Artículos de revista DIEC - IEKS Aldizkari artikuluak

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Open Access
Lossy mode resonance and hyperbolic mode resonance-based optical sensors by means of Y3Fe5O12 and SrTiO3 films deposition on planar substrates
(IEEE, 2025-07-02) Correa Fernández, Ángel; Gallego Martínez, Elieser Ernesto; Ruiz Zamarreño, Carlos; Matías Maestro, Ignacio; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
This letter describes the fabrication of sensor devices based on lossy mode resonance (LMR) and hyperbolic mode resonance (HMR) using for the first time as generating materials of the optical resonances both, yttrium iron garnet (Y3Fe5O12) and strontium titanate (SrTiO3) with a film thickness of 739.2 and 158.7 nm for Y3Fe5O12 (YIG) and SrTiO3, respectively. First-order resonances were observed at the visible region of the electromagnetic spectrum for both materials, LMR and HMR phenomena. RF sputtering deposition was used to fabricate metal oxide thin films on coverslips in a planar waveguide configuration, the Au metallic thin films were deposited by pulsed dc sputtering in a magnetron system from Moorfield. All devices were characterized under different surrounding medium refractive index. Sensitivities achieved values of 5862 and 5865 nm/RIU (refractive index unit) for HMR versions of Y3Fe5O12 and SrTiO3r, respectively. In addition, the response of the sensors to relative humidity and different ethanol concentrations was evaluated. The best results correspond to the Y3Fe3O3-based sensor, with a sensitivity of 0.2 nm/ppm and a limit of detection (LOD) of 183 ppm for ethanol, and 64 nm/%RH for RH, with an LOD of 2.23%RH, and because its resonance does not vanish unlike SrTiO3.
Open Access
Resonance-based optical gas sensors
(IEEE, 2025-07-02) Gallego Martínez, Elieser Ernesto; Ruiz Zamarreño, Carlos; Matías Maestro, Ignacio; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Gas sensors play a critical role in numerous human activities. Their necessity continues to grow across diverse fields as technological advancements drive demand for precision agriculture and bioengineering among other applications. Among existing sensor technologies, optical gas sensors stand out due to their ability to operate remotely in high-risk environments while remaining unaffected by electromagnetic interference. Resonance-based optical sensors offer targeted gas detection through the functionalization of their sensitive surfaces. This work focuses on reviewing the state of the art in resonance-based optical gas sensors (ROGSs), addressing their fundamental principles, recent advances in fabrication processes, waveguide designs, and materials employed both for resonance generation and as sensitive coatings. In addition, the review examines achieved sensitivity, emerging applications, and key developments in the field, including those efforts on improving ROGS performances by means of artificial intelligence techniques. The study encompasses optical sensors leveraging surface plasmon resonance, lossy mode resonance, and hyperbolic mode resonance¿the latter representing a notable breakthrough in recent years as a particular case of Bloch surface waves.
Open Access
HMR-based optical gas detection with CuO and ZnO coatings
(IEEE, 2025-07-02) Gallego Martínez, Elieser Ernesto; Ruiz Zamarreño, Carlos; Matías Maestro, Ignacio; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
This work presents the fabrication of hyperbolic mode resonance-based optical sensors by means of sputtered copper oxide (CuO) and zinc oxide (ZnO), and the study of their performance for gas sensing purposes. Two sensors were fabricated in a planar waveguide configuration with an intermediate gold thin film, and resonances were observed in the visible region of the electromagnetic spectrum. Both materials were analyzed with X-ray diffraction techniques, and their response was characterized by different concentrations of a group of gases comprised of nitric oxide, acetylene (C2H2), ethanol, carbon dioxide, and relative humidity. The best performance corresponds to the CuO sensor for C2H2 gas, presenting a sensitivity of 1.11 nm/parts per million (ppm) and a limit of detection of 12.6 ppb, with response and recovery times of 70 and 68 s, respectively. ZnO-based sensors allowed for a comprehensive study of ethanol in a range of thousands of ppm, while CuO-based sensors showed exceptional sensitivity for most gases in the range of a few ppm. All measurements were performed at room temperature.
