Tyndall National Institute - Journal Articles

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    Polaron assisted hopping mechanism in microwave processed Nd doped second layered aurivillius SrBi2Nb2O9 ceramics
    (Elsevier B.V., 2024-10-17) Pritam, Anurag; Irish Research Council; Shiv Nadar Foundation
    The polycrystalline Sr0.8Sn0.2Bi1.75Nd0.25Nb2O9 (NdSBN) was synthesized using the green synthesis microwave sintering method, which significantly reduced the processing parameters of the NdSBN ceramics. Orthorhombic crystal structure with A21am symmetry was revealed by Rietveld refinement study, whereas the doping-induced strain and crystallite size was studied using the Williamson Hall method. Crossectional SEM micrographs confirm the plate-like structure, with an average grain size of 273.7 nm. A diffuse type of phase transition was observed at 345 °C, which usually arises due to compositional fluctuations and mobile oxygen vacancies; further, the diffusiveness of the NdSBN was studied using Uchino and Nomura function, a modified version of Curie-Weiss law (CW). The frequency and temperature-dependent dielectric study of NdSBN ceramics display a Maxwell-Wagner relaxation with a high loss in a low frequency regime, possibly due to the presence of leakage current in the solid solution. Frequency dependent AC conductivity obeys Jonscher's power law, whereas DC conductivity supports polaron assisted hopping in NdSBN composition with dual activation energies of 0.55 eV and 0.75 eV, which correspond to electrons and ions, respectively. The non-Debye type relaxation mechanism in conjunction with negative temperature coefficient of resistance (NTCR) behavior was demonstrated by temperature dependent impedance spectroscopy, while modulus spectroscopy confirmed the multiple relaxation processes in NdSBN ceramics.
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    SkipNet: an adaptive neural network equalization algorithm for future passive optical networking
    (Optica Publishing Group, 2024-10-08) Murphy, Stephen L.; Townsend, Paul D.; Antony, Cleitus; Science Foundation Ireland
    In this paper, we propose an original adaptive neural network equalizer (NNE) algorithm named SkipNet, which is suitable for rapid training on a packet-by-packet basis for burst-mode non-linear equalization in upstream PON transmission. SkipNet uses the simple LMS algorithm and avoids complex neural network training algorithms such as backpropagation and mini-batch training. We demonstrate SkipNet on captured continuous mode 100 Gbit/s PAM4 signals using an SOA preamplifier to achieve the challenging 29 dB PON optical loss budget. The adaptive SkipNet equalizer is shown to overcome combinations of severe SOA patterning effects and fiber dispersion impairments to achieve >29dB dynamic range back-to-back and >22.9dB dynamic range for up to 81.6 ps/nm accumulated dispersion. It can adapt in as little as 250 training symbols to each impairment scenario, which is equivalent to existing FFE/DFE solutions, while matching the non-linear performance of previously proposed static NNE solutions. To the best of our knowledge, SkipNet is the first ever adaptive NNE framework that can realistically be trained and adapted on a packet-by-packet basis and within strict PON packet preamble lengths.
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    Compact multi-band filter/diplexer LNAs using split-type multi-resonant stages
    (Institute of Electrical and Electronics Engineers (IEEE), 2024-07-23) Cheng, Steven Matthew; Psychogiou, Dimitra
    This paper reports on the design and practical development of RF co-designed low-noise amplifiers (LNAs) with multi-band RF filter and diplexer capabilities. Split-type multi-resonant stages are used as complex-terminated matching networks to functionalize new classes of multi-band filtering LNAs (MBF-LNAs) and multi-band diplexer LNAs (MBD-LNAs). In this manner, the need for conventional matching networks or additional RF filtering is eliminated in the RF front-end, thus reducing its size. Miniaturization is further enhanced using split-type multi-resonant stages that are smaller than conventional transversal resonator arrays or filter-banks of in-line coupled resonators. The MBF-LNA and the MBD-LNA concepts are validated in S-band through the realization of two dual-band MBF-LNAs (MBF-LNA I and MBF-LNA II) and a quad-band MBD-LNA. Specifically, the MBF-LNA I exhibited a low noise figure (NF) of 0.65/0.9 dB and a gain of 19.1/16.5 dB for its passbands centered at 2.5/3.29 GHz. The MBFLNA II exhibited significantly higher isolation between the two passbands of 79.5 dB while having a NF of 1/1.5 dB and gain of 18.3/15.9 dB at 2.57/3.26 GHz. The MBD-LNA demonstrated two dual-band output channels with Channel 1 having a NF of 0.92/0.93 dB and gain of 17.2/15.2 dB at 2.38/3.29 GHz and Channel 2 having a NF of 0.82/1.02 dB and gain of 16.8/14.2 dB at 2.82/3.8 GHz.
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    ReS2/Si 2D/3D vertical heterojunction as a self-powered photodiode
    (AIP Publishing, 2024-10-24) Intonti, Kimberly; Pelella, Aniello; Neill, Hazel; Patil, Vilas; Hurley, Paul K.; Ansari, Lida; Gity, Farzan; Di Bartolomeo, Antonio; Science Foundation Ireland; Irish Research Council; Horizon 2020
    2D/3D van der Waals heterostructures provide an excellent platform for high-performance optoelectronic systems by combining the intrinsic properties of 2D and 3D materials. In this study, we fabricate and study a type II ReS2/Si van der Waals 2D/3D vertical heterojunction with multi-mode photodetection. In the dark, the heterojunction exhibits diode-like behavior with a low reverse current and a high rectification ratio of ∼103. Under illumination, the device shows a linear response to the light intensity. The ReS2/Si photodetector exhibits stable and repeatable switching behavior and can be operated in self-powered mode with a responsivity of about 0.10 mA/W at 10 mW incident power and a time response of 300 μs. Based on first-principles calculations, we propose a model to elucidate the photoconduction mechanisms occurring in the ReS2/Si heterostructure.
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    Distinguishing the energy and non-energy actions in balancing energy markets
    (Elsevier B.V., 2024-09-11) Haji Bashi, Mazaher; Gharibpour, Hassan; Carroll, David; Kerin, Martin J.; Lyons, Padraig
    In the European context, balancing energy markets are established to optimise transmission system operator balancing actions closer to real-time. These actions aim to match total generation and consumption subject to a suite of security constraints (e.g., reserve requirements). However, there is no clear border between those actions that are taken due to the reserve requirements (non-energy actions) and those that are primarily taken to supply the demand mismatches (energy actions). To recognise the effect of non-energy actions, existing methods require comparing the results of counterfactual optimisation problems in which the non-energy-action-related constraints were deliberately omitted. This paper proposes a one-off solution enabling TSOs to distinguish energy actions from non-energy ones in the balancing market scheduling problem. By decomposition of the dual variables and clustering the constraints as proposed in this paper, there is no need to solve repetitive counterfactual optimisation problems. Case studies show that in addition to the non-energy actions caused by non-energy-based balancing requirements, the proposed method is able to recognise the energy actions that should be taken due to the non-energy root causes. This feature enables TSOs to efficiently retrace the effect of non-energy actions on the energy-based dispatch instructions issued according to the balancing market schedule.