• 204

    Review of Antennas for Railway Communications


    This paper presents a review of the state-of-the-art antennas for the railway communications. There are various aspects that one should consider when designing an antenna, such as antenna size and directivity. While size constraints on railway antennas are not as critical as for mobile consumer counterparts, a radome structure is required to cover the antenna to minimize the aerodynamic resistance antenna. This paper reviews aerodynamic simulations to account for the drag coefficient of the antenna. In a low-frequency band (<5 GHz), railway antennas used to be omnidirectional in the horizontal plane. As the communication scheme advances toward 5G technology, high directivity is required for the railway antenna to compensate for the high path loss at high-frequency bands, i.e., 28-GHz band. We review recent studies of railway antennas over various frequency bands, such as LTE-R, LTE, and the lower and upper 5G bands. To accommodate multiple frequency bands with a single antenna, along with the aerodynamic radome cover, design techniques allowing multiple frequency bands are reviewed in this paper.
  • 203

    Enhanced energy harvesting ability of bismuth sodium titanate/ polyvinylidene fluoride composite film-based piezoelectric nanogenerators for mechanical energy scavenging and safety-walker applications


    Herein, we proposed a piezoelectric Bi0.5Na0.5TiO3 (BNT)/polyvinylidene fluoride (PVDF) flexible composite film-based peizoelectric nanogenerator (PNG) device as a highly efficient mechanical energy harvester. Initially, the BNT nanoparticles (NPs) with high dielectric constant were synthesized and loaded into a PVDF polymer matrix. The effect of BNT loading on the chemical property, dielectric property, and β phase of PVDF-based composite films was analyzed in depth. The various PNG devices based on the PVDF piezoelectric films with different concentrations of BNT NPs and aluminum electrodes were fabricated. The external force was applied to all the PNGs and their electrical output was systematically investigated to find the optimal concentration of BNT NPs inside the PVDF. The optimized 0.5 wt% BNT loaded PVDF composite film-based PNG device produced a highly efficient electrical output of about 19 V, 1.2 μA, and 3.5 mW/m2. The fabricated PNG device was robust and could generate highly stable electrical output over a long period. A highly efficient external electrical circuit was developed to effectively store the generated electricity from the PNG into various energy storage devices. Furthermore, the generated electrical energy was utilized to charge various energy storage capacitors and to power small electronics. Additionally, the flexible PNG device was demonstrated as a biomechanical energy harvester to convert various human movements into electricity successfully. Owing to the high flexibility, robustness, and energy conversion efficiency of the fabricated PNG device, it is expected to be utilized to harvest various mechanical movements available in daily life through large-scale technology. The unique PNG-powered self-illuminating bracelet-based safety walker system was proposed, which can be utilized in daily life to avoid accidents on roads and for many other applications.

  • 202

    Lead-free silver niobate microparticles-loaded PDMS composite films for high-performance clip-like hybrid mechanical energy harvesters


    A triboelectric nanogenerator (TENG) is a highly potential green energy harvesting technology to power small-scale electronic devices. Enhancing the overall electricity production capacity of TENGs is a primary concern for their utilization as an electricity generator in day-to-day life. Herein, we proposed a lead-free silver niobate (AgNbO3 (ANb)) microparticles (MPs)-embedded polydimethylsiloxane (PDMS) composite film-based clip-like hybrid nanogenerator (HNG) device, producing an enhanced electrical output from the applied mechanical movements. The ANb MPs with a high dielectric constant were initially synthesized and embedded inside the PDMS polymer matrix. Various HNGs were fabricated utilizing ANb MPs/PDMS composite films/aluminum tape as negative/positive triboelectric films, respectively and operated in contact-separation mode. The electrical output from them was comparatively analyzed to investigate an optimum concentration of the ANb MPs inside the PDMS film. The robust HNG with 5 wt % ANb MPs/PDMS composite film produced the highest electrical output with promising stability. Thereafter, three similar optimized HNGs were fabricated and integrated within a 3D-printed clip-like structure and the electrical output was thoroughly evaluated while combining multiple HNGs as well as from each independent HNG. The clip-like HNG device exhibited an electrical output of 340 V and 20 µA that can be further utilized to charge various capacitors and power portable electronics. Owing to the high resilience structure of the clip-like HNG device, it was also demonstrated to harvest biomechanical energy produced by human movements into electricity. The mechanical energy harvesting when the clip-like HNG device was attached to the accelerator pedal of the car and the pedal of a musical piano was successfully demonstrated.