Open Access
Asymmetric white matter degeneration in amyotrophic lateral sclerosis: a diffusion kurtosis imaging study of motor and extra-motor pathways
(Frontiers Media, 2025-04-25) Quizhpilema Cedeño, Juan Carlos; Legarda, Ane; Hidalgo, José Manuel ; Lecumberri Villamediana, Pablo; Jericó Pascual, Ivonne; Cabada Giadás, María Teresa; Ciencias de la Salud; Osasun Zientziak; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Gobierno de Navarra / Nafarroako Gobernua
Background: Amyotrophic Lateral Sclerosis (ALS) is a progressive neurodegenerative disease that lacks effective early biomarkers. This study investigated the potential of diffusion kurtosis imaging (DKI) as a non-invasive biomarker for detecting and monitoring ALS progression through a comprehensive analysis of white matter alterations. Methods: We performed a cross-sectional analysis of magnetic resonance images with advanced diffusion imaging techniques in ALS patients recruited from a neurodegenerative consultation service over a 3-year period and healthy controls. Our methodology employed multi-shell multi-tissue constrained spherical deconvolution (MSMT-CSD) for tract reconstruction and diffusion kurtosis imaging for microstructural analysis. The study focused particularly on the corticospinal tract and associated pathways, utilizing both tract-specific Bundle Analytics (BUAN) and whole-brain Tract-Based Spatial Statistics (TBSS) approaches. Results: The study included 33 ALS patients and 37 controls with no significant differences in age or gender. ALS patients predominantly presented with spinal onset and exhibited moderate functional impairment (ALSFRS-R: 39.09 ± 5). Whole-brain TBSS revealed widespread white matter alterations, with increased MD, RD, and AD, and decreased FA notably in the corona radiata, internal capsule, and corticospinal tracts. Detailed fiber tracking of the corticospinal tracts showed significant microstructural changes, with the left CST displaying pronounced increases in MD and AD alongside reduced FA, while the right CST exhibited distinctive regional variations. Additionally, analyses of the frontopontine and parietopontine tracts uncovered further alterations in diffusion metrics. Despite imaging findings, clinical-radiological correlations with functional scores and disease progression were not statistically significant. Conclusions: This study explores DKI as a potential biomarker for ALS pathology, revealing microstructural changes in both motor and extra-motor pathways. Using whole-brain TBSS analysis and tractography with DIPY, we identified an asymmetric pattern of degeneration and involvement of integrative neural networks, providing new insights into ALS pathophysiology. These findings contribute to our understanding of the complex structural alterations in ALS and suggest that DKI-derived metrics may have utility in characterizing the disease process.
Open Access
Clerics and priests as scientists in the Spanish Golden Age
(Nicolaus Copernicus University (Polonia), 2025-03-27) Del Villar, Ignacio; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza
The Spanish Golden Age was a very fruitful period in disciplines as varied as literature, painting and religion, while giving rise to the first global empire. However, the scientific-technological aspect of this period is little known, especially with regard to clerical and religious scientists, among whom are figures such as the Dominican Domingo de Soto, who contributed to physics with the concept of mass and the uniform acceleration of bodies in free fall; the Jesuit José de Acosta, which can be regarded as a precursor of biogeography; Nicolás Monardes, a pioneer in pharmacognosy who in his later years wore the habit of St. Peter and likely became a priest; Benito Daza de Valdés, who was most likely a Dominican and authored the first treatise on physiological optics; and Juan Caramuel, a bishop and polymath who conceptualized the binary system. This could support the idea expressed by some authors that scientific questions often arise in an environment with a deep interest in the transcendental, as is the case with these clerics presented here.
