Extraordinary acoustic transmission via supercoupling and self-interference cancellation

Supercoupling is a widely researched topic in wave engineering, which has been used to build coupling channels that can, in principle, support total transmission and complete phase uniformity, independent of the length of the channel. This has generally been accomplished by employing dispersion in media that display a near-zero index. In the field of acoustics, prior works have required the presence of periodic embedded resonators, such as membranes or Helmholtz resonators, in order to observe near-zero properties. Here it is shown, theoretically and experimentally, that supercoupling can occur in an acoustic channel without the presence of embedded resonators. A compressibility-near-zero (CNZ) acoustic channel was observed to show remarkable properties analogous to those found in electromagnetics. Furthermore, these principles are employed to develop an acoustic power divider, which takes advantage of the CNZ properties of the channel to also exhibit phase invariance at the output. In the next section, another extraordinary acoustic transmission phenomenon is explored, regarding the potential for sending and receiving from a single acoustic transducer at the same time and at the same frequency. This is made possible through an electrical circuit that is designed to cancel self-interfering signals in acoustic measurement systems. Systems that employ self-interference cancellation (SIC) are often referred to as simultaneous transmit and receive (STAR) or in-band full duplex (IBFD) systems, which have recently enabled sending and receiving of Radio Frequency (RF) signals at the same time and at the same frequency. This has led to commercialization efforts with the promise of doubling the throughput of traditional radio systems including Wi-Fi and 5G cellular communications. Prior to these advances, researchers in vibration control explored self-sensing actuator systems, also referred to as sensoriactuators or sensorless control systems. Inspired by these developments, these approaches are combined and extended to explore STAR functionality in an acoustic measurement system. First, self-interference cancellation (SIC) is applied to time-domain measurements to demonstrate the potential for a practical, single-transducer ultrasonic nondestructive evaluation (NDE) system to measure echo returns while it is actively transmitting at the same frequency. Theoretical models and experimental results are presented and discussed.Electrical and Computer Engineerin

Roadmap on structured waves

Structured waves are ubiquitous for all areas of wave physics, both classical and quantum, where the wavefields are inhomogeneous and cannot be approximated by a single plane wave. Even the interference of two plane waves, or a single inhomogeneous (evanescent) wave, provides a number of nontrivial phenomena and additional functionalities as compared to a single plane wave. Complex wavefields with inhomogeneities in the amplitude, phase, and polarization, including topological structures and singularities, underpin modern nanooptics and photonics, yet they are equally important, e.g., for quantum matter waves, acoustics, water waves, etc. Structured waves are crucial in optical and electron microscopy, wave propagation and scattering, imaging, communications, quantum optics, topological and non-Hermitian wave systems, quantum condensed-matter systems, optomechanics, plasmonics and metamaterials, optical and acoustic manipulation, and so forth. This Roadmap is written collectively by prominent researchers and aims to survey the role of structured waves in various areas of wave physics. Providing background, current research, and anticipating future developments, it will be of interest to a wide cross-disciplinary audience.Comment: 110 pages, many figure

Broken passivity and time-reversal-symmetry bounds in acoustics devices

We collect information about the world through our senses, two of which, hearing and touch, are attuned to the mechanical vibrations travelling around us. Scientists and engineers have learned to control these acoustic waves, and in so doing they have opened new possibilities in how we interact with each other and the natural world. One area of rapid progress is acoustic metamaterials, which are architected structures that can shape sound waves in ways that go beyond what is possible with natural materials. Given the potential of these new materials, it is important to consider their limits and identify the underlying physical principles responsible for them. In this dissertation we examine limitations in the response of acoustic materials and devices due to passivity and time-reversal symmetry. An important constraint that arises due to time-reversal symmetry is reciprocity. Reciprocity must be broken to create devices that allow sound through in only one direction. This work explores acoustic nonreciprocity with particular attention to applications in surface acoustic wave devices and topological acoustic demonstrations. One way to achieve acoustic nonreciprocity is with fluid flow. Based on this technique, we present an acoustic Mach-Zehnder isolator and nonreciprocal leaky-wave antenna. A different but equally fundamental and important constraint in acoustics technology is the trade-off between the size, efficiency, and bandwidth of a small resonator. By considering arbitrary stored and radiated sound fields surrounding a compact source, we derive a theoretical lower bound on the quality factor of a passive acoustic radiator. This work discusses opportunities to overcome this constraint by considering active resonators. We experimentally demonstrate a three-fold bandwidth improvement to the passive case by synthesizing a non-Foster circuit load for a piezoelectric sonar transducer. By using a Green’s function approach and by connecting the physics of a disordered array to the statistical theory of random walks, we also explore the physics of near-zero-index materials, and leverage their unusual sound-matter interactions to enable robust and highly directive acoustic sources. This work introduces an entirely new way to achieve highly directional sound beyond traditional techniques.Mechanical Engineerin