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  • 201

    Hydrogen Peroxide Tuned Morphology and Crystal Structure of Barium Vanadate-Based Nanostructures for Aqueous Zinc-Ion Storage Properties


    Improving the layered-structure stability and suppressing vanadium (V) dissolution during repeated Zn2+ insertion/extraction processes are key to promoting the electrochemical stability of V-based cathodes for aqueous zinc (Zn)-ion batteries (AZIBs). In this study, barium vanadate (Ba2V2O7, BVO) nanostructures (NSs) are synthesized using a facile hydrothermal method. The formation process of the BVO NSs is controlled by adjusting the concentration of hydrogen peroxide (H2O2), and these NSs are employed as potential cathode materials for AZIBs. As the H2O2 content increases, the corresponding electrochemical properties demonstrate a discernible parabolic trend, with an initial increase, followed by a subsequent decrease. Benefiting from the effect of H2O2 concentration, the optimized BVO electrode with 20 mL H2O2 delivers a specific capacity of 180.15 mA h g−1 at 1 A g−1 with good rate capability and a long-term cyclability of 158.34 mA h g−1 at 3 A g−1 over 2000 cycles. Thus, this study provides a method for designing cathode materials with robust structures to boost the electrochemical performance of AZIBs.

  • 200

    Facile hydrothermal synthesis of NiMoO4xH2O nanorods-like structures as bifunctional oxygen electrocatalysts for rechargeable zinc-air batteries


    Developing highly active and low-cost bifunctional catalyst materials to replace precious metal species is of utmost importance for the commercialization of clean and sustainable energy systems. In this report, homogenous NiMoO4·xH2nanorods (NRs)-like structured materials were synthesized by an annealing-free hydrothermal method. The synthesized electrode electrochemical properties were determined by linear sweep voltammetry using a rotating ring disk electrode to determine the characteristics of oxygen reduction reaction in an O2-saturated electrolyte solution. For the oxygen evolution reaction, the NiMoO4·xH2O NRs electrocatalyst showed lower overpotential of 185 mV to obtain 10 mA cm−2. Furthermore, the NiMoO4·xH2O NRs electrocatalyst-based zinc (Zn)-air battery exhibited lower voltage gaps and smaller electrochemical impedance spectroscopy values than the Pt/C catalyst. Importantly, the NiMoO4·xH2O NRs-based battery (60 cycles (∼1100 min)) revealed excellent cycling stability results when compared with the Pt/C-based battery (30 cycles (∼550 min)). The NR structured electrode provided good steady potential after being subjected to a fixed current density of 10 mA cm−2 for 100 h. Therefore, these results demonstrate that the synthesized NiMoO4·xH2O NRs material is promising as a bifunctional electrocatalyst for rechargeable Zn-air batteries.

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  • 199

    Binder-Free Electrospun Nickel Cerium Selenide Nanofiber Electrodes Based on Voltage-Stimulated Diameter Refinement for Solar-Charged Quasi-solid-State Wearable Supercapacitors


    Binder-free electrospining approach for fabricating bimetallic chalcogen electrodes is essential for cost- and time-cutting but challenging. Herein, we propose a novel direct spray technique in electrospinning method to fabricate binder-free electrospun nickel cerium selenide nanofiber (NCSNF) structured materials. The effect of the applied electrospinning voltage on the average fiber diameter is analyzed. Electrospinning voltage of 25 kV is applied for obtaining an average fiber diameter of < 100 nm (87 nm) with rough interconnected nanofibers. The optimized NCSNF electrode exhibits remarkable long-term cycling stability over 50,000 galvanostatic charge–discharge (GCD) cycles. Furthermore, radish-derived nanolayered carbon (RDNLC) is synthesized via pyrolysis and its electrochemical properties are evaluated. The optimized NCSNF and RDNLC electrodes are employed to fabricate a polyvinyl alcohol–potassium hydroxide gel electrolyte-based quasi-solid-state asymmetric supercapacitor (ASC). The quasi-solid-state ASC delivers a high energy density value of 22 Wh kg−1 with 85% capacitance retention and 95% Coulombic efficiency over 40,000 GCD cycles, and upon being extended to the 50,000 GCD cycles, the capacitance retention and Coulombic efficiency reached 71% and 95%, respectively. A solar-charged wristband-like device is designed as a wearable supercapacitor, and the integrated device is attached to the human hand for powering electronic gadgets in contorted states, thus demonstrating its potential for wearable applications.

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  • 198

    Facile synthesis of sulfur-doped nickel manganese oxide nanoflakes as an electrode material by ion exchange process for high-performance hybrid supercapacitors


    To address the hazardous environmental impacts of fossil fuels, green and renewable energy sources can solve these environmental complications. Herein, we reported the synthesis and properties of sulfur (S)-doped nickel manganese oxide (NMSx, where x is the millimolar concentration of the S source), which was prepared via a facile ion exchange process by maintaining the pH value of the solution. The optimized NMS20 nanoflakes (NFs) material possessed a highly porous morphology with a large active surface area (109.24 m2 g−1), enhancing its electrochemical performance. An NMS20 NFs electrode delivered an appreciable areal capacity of 175.02 µAh cm−2 in a 1 M KOH electrolytic solution. The electrode also exhibited good cycling stability with 85.8% capacity retention and 100% coulombic efficiency over 20,000 cycles. A hybrid supercapacitor (HSC) was constructed using NMS20 NFs as the positive electrode and activated carbon/nickel foam as the negative electrode. The HSC exhibited maximum areal energy and power densities of 84.47 µWh cm−2 and 15,000 µW cm−2, respectively, with 83.8% capacitance retention after 30,000 cycles. Practical application of the HSC device was demonstrated by powering various electronic devices.

