13,752 research outputs found

    Integrated Optical Fiber Sensor for Simultaneous Monitoring of Temperature, Vibration, and Strain in High Temperature Environment

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    Important high-temperature parts of an aero-engine, especially the power-related fuel system and rotor system, are directly related to the reliability and service life of the engine. The working environment of these parts is extremely harsh, usually overloaded with high temperature, vibration and strain which are the main factors leading to their failure. Therefore, the simultaneous measurement of high temperature, vibration, and strain is essential to monitor and ensure the safe operation of an aero-engine. In my thesis work, I have focused on the research and development of two new sensors for fuel and rotor systems of an aero-engine that need to withstand the same high temperature condition, typically at 900 °C or above, but with different requirements for vibration and strain measurement. Firstly, to meet the demand for high temperature operation, high vibration sensitivity, and high strain resolution in fuel systems, an integrated sensor based on two fiber Bragg gratings in series (Bi-FBG sensor) to simultaneously measure temperature, strain, and vibration is proposed and demonstrated. In this sensor, an L-shaped cantilever is introduced to improve the vibration sensitivity. By converting its free end displacement into a stress effect on the FBG, the sensitivity of the L-shaped cantilever is improved by about 400% compared with that of straight cantilevers. To compensate for the strain sensitivity of FBGs, a spring-beam strain sensitization structure is designed and the sensitivity is increased to 5.44 pm/με by concentrating strain deformation. A novel decoupling method ‘Steps Decoupling and Temperature Compensation (SDTC)’ is proposed to address the interference between temperature, vibration, and strain. A model of sensing characteristics and interference of different parameters is established to achieve accurate signal decoupling. Experimental tests have been performed and demonstrated the good performance of the sensor. Secondly, a sensor based on cascaded three fiber Fabry-Pérot interferometers in series (Tri-FFPI sensor) for multiparameter measurement is designed and demonstrated for engine rotor systems that require higher vibration frequencies and greater strain measurement requirements. In this sensor, the cascaded-FFPI structure is introduced to ensure high temperature and large strain simultaneous measurement. An FFPI with a cantilever for high vibration frequency measurement is designed with a miniaturized size and its geometric parameters optimization model is established to investigate the influencing factors of sensing characteristics. A cascaded-FFPI preparation method with chemical etching and offset fusion is proposed to maintain the flatness and high reflectivity of FFPIs’ surface, which contributes to the improvement of measurement accuracy. A new high-precision cavity length demodulation method is developed based on vector matching and clustering-competition particle swarm optimization (CCPSO) to improve the demodulation accuracy of cascaded-FFPI cavity lengths. By investigating the correlation relationship between the cascaded-FFPI spectral and multidimensional space, the cavity length demodulation is transformed into a search for the highest correlation value in space, solving the problem that the cavity length demodulation accuracy is limited by the resolution of spectral wavelengths. Different clustering and competition characteristics are designed in CCPSO to reduce the demodulation error by 87.2% compared with the commonly used particle swarm optimization method. Good performance and multiparameter decoupling have been successfully demonstrated in experimental tests

    An Investigation of Untapered and Tapered Fibre Transmission Properties

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    This thesis is about investigation of untapered and tapered fibre transmission properties by experimentation and simulation. Tapered fibre fabricated from commercial products and custom fibre from Bath University was investigated including different fibre type, taper length, and taper ratios. Simulations of untapered and tapered fibre by consideration of geometrical optics using Zemax are presented and compared to electromagnetic waveguide simulations using COMSOL. In addition, the impact of modal noise in tapered fibre is investigated, especially graded-index tapers, by quantifying macro- and micro-bending loss. Moreover, the fabrication of build-inhouse connector tapered fibre is introduced as a robust and cost-saving tool for spectrograph link. Lastly, a tapered fibre is tested with a compact EXOplanet high-resolution SPECtrograph (EXOhSPEC) of the University of Hertfordshire using Tungsten and ThAr lamps. Although the cladding light is detected clearly in custom graded-index taper, the light throughput in EXOhSPEC is improved. Overall these results indicate the potential for reasonable fibre-fed spectrograph performance using a ’single tapered fibre’

