Advanced Nanoelectromechanical Systems for Next Generation Energy Harvesting

The ever-increasing desire to produce portable, mobile and self-powered wireless micro-/nano systems (MNSs) with extended lifetimes has lead to the significant advancement in the area of mechanical energy harvesting over the last few years and it has been possible not only because has nanotechnology evolved as a powerful tool for the manipulation of matter on an atomic, molecular, and supramolecular scale, but also different micro-/nano fabrication techniques have enabled researchers and scientists to create, visualize, analyse and manipulate nano-structures, as well as to probe their nano-chemistry, nano-mechanics and other properties within the systems. The dissertation first discusses briefly about energy harvesting technologies for self-powered MNSs, for example a wireless aircraft structural health monitoring (SHM) system, with a particular focus on piezoelectric nanogenerators (PENG) and triboelectric nanogenerators (TENG) as they are the most promising approaches for converting ambient tiny mechanical energy into electrical energy efficiently and effectively and then it analyzes the theoretical and experimental methodologies for efficient energy harvesting using PENG, TENG and hybrid devices. The piezoelectric property intertwined with the semiconducting behaviour of different ZnO nanostructures has made them ideal candidate for piezoelectric energy harvesting, also intensive and state-of-the-art research has been going on to enhance the performance of the PENG devices based on 1D and 2D ZnO nanostructures. In this work, a high performance and consolidated PENG device based on the integration of ZnO nanowires and nanoplates on the same substrate has been demonstrated, that produces an output electrical power of 8.4 µW/cm2 at the matched load of 10MΩ that manifests their ability for powering up different MNSs. Since hybrid nanogenerators (HNG) integrate different types of harvesters in a single unit, where several energy sources can be leveraged either simultaneously or individually, in the next part of this work, a HNG device integrating PENG and TENG components has been designed, fabricated and characterized where PENG and TENG parts mutually enhance the performance of each other resulting an instantaneous peak power density of 1.864mW/cm2 and subsequently the device has been used to charge several commercial capacitors to corroborate their potential for aircraft SHM applications. Moreover, the hybrid device exhibits strong potential for wearable electronics as it can harvest energy from human walking and normal hand movements. However, successful implementation of self-powered electronics, such as a wireless aircraft SHM depends not only on the performance of individual parts but also on components integration within the system, where each device/system node within the network consists of a low-power microcontroller unit, high-performance data-processing/storage units, a wireless signal transceiver, ultrasensitive sensors based on a micro-/nano electro-mechanical system, and most importantly the embedded powering units. This dissertation aims to deepen the understanding of the different energy harvesting methods utilizing the knowledge of nanoscale phenomena and nanofabrication tools along with the associated prospects and challenges and thus, this research in the field of energy harvesting using advanced nano electro-mechanical systems could have a substantial impact on many areas, ranging from the fundamental study of new nanomaterial properties and different effects in nanostructures to diverse applications

Design of high-performance Triboelectric Nanogenerators (TENGs) for energy harvesting applications