Open Access
Non-line-of-sight 300 GHz band wireless link enabled by a frequency dependent reflective surface
(IEEE, 2025-05-01) Dutin, Frédéric; Beaskoetxea Gartzia, Unai; Torres Landívar, Víctor; Szriftgiser, Pascal ; Teniente Vallinas, Jorge; Ducournau, Guillaume; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC
Reconfigurable intelligent surface is a promising technology for the up-coming sixth-generation (6G) of cellular communication networks. In this context, an experimental study of specular and nonspecular reflections of a reflective surface (RS) by scattering parameter measurements in the 300 GHz range is presented. Here, we compare the insertion loss of a fixed and passive RS at its optimal output deflection angle with respect to the specular reflection on a metallic plate. We propose a methodology to assess the losses induced by the surface and validate the use of the device within a THz link. At its best, around 290 GHz, the surface insertion loss is less than 3 dB compared to the metallic plate. We then investigate a non-line-of-sight (LoS) THz link operating in QSPK and QAM-16 coherent transmission using the RS. Data rates up to 10 Gbits/s for QSPK and 20 Gbits/s for QAM-16 are obtained. This is, to the best authors knowledge, the first demonstration of a NLoS THz data-link including such RS.
Open Access
Hybrid modelling and identification of mechanical systems using Physics-Enhanced Machine Learning
(Elsevier, 2025-11-15) Merino Olagüe, Mikel; Iriarte Goñi, Xabier; Castellano Aldave, Jesús Carlos; Plaza Puértolas, Aitor; Ingeniería; Ingeniaritza; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Obtaining mathematical models for mechanical systems is a key subject in engineering. These models are essential for calculation, simulation and design tasks, and they are usually obtained from physical principles or by fitting a black-box parametric input-output model to experimental data. However, both methodologies have some limitations: physics based models may not take some phenomena into account and black-box models are complicated to interpretate. In this work, we develop a novel methodology based on discrepancy modelling, which combines physical principles with neural networks to model mechanical systems with partially unknown or unmodelled physics. Two different mechanical systems with partially unknown dynamics are successfully modelled and the values of their physical parameters are obtained. Furthermore, the obtained models enable numerical integration for future state prediction, linearization and the possibility of varying the values of the physical parameters. The results show how a hybrid methodology provides accurate and interpretable models for mechanical systems when some physical information is missing. In essence, the presented methodology is a tool to obtain better mathematical models, which could be used for analysis, simulation and design tasks.
Embargo
Dispersion effects in thermal emission from temporal metamaterials: high-frequency cutoffs
(Optica, 2025-02-03) Vertiz Conde, Amaia; Liberal Olleta, Íñigo; Vázquez Lozano, Juan Enrique; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
The latest breakthroughs in time-varying photonics are fueling novel, to the best of our knowledge, thermal emission phenomena, e.g., showing that the dynamic amplification of quantum vacuum fluctuations, induced by the time modulation of material properties, enables a mechanism to surpass the blackbody spectrum. So far, this issue has only been investigated under the assumption of non-dispersive time modulations. In this work, we identify the existence of a nonphysical diverging behavior in the time-modulated emission spectra at high frequencies and prove that it is actually attributed to the simplistic assumption of a non-dispersive (temporally local) response of the time modulation associated with memory-less systems. Accordingly, we upgrade the theoretical formalism by introducing a dispersive response function, showing that it leads to a high-frequency cutoff, thereby eliminating the divergence and hence allowing for the proper computation of the emission spectra of time-modulated materials.
