Compensation des non-linéarités des systèmes haut-parleurs à pavillon

The assumptions of linearity and autonomy assumed in circuit theory are known to be respected only partially by electroacoustic transducers. In particular, the dynamics range of the latter is limited by the audible nonlinear effects that they are causing. In the domain of active noise control, the distortion products limit noise reduction performance. The present thesis work stems from characterization of these observations. We want to design a real-time system compensating the nonlinearities of electroacoustic devices. The first part of this report concerns the nonlinearity effects. It is shown that the use of classical characterization methods of an electroacoustic device (harmonic distortion, intermodulation, frequency difference ...) is limited. Hence, they can not be used to determine the nonlinearity laws themselves, but rather only their effects for arbitrary excitations. First, a method based on multitone harmonic excitations has been proposed and validated. It has been applied for the characterization of loudspeaker prototypes using several different technologies, which are used for active noise reduction in an aircraft turboreactor. The second part of this work addresses the elaboration and validation of a nonlinearity effect compensation method. This method is based on the description of the nonlinearities by the Volterra series. For this, we need to place an upstream system, characterized by the inverse nonlinearity law of the loudspeaker system. After having determined precisely the Volterra kernels of the system to be characterized, the kernels of the upstream compensation system are determined by assuming that their cascade obeys to a linear law. For this purpose, a kernel measurement method in the frequency domain has been developed, validated and tested. Since we are concerned with loudspeakers, we took their flying time into account. The compensation method has been validated by computing the simulated response of the compensation circuit. Resulting analog signals have then been applied to the loudspeaker. Measured performances fulfill the expectations. In the last part, the compensation method has been applied in a real-time Digital Signal Processing) DSP controller, which allowed to realize a demonstrator to the implemented for future industrial applications

Modèle de réponse vibratoire de planchers légers par méthodes analytiques

Pouvoir prédire le bruit transmis par un élément constructif est depuis plusieurs années une grande préoccupation. Cette problématique a été largement traitée pour les bruits aériens, mais reste plus complexe pour les bruits d'impacts. En effet les caractéristiques de l'excitation en termes d'amplitude et de contenu fréquentiel dans le cas d'un bruit d'impact dépendent autant de l'excitateur (la source de choc) que du récepteur (la paroi impactée). Or, ces bruits figurent en bonne place des sources d'insatisfaction citées par les occupants de bâtiments résidentiels, en particulier dans le cas de constructions légères. Un outil de synthèse sonore serait alors idéal pour à la fois pouvoir prédire les niveaux sonores dus à diverses sources d'impacts mais aussi évaluer le ressenti des occupants par l'écoute. Cette étude s'intéresse à simuler dans le domaine temporel la réponse vibratoire de planchers légers soumis à une excitation mécanique ponctuelle. Dans cette optique, un modèle analytique des modes de vibration d'une plaque mince orthotrope est utilisé. Pour des éléments constructifs homogènes, en béton plein par exemple, ce modèle permet de reproduire la réponse vibratoire temporelle avec un jeu limité de données d'entrées et sans nécessiter des ressources de calcul importantes. Cependant, les planchers légers sont souvent constitués de panneaux équipés de raidisseurs (solives) ou bien de lames assemblées entre elles (cas des éléments en bois lamellé croisé, dits « CLT »). Dans cette étude, ces spécificités de conception sont prises en compte en modélisant les planchers par des plaques minces orthotropes, dont les caractéristiques sont obtenues par une méthode d'homogénéisation. Après une présentation du modèle utilisé et des hypothèses sur lesquelles il s'appuie, deux applications sont présentées : la première concerne un plancher bois sur solives, et la seconde un plancher en CLT 3 couches. Les réponses vibratoires obtenues sont comparées à des résultats de mesures en laboratoire ou de simulations par éléments finis. Les résultats et perspectives sont ensuite discutés

Viable pathogen aerosols produced during laser dermatology surgery - a quantified analysis

The use of laser processes for surgical, medical and cosmetic procedures has been increasing with five hundred thousand workers exposed to laser surgical smoke per year. The use of lasers introduces direct beam hazards into the environment but also generates unique hazards such as material ejected from the laser process. Within this material can be potentially harmful particulate when inhaled by humans, accompanying this particulate is a foul unwanted odour. Along with the generation of these particles it is extremely possible for viable biological organisms to be generated with the particulate. Airborne particulate matter or bio-aerosols are not just a hazard to the patient, but also to other people in the environment around the laser process. The aim of this paper is to investigate and quantify the aerosol danger to both patients and operators when utilising lasers within surgical procedures, while suggesting a suitable initial solution. The tailored research for this aim will focus on whether a suitable extraction system can be developed and the effects that different types of lasers have on the size and visuals of any particulate generated. To determine whether there is a risk of infection and to ascertain the level of infection control, the possibility of viable bio-aerosols being detected after a laser process should be considered. The experiments are split into 3 sections; section 1 is the testing of the extraction system using a smoke generation system to ascertain visual proof of a functioning extraction system, section 2 is the testing of the effect of laser irradiance on the tissue simulant to determine the effect of varying laser types on the particulate generated and section 3 is the generation and measurement of bio-aerosols with the use of bio markers to test for survival of laser processing and transmission