The growing concerns around the long-term viability of the fossil fuel-based energy and its associated environmental cost are necessitating new research paradigms for energy generation and harvesting. An attractive and effective way to respond to the current energy crisis is through the harvesting of ambient mechanical energy from our environment. The conventional mechanical energy harvesting technologies are highly dependent on either the use of rare earth magnetic materials, high precision microfabrication techniques or composed of brittle materials, which are required to be driven at very high resonant frequencies, not frequently encountered beyond an industrial setting. Recently, triboelectric nanogenerators (TENG), based on the triboelectrification and electrostatic induction effects, have been demonstrated as a novel harvesting technique to collect and transform ambient mechanical energy into electric power. Unlike the other mechanical energy harvesters, the low-cost TENGs fabricated using commodity polymers and facile fabrication techniques, operate at low frequencies (1-10 Hz) with a high energy conversion efficiency. One of the key areas in TENG research is the enhancement of their electrical output to make them suitable for either making a self-powered system viable or powering small portable electronics directly. Except for the judicious use of tribo-materials or the tribo-layer architecture optimisation, the rest of the methods for enhancing the TENG output are reliant on expensive equipment and complicated processing, that undermine the advantages of TENGs and may not provide the required stability and reliability. This PhD study aims to establish novel strategies to enhance output performance of TENG by developing new tribo-materials and phenomena such as coupling of tribo-piezoelectric effects to showcase potential applications of the TENG devices. The research work conducted and the achievements are summarized as follows. Firstly, a novel output performance improvement strategy of utilising stress-induced polarization effect of the piezoelectric materials was proposed. An interfacial layer of piezoelectric zinc oxide (ZnO) nanosheets was deposited to generate additional piezoelectric charge induced by the vertical contact-separate generation cycle. This extra piezoelectric charge is injected into the upper polydimethylsiloxane (PDMS) tribo-negative layer for the enhancement of the surface charge density from ~110 μC.m-2 to ~225.7 μC.m-2. The introduction of the ZnO and Zn-Al:Layered Double Hydroxides (LDH), as charge injection layer and anionic clay, enhanced the instantaneous power output from ~11 W.m-2 to 47 W.m-2. Subsequently, based on a similar principle, a novel composite of lead-free perovskite, zinc stannate (ZnSnO3), and a fluoropolymer, poly(vinylidene fluoride), PVDF, was proposed for the stress-polarisation tribo-negative behaviour with a simplified structure. The PVDF-ZnSnO3 composite membranes were realised through a facile phase-inversion technique leading to higher piezoelectric constant (76.3 pm.V-1) and β-phase (72%) for the composites. When applied to the TENG devices, the PVDF-ZnSnO3 membranes allowed spontaneous polarisation effects which led to significant enhancement of the electrical outputs, with maximum peak-to-peak voltage and effective transferred current density of ~600 V and ~206 µC.m-2, respectively. The surface charge enhancement and distribution of the composite membrane were also probed and demonstrated through the electrostatic force (EFM) and piezoelectric force microscopy (PFM). To overcome the difficulty in processing of the currently known most tribo-negative material, polytetrafluoroethylene (PTFE), an emulsion electrospinning technique incorporating polyethene oxide (PEO) was introduced. It was observed that the subsequent thermal removal of PEO led to a significant degradation in the surface charge density of the obtained PTFE nanofibrous membranes, which was overcome using a facile negative ion-injection process. The measured electrical outputs, with a maximum peak-to-peak voltage output of ~900 V and charge density of ∼149 μC.m−2, demonstrated the excellent effect of the enhanced contact area to the improvement of the outputs. The work eliminates the demonstrated need for surface micro structuring using reactive ion etching of PTFE surfaces by introducing a relatively simple, costeffective, and environmentally friendly technique for fabricating fibrous fluoropolymers tribonegative layer for the energy harvesting applications. Finally, a unique mouldable material, aniline formaldehyde resin (AFR) was synthesised and characterised. The synthesised AFR, as a resinous polymer with significant amine (-NH2) groups acquires the most surface positive charge, is applied as a tribo-positive material. The heatpressed AFR thin-film based TENG was subsequently tested to demonstrate its outstanding performance serving as a tribo-positive layer compared to the Polyamide 6 (PA6) and polyethene oxide (PEO), as one of the most common used tribo-positive materials. In addition, a Kelvin Probe Force Microscopy (KPFM) was subsequently employed to study the surface potential of the produced AFR layer and the surface potential change of the contact layers during the energy generation cycles. All of the produced high-performance TENGs (power output ranging from 9 - 47 W.m-2) have the potential to be utilised further in enabling self-powered systems and can serve as a new alternative energy harvesting source of great significance

Low-power techniques for wireless gas sensing network applications: pulsed light excitation with data extraction strategies