Open Access
Method to use transport microsimulation models to create synthetic distributed acoustic sensing datasets
(MDPI, 2025-05-07) Robles Urquijo, Ignacio; Benavente, Juan; Blanco García, Javier; Diego González, Pelayo; Loayssa Lara, Alayn; Sagüés García, Mikel; Rodríguez Cobo, Luis; Cobo, Adolfo; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC
This research introduces a new method for creating synthetic Distributed Acoustic Sensing (DAS) datasets from transport microsimulation models. The process involves modeling detailed vehicle interactions, trajectories, and characteristics from the PTV VISSIM transport microsimulation tool. It then applies the Flamant-Boussinesq approximation to simulate the resulting ground deformation detected by virtual fiber-optic cables. These synthetic DAS signals serve as large-scale, scenario-controlled, labeled datasets on training machine learning models for various transport applications. We demonstrate this by training several U-Net convolutional neural networks to enhance spatial resolution (reducing it to half the original gauge length), filtering traffic signals by vehicle direction, and simulating the effects of alternative cable layouts. The methodology is tested using simulations of real road scenarios, featuring a fiber-optic cable buried along the westbound shoulder with sections deviating from the roadside. The U-Net models, trained solely on synthetic data, showed promising performance (e.g., validation MSE down to 0.0015 for directional filtering) and improved the detectability of faint signals, like bicycles among heavy vehicles, when applied to real DAS measurements from the test site. This framework uniquely integrates detailed traffic modeling with DAS physics, providing a novel tool to develop and evaluate DAS signal processing techniques, optimize cable layout deployments, and advance DAS applications in complex transportation monitoring scenarios. Creating such a procedure offers significant potential for advancing the application of DAS in transportation monitoring and smart city initiatives.
Open Access
A hybrid technique for mutual coupling reduction in a compact dual-band millimeter-wave MIMO antenna
(IEEE, 2025-07-01) Ahmad, Jawad; Hashmi, Mohammad; Falcone Lanas, Francisco; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC
This letter reports a hybrid approach employing metallic vias and metasurface for mutual coupling reduction in a MIMO antenna at mmWave frequencies. Initially, a dual-band coaxial-fed antenna, operating at 27 GHz and 28 GHz, is designed using modified K-shaped patch arms with a tapered profile which is then used to develop a four-element dual-band MIMO array. Subsequently, metallic vias are incorporated to suppress surface wave-induced coupling. Finally, metasurface slab is integrated to mitigate near-field interactions. The proposed design achieves an impedance bandwidth of 26.75-27.28 GHz and 27.77-28.19 GHz, with coupling levels below 30 dB, and broadside radiation patterns with respective peak gains of 6.52 dBi and 6.74 dBi. Furthermore, the proposed design exhibits an envelope correlation coefficient (ECC) of less than 0.05 for isotropic and less than 0.25 for Gaussian environments. An excellent agreement between the experimental and simulation results validate the proposed design approach.
Open Access
Modeling and optimal sizing of thyristor rectifiers for high-power hydrogen electrolyzers
(IEEE, 2025-05-01) Iribarren Zabalegui, Álvaro; Barrios Rípodas, Ernesto; Sanchis Gúrpide, Pablo; Ursúa Rubio, Alfredo; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Thyristor rectifiers are currently the most common solution for supplying high-power electrolyzers. These rectifiers typically include a dc inductance, which significantly increases system costs. However, this inductance can be avoided by relying solely on ac-side inductances, required for grid current harmonic filtering, although this approach introduces specific challenges. Traditional analytical models of thyristor rectifiers are unable to determine the electrolyzer operating point for a given firing angle and may lead to incorrect system sizing, ultimately preventing the converter from delivering nominal power. This limitation arises from the fact that existing models are formulated for inductive or constant-current loads, whereas electrolyzers exhibit electrical behavior closer to constant-voltage loads. In this paper, a novel analytical model of 6- and 12-pulse thyristor rectifiers with constant-voltage load is developed. The model enables the analysis and optimal sizing of thyristor rectifiers directly connected to electrolyzers without a dc-side inductance. Its accuracy has been validated through both simulations and experimentally using a laboratory-scale prototype. Furthermore, the model has been applied to optimally size a 12-pulse rectifier supplying a 5.5 MW electrolyzer, demonstrating its suitability for the design of thyristor rectifier systems in industrial-scale electrolysis applications and highlighting its advantages over traditional approaches.
