Interconnection between machines, devices and people is one of the key aspects of the contemporary society and its working paradigms, which are driving the so called Fourth industrial revolution or Industry 4.0 (Hannover Fair, 2011). In this perspective, Machine to Machine communication (M2M) and Internet of Things (IoT) are able to provide increased automation, improved communication and self-monitoring, in different environments and industrial processes. A driving central force of innovation is represented by smart sensors and devices, which generate the data and allow further functionality from self-monitoring and self-configuration to condition monitoring of complex processes. This new generation of sensors has to be small, economically feasible and autonomous. The reduced power requirements of recent small electronic components, makes on-chip energy harvesting solutions a promising alternative to batteries or complex wiring. Amongst others, vibration-based energy harvesting schemes are particularly attractive due to the numerous and continuous sources of vibration present in the environment. However, due to the low amount of energy involved in common ambient vibrations, it is interesting to focus, or trap, waves from a larger region outside the device into a confined region in the near vicinity of the sensor; once the wave is localised, by using electromagnetic, electrostatic, or piezoelectric effects, efficient conversion from elastic to electric energy can be achieved. This work contains current developments in this technology, by presenting innovative energy harvesting solutions based on the introduction of piezoelectric materials inside graded metamaterials made of arrays of resonators. Starting from the investigation of novel wave phenomena in inhomogeneous media and elastic metamaterials, advanced multiresonator designs for energy harvesting are proposed. The major contributions of this Thesis are: - study of wave propagation in elastic solids based on spatial heterogeneities. It is demonstrated that high vibration attenuation can be achieved in inhomogeneous structures independently on periodicity. Moreover, simple lumped models allow to characterise the behaviour of such structures, providing a rapid analytical tool for the definition of efficient designs; - investigation of wave conversion phenomena in elastic half-spaces with graded arrays of resonators. Reversed mode conversion from surface Rayleigh to Shear (S) and Pressure (P) bulk waves is demonstrated leveraging on the Umklapp phenomenon. This mechanism allows to manipulate surface waves, focusing the elastic energy in specific regions of space for a broadband input frequency spectrum; - modeling, design, and experimental study of graded metamaterials based on the rainbow effect, i.e. the spatial signal separation depending on frequency, for energy harvesting purposes. Advanced multiresonator designs based on rainbow reflection, rainbow trapping and topological edge modes are investigated. Enhancement of the energy harvesting performances with respect to conventional solutions is demonstrated, for both the peak power production and the total transduced energy along time.
L'interconnessione tra macchine, dispositivi e persone è uno degli aspetti chiave della società contemporanea e dei suoi paradigmi di lavoro, che stanno guidando la cosiddetta Quarta rivoluzione industriale o Industria 4.0 (Fiera di Hannover, 2011). In questa prospettiva, la comunicazione Machine to Machine (M2M) e Internet of Things (IoT) sono in grado di fornire maggiore automazione, migliore comunicazione e automonitoraggio, in diversi ambienti e processi industriali. Una centrale forza trainante dell'innovazione è rappresentata da sensori e dispositivi intelligenti, che generano i dati e consentono ulteriori funzionalità, dall'auto-monitoraggio e auto-configurazione, al monitoraggio delle condizioni di processi complessi. Questa nuova generazione di sensori deve essere piccola, economicamente fattibile e autonoma. I ridotti requisiti di alimentazione di recenti piccoli componenti elettronici rendono le soluzioni di raccolta di energia on-chip una promettente alternativa alle batterie o al cablaggio complesso. Tra gli altri, gli schemi di raccolta di energia basati sulle vibrazioni sono particolarmente attraenti a causa delle numerose e continue fonti di vibrazione presenti nell'ambiente. Tuttavia, a causa della bassa quantità di energia coinvolta nelle comuni vibrazioni ambientali, è interessante focalizzare, o intrappolare onde da una regione più ampia al di fuori del dispositivo in una regione ristretta nelle immediate vicinanze del sensore; una volta localizzata l'onda, utilizzando effetti elettromagnetici, elettrostatici o piezoelettrici, è possibile ottenere una conversione efficiente da energia elastica a energia elettrica. Questo lavoro contiene gli sviluppi attuali di questa tecnologia, presentando soluzioni innovative di energy harvesting basate sull'introduzione di materiali piezoelettrici all'interno