Ultrasound contrast agents (UCA) is a relatively new tool, used in medical ultrasound imaging to enhance the diagnostic abilities of ultrasound and potentially offer a therapeutic value in medical ultrasounds. UCAs are bi or single-layered bubbles, that contain a highly backscattering gas. By injecting them into the blood flow, we locally increase the echogenicity and therefor enhance the contrast of the blood-tissue interface. This way we can provide a improved image of the structure of the organs, we can more accurately diagnose abnormal of defected areas on them, and if the containing gas is replaced with an appropriate drug, focus drug delivery can be achieved, providing potential healing of the disease. ! Up to now, most of the studies done in order to investigate the microbubbles - ultrasound interaction are mostly population studies, which due to their roughly approach cannot clearly diagnose and explain the complex nonlinear and dynamic properties of UCAs and their response to ultrasound field. Because of that, our knowledge on the UCAsʼ, is yet limited although the potential improvements at imaging and therapeutic technics that would be gained from a thorough understanding of this interactions can be very big. ! In this thesis, a study of single microbubbles is presented, using a system developed by the group of Ultrasound imaging in Edinburgh University. The system uses a specially modified commercial ultrasound machine, phased array probes and a specially designed single microbubbles measuring system. The system has the ability to feed, insonify and capture the backscattered echo from a single microbubble, with the use of fully calibrated and characterized ultrasound - probe system. The aim of the project is to contribute in the understanding of the behavior of the UCAs when insonified with an ultrasound wave, and the underlying physical mechanism behind that. The response of two different commercially available UCAs under insonification by ultrasound waves of varying acoustical pressure is presented. The UCAs used are Definity and biSphere. In total echoes from 842 biSphere and 1994 Definity microbubbles have ben captured and the data have been analyzed with in house made matlab codes. Also the response of the bubbles when insonified by consequent pulses of different repetition frequency has been investigated. For this reason, echoes from other 1221 Definity and 459 biSphere microbubbles have been captured and analyzed. The fully understanding of the agent - ultrasound interaction mechanisms can be the basis for creating improved signal processing tools for ultrasound imaging contrast enhancement that would improve imaging abilities of the modality, and potentially use of UCAs as a therapeutic mean. / Οι μικροφυσαλίδες ενίσχυσης της αντίθεσης στην υπερηχοτομογραφία είναι ένα σχετικά καινούργιο “εργαλείο”, το οποίο χρησιμοποιείται προκειμένου να βελτιώσει τις διαγνωστικές ιδιότητες της υπερηχοτομογραφίας και δυνητικά να προσφέρει μια θεραπευτική αξία σε αυτήν. Οι μικροφυσαλίδες είναι φυσαλίδες μονού ή διπλού κελύφους, με διάμετρο της τάξης των 3 μm, οι οποίες περιέχουν αέριο που αντανακλά έντονα τον ήχο. Εισάγοντας τις φυσαλίδες