICATIONS, Vol: 102, Pages: 2063-2076, ISSN: 0929-6212
Zhang L, Liu Z, Papavassiliou C, et al., 2018, Formation path control method for group coordination based on fuzzy logic control method, CLUSTER COMPUTING-THE JOURNAL OF NETWORKS SOFTWARE TOOLS AND APPLICATIONS, Vol: 21, Pages: 855-868, ISSN: 1386-7857
Zhang L, Zhang L, Wang B, et al., 2018, Hybrid Prediction Method for the Electromagnetic Interference Characteristics of Printed Circuit Boards Based on the Equivalent Dipole Model and the Finite-Difference Time Domain Method, IEEE ACCESS, Vol: 6, Pages: 6520-6529, ISSN: 2169-3536
In this paper, we propose a hybrid modeling method for analyzing the electromagnetic compatibility characteristics of printed circuit boards (PCBs). The method uses an equivalent magnetic dipole array deduced from near-field scanning results obtained at a certain height over the PCB surface under test and the finite-difference time domain (FDTD) algorithm. The array of dipoles can simulate the PCB electromagnetic emissions, including the ground plane effect at a particular high frequency; the equivalent dipole array can then be imported into the FDTD calculation space for calculating the electromagnetic fields generated by the dipole array. In our experiment, we obtained the tangential magnetic field distribution of the PCB surface using near-field scanning, from where the tangential magnetic field component, orientation, and the magnitude and phase of the dipoles could be deduced. We used the proposed method to model two different modules on a highly integrated circuit. The results of the proposed method and those obtained by near-field scanning are nearly the same, which demonstrates the effectiveness and accuracy of the proposed method. We therefore conclude that the proposed modeling approach presents a new technique for studying the electromagnetic interference of PCBs.
von Rosenberg W, Chanwimalueang T, Goverdovsky V, et al., 2017, Hearables: feasibility of recording cardiac rhythms from head and in-ear locations, Royal Society Open Science, Vol: 4, ISSN: 2054-5703
Mobile technologies for the recording of vital signs and neural signals are envisaged to underpin the operation of future health services. For practical purposes, unobtrusive devices are favoured, such as those embedded in a helmet or incorporated onto an earplug. However, these locations have so far been underexplored, as the comparably narrow neck impedes the propagation of vital signals from the torso to the head surface. To establish the principles behind electrocardiogram (ECG) recordings from head and ear locations, we first introduce a realistic three-dimensional biophysics model for the propagation of cardiac electric potentials to the head surface, which demonstrates the feasibility of head-ECG recordings. Next, the proposed biophysics propagation model is verified over comprehensive real-world experiments based on head- and in-ear-ECG measurements. It is shown both that the proposed model is an excellent match for the recordings, and that the quality of head- and ear-ECG is sufficient for a reliable identification of the timing and shape of the characteristic P-, Q-, R-, S- and T-waves within the cardiac cycle. This opens up a range of new possibilities in the identification and management of heart conditions, such as myocardial infarction and atrial fibrillation, based on 24/7 continuous in-ear measurements. The study therefore paves the way for the incorporation of the cardiac modality into future ‘hearables’, unobtrusive devices for health monitoring.
Zhang L, Zhang L, Liu S, et al., 2017, Three-Dimensional Underwater Path Planning Based on Modified Wolf Pack Algorithm, IEEE ACCESS, Vol: 5, Pages: 22783-22795, ISSN: 2169-3536
Goverdovsky V, von Rosenberg W, Nakamura T, et al., 2017, Hearables: multimodal physiological in-ear sensing, Scientific Reports, Vol: 7, ISSN: 2045-2322
Future health systems require the means to assess and track the neural and physiological function of a user over long periods of time, and in the community. Human body responses are manifested through multiple, interacting modalities – the mechanical, electrical and chemical; yet, current physiological monitors (e.g. actigraphy, heart rate) largely lack in cross-modal ability, are inconvenient and/or stigmatizing. We address these challenges through an inconspicuous earpiece, which benefits from the relatively stable position of the ear canal with respect to vital organs. Equipped with miniature multimodal sensors, it robustly measures the brain, cardiac and respiratory functions. Comprehensive experiments validate each modality within the proposed earpiece, while its potential in wearable health monitoring is illustrated through case studies spanning these three functions. We further demonstrate how combining data from multiple sensors within such an integrated wearable device improves both the accuracy of measurements and the ability to deal with artifacts in real-world scenarios.