Open Access
Single-pixel compressive terahertz 3D imaging
(IEEE, 2025-04-24) Ndagijimana, Adolphe; Ederra Urzainqui, Íñigo; Heredia Conde, Miguel; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC
Terahertz (THz) imaging contends with the lack of cost-effective, off-the-shelf high-resolution array detectors and the slow acquisition speeds associated with pixel-by-pixel raster scanning. Single-pixel imaging with Compressive Sensing (CS) represents a potential solution for resolution and acquisition speed in a cost-efficient manner. Our paper introduces a novel approach for extending 2D single-pixel THz imaging systems to 3D using a single frequency. By leveraging the single-pixel approach, we achieve 3D resolution while avoiding mechanical scanning, and the use of a single frequency eliminates the need for bandwidth, a significant limitation of conventional techniques, where design of THz sources and detectors with large bandwidth remains challenging and typically complex. The Order Recursive Matching Pursuit (ORMP) algorithm is used as the sparse recovery method to exploit the sparsity/compressibility of the 3D THz signal and enable sampling at a rate far lower than that required by the Nyquist Theorem. The 2D sensing matrix is obtained by analyzing the diffracted propagation of THz imaging systems on a 2D surface perpendicular to the optical axis. Moreover, the 3D sensing matrix is based on the diffracted propagation of 2D surfaces at different sampling depth positions. Our system can quickly capture the reflective properties of every point in a 3D space using a single-pixel camera setup that leverages CS, making it a simple and efficient method for creating a fast 3D THz imaging system, particularly suited to high-frequency THz sources that operate efficiently at a single frequency or at small bandwidth.
Open Access
Cavity-stacked filter in CLAF-SIW technology for millimeter waves
(Elsevier, 2025-03-01) Segura-Gómez, Cleofás; Biedma-Pérez, Andrés; Santiago Arriazu, David; Palomares-Caballero, Ángel; Arregui Padilla, Iván; Gómez Laso, Miguel Ángel; Padilla, Pablo; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC
This work presents the design of a cavity-stacked bandpass filter (BPF) using contactless air-filled substrate integrated waveguide (CLAF-SIW) technology for millimeter-wave frequencies. This technology is a variant of air-filled SIW technology, incorporating contactless techniques. It enables the reduction of dielectric losses in SIW filters while supporting multilayer structures with robust assembly. The cavity-stacked filter topology allows for very good frequency responses with a reduced footprint and no transitions needed. As an example, a 4th-order Chebyshev bandpass filter composed of four stacked cavities, coupled through irises, is shown. The iris layers are fabricated by metallizing the slot edges of a PCB, while the cavity layers are implemented using CLAF-SIW. The filter has been designed and manufactured to provide a passband response from 36 GHz to 37.5 GHz. A good agreement between measurement and simulation has been achieved. The losses in the proposed CLAF-SIW filter are primarily due to the metal roughness of the low-cost commercial laminates used.
Open Access
A 3-D-printing-oriented coaxial-line filter with wide out-of-band rejection
(IEEE, 2025-06-18) Baranowski, Michal; Pons Abenza, Alejandro; Arregui Padilla, Iván; Lopetegui Beregaña, José María; Álvarez Botero, Germán Andrés; Lamecki, Adam; Gómez Laso, Miguel Ángel; Martín Iglesias, Petronilo; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC
In this letter, a novel design for a 3-D-printed, self-supported coaxial-line X-band filter is presented. The filter is intended for Earth observation (EO) data downlink systems, where it must effectively reject signals in a wide frequency range. The filter design incorporates a 15th-order low-pass filter structure with a smooth profile, integrated with a short bandpass section with four $\lambda /4$ short-circuited stubs. The optimization of the low-pass section is attained by means of shape deformation, including the inner and outer coaxial conductors, and leads to a wide rejection band up to around 40 GHz, to suppress the third harmonic and other undesired out-of-band frequencies. A prototype was fabricated in one piece in an aluminum alloy using selective laser melting (SLM) and measured, exhibiting excellent agreement with simulations. In terms of out-of-band performance, the proposed coaxial-line filter is superior to other related state-of-the-art solutions.
