arXiv subjects

Roshan Nepal

Publications and source records attributed to Roshan Nepal.

7 recordsLinked to original sources

arXiv2026

Battery-Free and Gateway-Free Cellular IoT Water Leak Detection System

This paper presents a battery-free and gateway-free water leak detection system capable of direct communication over LTE-M (Cat-M1). The system operates solely on energy harvested through a hydroelectric mechanism driven by an electrochemical sensor, thereby removing the need for conventional batteries. To address the stringent startup and operational power demands of LTE-M transceivers, the architecture incorporates a compartmentalized sensing module and a dedicated power management subsystem, comprising a boost converter, supercapacitor based energy storage, and a hysteresis controlled load isolation circuit. This design enables autonomous, direct to cloud data transmission without reliance on local networking infrastructure. Experimental results demonstrate consistent LTE-M beacon transmissions triggered by water induced energy generation, underscoring the system's potential for sustainable, maintenance free, and globally scalable IoT leak detection applications in smart infrastructure.

eess.SY↗

arXiv2026

Battery-less Long-Range LTE-M Water Leak Detector

This work presents a self powered water leak sensor that eliminates both batteries and local gateways. The design integrates a dual compartment electrochemical harvester, a low input boost converter with supercapacitor storage, and a comparator gated LTE-M radio built on the Nordic Thingy:91 platform. Laboratory tests confirm that the system can be awakened from a dormant state in the presence of water, harvest sufficient energy, and issue repeated cloud beacons using the water exposure as the power source. Beyond conventional LTE-M deployments, the system's compatibility with 3GPP standard cellular protocols paves the way for future connectivity via non terrestrial 5G networks, enabling coverage in infrastructure scarce regions.

eess.SY↗

arXiv2025

Towards Long-Range, Battery-less Water Leak Detection: A LoRa-Based Approach

This paper presents a battery-less, self-powered water leak detection system that utilizes LoRa communication for long-range, real-time monitoring. The system harvests hydroelectric energy through a layered stack of conductive nanomaterials and metals, achieving a peak short-circuit current of over 500 mA and 1.65 V open-circuit voltage upon exposure to water. To address LoRa's higher power demands, an energy management subsystem -- comprising a DC-DC boost converter and a 100 mF supercapacitor -- ensures stable power delivery for the LLCC68 LoRa module. Experimental results demonstrate the system's ability to detect leaks as shallow as 0.5 mm, activate within 50 seconds across varying water depths, and transmit data reliably over LoRaWAN. This solution eliminates battery dependency, offering a scalable, maintenance-free approach for industrial, commercial, and residential applications, while advancing sustainable IoT infrastructure.

eess.SY↗

arXiv2023

Tuning Structural, Transport and Magnetic Properties of Epitaxial SrRuO3 through Ba-Substitution

The perovskite ruthenates (ARuO3, A = Ca, Ba, or Sr) exhibit unique properties owing to a subtle interplay of crystal structure and electronic-spin degrees of freedom. Here, we demonstrate an intriguing continuous tuning of crystal symmetry from orthorhombic to tetragonal (no octahedral rotations) phases in epitaxial SrRuO3 achieved via Ba-substitution (Sr1-xBaxRuO3 with 0 < x < 0.7). An initial Ba-substitution to SrRuO3 not only changes the ferromagnetic properties, but also tunes the perpendicular magnetic anisotropy via flattening the Ru-O-Ru bond angle (to 180°), resulting in the maximum Curie temperature and an extinction of RuO6 rotational distortions at x = 0.20. For x > 0.2, the suppression of RuO6 octahedral rotational distortion dominantly enhances the ferromagnetism in the system, though competing with the impact of the RuO6 tetragonal distortion. Further increasing x > 0.2 gradually enhances the tetragonal-type distortion, resulting in the tuning of Ru-4d orbital occupancy and suppression of ferromagnetism. Our results demonstrate that isovalent substitution of the A-site cations significantly and controllably impacts both electronic and magnetic properties of perovskite oxides.

cond-mat.mtrl-sci↗

arXiv2022

Thickness Dependent Itinerant Ferromagnetism in Ultrathin Ba-Doped SrRuO3 films

The electronic and magnetic properties in ABO3 perovskite oxides are extremely sensitive to lattice structure but also the dimensionality, such as the thickness in thin film form. Here, we report the thickness-dependent electro-magnetic properties of ultrathin epitaxially stabilized Sr1-xBaxRuO3 (x = 0.08, 0.2) thin films on SrTiO3 (001) substrate. The results reveal that the Ba-doping (0.08 < x < 0.20) reduces RuO6 orthorhombic distortions existing in SrRuO3 and induces a tetragonal distortion as evidenced by out-of-plane lattice expansion. A metal-to-insulator transition, accompanied by a ferromagnetic to non-magnetic transition occurs with reducing film thickness from 10 to 3 unit-cell (u.c.) for both x = 0.08 and 0.2, regardless of the doping level. The results suggest that the effects of compositional vacancies and surface/interface contributions introduced via dimensional confinement are more dominant than A-site chemical disorder or structural distortion for the loss of metallicity and ferromagnetism in ultra-thin epitaxial films.

cond-mat.mtrl-sci↗

arXiv2021

Magnetic Texture in Insulating Single Crystal High Entropy Oxide Spinel Films

Magnetic insulators are important materials for a range of next generation memory and spintronic applications. Structural constraints in this class of devices generally require a clean heterointerface that allows effective magnetic coupling between the insulating layer and the conducting layer. However, there are relatively few examples of magnetic insulators which can be synthesized with surface qualities that would allow these smooth interfaces and precisely tuned interfacial magnetic exchange coupling which might be applicable at room temperature. In this work, we demonstrate an example of how the configurational complexity in the magnetic insulator layer can be used to realize these properties. The entropy-assisted synthesis is used to create single crystal (Mg0.2Ni0.2Fe0.2Co0.2Cu0.2)Fe2O4 films on substrates spanning a range of strain states. These films show smooth surfaces, high resistivity, and strong magnetic responses at room temperature. Local and global magnetic measurements further demonstrate how strain can be used to manipulate magnetic texture and anisotropy. These findings provide insight into how precise magnetic responses can be designed using compositionally complex materials that may find application in next generation magnetic devices.

cond-mat.mtrl-sci↗

arXiv2019

Fermions and bosons in nonsymmorphic PdSb2 with sixfold degeneracy

PdSb2 is a candidate for hosting 6-fold-degenerate exotic fermions (beyond Dirac and Weyl fermions).The nontrivial band crossing protected by the nonsymmorphic symmetry plays a crucial role in physical properties. We have grown high-quality single crystals of PdSb2 and characterized their physical properties under several stimuli (temperature, magnetic field, and pressure). While it is a diamagnetic Fermi-liquid metal under ambient pressure, PdSb2 exhibits a large magnetoresistance with continuous increase up to 14 T, which follows the Kohler's scaling law at all temperatures. This implies one-band electrical transport, although multiple bands are predicted by first principles calculations. By applying magnetic field along the [111] direction, de Haas-van Alphen oscillations are observed with frequency of 102 T. The effective mass is nearly zero (0.045m0) with the Berry phase close to π, confirming that the band close to the R point has a nontrivial character. Under quasihydrostatic pressure (p), evidence for superconductivity is observed in the resistivity below the critical temperature Tc. The dome-shaped Tc versus p is obtained with maximum Tc~2.9 K. We argue that the formation of Cooper pairs (bosons) is the consequence of the redistribution of the 6-fold-degenerate fermions under pressure.

cond-mat.str-el↗