BENDING WAVES FOCUSING IN ARBITRARY SHAPED PLATE-LIKE STRUCTURES: APPLICATION TO SPATIAL AUDIO

Advanced audio applications are more and more demanding with respect to the visual impact of loudspeakers while still requiring more channels for high quality spatial sound rendering. The use of arbitrary plate-like structures driven by electromagnetic actuators or by piezoelectric elements appears as a promising solution to tackle both issues. However, to meet spatial rendering audio constraints (omnidirectional piston-like sources), the generated bending waves must be focused to a certain extent within the host plate. Theoretically, this means being able to invert the spatio-temporal wave propagation operator for the generated bending waves to fit a given target shape. Several methods are here investigated to perform this task depending on the available knowledge of wave propagation in the plate (theoretical, partial spatial and full spatial knowledge). The various methods are presented in a unified theoretical framework and their performances are compared in terms of sound radiation by means of two key performance indexes.This work was financially supported by the French National Research Agency (ANR, contract ANR-17-CE33-0004)

Design and validation of a structural health monitoring system for aeronautical structures.

Structural Health Monitoring (SHM) is an area where the main objective is the verification of the state or the health of the structures in order to ensure proper performance and maintenance cost savings using a sensor network attached to the structure, continuous monitoring and algorithms. Different benefits are derived from the implementation of SHM, some of them are: knowledge about the behavior of the structure under different loads and different environmental changes, knowledge of the current state in order to verify the integrity of the structure and determine whether a structure can work properly or whether it needs to be maintained or replaced and, therefore, to reduce maintenance costs. The paradigm of damage identification (comparison between the data collected from the structure without damages and the current structure in orderto determine if there are any changes) can be tackled as a pattern recognition problem. Some statistical techniques as Principal Component Analysis (PCA) or Independent Component Analysis (ICA) are very useful for this purpose because they allow obtaining the most relevant information from a large amount of variables. This thesis uses an active piezoelectric system to develop statistical data driven approaches for the detection, localization and classification of damages in structures. This active piezoelectric system is permanently attached to the surface of the structure under test in order to apply vibrational excitations and sensing the dynamical responses propagated through the structure at different points. As pattern recognition technique, PCA is used to perform the main task of the proposed methodology: to build a base-line model of the structure without damage and subsequentlyto compare the data from the current structure (under test) with this model. Moreover, different damage indices are calculated to detect abnormalities in the structure under test. Besides, the localization of the damage can be determined by means of the contribution of each sensor to each index. This contribution is calculated by several different methods and their comparison is performed. To classify different damages, the damage detection methodology is extended using a Self-Organizing Map (SOM), which is properly trained and validated to build a pattern baseline model using projections of the data onto the PCAmodel and damage detection indices. This baseline is further used as a reference for blind diagnosis tests of structures. Additionally, PCA is replaced by ICAas pattern recognition technique. A comparison between the two methodologies is performed highlighting advantages and disadvantages. In order to study the performance of the damage classification methodology under different scenarios, the methodology is tested using data from a structure under several different temperatures. The methodologies developed in this work are tested and validated using different structures, in particular an aircraft turbine blade, an aircraft wing skeleton, an aircraft fuselage,some aluminium plates and some composite matarials plates.La monitorización de daños en estructuras (SHM por sus siglas en inglés) es un área que tiene como principal objetivo la verificación del estado o la salud de la estructura con el fin de asegurar el correcto funcionamiento de esta y ahorrar costos de mantenimiento. Para esto se hace uso de sensores que son adheridos a la estructura, monitorización continua y algoritmos. Diferentes beneficios se obtienen de la aplicación de SHM, algunos de ellos son: el conocimiento sobre el desempeño de la estructura cuando esta es sometida a diversas cargas y cambios ambientales, el conocimiento del estado actual de la estructura con el fin de determinar la integridad de la estructura y definir si esta puede trabajar adecuadamente o si por el contrario debe ser reparada o reemplazada con el correspondiente beneficio del ahorro de gastos de mantenimiento. El paradigma de la identificación de daños (comparación entre los datos obtenidos de la estructura sin daños y la estructura en un estado posterior para determinar cambios) puede ser abordado como un problema de reconocimiento de patrones. Algunas técnicas estadísticas tales como Análisis de Componentes Principales (PCA por sus siglas en inglés) o Análisis de Componentes Independientes (ICA por sus siglas en ingles) son muy útiles para este propósito puesto que permiten obtener la información más relevante de una gran cantidad de variables. Esta tesis hace uso de un sistema piezoeléctrico activo para el desarrollo de algoritmos estadísticos de manejo de datos para la detección, localización y clasificación de daños en estructuras. Este sistema piezoeléctrico activo está permanentemente adherido a la superficie de la estructura bajo prueba con el objeto de aplicar señales vibracionales de excitación y recoger las respuestas dinámicas propagadas a través de la estructura en diferentes puntos. Como técnica de reconocimiento de patrones se usa Análisis de Componentes Principales para realizar la tarea principal de la metodología propuesta: construir un modelo PCA base de la estructura sin daño y posteriormente compararlo con los datos de la estructura bajo prueba. Adicionalmente, algunos índices de daños son calculados para detectar anormalidades en la estructura bajo prueba. Para la localización de daños se usan las contribuciones de cada sensor a cada índice, las cuales son calculadas mediante varios métodos de contribución y comparadas para mostrar sus ventajas y desventajas. Para la clasificación de daños, se amplia la metodología de detección añadiendo el uso de Mapas auto-organizados, los cuales son adecuadamente entrenados y validados para construir un modelo patrón base usando proyecciones de los datos sobre el modelo PCA base e índices de detección de daños. Este patrón es usado como referencia para realizar un diagnóstico ciego de la estructura. Adicionalmente, dentro de la metodología propuesta, se utiliza ICA en lugar de PCA como técnica de reconocimiento de patrones. Se incluye también una comparación entre la aplicación de las dos técnicas para mostrar las ventajas y desventajas. Para estudiar el desempeño de la metodología de clasificación de daños bajo diferentes escenarios, esta se prueba usando datos obtenidos de una estructura sometida a diferentes temperaturas. Las metodologías desarrolladas en este trabajo fueron probadas y validadas usando diferentes estructuras, en particular un álabe de turbina, un esqueleto de ala y un fuselaje de avión, así como algunas placas de aluminio y de material compuest