αυτές στην ροή του αίματος του ασθενούς, ενισχύουμε τοπικά την ηχογένεια και κατ΄ επέκταση βελτιώνουμε την αντίθεση μεταξύ του αίματος και των παρακείμενων ιστών. Με αυτό τον τρόπο μπορούμε να αποκτήσουμε μια καλύτερη εικόνα της δομής των οργάνων, να διαγνώσουμε με ακρίβεια την παθοφυσιολογία συγκεκριμένων περιοχών πάνω σε αυτά και, εάν το αέριο των φυσαλίδων αντικατασταθεί με την κατάλληλη φαρμακευτική ουσία, να επιτύχουμε στοχευμένη εφαρμογή της φαρμακευτικής θεραπείας, οδηγώντας σε πιθανή ίαση της ασθένειας. ! Μέχρι τώρα, το μεγαλύτερο μέρος των μελετών που έχουν γίνει με σκοπό την διερεύνηση της αλληλεπίδρασης των φυσαλίδων με τους υπερήχους βασίζονται σε πληθυσμιακές μελέτες, οι οποίες λόγω της γενικής (σε επίπεδο πληθυσμού) προσέγγισής τους, δεν μπορούν με σαφήνεια να διαγνώσουν και να εξηγήσουν τις σύνθετες μη γραμμικές και δυναμικές ιδιότητες των μικροφυσαλίδων, καθώς και την συμπεριφορά τους όταν βρεθούν μέσα στο υπερηχητικό πεδίο. Εξαιτίας αυτού, η γνώση μας σχετικά με τις μικροφυσαλίδες ενίσχυσης της αντίθεσης είναι ακόμα περιορισμένη, αν και οι πιθανές βελτιώσεις τόσο στις απεικονιστικές όσο και στις θεραπευτικές τεχνικές των υπερήχων που θα μπορούσαν να επιτευχθούν μέσα από την κατανόηση αυτής της αλληλεπίδρασης θα ήταν ιδιαίτερα σημαντικές. ! Σε αυτή την εργασία, παρουσιάζεται μια μελέτη των μικροφυσαλίδων όχι σε επίπεδο πληθυσμού αλλά σε επίπεδο μονάδας, η οποία έγινε με την χρήση μιας καινοτόμου πειραματικής διάταξης που αναπτύχθηκε από την ομάδα Υπερηχοτομογραφίας του Πανεπιστήμιου του Εδιμβούργου. Η διάταξη αυτή χρησιμοποιεί έναν ειδικά τροποποιημένο εμπορικό υπερηχοτομογράφο, phased array εκπομπούς, και ένα επίσης ειδικά κατασκευασμένο σύστημα μέτρησης της απόκρισης των μιρκοφυσαλίδων σε επίπεδο μονάδας. Το σύστημα αυτό έχει την δυνατότητα να εισάγει, να διεγείρει με υπερήχους, καθώς και να συλλέγει την ανάκλαση από τις μικροφυσαλίδες, μία προς μία. Σκοπός της εργασίας αυτής είναι να συμβάλει όσο το δυνατόν περισσότερο στην κατανόηση της συμπεριφοράς των μικροφυσαλίδων όταν αυτές διεγείρονται από υπερηχητικά κύματα, καθώς και των υπεύθυνων, για την συμπεριφορά αυτή, φυσικών μηχανισμών. ! Στην παρούσα εργασία παρουσιάζεται η απόκριση δυο διαφορετικών εμπορικά διαθέσιμων τύπων μικροφυσαλίδων, σε υπερηχητικά κύματα διαφορετικών ακουστικών πιέσεων. Οι μικροφυσαλίδες που χρησιμοποιήθηκαν είναι οι Definity και οι biSphere. Συνολικά, η ανάκλαση από 842 biSphere και 1994 Definity μικροφυσαλίδες έχει καταγραφεί, και τα δεδομένα έχουν αναλυθεί με κώδικα Matlab, ο οποίος αναπτύχθηκε στο εργαστήριο ειδικά για την ανάλυση αυτή. ! Επίσης, ερευνάται η απόκριση των φυσαλίδων όταν διεγείρονται από αλλεπάληλους υπερηχητικούς παλμούς, διαφορετικών συχνοτήτων επανάληψης. Για τον σκοπό αυτό, καταγράφηκαν και αναλύθηκαν ανακλάσεις από ακόμα 1221 Definity και 459 biSphere μικροφυσαλίδες. ! Η πλήρης κατανόηση της αλληλεπίδρασης των μικροφυσαλίδων με τους υπερήχους μπορεί να αποτελέσει την βάση για την ανάπτυξη βελτιωμένων τεχνικών επεξεργασίας σήματος για την απεικονιστική υπεηχοτομογραφία, οι οποίες μπορούν να βελτιώσουν τις δυνατότητες των υπερήχων, και δυνητικά να μετατρέψουν τις μικροφυσαλίδες ενίσχυσης σε ένα μέσο ίασης ασθενειών.