Aquesta tesi està enfocada en dues línies d'investigació. La primera aborda el desenvolupament d'una metodologia basada en llum polsada per modulació de sensors químic-resistius per a l'extracció d'informació del senyal transitòri, i la segona planteja la implementació d'una xarxa sense fils de sensors (WSN) basada en tecnologia LoRa per al monitoratge de la qualitat de l'aire (AQM) i la detecció d'esdeveniments de fuita de gasos. Aquest document està estructurat en quatre capítols organitzats de la següent manera: el Capítol 1 presenta l'estat de l'art, una introducció als mecanismes de millora de l'comportament dels sensors químic-resistius, així com una introducció a la implementació de xarxes sense fils de sensors per a la monitorització de la qualitat de l'aire; el Capítol 2 està compost pels dos articles publicats relacionats amb la metodologia basada en la modulació utilitzant llum polsada per a l'extracció d'informació del senyal transitòria de sensors químic-resistius; el Capítol 3 presenta l'article publicat relacionat amb la implementació d'una WSN per a AQM; el Capítol 4 presenta les conclusions derivades dels resultats obtinguts durant el desenvolupament de el projecte de tesi i les recomanacions per al treball futur associat a la continuïtat dels principals resultats d'aquesta tesiLa presente tesis está enfocada en dos líneas de investigación, La primera aborda el desarrollo de una metodología basada en luz pulsada para modulación de sensores químico-resistivos para la extracción de información de la señal transitoria; y la segunda plantea la implementación de una red inalámbrica de sensores (WSN) basada en tecnología LoRa para la monitorización de la calidad del aire (AQM) y la detección de eventos de fuga de gases. Este documento está estructurado en cuatro capítulos organizados de la siguiente forma: el Capítulo 1 presenta el estado del arte, una introducción a los mecanismos de mejora del comportamiento de los sensores químico-resistivos, así como una introducción a la implementación de redes inalámbricas de sensores para la monitorización de la calidad del aire; el Capítulo 2 está compuesto por los dos artículos publicados relacionados con la metodología basada en la modulación utilizando luz pulsada para la extracción de información de la señal transitoria de sensores químico-resistivos; el Capítulo 3 presenta el artículo publicado relacionado con la implementación de una WSN para AQM; el Capítulo 4 presenta las conclusiones derivadas de los resultados obtenidos durante el desarrollo de el proyecto de tesis y las recomendaciones para el trabajo futuro asociado a la continuidad de los principales resultados de esta tesis.The present thesis project is focused in two different yet related research lines. The first one addresses the development of a pulsed light-based chemiresistive sensor modulation methodology for transient information extraction. The second research line developed deals with the implementation of a LoRa-based portable, scalable, low-cost, and low power Wireless Sensor Network (WSN) for Air Quality Monitoring (AQM) and gas leakage events detection. This document is structured in four Chapters organized as follows: Chapter 1 presents the state of the art, an introduction to sensing performance enhancement and transient data extraction methods, as well as an introduction to the implementation of WSN for AQM; Chapter 2 is composed of the two published paper related to the pulsed light modulation methodology for transient information extraction; Chapter 3 presents the published paper related to the implementation of a LoRa-based WSN for AQM; Chapter 4 states the conclusions derived from the results obtained during this thesis project and the recommendations for the future work associated to the continuity of this thesis findings

Fibre-sized energy generation in multi-functional fabrics

This study investigates the prospects of manufacturing Piezo-fabrics with embedded piezoelectric yarns that have the potential to convert the human movement-induced mechanical strain on the fabric into electrical energy. The impact of fabric architecture on electrical power output and the translation of simulated work (in ANSYS) into real electrical outputs through the experimental validation of the piezoelectric yarns was also investigated

Flexible sensors—from materials to applications

Flexible sensors have the potential to be seamlessly applied to soft and irregularly shaped surfaces such as the human skin or textile fabrics. This benefits conformability dependant applications including smart tattoos, artificial skins and soft robotics. Consequently, materials and structures for innovative flexible sensors, as well as their integration into systems, continue to be in the spotlight of research. This review outlines the current state of flexible sensor technologies and the impact of material developments on this field. Special attention is given to strain, temperature, chemical, light and electropotential sensors, as well as their respective applications

A hybrid piezoelectric and electrostatic energy harvester for scavenging arterial pulsations

Implantable and wearable biomedical devices suffer from a limited lifespan of on-board batteries which results in a requirement to change the battery or the device itself causing additional physical discomfort. In order to overcome this, various energy harvesters have been developed. The human body possesses several types of energy available for scavenging through appropriately designed energy harvesting devices, while cardiovascular system in particular represents a constant reliable source of mechanical energy from vibration. Most conventional energy harvesters exploit only a single phenomenon, such piezo- or triboelectricity, thus producing reduced power density. As an improvement, hybridisation of energy harvesters intends to negate this drawback by simultaneously scavenging energy by multiple harvesters. In the present work, the reverse electrowetting on dielectric (REWOD) phenomenon is combined with the piezoelectric effect in a proof-of-concept hybrid harvester for scavenging biomechanical energy from arterial or other type pulsations. A mathematical model of the harvester was developed, and a computational investigation using CFD, and fluid-structure interaction simulations were carried out using the COMSOL Multiphysics software. The effect of the materials of piezoelectric film and geometrical features of the harvester on parameters such as the displacement, the frequency of pulsations and the energy produced were studied. An experimental setup that could imitate the displacements caused from arterial pulsations was designed and the produced electrical energy characteristics were analysed. A comparison between experimental and computational data was carried out and demonstrated a good agreement. Dependencies between geometrical parameters and electrical output were obtained, recommendation on piezoelectric materials and design solutions were provided