Zhang L, Chen H, Liu S, et al., 2017, On-line compressed sensing method and its application in magnetic flux leakage detection, Yi Qi Yi Biao Xue Bao/Chinese Journal of Scientific Instrument, Vol: 38, Pages: 1597-1605, ISSN: 0254-3087
In this dissertation, taking the magnetic flux leakage (MFL) detection system for long-distance oil pipeline as study object, the online compression algorithm of magnetic flux leakage detection data is studied. Aiming at the problem that traditional data compression method is difficult to apply in the embedded online work environment, compressed sensing (CS) theory is introduced and an online CS compression method for MFL detection data is proposed. The wavelet base is determined as the best sparse representation base of the magnetic flux leakage signal, and the mathematical expression of the wavelet sparse base matrix is derived; A measurement matrix optimization algorithm based on Welch bound and PRP conjugate gradient algorithm is proposed; An important data segment screening method of the MFL detection data is proposed, which greatly reduces the data storage size. The simulation results show that the proposed online compression algorithm greatly reduces the computation complexity of compression encoding in online environment, has the advantages of simple and rapid operation, high compression ratio, high reconstruction precision and etc., and meets the actual requirements of MFL detection data online compression.
Seimeni MA, Tsivgoulis GI, Gkonis PK, et al., 2017, On the performance evaluation of two novel fractional frequency reuse approaches for OFDMA multi-user multi-cellular networks, Pages: 88-91
The paper studies two resource allocation strategies (GRID, anti-EMI) for multi-user OFDMA systems. These strategies are evaluated after being compared with the Round Robin and the FFR strategy in terms of mean throughput and mean dissipated power. All investigated strategies assign resources without Channel State Information (CSI), while both GRID and anti-EMI inherently combat Co-Channel Interference (CCI); hence they enhance mean throughput. Simulations indicate that GRID outperforms Round Robin and FFR in all scenarios into consideration and competes the anti-EMI strategy in various network orientations. The latter is justified especially for highly populated scenarios (i.e. 50% probability failure and 2 subcarriers per MT). As for the FFR strategy, simulations verify that the spectral efficiency is not the optimum, which fact has been already verified in the respective literature as well. Finally, the platform can inherently spare around the 70% of the maximum available power.
Serb A, Papavassiliou C, Prodromakis T, 2017, A memristor-CMOS hybrid architecture concept for on-line template matching, IEEE International Symposium on Circuits and Systems (ISCAS), Publisher: IEEE, Pages: 2651-2654, ISSN: 0271-4302
Serb A, Redman-White W, Papavassiliou C, et al., 2016, Practical determination of individual element resistive states in selectorless RRAM arrays, IEEE Transactions on Circuits and Systems Part 1: Regular Papers, Vol: 63, Pages: 827-835, ISSN: 1549-8328
Three distinct methods of reading multi-level cross-point resistive states from selector-less RRAM arrays are implemented in a physical system and compared for read-out accuracy. They are: the standard, direct measurement method and two methods that attempt to enhance accuracy by computing cross-point resistance on the basis of multiple measurements. Results indicate that the standard method performs as well as or better than its competitors. SPICE simulations are then performed with controlled amounts of non-idealities introduced in the system in order to test whether any technique offers particular resilience against typical practical imperfections such as crossbar line resistance. We conclude that even though certain non-idealities are shown to be minimized by different circuit-level read-out strategies, line resistance within the crossbar remains an outstanding challenge.