Light Matter Interaction in Epsilon Near Zero Metal/Insulator Layered Nanocavities Thesis

Light-matter interaction has been a widely investigated phenomena enlarging the area of nanophotonics beyond the limit. This stand out to be the back bone for future generation optical devices. Light confinement and propagation in a small volume gives rise to several rich optical properties. This can be realized in different type of nanostructured materials. Metal(M)/Insulator(I) multilayer nanocavities are highly versatile systems for light confinement and wave guiding at nanoscale. Their physical behavior is discussed successfully by electromagnetic theory. However, it is still obscured about the nature of cavity modes in layered metal/insulator nanocavities. The reason why such cavity mode can be excited without having any momentum matching technique are yet to be investigated. We start with a quantum treatment of the MIM as a double barrier quantum well where the resonant modes are assisted by tunneling of photons. The lossless characteristics of these modes with zero wavevector condition are inherent to the epsilon-nearzero (ENZ) band. We further investigated the coupling between epsilon near zero assisted volume plasmons in MIMIM nanocavities where one MIM cavity placed above the other. Strong coupling has been demonstrated in this system by an anticrossing of the ENZ modes in the individual cavities, where the splitting depends strongly on the thickness of the central metal layer. The properties of ENZ bulk plasmon modes for MIM and MIMIM systems are exploited to achieve both enhancement of spontaneous emission and decay rate of the perovskite nanocrystal film placed on the top of the nanocavity. However, the enhancement is within the limit of weak coupling regime. In order to achieve strong coupling between ENZ mode of cavity and emission mode of the fluorophore, one need to embed the fluorophore inside the cavity. But it has been realized that in such a case, long term stability of fluorophore by retaining its original optical properties are primary challenges. We studied the optical properties of nanocrystal layer that were overcoated with alumina by atomic layer deposition. This enabled us to effectively embed the NCs inside the dielectric layers of planar MIM and MIMIM nanocavities

A Platform for Practical Nanophotonic Systems Nitrides and Oxides for Integrated Plasmonic Devices

The fields of nanophotonics and metamaterials have revolutionized the way we think of optical space (ε,µ), enabling us to engineer the refractive index almost at will, to confine light to the smallest of volumes, as well as to manipulate optical signals with extremely small foot prints and energy requirements. Throughout the past, this field of research has largely been limited to the use of noble metals as plasmonic materials, largely due to the high conductivity (low loss) and wide availability in research institutions. However, the research which follows focuses on the development of two alternative material platforms for nanophotonics: namely the transition metal nitrides and the transparent conducting oxides. Through this research, we have explored the nonlinear optical properties of thin films, demonstrating unique and ultrafast dynamic response, and have designed and realized high performance integrated plasmonic devices. Ultimately, this work aims to demonstrate the impact and potential of alternative plasmonic materials for numerous nanophotonic applications

Multiple light scattering in atomic media : from metasurfaces to the ultimate refractive index