Infrastructure deterioration is an international problem requiring significant attention. One particular manifestation of this deterioration is the occurrence of sub-surface cracking (delaminations) in reinforced concrete bridge decks. Of many techniques available for inspection, air-coupled impact-echo testing, or sounding, is a non-destructive evaluation technique to determine the presence and location of delaminations based upon the acoustic response of a bridge deck when struck by an impactor. In this work, two automated air-coupled impact echo sounding devices were designed and constructed. Each device included fast and repeatable impactors, moving platforms for traveling across a bridge deck, microphones for air-coupled sensing, distance measurement instruments for keeping track of impact locations, and signal processing modules. First, a single-channel automated sounding device was constructed, followed by a multi channel system that was designed and built from the findings of the single-channel apparatus. The multi channel device performed a delamination inspection in the same manner as the single-channel device but could complete an inspection of an entire traffic lane in one pass. Each device was tested on at least one concrete bridge deck and the delamination maps produced by the devices were compared with maps generated from a traditional chain-drag sounding inspection. The comparison between the two inspection approaches yielded high correlations for bridge deck delamination percentages. Testing with the two devices was more than seven and thirty times faster, respectively, than typical manual sounding procedures. This work demonstrates a technological advance in which sounding can be performed in a manner that makes complete bridge deck scanning for delaminations rapid, safe, and practical.

Commercial aircraft are subject to noise regulations imposed by the Federal Aviation Administration. Currently, the FAA limits overland flight of supersonic airplanes due to the negative effect of the sonic boom on communities. The annoyance produced by the impulsive signature of sonic booms, particularly indoors, cannot exceed that of the broadband, low-overpressure noise produced by subsonic airplanes for the restriction to be lifted. Therefore, the ability to understand and accurately reproduce the acoustic response of a sonic boom is important for psychoacoustic classification of their tolerability within residences. This thesis presents and interprets results of the propagation and transmission of simulated sonic booms incident on wood-framed structures. The testing environment, sonic boom simulation method, and associated instrumentation are described. The effects of the traveling blast on the structure are investigated through pressure loading and structural response measurements. The ensuing interior acoustic responses for several different configurations are presented, including the effects of room cavity interaction and exposure of the room cavities to the traveling wave through an open door. Calculated transfer functions between the interior acoustic response and the free-field incident wave are computed to assess the extent to which wood-framed buildings transmit energy to their cavities. In all cases tested, significant transmission of the sonic boom's low frequency content into the structures was apparent through direct apertures and the excitation of structural components. The data show that sonic booms provide significant excitation of structural and acoustic modes that drives the interior acoustic response in residential structures. / Master of Science

Recent progresses by the aircraft industry in the development of a quieter supersonic transport have opened the possibility of overland supersonic flights, which are currently banned by aviation authorities in most countries. For the ban to be lifted, the sonic booms the aircraft generate at supersonic speed must be acceptable from a human-perception point of view, in particular inside buildings. The problem of the transmission of sonic booms inside buildings can be divided in several aspects such as the external pressure loading, structure vibration, and interior acoustic response. Past investigations on this problem have tackled all these aspects but were limited to simple structures and often did not account for the coupled fluid-structure interaction. A more comprehensive work that includes all the effects of sonic booms to ultimately predict the noise exposure inside realistic building structures, e.g. residential houses, has never been reported. Thus far, these effects could only be investigated experimentally, e.g. flight tests. In this research, a numerical model and a computer code are developed within the above context to predict the vibro-acoustic response of simplified building structures exposed to sonic booms, at low frequency. The model is applicable to structures with multiple rectangular cavities, isolated or interconnected with openings. The response of the fluid-structure system, including their fully coupled interaction, is computed in the time domain using a modal-decomposition approach for both the structural and acoustic systems. In the dynamic equations, the structural displacement is expressed in terms of summations over the "in vacuo" normal modes of vibration. The interior pressure is expressed in terms of summations over the acoustic modes of the rooms with perfectly reflecting surfaces (hard walls). This approach is simple to implement and computationally efficient at low frequency, when the modal density is relatively low. The numerical model is designed specifically for this application and includes several novel formulations. Firstly, a new shell finite-element is derived to model the structural components typically used in building construction that have orthotropic characteristics such as plaster-wood walls, floors, and siding panels. The constitutive matrix for these types of components is formulated using