    Recent developments in 2D materials for energy harvesting applications

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    The ever-increasing demand for energy as a result of the growing interest in applications, such as the Internet of Things and wearable systems, etc, calls for the development of self-sustained energy harvesting solutions. In this regard, 2D materials have sparked enormous interest recently, due to their outstanding properties, such as ultra-thin geometry, high electromechanical coupling, large surface area to volume ratio, tunable band gap, transparency and flexibility. This has given rise to noteworthy advancements in energy harvesters such as triboelectric nanogenerators (TENGs), piezoelectric nanogenerators (PENGs) and photovoltaics based on 2D materials. This review introduces the properties of different 2D materials including graphene, transition metal dichalcogenides, MXenes, black phosphorus, hexagonal boron nitride, metal-organic frameworks and covalent-organic frameworks. A detailed discussion of recent developments in 2D materials-based PENG, TENG and photovoltaic devices is included. The review also considers the performance enhancement mechanism and importance of 2D materials in energy harvesting. Finally, the challenges and future perspectives are laid out to present future research directions for the further development and extension of 2D materials-based energy harvesters

    Beam scanning by liquid-crystal biasing in a modified SIW structure

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    A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

    Study of neural circuits using multielectrode arrays in movement disorders

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    Treballs Finals de Grau d'Enginyeria Biomèdica. Facultat de Medicina i Ciències de la Salut. Universitat de Barcelona. Curs: 2022-2023. Tutor/Director: Rodríguez Allué, Manuel JoséNeurodegenerative movement-related disorders are characterized by a progressive degeneration and loss of neurons, which lead to motor control impairment. Although the precise mechanisms underlying these conditions are still unknown, an increasing number of studies point towards the analysis of neural networks and functional connectivity to unravel novel insights. The main objective of this work is to understand cellular mechanisms related to dysregulated motor control symptoms in movement disorders, such as Chorea-Acanthocytosis (ChAc), by employing multielectrode arrays to analyze the electrical activity of neuronal networks in mouse models. We found no notable differences in cell viability between neurons with and without VPS13A knockdown, that is the only gene known to be implicated in the disease, suggesting that the absence of VPS13A in neurons may be partially compensated by other proteins. The MEA setup used to capture the electrical activity from neuron primary cultures is described in detail, pointing out its specific characteristics. At last, we present the alternative backup approach implemented to overcome the challenges faced during the research process and to explore the advanced algorithms for signal processing and analysis. In this report, we present a thorough account of the conception and implementation of our research, outlining the multiple limitations that have been encountered all along the course of the project. We provide a detailed analysis on the project’s economical and technical feasibility, as well as a comprehensive overview of the ethical and legal aspects considered during the execution

    Determining the most efficient geometry through simulation study of ZnO nanorods for the development of high-performance tactile sensors and energy harvesting devices

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    The piezoelectric nanomaterial ZnO exhibits an excellent piezoelectric response that can transduce mechanical energy into electrical signals by applying pressure. The piezoelectric behavior of ZnO nanostructures (especially nanorods or microrods) is getting considerable attention in the fabrications of piezo tactile sensors, energy harvesting devices, and other self-powering implantable devices. Especially vertically aligned ZnO nanorods are of high interest due to their higher value of piezoelectric coefficient along the z-direction. In this report, various geometries and alignments of ZnO nanorods are explored and their effect on strength of piezoelectric output potential has been simulated by COMSOL Multiphysics software. Best suited geometry and inclination are explored in this simulation to achieve high piezoelectric output in haptic and energy harvester devices. The simulation results show out of many geometries and inclinations the highest piezoelectric output is demonstrated by the inclined ZnO nanorods due to the application of higher torque force or shear stress in similar applied force. The high torque force or shear stress at 60 degree orientation and optimized contributions from all the piezoelectric coefficients resulted in a high piezoelectric output potential close to 215 mV which is much higher than the vertically aligned ZnO nanorod which is approximately 25 mV. The results are contrary to the accepted understanding that the vertical ZnO nanorods should produce the highest output voltage due to the high piezoelectric coefficient along the z-axis.Comment: 22 pages, 8 figure

    Self-healing by Diels-Alder cycloaddition in advanced functional polymers: A review