Atti del XXXV Convegno Nazionale di Idraulica e Costruzioni Idrauliche

La XXXV edizione del Convegno Nazionale di Idraulica e Costruzioni Idrauliche (IDRA16), co-organizzata dal Gruppo Italiano di Idraulica (GII) e dal Dipartimento di Ingegneria Civile, Chimica, Ambientale, e dei Materiali (DICAM) dell’Alma Mater Studiorum - Università di Bologna, si è svolta a Bologna dal 14 al 16 settembre 2016. Il Convegno Nazionale è tornato pertanto ad affacciarsi all’ombra del “Nettuno”, dopo l’edizione del 1982 (XVIII edizione). Il titolo della XXXV edizione, “Ambiente, Risorse, Energia: le sfide dell’Ingegneria delle acque in un mondo che cambia”, sottolinea l’importanza e la complessità delle tematiche che rivestono la sfera dello studio e del governo delle risorse idriche. Le sempre più profonde interconnessioni tra risorse idriche, sviluppo economico e benessere sociale, infatti, spronano sia l’Accademia che l’intera comunità tecnico-scientifica nazionale ed internazionale all’identificazione ed alla messa in atto di strategie di gestione innovative ed ottimali: sfide percepite quanto mai necessarie in un contesto ambientale in continua evoluzione, come quello in cui viviamo. La XXXV edizione del Convegno di Idraulica e Costruzioni Idrauliche, pertanto, si è posta come punto d’incontro della comunità tecnico-scientifica italiana per la discussione a tutto tondo di tali problematiche, offrendo un programma scientifico particolarmente ricco e articolato, che ha coperto tutti gli ambiti riconducibili all’Ingegneria delle Acque. L’apertura dei lavori del Convegno si è svolta nella storica cornice della Chiesa di Santa Cristina, uno dei luoghi più caratteristici e belli della città ed oggi luogo privilegiato per l’ascolto della musica classica, mentre le attività di presentazione e discussione scientifica si sono svolte principalmente presso la sede della Scuola di Ingegneria e Architettura dell’Università di Bologna sita in Via Terracini. Il presente volume digitale ad accesso libero (licenza Creative Commons 4.0) raccoglie le memorie brevi pervenute al Comitato Scientifico di IDRA16 ed accettate per la presentazione al convegno a valle di un processo di revisione tra pari. Il volume articola dette memorie in sette macro-tematiche, che costituiscono i capitoli del volume stesso: I. meccanica dei fluidi; II. ambiente marittimo e costiero; III. criteri, metodi e modelli per l’analisi dei processi idrologici e la gestione delle acque; IV. gestione e tutela dei corpi idrici e degli ecosistemi; V. valutazione e mitigazione del rischio idrologico e idraulico; VI. dinamiche acqua-società: sviluppo sostenibile e gestione del territorio; VII. monitoraggio, open-data e software libero. Ciascuna macro-tematica raggruppa più sessioni specialistiche autonome sviluppatesi in parallelo durante le giornate del Convegno, i cui titoli vengono richiamati all’interno del presente volume. La vastità e la diversità delle tematiche affrontate, che ben rappresentano la complessità delle numerose sfide dell’Ingegneria delle Acque, appaiono evidenti dalla consultazione dell’insieme di memorie brevi presentate. La convinta partecipazione della Comunità Scientifica Italiana è dimostrata dalle oltre 350 memorie brevi, distribuite in maniera pressoché uniforme tra le sette macro-tematiche di riferimento. Dette memorie sono sommari estesi di lunghezza variabile redatti in lingua italiana, o inglese. In particolare, la possibilità di stesura in inglese è stata concessa con l’auspicio di portare la visibilità del lavoro presentato ad un livello sovranazionale, grazie alla pubblicazione open access del volume degli Atti del Convegno. Il volume si divide in tre parti: la parte iniziale è dedicata alla presentazione del volume ed all’indice generale dei contributi divisi per macro-tematiche; la parte centrale raccoglie le memorie brevi; la terza parte riporta l’indice analitico degli Autori, che chiude il volume