(English) Our ability to confine, guide, and bend light has led to astonishing technological achievements, playing a fundamental role in diverse fields like microscopy, photochemistry, telecommunications or material design. The key property of materials that allows to control light is the refractive index. Notably, regardless of very different microscopic structures, all natural materials exhibit a modest, near-unity index of refraction, n ~ 1. This universality suggests the existence of some simple, ubiquitous origin, whose complete characterization from microscopic considerations, surprisingly, is still missing. Moreover, one can wonder which principles might allow to synthesize a material with an ultra-high index, to boost the performance of photonic devices. In this thesis, we address these questions from an atomic-physics standpoint, exploring if the macroscopic optical properties can be related to simple, electrodynamical processes occurring between well-separated atoms, which only interact via light scattering. Standard theories neglect that light can be scattered multiple times, and lead to unphysical predictions when strong interference occurs between the coherent atomic emission, such as in dense atomic ensembles or ordered lattices. We here develop new techniques to address the physics of multiple light scattering, with the ultimate goal of understanding the fundamental limits to the refractive index, as well as proposing unexpected photonic applications. Our results are divided in three parts. First, we investigate an ensemble of ideal atoms with increasing atomic density, starting from the dilute gas limit, up to dense regimes where a non-perturbative treatment of multiple scattering and near-field interactions is required. In this situation, we find that these effects limit the index to a maximum value of n ~ 1.7, in contrast with standard theories. We propose an explanation based upon strong-disorder renormalization group theory, in which the near-field interactions combined with random atomic positions result in an inhomogeneous broadening of the atomic resonance frequencies. This basic mechanism ensures that regardless of the physical atomic density, light at any given frequency only interacts with at most a few near-resonant atoms per cubic wavelength, thus limiting the index attainable. Afterwards, we show that a radically different behavior is expected for an ideal, atomic crystal. As long as the inter-atomic interactions are only mediated by multiple scattering, each 2D array of the crystal exhibits a lossless, single-mode response, which builds up a very large and purely real refractive index. To address the limits to this picture, we extend our theoretical analysis to much higher densities, where the electronic orbitals on neighboring nuclei begin to overlap. We develop a minimal model to include the onset of this regime into our non-perturbative analysis of multiple light scattering, arguing that the emergence of quantum magnetism, density-density correlations and tunneling dynamics of the electrons effectively suppresses the single-mode response, decreasing the index back to unity. Nonetheless, right before the onset of chemistry, our theory predicts that an ultra-high-index (n ~ 30) and low-loss material could in principle be allowed by the laws of nature. Finally, inspired by the impressive optical response of atomic arrays, we propose their use as a more complex optical device, namely a thin lens. The building blocks of this "atomic metalens" are composed of three consecutive 2D arrays, whose distance and lattice constants are suitably chosen to guarantee a high transmission of light, as well as an arbitrary phase shift. To characterize its efficiency and prove its robustness against losses, we perform large-scale numerical simulations, on a number of atoms between one and two orders of magnitude larger than comparable works.(Español) Nuestra capacidad de confinar y guiar la luz nos ha llevado a logros tecnológicos asombrosos, jugando un papel fundamental en campos tan diversos como la fotoquímica, las telecomunicaciones o el diseño de materiales. La propiedad clave de un material para controlar la luz es su índice de refracción. En particular, todos los materiales naturales exhiben un índice de refracción modesto, cercano a la unidad, n ~ 1. Esta universalidad sugiere la existencia de algún origen simple y ubicuo, cuya caracterización completa a partir de consideraciones microscópicas, sorprendentemente, aún falta. Además, para aumentar el rendimiento de los dispositivos fotónicos, es crucial entender si los principios físicos permiten o prohíben la síntesis de materiales con índices más altos. En esta tesis, abordamos estas cuestiones desde un punto de vista atómico, estudiando si las propiedades ópticas macroscópicas pueden deberse a procesos electrodinámicos entre átomos bien separados, que solo interactúan a través de la dispersión de la luz. Las teorías estándar ignoran que la luz puede dispersarse varias veces y conducen a predicciones erradas en situaciones de fuerte interferencia, como en redes cristalinas o conjuntos densos de átomos. Aquí, desarrollamos nuevas técnicas para tratar la dispersión múltiple de la luz, con el objetivo final de comprender los límites fundamentales del índice de refracción, así como proponer aplicaciones fotónicas innovadoras. Nuestros resultados se dividen en tres partes. Primero, investigamos un conjunto desordenado de átomos con densidad creciente, hasta regímenes donde se requiere un tratamiento completo de la dispersión múltiple y de las interacciones de campo cercano. En esta situación, encontramos que estos efectos limitan el índice de refracción a un valor máximo de n ~ 1,7. Proponemos una explicación basada en la teoría del grupo de renormalización, en la que las interacciones de campo cercano, combinadas con posiciones atómicas aleatorias, desarrollan una ampliación no homogénea de las frecuencias atómicas de resonancia. Este mecanismo asegura que, independientemente de la densidad atómica, la luz (para cualquier frecuencia dada) solo interactúa con unos pocos átomos resonantes por unidad cúbica de longitud de onda, limitando la respuesta óptica. Un comportamiento radicalmente diferente se manifiesta en una red cristalina de átomos. Siempre que las interacciones solo estén mediadas por dispersión múltiple, cada capa del cristal exhibe una respuesta monomodo sin pérdidas, que genera un índice de refracción muy grande y puramente real. Para abordar los límites de esta respuesta física, ampliamos nuestro análisis teórico hasta densidades tan altas que los orbitales electrónicos de los núcleos vecinos comienzan a superponerse. Desarrollamos un modelo para incluir el inicio de este régimen en nuestro análisis, argumentando que la aparición del magnetismo cuántico, las correlaciones de densidad y la dinámica de efecto túnel de los electrones suprimen efectivamente la respuesta monomodo, bajando nuevamente el índice a la unidad. No obstante, justo antes del inicio de los procesos químicos, nuestra teoría predice la posibilidad teórica de sintetizar un material con un índice de refracción sorprendentemente alto (n ~ 30) y pérdidas bajas. Por último, inspirándonos en la impresionante respuesta óptica de las redes atómicas, proponemos su uso para imitar un dispositivo óptico complejo, a saber, una lente delgada. El componente básico de esta "metalente atómica" está compuesto por tres redes atómicas bidimensionales consecutivas, cuyas distancias y constantes de red se eligen adecuadamente para garantizar una alta transmisión de la luz, así como un cambio de fase arbitrario. Para caracterizar su eficiencia y probar su robustez frente a pérdidas, realizamos simulaciones numéricas incluyendo un gran número de átomos, entre uno y dos órdenes de magnitud mayor que en trabajos comparables.DOCTORAT EN FOTÒNICA (Pla 2013

