Tyndall National Institute - Journal Articles
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Item Microneedle electrodes: materials, fabrication methods, and electrophysiological signal monitoring-narrative review(Springer Nature, 2025) Singh, Om Prakash; El-Badawy, Ismail M.; Sundaram, Sornambikai; O'Mahony, Conor; Higher Education Authority; Science Foundation Ireland; European Regional Development FundFlexible, microneedle-based electrodes offer an innovative solution for high-quality physiological signal monitoring, reducing the need for complex algorithms and hardware, thus streamlining health assessments, and enabling earlier disease detection. These electrodes are particularly promising for improving patient outcomes by providing more accurate, reliable, and long-term electrophysiological data, but their clinical adoption is hindered by the limited availability of large-scale population testing. This review examines the key advantages of flexible microneedle electrodes, including their ability to conform to the skin, enhance skin-electrode contact, reduce discomfort, and deliver superior signal fidelity. The mechanical and electrical properties of these electrodes are thoroughly explored, focusing on critical aspects like fracture force, skin penetration efficiency, and impedance measurements. Their applications in capturing electrophysiological signals such as ECG, EMG, and EEG are also highlighted, demonstrating their potential in clinical scenarios. Finally, the review outlines future research directions, emphasizing the importance of further studies to enhance the clinical and consumer use of flexible microneedle electrodes in medical diagnostics.Item Time-resolved eye diagrams to exploit hidden high-energy branches in a nonlinear wideband vibration-energy harvester(American Physical Society, 2023-08-01) Paul, Kankana; Roy, Saibal; Amann, Andreas; Science Foundation Ireland; Horizon 2020A wideband vibration energy harvester with multiple nonlinear forces is investigated. The nonlinearities are due to repulsive magnets and hardening springs, which gives rise to multistabilities between a number of energy branches. Not all branches are accessible by a simple up or down sweep of the driving frequency and in particular the highest energy branch is often hidden, requiring a suitable frequency schedule to be accessed. Detailed theoretical understanding of the energy branch structure along with robust experimental methods are essential for characterizing each of the energy branches to enhance the energy output from such a vibration energy harvesting system. We introduce a graphical representation in the form of eye diagrams based on time-resolved measurements of acceleration and output voltage to study the dynamical features of the different branches. This generic approach allows us to optimize the design, which results in 1.3 mW of power generated at 1 g over the 44-Hz frequency bandwidth while maintaining a small footprint of 1.23 cm3. The energy conversion ratio of the energy harvester at 120-Hz drive frequency is 0.52 for the high-energy branch.Item Low-power actuators for programmable photonic processors(Society of Photo‑Optical Instrumentation Engineers (SPIE), 2023-03-15) Khan, Muhammad Umar; Zand, Iman; Van Iseghem, Lukas; Edinger, Pierre; Jo, Gaehun; Bleiker, Simon J.; Takabayashi, Alain Y.; Antony, Cleitus; Jezzini, Moises; Talli, Giuseppe; Sattari, Hamed; Lee, Jun Su; Mallik, Arun Kumar; Verheyen, Peter; Lerma Arce, Cristina; Garcia Porcel, Marco; Jonuzi, Tigers; Picavet, Ewout; Nagarjun, K. P.; Watté, Jan; Quack, Niels; Niklaus, Frank; Gylfason, K. B.; De Buysser, Klaartje; Beeckman, Jeroen; Bogaerts, Wim; Kitayama, Ken-ichi; Jalali, BahramThe demand for efficient actuators in photonics has peaked with increasing popularity for large-scale general-purpose programmable photonics circuits. We present our work to enhance an established silicon photonics platform with low-power micro-electromechanical (MEMS) and liquid crystal (LC) actuators to enable largescale programmable photonic integrated circuits (PICs).Item Anisotropic magnetic and electrical properties in textured single phase multiferroic Bi4.5Sm0.5Ti3Fe0.8Cr0.2O15 ceramics(Elsevier, 2025) Pritam, Anurag; Abdi, Gisya; Hussian, Sabir; Sikora, Marcin; Shiv Nadar FoundationHere we report the synthesis of single-phase Cr and Sm doped Aurivillius Bi5Ti3FeO15 (SBTFO) ceramics using conventional solid-state route method. The prepared composition exhibits the anticipated four-layered Aurivillius structure having an orthorhombic crystal structure and A21am space group, as confirmed by the XRD in conjunction with the Rietveld refinement. Additionally, the doping-induced crystallite size and strain were analyzed using a Williamson Hall plot, whereas cross-sectional FESEM revealed the plate-like structure having an average crystallite size of 0.5 μm. The SBTFO ceramics demonstrate exemplary ferroelectric and ferromagnetic properties with remnant polarization (2Pr) and remnant magnetization (2Mr) of 0.96 μC/cm2 and 0.06 emug−1, respectively. The temperature and frequency dependence of dielectric study reveals a Maxwell-Wagner relaxation with a higher loss in a low frequency regime perhaps due to leakage current in the system. The frequency dependent AC conductivity investigation adheres to Jonscher's formulation, indicating that the long-range hopping mechanism governs the conduction process, with an activation energy of 0.56 eV. Non-Debye type relaxation mechanism coupled with negative temperature coefficient of resistance (NTCR) behavior was specified by temperature dependent impedance spectroscopy, whereas the modulus spectroscopy revealed the multiple relaxation phenomena. Furthermore, the impedance and modulus processes computed activation energy of 0.74 eV and 0.32 eV, respectively, indicate the involvement of distinct charge carriers in the relaxation and conduction processes. The present work illustrates a versatile approach for designing high-performance, room-temperature multiferroic materials, demonstrating their potential for next-generation industrial applications, including non-volatile memory, spintronic devices, and multifunctional sensors.Item Ultrafast dynamics of hot carriers: Theoretical approaches based on real-time propagation of carrier distributions(American Institute of Physics, 2025-02-14) Sjakste, Jelena; Sen, Raja; Vast, Nathalie; Saint-Martin, Jerome; Ghanem, Mohammad; Dollfus, Philippe; Murphy-Armando, Felipe; Kanasaki, Junichi; Japan Society for the Promotion of Science; Science Foundation Ireland; Agence Nationale de la RechercheIn recent years, computational approaches which couple density functional theory (DFT)-based description of the electron–phonon and phonon–phonon scattering rates with the Boltzmann transport equation have been shown to obtain the electron and thermal transport characteristics of many 3D and 2D semiconductors in excellent agreement with experimental measurements. At the same time, progress in the DFT-based description of the electron–phonon scattering has also allowed to describe the non-equilibrium relaxation dynamics of hot or photo-excited electrons in several materials, in very good agreement with time-resolved spectroscopy experiments. In the latter case, as the time-resolved spectroscopy techniques provide the possibility to monitor transient material characteristics evolving on the femtosecond and attosecond time scales, the time evolution of photo-excited, nonthermal carrier distributions has to be described. Similarly, reliable theoretical approaches are needed to describe the transient transport properties of devices involving high energy carriers. In this review, we aim to discuss recent progress in coupling the ab initio description of materials, especially that of the electron–phonon scattering, with the time-dependent approaches describing the time evolution of the out-of-equilibrium carrier distributions, in the context of time-resolved spectroscopy experiments as well as in the context of transport simulations. We point out the computational limitations common to all numerical approaches, which describe time propagation of strongly out-of-equilibrium carrier distributions in 3D materials, and discuss the methods used to overcome them.