simple analytical expressions based on the orthotropic constants of an equivalent orthotropic plate. This approach is computationally efficient since there is no need to model all the individual subcomponents of the assembly (studs, sheathing, etc.) and their interconnections. Secondly, a dedicated finite-element module is developed that implements the new shell element for orthotropic components as well as a conventional shell element for isotropic components, e.g. window panels and doors. The finite element module computes the "in vacuo" structural modes of vibration. The modes and external pressure distribution are then used to compute modal loads. This dedicated finite-element module has the main advantage of overcoming the need, and subsequent complications, for using a large commercial finite-element program. Lastly, a novel formulation is developed for the fully coupled fluid-structure model to handle room openings and compute the acoustic response of interconnected rooms. The formulation is based on the Helmholtz resonator approach and is applicable to the very low frequency-range, when the acoustic wavelength is much larger than the opening dimensions. Experimental validation of the numerical model and computer code is presented for three test cases of increasing complexity. The first test structure consists of a single plaster-wood wall backed by a rigid rectangular enclosure. The structure is excited by sonic booms generated with a speaker. The second test structure is a single room made of plaster-wood walls with two double-panel windows and a door. The third test structure consists of the first room to which a second room with a large window assembly was added. Several door configurations of the structure are tested to validate the formulation for room openings. This latter case is the most realistic one as it involves the interaction of several structural components with several interior cavities. For the last two test cases, sonic booms with realistic durations and amplitudes were generated using an explosive technique. Numerical predictions are compared to the experimental data for the three test cases and show a good overall agreement. Finally, results from a parametric study are presented for the case of the single wall backed by a rigid enclosure. The effects of sonic-boom shape, e.g. rise time and duration, and effects of the structure geometry on the fluid-structure response to sonic booms are investigated. / Ph. D.

L’objectif de ce travail est la compréhension et la modélisation des phénomènes physiques qui gouvernent la réponse vibro-acoustique d’une cascade de distribution de poids lourd. On s’intéresse en particulier au bruit de sirènement d’une cascade de six engrenages, qui correspond à la réponse aux excitations internes générées par le processus d’engrènement et au bruit de claquement, qui correspond à la réponse aux vibro-impacts entre dentures sous charge induits par les fluctuations des efforts extérieurs couplées aux excitations internes. Dans un premier temps, les corrections de denture sont optimisées par une méthode méta-heuristique (essaims particulaires), afin de minimiser les fluctuations des erreurs statiques de transmission en prenant en compte la large plage de couples de fonctionnement et les dispersions géométriques induites par les tolérances de fabrication des engrenages. Le bruit de sirènement est alors modélisé à partir d’une méthode spectrale qui prend en compte le couplage entre les différentes excitations internes de la cascade de dentures. Le gain apporté par l’optimisation des corrections sur le bruit de sirènement de la cascade de dentures a pu être estimé. Dans un second temps, le bruit de claquement est analysé à partir de modèles non linéaires prenant en compte les jeux entre dentures. Une méthode de continuation couplée à une discrétisation par la méthode des différences centrées et une méthode d’intégration temporelle directe sont mises en oeuvre. Le comportement dynamique de la cascade induit par la fluctuation des efforts extérieurs couplée aux excitations internes est complexe : les réponses des différents pignons peuvent être périodiques, pseudo-périodiques ou chaotiques avec possibilité d’observer des pertes de contact multiples, et notamment des chocs entre les flancs rétros des dentures si l’acyclisme moteur est élevé. Les régimes de type vibro-impacts peuvent être établis sur une large plage de vitesses de fonctionnement. / The aim of this work is to characterize the vibro-acoustic response of a truck timing gear cascade, and especially the whining noise induced by internal excitations generated by the meshing process and the hammering noise induced by vibro-impacts between gears under fluctuations of external forces coupled with internal excitations. The tooth corrections are optimized with a meta-heuristic method (particle swarm)in order to minimize the fluctuations of static transmission errors. A robustness analysis is performed taking into account the wide range of operating torque and the geometric dispersions induced by gear manufacturing tolerances. The whining noise is then modelled using a spectral method considering the coupling between the different internal excitations. The gain provided by the optimization of tooth corrections on the whining noise of the timing gear cascade can thus be estimated. In a second step, the hammering noise is analyzed using nonlinear models which include the gears’ backlashes. A continuation method coupled with centered finite differences method is implemented, as well as a direct time integration method. The dynamic behaviour of the cascade induced by fluctuating external forces coupled with internal excitations is complex : the gear responses can be periodic, pseudoperiodic,or chaotic, with possibility of multiple contact losses, including collisions between reverse flanks when the engine torque fluctuation is high. Vibro-impact regimes can be observed over a wide range of operating conditions.