HIGH WAVE VECTOR ACOUSTIC METAMATERIALS: FUNDAMENTAL STUDIES AND APPLICATIONS

Acoustic metamaterials are artificially engineered structures with subwavelength unit cells that hold extraordinary acoustic properties. Their ability to manipulate acoustic waves in ways that are not readily possible in naturally occurring materials have garnered much attention by researchers in recent years. In this dissertation work, acoustic metamaterials that enable wave propagation with high wave vector values are studied. These materials render several key properties, including energy confinement and transport, wave control enhancement, and enhancement of acoustic radiation, which are exploited for enhancing acoustic wave emission and reception. The dissertation work is summarized as follows. First, to enable experimental studies of the deep subwavelength cavities in these metamaterials, a low dimensional fiber optic probe was developed, which allows direct characterization of the intrinsic properties of the metamaterials without seriously disrupting the acoustic fields. Second, low dimensional acoustic metamaterials for enhancing acoustic reception were realized and studied. These metamaterials were demonstrated to achieve both passive and active functionalities, including passive signal amplification and frequency filtering, as well as active tuning for switching and pulse retardation control. Third, a metamaterial emitter was realized and studied, which is capable of enhancing the radiative properties of an embedded emitter. Parametric studies enhanced the understanding of the effects of different geometric parameters on the radiation performance of the structure. Finally, the metamaterial emitter and receiver were combined to form a metamaterial-based sonar system. For the first time, the superior performance of the metamaterial enhanced sonar system over conventional sonar systems was analytically and experimentally demonstrated. As a proof of concept, a robotic sonar platform equipped with the metamaterial system was shown to possess remarkably better tracking performance compared to the conventional system. Through this dissertation work, an enhanced understanding of high-k acoustic metamaterials has been achieved, and their applications in acoustic sensing, emission enhancement, and sonar systems have been demonstrated

Numerical Analysis of Coupled Thermal-Electromagnetic Problems in Superconducting Cables