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    The ability of artificial materials to be healed efficiently, mimicking the living organisms, exhibits a great deal of potential advantages that can revolutionise the operation and maintenance of materials used in various applications. Such self-healable smart materials have been extensively researched in the last few decades, leading to the development of different physical and chemical synthesis approaches. Among these methods, chemical techniques based on reversible cycloadditions or disulfide bonding provide obvious advantages in terms of repeatability, which holds prime importance in determining the commerciality of the healing approach. This review compiles the recent advances in the field of self-healing polymers where the healing ability is introduced by reversible cycloaddition reactions while focusing mainly on the Diels-Alder (DA) reaction. DA is a [4 + 2] cycloaddition reaction where diene and dienophile pairs are used to fabricate thermally reversible crosslinked networks. These covalent bonds provide the necessary reversibility to the healing matrix and impart the desired strength to the polymeric material. There is a considerable body of recent literature where DA bonding has been employed either on its own or along with other healing mechanisms to impart self-healing to polymers. However, lack of a systematic review discussing these works makes it difficult for a beginner to cope with advancements in this field. Most early studies have focused on the healing stimuli and efficiency of healing in polymers but with this review, we would like to explore the healing thermodynamics governing the rupture–repair process in DA polymers along with the use of advanced spectroscopic techniques to study them and their applicability in thermosets, epoxy resins, biopolymers, and polymer nanocomposites. Novel applications for such advanced functional polymers, multifunctional healable polymers, and the outlook for future research, opportunities and challenges in the area are also discussed

    Tailoring Light-Matter Interaction via Advanced Nanophotonic Structures : From Passive to Dynamically Tunable Systems

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    Light-matter interaction is the fundamental principle of photonics that governs numerous disruptive applications. Dynamically tuning the light-matter interaction is key to designing advanced photonic devices with improved and enhanced functionalities. Specifically, having active control of the amplitude, wavelength, phase, and polarization of light is vital. It essentially addresses the key pillars of photonics, ranging from generating, guiding, manipulating, amplifying, and detecting light. This thesis presents a framework and platform to model, tailor, and enhance the light-matter interactions in nanophotonic structures. Epsilon-near-zero (ENZ) materials, plasmonic nanostructures, and metal-insulator-metal (MIM) cavities were utilized as a light-matter interaction platform. First, the underlying mechanism of emission enhancement was unravelled by integrating fluorescent dye with the MIM cavity. This study suggests a pathway for engineering the emission properties of an emitter through both Purcell and excitation rate enhancement. Following this, dynamic emission tuning was achieved, whereby a fluorescent dye containing hydrogel integrated MIM cavity was utilized. The thickness of the insulator layer was tuned by changing the ambient humidity, which resulted in spectral tuning of cavity resonance, hence the active tuning of emission. The coupling strength quantifies the light-matter interaction, so tuning the coupling strength is another way to tailor the light-matter interaction. By developing a novel electrical gating scheme, an active tuning of the coupling strength was demonstrated in a strongly coupled system comprised of ENZ materials that support ENZ mode and gold nanorods supporting the localized surface plasmon mode. Lastly, by harnessing the vanishing index of the ENZ material, less sensitivity of the spectral position of photonic resonance towards the geometrical perturbations was obtained through a polarization-independent plasmonic structure on an ENZ substrate. Overall, this thesis shows broad opportunities for using nanophotonic systems to tailor light-matter interactions dynamically

    Enhancement of Ionic Conductivity with Lattice Structure Manipulation in Al-doped Li7La3Zr2O17 Solid-State Electrolytes