Open Access
Multi antenna structure assisted by metasurface concept providing circular polarization for 5G millimeter wave applications
(Nature, 2025-05-21) Althuwayb, Ayman Abdulhadi; Ali, Esraa Mousa; Alibakhshikenari, Mohammad; Virdee, Bal S.; Rashid, Nasr; Kaaniche, Khaled; Atitallah, Ahmed Ben; Elhamrawy, Osama I.; Falcone Lanas, Francisco; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC
This paper presents a circularly polarized multi-antenna structure designed for 5G millimeter-wave applications. The structure is based on circular patch radiators, each enhanced with metasurface (MTS) characteristics through the integration of multi-split ring slots. Each radiating element is enclosed within a decoupling wall constructed from a microstrip transmission line, which features both wide (capacitive) and thin (inductive) impedance profiles. The antennas are excited from below using metallic pins, which connect to the radiators through via-holes stemming from coplanar waveguide ports on the ground plane. Experimental results demonstrate a wide bandwidth from 25.6 to 29.7 GHz, corresponding to a fractional bandwidth of 14.82%. Additionally, the antenna exhibits stable radiation patterns, with an average gain of 2.7 dBi and a radiation efficiency of 57%. Using a single radiator configuration, a 3 × 3 antenna array was implemented. In this design, electromagnetic coupling between adjacent radiators is significantly reduced. The resulting array, measuring 20 × 20 × 0.32 mm3, achieves excellent performance across a wide frequency range from 24 to 31 GHz, corresponding to a bandwidth of 25.45%. Key metrics include an average isolation between radiating elements exceeding 17 dB and an average gain and radiation efficiency of 9.0 dBi and 91.5%, respectively.
Open Access
Power converter for ultra low-frequency and low-voltage energy harvesters
(SpringerOpen, 2025-05-29) Hualde Otamendi, Mikel; Cruz Blas, Carlos Aristóteles de la; Castellano Aldave, Jesús Carlos; Carlosena García, Alfonso; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC
Energy conversion mechanisms present in some harvesters are only able to provide very low voltage (mV) and fre‑ quency (few Hz) electrical signals, which may also have a bipolar nature (AC). These characteristics make unusable most conventional power converters to extract from them a DC voltage. This letter describes an autonomous selfstarting ultra-low voltage and frequency AC-DC converter that can start the operation for AC signals around 25 mV, and below 10 Hz. The converter has been designed with ultra-low vibration harvesters in mind, but is also of appli‑ cation to, for instance, thermoelectric generators (TEG). The circuit is basically an oscillator driven by the harvester output, which therefore converts a low-frequency and low-voltage signal into large signal oscillation amenable for further DC conversion. The proposed circuit is based on the classical Hartley oscillator, which is modifed in a non‑ trivial confguration, and optimized to be able to operate with bipolar, low frequency and voltage driving signals. This is achieved with a minimum number of passive components and a single JFET transistor. A practical prototype has been fabricated, and measurement results are obtained, demonstrating the feasibility of the approach. Moreover, a vibration harvester with the power converter proposed has been tested in real conditions in a wind turbine.
Open Access
Multidirectional bending sensor using capillary fibers and machine learning for real-time applications
(IEEE, 2025-02-25) Vanegas Tenezaca, Evelyn Dayanara; Galarza Galarza, Marko; Dauliat, Romain; Jamier, Raphael; Roy, Philippe; López-Amo Sáinz, Manuel; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC; Universidad Publica de Navarra / Nafarroako Unibertsitate Publikoa
In this article, the design and implementation of a bidirectional curvature sensor based on a fiber-optic interferometer are presented. The sensor structure was fabricated by fusing a capillary fiber fragment between single-mode fibers (SMFs), with the addition of a long end capillary to promote a long interferometric section, forming a Fabry-Perot (FP) cavity. Detailed analysis of the curvature data was carried out using machine learning techniques, allowing accurate classification of curvature in both directions of rotation. The experimental results showed excellent agreement (R2: 0.9998) with the predicted values. The sensor exhibits a maximum error of 1.9485°. This approach presents significant potential for applications requiring accurate real-time curvature measurements.