Superconducting materials, being characterized by a negligible electrical resistance under peculiar working conditions, provide extraordinary electromagnetic performances. The research field on electromagnets has taken a lot of advantages from this technology, since the huge electrical current densities that these materials sustain enable to produce very strong magnetic fields, up to more than 10 T, with negligible losses compared to the normal-conducting coils. The development of superconductors technology during the last years has enabled projects that only some decades ago were considered not feasible, both technically and economically. Among them, the most notable are fusion reactors like ITER, presently under construction in Cadarache (France), and particle accelerators for high energy physics such as the Large Hadron Collider (LHC) operating at CERN in Geneva (Switzerland). The present work regards the THELMA code, a coupled thermal-electromagnetic numerical model for the description of superconducting cables and magnets. This software was initially intended for the simulation of the electromagnetic behavior in the so-called Cable-In-Conduit-Conductors (CICC), largely used in fusion machines like ITER. During the PhD activity, a brand-new thermal model has been developed and added to the pre-existing code to describe problems in which the system thermal evolution cannot be assessed a priori. Moreover, the code has been extended to deal also with the Rutherford cables, a type of superconducting cable widely used in accelerator magnets like those of LHC. Finally, the code has been applied to several case studies, both in the field of accelerator and fusion magnets. This thesis is structured in the following way. The first two chapters are a general introduction to superconductivity: the first is a presentation of this phenomenon and its applications, intended for readers that are not familiar with this technology, whereas the second is a more detailed description of the superconducting wires and cables studied during this PhD activity. In the second part of the thesis, the THELMA numerical code is widely described. In chapter 3, the geometrical, electromagnetic and thermal models are presented, with a particular focus on the brand-new parts developed during this PhD activity, such as the Rutherford cable geometrical model, the thermal model and the coupling among electromagnetic and thermal routines. The THELMA model for electrical and thermal contact resistances is instead widely explained in chapter 4, together with the numerical analysis of several experimental measurements on both Rutherford and CICC cables. The third part of the work is instead focused on some examples of the application of the THELMA coupled code, performed during the PhD activity. In chapter 5 the analysis of the voltage-temperature characteristic on a CICC sample is presented, as a validation and an example of the code capability of reproducing non-trivial experimental findings. In chapter 6, the problem of the longitudinal propagation of a thermal-electromagnetic instability (quench) in impregnated Rutherford coils is analyzed with experimental, analytical and numerical tools. In chapter 7, the predictive analyses in terms of current distribution and losses in the CICC magnet NAFASSY are reported. Further details regarding useful material properties and some analytical and numerical models can be found in the appendices.I materiali superconduttori, essendo caratterizzati in particolari condizioni da una resistenza elettrica trascurabile, offrono straordinarie prestazioni elettromagnetiche. La ricerca sugli elettromagneti ha ottenuto notevoli vantaggi da questa tecnologia, in quanto le enormi densit\ue0 di corrente elettrica che questi materiali sopportano possono essere usate per generare campi magnetici estremamente intensi, anche maggiori di 10 T, con delle perdite trascurabili in confronto agli avvolgimenti normoconduttivi. Lo sviluppo della tecnologia dei superconduttori avvenuto negli ultimi anni ha permesso progetti che solo pochi decenni fa erano considerati irrealizzabili, sia dal punto di vista tecnico che economico. Tra questi, i pi\uf9 importanti sono senz\u2019altro i reattori per fusione nucleare come ITER, attualmnente in costruzione a Cadarache (Francia), e acceleratori di particelle per la fisica delle alte energie come il Large Hadron Collider (LHC) del CERN a Ginevra (Svizzera). In questa tesi viene presentato il codice THELMA, un modello numerico per la descrizione accoppiata del comportamento termo-elettromagnetico di cavi e magneti superconduttori. Questo codice era stato inizialmente creato per la simulazione del comportamento elettromagnetico dei cosiddetti Cable-In-Conduit-Conductors (CICC), ampiamente usati in macchine per la fusione nucleare come ITER. Durante l\u2019attivit\ue0 di dottorato, \ue8 stato implementato un nuovo modello termico in aggiunta al codice preestitente, in grado di descrivere problemi nei quali l\u2019evoluzione termica del sistema non pu\uf2 essere prevista a priori. Inoltre, il codice \ue8 stato esteso per descrivere i cavi di tipo Rutherford, usati comunemente nei magneti per acceleratori di particelle come quelli di LHC. Infine, il codice \ue8 stato applicato per l\u2019analisi di diversi casi di studio, sia nell\u2019ambito dei magneti per acceleratori di particelle che per fusione nucleare. La tesi \ue8 strutturata nella seguente maniera. I primi due capitoli sono un\u2019ampia introduzione alla superconduttivit\ue0: il primo \ue8 una presentazione generale di questo fenomeno e sulle sue applicazioni, pensata per chi non dovesse avere familiarit\ue0 con questa tecnologia, mentre il secondo contiene una descrizione pi\uf9 dettagliata dei fili e cavi superconduttori presi in considerazione durante questo dottorato di ricerca. Una descrizione dettagliata del codice numerico THELMA \ue8 invece riportata nella seconda parte della tesi. Nel capitolo 3 vengono presentati i modelli geometrici, elettromagnetici e termici, con particolare dettaglio relativamente alle parti sviluppate durante l\u2019attivit\ue0 di dottorato, quali il modello geometrico del cavo Rutherford, il modello termico e l\u2019accoppiamento tra il modello termico e quello elettromagnetico. Il modello di THELMA per le resistenze di contatto elettriche e termiche \ue8 invece descritto nel capitolo 4, insieme all\u2019analisi numerica di alcuni misure sperimentali sia su cavi Rutherford che CICC. La terza parte della tesi \ue8 invece focalizzata su alcuni esempi di applicazione del codice accoppiato THELMA, svolti durante l\u2019attivit\ue0 di dottorato. Nel capitolo 5 viene analizzata la caratteristica tensione-temperatura di un campione di cavo CICC, quale esempio di validazione sperimentale nella quale il codice \ue8 in grado di riprodurre fenomeni di difficile comprensione. Il capitolo 6 presenta il problema della propagazione longitudinale di un\u2019instabilit\ue0 termo-elettromagnetica in avvolgimenti impregnati di cavi Rutherford, analizzato con strumenti sperimentali, analitici e numerici. Nel capitolo 7 sono invece descritte le analisi predittive in termini di perdite e distribuzione di corrente riguardo il magnete CICC NAFASSY. Ulteriori dettagli riguardanti le propriet\ue0 dei materiali e alcuni modelli analitici e numerici sono infine riportati nelle appendici