di metamateriali graded costituiti da array di risonatori. Partendo dallo studio di nuovi fenomeni d’onda in mezzi disomogenei e metamateriali elastici, vengono proposti dei progetti avanzati di multi-risonatori per la raccolta di energia. I principali contributi di questa Tesi sono: - studio della propagazione d’onda in solidi elastici caratterizzati da eterogeneità spaziali. Si dimostra che è possibile ottenere un'elevata attenuazione delle vibrazioni in strutture disomogenee indipendentemente dalla periodicità. Inoltre, semplici modelli concentrati consentono di caratterizzare il comportamento di tali strutture, fornendo un rapido strumento analitico per la definizione di sistemi efficienti; - studio dei fenomeni di conversione delle onde in semispazi elastici con array graded di risonatori. La conversione, in modalità inversa, da onde di Rayleigh di superficie a onde di taglio (T) e di pressione (P) viene dimostrata facendo leva sul fenomeno Umklapp. Questo meccanismo permette di manipolare le onde superficiali, focalizzando l'energia elastica in specifiche regioni dello spazio per un ampio spettro di frequenze in ingresso; -modellazione, progettazione e studio sperimentale di metamateriali graded basati sull'effetto arcobaleno, ovvero la separazione spaziale del segnale in base alla frequenza, per scopi di energy harvesting. Vengono studiati sistemi avanzati multi-risonanti basati su riflessione arcobaleno, intrappolamento arcobaleno e modi di bordo topologici. Viene dimostrato il miglioramento delle prestazioni di energy harvesting rispetto alle soluzioni convenzionali, sia per la produzione di potenza di picco che per l'energia totale trasdotta nel tempo.
Graded elastic metamaterials for energy harvesting
De Ponti, Jacopo Maria
2020/2021
Abstract
Interconnection between machines, devices and people is one of the key aspects of the contemporary society and its working paradigms, which are driving the so called Fourth industrial revolution or Industry 4.0 (Hannover Fair, 2011). In this perspective, Machine to Machine communication (M2M) and Internet of Things (IoT) are able to provide increased automation, improved communication and self-monitoring, in different environments and industrial processes. A driving central force of innovation is represented by smart sensors and devices, which generate the data and allow further functionality from self-monitoring and self-configuration to condition monitoring of complex processes. This new generation of sensors has to be small, economically feasible and autonomous. The reduced power requirements of recent small electronic components, makes on-chip energy harvesting solutions a promising alternative to batteries or complex wiring. Amongst others, vibration-based energy harvesting schemes are particularly attractive due to the numerous and continuous sources of vibration present in the environment. However, due to the low amount of energy involved in common ambient vibrations, it is interesting to focus, or trap, waves from a larger region outside the device into a confined region in the near vicinity of the sensor; once the wave is localised, by using electromagnetic, electrostatic, or piezoelectric effects, efficient conversion from elastic to electric energy can be achieved. This work contains current developments in this technology, by presenting innovative energy harvesting solutions based on the introduction of piezoelectric materials inside graded metamaterials made of arrays of resonators. Starting from the investigation of novel wave phenomena in inhomogeneous media and elastic metamaterials, advanced multiresonator designs for energy harvesting are proposed. The major contributions of this Thesis are: - study of wave propagation in elastic solids based on spatial heterogeneities. It is demonstrated that high vibration attenuation can be achieved in inhomogeneous structures independently on periodicity. Moreover, simple lumped models allow to characterise the behaviour of such structures, providing a rapid analytical tool for the definition of efficient designs; - investigation of wave conversion phenomena in elastic half-spaces with graded arrays of resonators. Reversed mode conversion from surface Rayleigh to Shear (S) and Pressure (P) bulk waves is demonstrated leveraging on the Umklapp phenomenon. This mechanism allows to manipulate surface waves, focusing the elastic energy in specific regions of space for a broadband input frequency spectrum; - modeling, design, and experimental study of graded metamaterials based on the rainbow effect, i.e. the spatial signal separation depending on frequency, for energy harvesting purposes. Advanced multiresonator designs based on rainbow reflection, rainbow trapping and topological edge modes are investigated. Enhancement of the energy harvesting performances with respect to conventional solutions is demonstrated, for both the peak power production and the total transduced energy along time.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/170928