Berdan R, papavassiliou C, Khiat A, et al., 2016, Live demonstration: characterization of RRAM crossbar arrays at a click of a button, 2016 IEEE International Symposium on Circuits and Systems (ISCAS), Publisher: IEEE, Pages: 1443-1443
We demonstrate a desktop platform which has the ability of fully characterizing RRAM crossbar arrays while not compromising on ease-of-use. The setup consists of our bespoke PCB system connected to a local PC (laptop), on which a Pyhton interface allows the user to directly interact with individual RRAM cells packaged in either crossbar or stand-alone configurations. The platform is capable of current-compliant forming among other exotic pulsing schemes, used for exposing IV and switching characteristics or utilising the devices for a wide range of applications. These operations can be applied on one, or several cells, in an automated fashion, drastically accelerating data acquisition.
Seimeni MA, Gkonis PK, Kaklamiani DI, et al., 2016, Resource management in OFDMA heterogeneous network, 2016 Wireless Telecommunications Symposium (WTS), Publisher: IEEE
In this study, a Long Term Evolution Advanced (LTEa) ??? based multi-user Orthogonal Frequency Division Multiple Access (OFDMA) heterogeneous network has been simulated and a resource allocation strategy has been proposed. The strategy under consideration can inherently mitigate electromagnetic interference, hence increases the mean number of terminals, and requires no channel state information (CSI). To evaluate the performance of the network platform and the proposed strategy, the system is studied for different network orientations. According to the results, the platform is a good reality simulator, whereas owning to the proposed Radio Resource Management (RRM) algorithm the mean capacity can reach a 12-fold increase especially for highly noisy operating environments.
Goverdovsky V, Yates DC, Willerton M, et al., 2016, Modular Software-Defined Radio Testbed for Rapid Prototyping of Localization Algorithms, IEEE Transactions on Instrumentation and Measurement, Vol: 65, Pages: 1577-1584, ISSN: 1557-9662
A fully synchronized modular multichannel software-defined radio (SDR) testbed has been developed for the rapid prototyping and evaluation of array processing algorithms. Based on multiple universal software radio peripherals, this testbed is low cost, wideband, and highly reconfigurable. The testbed can be used to develop new techniques and algorithms in a variety of areas including, but not limited to, direction finding, source triangulation, and wireless sensor networks. A combination of hardware and software techniques is presented, which is shown to successfully remove the inherent phase and frequency uncertainties that exist between the individual SDR peripherals. The adequacy of the developed techniques is demonstrated through the application of the testbed to super-resolution direction finding algorithms, which rely on accurate phase synchronization.
Zhang L, Cao A, Papavassiliou C, et al., 2016, A novel hybrid PWM for multilevel converter, Journal of Computational and Theoretical Nanoscience, Vol: 13, Pages: 1985-1991, ISSN: 1546-1955
In this paper, we proposed a novel hybrid PWM technique for cascaded H-bridge multilevel converter. This technique is based on combining CD-PWM and PS-PWM techniques by replacing a single triangular carrier of PS-PWM with several little triangular carriers distributed vertically as the PD-PWM technique. The performance comparison of PS-PWM, CD-PWM, traditional hybrid PWM and the proposed technique is presented for a 5-level CHB multilevel inverter with the same device switching frequency. In order to demonstrate the generalizability of this technique, we did the same simulation experiment in the 7-level cascaded multilevel converter. The results show that compared with other techniques the proposed technique not only has an overall smaller total harmonic distortion (THD) of line voltage and line current, especially in the low modulation index, but also has larger fundamental amplitude within whole range of the modulation ratio. In addition, the advantage of this technique for 7-level cascaded multilevel converter is not changed. Simulation experimental results prove the harmonic performance of the novel hybrid PWM technique is better and the dc-link voltage utilization has a significant improvement than other techniques. The novel hybrid PWM technique also can be used for different level cascaded multilevel converter with the same performance.