Application of sound source separation methods to advanced spatial audio systems

This thesis is related to the field of Sound Source Separation (SSS). It addresses the development and evaluation of these techniques for their application in the resynthesis of high-realism sound scenes by means of Wave Field Synthesis (WFS). Because the vast majority of audio recordings are preserved in twochannel stereo format, special up-converters are required to use advanced spatial audio reproduction formats, such as WFS. This is due to the fact that WFS needs the original source signals to be available, in order to accurately synthesize the acoustic field inside an extended listening area. Thus, an object-based mixing is required. Source separation problems in digital signal processing are those in which several signals have been mixed together and the objective is to find out what the original signals were. Therefore, SSS algorithms can be applied to existing two-channel mixtures to extract the different objects that compose the stereo scene. Unfortunately, most stereo mixtures are underdetermined, i.e., there are more sound sources than audio channels. This condition makes the SSS problem especially difficult and stronger assumptions have to be taken, often related to the sparsity of the sources under some signal transformation. This thesis is focused on the application of SSS techniques to the spatial sound reproduction field. As a result, its contributions can be categorized within these two areas. First, two underdetermined SSS methods are proposed to deal efficiently with the separation of stereo sound mixtures. These techniques are based on a multi-level thresholding segmentation approach, which enables to perform a fast and unsupervised separation of sound sources in the time-frequency domain. Although both techniques rely on the same clustering type, the features considered by each of them are related to different localization cues that enable to perform separation of either instantaneous or real mixtures.Additionally, two post-processing techniques aimed at improving the isolation of the separated sources are proposed. The performance achieved by several SSS methods in the resynthesis of WFS sound scenes is afterwards evaluated by means of listening tests, paying special attention to the change observed in the perceived spatial attributes. Although the estimated sources are distorted versions of the original ones, the masking effects involved in their spatial remixing make artifacts less perceptible, which improves the overall assessed quality. Finally, some novel developments related to the application of time-frequency processing to source localization and enhanced sound reproduction are presented.Cobos Serrano, M. (2009). Application of sound source separation methods to advanced spatial audio systems [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/8969Palanci