Open Access
A novel aging modeling approach for second-life lithium-ion batteries
(Elsevier, 2025-02-10) Pérez Ibarrola, Ane; San Martín Biurrun, Idoia; Sanchis Gúrpide, Pablo; Ursúa Rubio, Alfredo; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa; Gobierno de Navarra / Nafarroako Gobernua
The electric mobility industry is booming. In order to reduce the environmental impact of this boom, there is the potential to reuse the batteries from electric vehicles. However, the technical and economic feasibility of the second-life of lithium-ion batteries remains in question. This is due to the intricate non-linear mechanisms that occur during battery degradation, leading to capacity and power loss. Ongoing research aims to create models that can predict the state of battery degradation. However, most studies have focused on the battery's first life, operating within a limited state of health range and requiring constant monitoring of the battery's exposure conditions. While these models provide satisfactory results for the battery's performance in vehicles, they cannot be directly applied to second-life scenarios. In response to this issue, this article proposes a degradation modeling method for second-life batteries based on identifying and linearizing different degradation trends within the battery. This approach allows the application of the model without prior knowledge of the battery's history. It has been validated for a state of health range of 95% to 20%, through both conventional charge-discharge tests and a real-world scenario involving a smart charging station for urban buses. The results obtained with the developed model are overall satisfactory, achieving a MAPE below 3% for capacity and 1.4% for internal resistance in the real-world scenario.
Open Access
Robust filter design built in a contactless metallic multilayer waveguide at W-band
(IEEE, 2025-05-15) Garcia-Martinez, Sergio (0000-0002-2427-8264); Santiago Arriazu, David; Tamayo-Domínguez, Adrián; Sánchez-Olivares, Pablo; Arregui Padilla, Iván; Lopetegui Beregaña, José María; Gómez Laso, Miguel Ángel; Fernández-González, José Manuel; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Institute of Smart Cities - ISC
This article presents the design and experimental validation of a W-band waveguide cavity filter operating around 91 GHz, using a periodic electromagnetic bandgap (EBG) structure with glide symmetry to implement the filter in a stack of multiple thin metallic sheets without electric contact between them. The filter is based on vertically stacked cavities that use the TE103 mode, which offers increased robustness to manufacturing and assembly errors due to the large dimensions of the cavity. The glide-symmetric circular hole EBG structure is analyzed and integrated to suppress unwanted field leakage between the metallic layers with a broad stopband. The proposed filter maintains effective operation in the 88–94-GHz frequency range, even with gap variations between layers of up to 20 µm. The filter is fabricated using laser cutting, achieving a low surface roughness and high dimensional accuracy. Experimental measurements show excellent agreement with the simulations, with a return loss greater than 20 dB and an insertion loss below 0.5 dB. These results demonstrate the possibility to achieve high performance filters at millimeter-wave frequencies while maintaining low fabrication complexity and cost using the multilayer waveguide technology.
Open Access
Techno-economic assessment of MW-scale solid oxide electrolysis hydrogen production plant: integrating possibilities in Spain
(Elsevier, 2024-12-22) Jiménez-Martín, Gonzalo; Judez, Xabier; Aguado Alonso, Mónica; Garbayo, Iñigo; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoa eta Telekomunikazio Ingeniaritza; Gobierno de Navarra / Nafarroako Gobernua
Solid oxide electrolysis (SOE) is regarded as the most efficient green hydrogen production technology. However, the cost competitiveness of this technology for large-scale hydrogen production is at stake due to the complexity of operating at high temperatures. This study aims to estimate the levelized cost of hydrogen (LCOH) of a MWscale SOE system and its possible integration in Spain. The heat exchanger network of a SOE system has been optimized by a pinch analysis and the techno-economic feasibility of the system has been assessed. Even if initial LCOH estimations of >6 €⋅kg− 1 are obtained with the electricity and stack costs as the major contributors, optimistic scenarios indicate that LCOH can be reduced below 4 €⋅kg− 1 , or even further by coupling the systems to heat-intensive industries such as Spanish cement or steel factories.