Study of collagen structure in canine myxomatous mitral valve disease

Myxomatous mitral valve disease (MMVD) is the single most common acquired cardiac disease of dogs, and is a disease of significant veterinary importance. It also bears close similarities to mitral valve prolapse in humans and therefore is a disease of emerging comparative interest. Realising the importance of collagen fibres in mitral heart valves and considering the paramount significance of myxomatous mitral valve disease, a better understanding of the pathogenesis of MMVD is essential. Thus, this study was designed to investigate the changes in collagen molecules, including fibril structure, fibril orientation, d-spacing, collagen density, collagen content, thermal stability, and the status of mature and immature crosslinks. A combination of biophysical and biochemical tools such as x-ray diffraction, neutron diffraction, HPLC were utilised in order to fulfil the objectives. Biochemical assay of hydroxyproline revealed a 10% depletion of collagen in mildly affacted (grade I and II) leaflets, while a 20% depletion of fibrillar collagen was revealed by mapping the collagen fibrils onto the anatomy of cardiac leaflets using x-ray data. Differential scanning calorimetry showed that there were no significant differences in the onset temperature of denaturation of collagen between the healthy and affected leaflets. However, in affected areas of leaflets, the enthalpy of denaturation significantly dropped by 20%. In the affected regions, neutron diffraction results showed an increase in the immature reducible cross-links though the low number of the samples can be considered a limiting factor in this regard. However, the HPLC results showed a 25% decrease in the number of mature cross-links. Additionally, the recently introduced imaging technologies to biology and medicine such as differential enhancing imaging (DEI) and coherent anti-Stokes Raman scattering spectroscopy (CARS) were, to the author’s best knowledge, applied for the first time to this disease. In doing so, this thesis furthers our understanding of the pathogenesis of MMVD, especially in relation to the collagen. The thesis provides new findings about MMVD and demonstrates the potential of biophysical tools for studying similar conditions