Novel miniature matrix array transducer system for loudspeakers

Conventional pistonic loudspeakers, by employing whole-body vibration of the diaphragm, can reproduce good quality sound at the low end of the audio spectrum. Flat panel speakers, on the other hand, are better at high frequency operation as the reproduced sound at high frequency from a flat panel speaker is not omni-directional as in the case of a conventional loudspeaker. Although flat-panel speakers are compact, small and have a better high frequency response the poor reproduction of bass sound limits its performance severely. In addition, the flat panel speakers have a poor impulse response. The reason for such poor bass and impulse response is that, unlike the whole body movement of a conventional loudspeaker diaphragm, different parts of the panel in a flat panel loudspeaker vibrates independently. A novel loudspeaker has been successfully designed, developed and operated using miniature electromagnetic transducers in a matrix array configuration. In this device, the whole body vibration of the panel reduces the poor bass and impulse response associated with present flat panel speakers. The multi-actuator approach combines the advantages of conventional whole body motion with that of modern flat panel speakers. An innovative miniature electromagnetic transducer for the proposed loudspeaker has been designed, modelled and built for analysis. Frequency Responses show that this novel transducer is suitable for loudspeaker application because of its steady and consistent output over the whole audible frequency range and for various excitation currents. Measurements on various device configurations of this novel miniature electromagnetic transducer show that a moving coil transducer configuration having a magnetic diaphragm is best suited for loudspeaker applications. Finite element modeling has been used to examine single transducer operation and the magnetic interaction between neighbouring transducers in a matrix array format. Experimental results show the correct positioning of the transducers in a matrix configuration reduces the effects of interferences on the magnetic transducers. In addition, experimental results from the pressure response measurement show an improvement in bass response for the longer array speaker.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

A novel miniature matrix array transducer system for loudspeakers

Conventional pistonic loudspeakers, by employing whole-body vibration of the diaphragm, can reproduce good quality sound at the low end of the audio spectrum. Flat panel speakers, on the other hand, are better at high frequency operation as the reproduced sound at high frequency from a flat panel speaker is not omni-directional as in the case of a conventional loudspeaker. Although flat-panel speakers are compact, small and have a better high frequency response the poor reproduction of bass sound limits its performance severely. In addition, the flat panel speakers have a poor impulse response. The reason for such poor bass and impulse response is that, unlike the whole body movement of a conventional loudspeaker diaphragm, different parts of the panel in a flat panel loudspeaker vibrates independently. A novel loudspeaker has been successfully designed, developed and operated using miniature electromagnetic transducers in a matrix array configuration. In this device, the whole body vibration of the panel reduces the poor bass and impulse response associated with present flat panel speakers. The multi-actuator approach combines the advantages of conventional whole body motion with that of modern flat panel speakers. An innovative miniature electromagnetic transducer for the proposed loudspeaker has been designed, modelled and built for analysis. Frequency Responses show that this novel transducer is suitable for loudspeaker application because of its steady and consistent output over the whole audible frequency range and for various excitation currents. Measurements on various device configurations of this novel miniature electromagnetic transducer show that a moving coil transducer configuration having a magnetic diaphragm is best suited for loudspeaker applications. Finite element modeling has been used to examine single transducer operation and the magnetic interaction between neighbouring transducers in a matrix array format. Experimental results show the correct positioning of the transducers in a matrix configuration reduces the effects of interferences on the magnetic transducers. In addition, experimental results from the pressure response measurement show an improvement in bass response for the longer array speake