Seimeni MA, Gkonis PK, Kaklamani DI, et al., 2015, Resource exploitation in multi-carrier multi-cellular networks
The purpose of this paper is to examine the algorithmic quality of a semi-Random subcarrier allocation strategy and a Block Anti-Jamming Subcarrier Scavenging (BAJSS) strategy in terms of mean capacity, mean Bit Error Rate (BER), complexity as well as Jain's fairness index (power, capacity). These strategies are implemented in a LTE OFDMA multicellular network platform, which executes a fixed, sufficient for convergence, Monte Carlo (MC) runs. Both strategies are based on anti-jamming criteria so as to further mitigate Intra-Channel Interference (ICI). According to the results, semiRandom outperforms BAJSS and the traditional random strategy in terms of mean capacity, mean BER and power dissipation at the cost however of increased computational complexity.
Seimeni MA, Gkonis PK, Kaklamani DI, et al., 2015, Orchestration of multicellular heterogeneous networks, resources management, and electromagnetic interference mitigation techniques, ICT Express, Vol: 1, Pages: 110-115
The primary goal of this study is to develop a simulation platform that ensures a synergy between WiMAX and WiFi at the PHY and MAC layers, manages the available resources efficiently, mitigates electromagnetic interference (EMI), and enhances the overall performance of heterogeneous networks. To achieve this synergy, the OFDMA physical layer protocol is implemented and combined with radio resource exploitation strategies and judicious power allocation to users. The COOPERATIVE subcarrier allocation strategy outperforms the RANDOM strategy in terms of mean capacity and EMI mitigation, because it efficiently manages radio resources and inherently combats CCI (hence, EMI is mitigated). Results also show that in real scenarios (low SINRWiFi), the synergy between WiMAX and WiFi leads to a high mean capacity (and in some cases, a 15-fold increase). In terms of power levels, the dissipation by a user corresponds to less than 23% of the total available power (1 W).
Seimeni MA, Gkonis PK, Kaklamani DI, et al., 2015, On BER evaluation of a Regional Anti-Jamming Subcarrier strategy for MIMO-OFDMA systems
The goal of the present study is to evaluate the Bit Error Rate (BER) of a MIMO-OFDMA multicellular network, when the Regional Anti-Jamming Subcarrier Scavenging (RAJSS) strategy is employed. Throughput and power consumption per mobile terminal (MT) are provided as output metrics, and compared to other subcarrier allocation strategies. The system platform, which is compatible with all studied strategies, carries out a sufficient number of independent Monte Carlo (MC) simulations for different network orientations. Each MC comprises two stages. In the first stage, base stations (BSs) assign their available subcarriers to the MTs without any Channel State Information (CSI), and in the last stage the MTs try to fully recover the transmitted signal. Results indicate that the RAJSS strategy outperforms the other studied strategies, in terms of BER-Throughput gain and algorithmic fairness. However, algorithmic complexity of the RAJSS algorithm is increased; hence in low Signal to Noise (SNR) scenarios simulations time span is apparently high. RAJSS is, finally, compared to a strategy which assigns to the terminals the subcarriers which show the best quality (highest SNR). To do so, CSI is considered. In this case and in some scenarios, RAJSS algorithm has improved performance.
Berdan R, Serb A, Khiat A, et al., 2015, A mu-controller-based system for interfacing selectorless RRAM crossbar arrays, IEEE Transactions on Electron Devices, Vol: 62, Pages: 2190-2196, ISSN: 0018-9383
Selectorless crossbar arrays of resistive randomaccess memory (RRAM), also known as memristors, conduct large sneak currents during operation, which can significantly corrupt the accuracy of cross-point analog resistance (M t ) measurements. In order to mitigate this issue, we have designed, built, and tested a memristor characterization and testing (mCAT) instrument that forces redistribution of sneak currents within the crossbar array, dramatically increasing M t measurement accuracy. We calibrated the mCAT using a custom-made 32 × 32 discrete resistive crossbar array, and subsequently demonstrated its functionality on solid-state TiO 2-x RRAM arrays, on wafer and packaged, of the same size. Our platform can measure standalone M t in the range of 1 kΩ to 1 MΩ with <;1% error. For our custom resistive crossbar, 90% of devices of the same resistance range were measured with <;10% error. The platform's limitations have been quantified using large-scale nonideal crossbar simulations.
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