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  • 197

    Multimodal Energy Generation and Intruder Sensing Platform via Aluminum Titanate/Poly-Glucosamine Composite Film-Based Hybrid Nanogenerators


    Recently, a new class of portable self-powered electronic systems is developed that utilizes highly efficient hybrid nanogenerators that convert mechanical energy into electricity to power various sensors/small-scale electronics. This article proposes aluminum titanate (Al2TiO5) microparticles (AlT MPs) loaded poly-glucosamine (PGA) composite film-based high-performance hybrid nanogenerators (HNG) employed as a self-powered sensor for signal indication and as an intruder sensing platform. Initially, AlT MPs are synthesized and various concentrations are loaded into PGA. HNGs are fabricated using composite films/ polydimethylsiloxane, and Al as the positive/negative triboelectric layers and electrode film, respectively. The fabricated HNGs operate in the contact-separation mode and their produced electrical outputs are comparatively studied to determine the most suitable AlT concentration. The optimized HNG produces the highest electrical output of ≈211 V, ≈5.5 µA, and 79.5 µC/m2. The optimized HNG is employed as a biomechanical energy harvester to scavenge energy from various biomechanical movements and power portable electronics utilizing the developed highly efficient power management circuit. Thereafter, multiple HNGs are utilized to fabricate a self-powered wireless sensing system and real-time intruder sensing platform. The proposed highly efficient HNG-based self-powered wireless sensing platform is a promising technology that can be used on a large scale in various applications.

  • 196

    Enhanced Electrical Output via a 3D Printed Dual Nanogenerator Based on Bi2WO6 for Mechanical Energy Harvesting and Sensing pplications


    Triboelectric nanogenerators (TENGs) have gained significant attention for harvesting mechanical energy from everyday scenarios. Maximizing the TENG’s electrical output involves factors like dielectric film properties, where surface charge density is correlated with the dielectric constant. This study focuses on synthesizing biconcave bismuth tungstate [Bi2WO6 (BWO)] microparticles and embedding them into a polydimethylsiloxane polymer matrix to create a dual-purpose nanogenerator for energy harvesting and sensing applications. The investigation starts with a thorough analysis of the BWO material properties, followed by fine-tuning of dielectric features and optimizing the electrical performance of the composite film through various BWO concentrations. The 2.5 wt % BWO-based film nanogenerator exhibits enhanced dielectric constant, voltage, current, and charge values of approximately 5, 200 V, 4 μA, and 5 nC, respectively. This optimal composite material serves as the foundation for a hybrid nanogenerator (HNG) that synergistically exploits triboelectric and piezoelectric effects for simultaneous energy harvesting from mechanical and vibrational sources. A significant boost in the electrical output emerges through combining multiple energy harvesters. The harvested energy is used in powering portable electronics. The HNG is also employed in the wireless signal transmission in the sensor system and further in a wireless power transfer setup, showing the broad prospects of the fabricated HNGs in applications.

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  • 195

    Mechanical and Acoustic-Driven BiFeO3 Composite Films-Based Hybrid Nanogenerator for Energy Harvesting and Sensing Applications


    Nanogenerators for acoustic energy harvesting are still in the early stage of development, and many challenges such as the optimization of device structure and the design of efficient and sensitive materials need to be addressed. To solve the above-mentioned problems, herein, advancement in synthesized multiferroic material for hybridizing the nanogenerator and efficient harvesting of various energies such as acoustic, mechanical, and vibrational energies is reported. Initially, bismuth ferrate (BiFeO3, BFO)-based composite films are prepared with high ferroelectric and dielectric coefficients. The hybrid nanogenerator (HNG) based on a 3D-printed structure has the highest electrical output which is further improved depending on the BFO loading concentration in the composite film. The 0.5 wt% BFO-loaded PVDF-based HNG offers the enhanced open circuit voltage, short circuit current, and charge density values of ≈30 V, ≈1 µA, and ≈10 µC/m2, respectively. The optimized HNG is employed to harvest mechanical energy from everyday human life. Furthermore, the HNG layers are used in the fabrication of a multi-energy harvester/sensor (MEH/S) which can harvest/sense various vibrational and acoustic energies under different acoustic frequencies and amplitudes, respectively. The harvested energy from the MEH/S is tested to power portable electronics.