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    High ionic conductivity is usually observed in the cubic phase of garnet Li7La3Zr2O12 (LLZO), which can be stabilized by dopants including Ca2+, Fe3+, Al3+, Ga3+, Ti4+, and Si4+. However, the ionic conductivity shows a strong dependence on both the lithium and the dopant atomic occupancy of the garnet LLZO crystal structure (space group Ia-3d), i.e., the 24d (LiO4) or 96h (LiO6) sites. Dopants occupying the 24d site can induce a strong local electric field which blocks the Li+ diffusion path. By employing SPS (Spark Plasma Sintering) to improve Al-LLZO's electrochemical performance, the mechanism of phase evaluation and atomic occupancy grove electrochemical performance was revealed. In the first study, high energy in the SPS induces Al3+ diffusion in LLZO lattices, transforming tetragonal phase LLZO into cubic phase LLZO. The Inter- and intra-grain effects on the ionic conductivity of LLZO SSE are discussed. As a result of the removal of low-conductivity impurities and an increase in bulk density, inter-grain ionic conductivity increases. In addition, the superior intra-grain ionic conductivity correlates with an increasing trend in LLZO SSE and an apparent decrease in secondary phase content. A rise in 24dLi1/96hLi2 occupancy ratio and a decrease in 24dAl1/96hAl2 correlates with increased ionic conductivity within the LLZO lattice. After SPS treated at 1100 oC, the ionic conductivity of LLZO prepared by SPS can reach 2.6×10-4 S cm-1, and the electronic conductivity is maintained at a low level. Moreover, this study provides insight into the relationship and correlation between two major factors (phase evaluation and atomic occupation) and ionic conductivity. However, the sparking plasma sintering (SPS) process, which limits the diffusion and relaxation time of the material, introduces a metastable state of the cubic LLZO with strong lattice distortion and inadequate ion distribution. In the second study, post-annealing promotes ion rearrangement, especially the Al3+ migration from the 24d to 96h sites, which is driven by the mitigation of the metastable state as identified by structure and composition analysis. Ionic conductivity as high as 3.3×10-4 S cm-1 is achieved along with low electronic conductivity of 5.17×10-7 S cm-1 by post-annealing at 500 oC in an oxygen environment after the SPS process. This work demonstrated a strategy to fabricate LLZO solid-state electrolyte with high ionic conductivity by manipulating its metastable state. It revealed that atomic occupation is a vital factor in influencing ionic conductivity besides doping content and bulk density. In addition, this work also prepared Ga and Ta doped LLZO powder and the effects of Ga and Ta substitutions on sintering have been meticulously studied. LLZO can be doped with Ga3+ and Ta5+ to achieve cubic crystal structure. The crystal structure is adjusted by Ga3+ substitution at Li+ sites and Ta5+ substitution at Zr4+

    Polymer-Based Micromachining for Scalable and Cost-Effective Fabrication of Gap Waveguide Devices Beyond 100 GHz

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    The terahertz (THz) frequency bands have gained attention over the past few years due to the growing number of applications in fields like communication, healthcare, imaging, and spectroscopy. Above 100 GHz transmission line losses become dominating, and waveguides are typically used for transmission. As the operating frequency approaches higher frequencies, the dimensions of the waveguide-based components continue to decrease. This makes the traditional machine-based (computer numerical control, CNC) fabrication method increasingly challenging in terms of time, cost, and volume production. Micromachining has the potential of addressing the manufacturing issues of THz waveguide components. However, the current microfabrication techniques either suffer from technological immaturity, are time-consuming, or lack sufficient cost-efficiency. A straightforward, fast, and low-cost fabrication method that can offer batch fabrication of waveguide components operating at THz frequency range is needed to address the requirements.A gap waveguide is a planar waveguide technology which does not suffer from the dielectric loss of planar waveguides, and which does not require any electrical connections between the metal walls. It therefore offers competitive loss performance together with providing several benefits in terms of assembly and integration of active components. This thesis demonstrates the realization of gap waveguide components operating above 100 GHz, in a low-cost and time-efficient way employing the development of new polymer-based fabrication methods.A template-based injection molding process has been designed to realize a high gain antenna operating at D band (110 - 170 GHz). The injection molding of OSTEMER is an uncomplicated and fast device fabrication method. In the proposed method, the time-consuming and complicated parts need to be fabricated only once and can later be reused.A dry film photoresist-based method is also presented for the fabrication of waveguide components operating above 100 GHz. Dry film photoresist offers rapid fabrication of waveguide components without using complex and advanced machinery. For the integration of active circuits and passive waveguides section a straightforward solution has been demonstrated. By utilizing dry film photoresist, a periodic metal pin array has been fabricated and incorporated in a waveguide to microstrip transition that can be an effective and low-cost way of integrating MMIC of arbitrary size to waveguide blocks
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