The design of medical laser surgery dermatology handpieces for radiation control and direct extraction of infectious laser generated plume

Surgical skin treatments such as; laser ablation, laser scalpels, hair removal, tattooed removal etc can all generate direct and secondary optical radiation hazards, however, because they are designed to intentionally destroy human tissue, they also generate gaseous and particulate emissions. This second family often referred to as; surgical smoke, surgical smoke plume and surgical fume, have now been identified as producing viable bio-active aerosols, these by-products now pose infectious hazards to the patient and staff of the operating room. Local extraction is sometimes used to try and reduce the airborne concentration of these byproducts though in virtually all cases the smell of the process is detectable by all. The optical radiation hazard usually dictates the wearing of protective eyewear to provide some level of personal protection. A major health concern to all medical and cosmetic facilities is that of infection control. Surgical smoke is usually overlooked as a source of infection within the operating environment and it has been known since the mid-1980s that the particulate can carry with it live pathogens from the patient which can now be in skin contact or respired by the operating staff. A paper presented by the authors in the Medical Session here at ILSC provides possibly the first quantitative analysis of the hazards the surgeon and other staff are subject to. This paper examines the practical limitations of the existing approaches and provides some simple practical control measures that provide complete radiation containment as well as enable complete particulate and gas extraction without any reliance on any form of personal protection for the patient and operating staff. These designs have now been tested and are shown to offer 100% effective plume extraction and radiation containment

Horn loudspeakers nonlinearity comparison and linearization using volterra series

The characterization of a weakly nonlinear electroacoustic device with usual methods of measurement (THD, intermodulation) does not illustrate the nonlinearities themselves, but only some of their effects. Device linearization can be achieved by applying the inverse nonlinearity upstream of the device, under the condition that the nonlinearity law is known in detail. This paper presents nonlinearities behavior comparison of horn loudspeakers of different frequency ranges using an experimental method of weak nonlinearity characterization and compensation, based on a representation of the nonlinearity by Volterra series using multitone excitations

Investigation of wooden floor junction in terms of sound wave propagation

In modern building construction, where light weight structures are preferred for cost reasons, the sound transmission is often a problem to be considered carefully, hence the many studies addressing this issue. Various modal methods are frequently used to investigate the vibration pattern of light weight building structures in the low frequency range. The experimental determination of time average transmission and reflection coefficient has been developed for a wooden floor. In this investigation the wave approach is combined with the continuity equation. By doing so, both the flexural wave propagation and the in-plane wave motion can be taken into account. The mismatch impedance is also an important factor, since there is a change of material at the junction, and is therefore included in this study. The scattering matrix formulation is used to separate the transmitted wave and the reflected wave as the structural wave propagates towards a junction, but also to calculate the corresponding transmission and reflection coefficients. One type of junction has been studied with the help of accelerometer matrices: the T junction of a floor structure, together with its reinforcement beams. The experimental results are presented and commented

Raman spectroscopic characterisation of inorganic fibres and particles and their coverage by wetting agents.

Inorganic fibres especially asbestos have been widely used as a raw material in the construction industries. However, asbestos is now recognised as a carcinogenic material. Therefore, asbestos removal is being widely undertaken. But the hazards increase at this stage as the material is disturbed. Dry removal was found to be an exhausting operation producing a high concentration of fibres. The spraying or injection of wetting agent into the material reduces the hazard associated with the removal process by aggregating the fibres together. The airborne concentration of fibres is then considerably reduced. Raman microspectroscopy has been shown to be a very powerful technique for the identification of micrometer-sized fibres and particles, with little or no sample preparation. Such spectra are sensitive to the composition of the material and can often be used to distinguish between similar species. Raman microscopy also provides important information about surface coverage of such materials with a spatial resolution between 2 and 4 um. Raman spectra were obtained from five asbestos reference standards in comparison with four non-fibrous analogues. The different species such as amosite, anthophyllite, chrysotile, crocidolite and tremolite gave distinct spectra. There were no very distinct differences between the spectra of asbestos fibres and their non-fibrous forms except sometimes in the v(OH) stretching region or band width in the case of tremolite. The reference spectra have been used for identification of known and unknown (industrial samples) fibres on cellulose filters. Moreover, other inorganic particles on cellulose filters have been identified. The discrimination between pure diesel and coal particles on quartz filters and the identification of gunshot residues on paper substrates were also successfully achieved. The coverage of wetting agents on the surface of inorganic fibres connected with asbestos removal operations have been also investigated. Basic laboratory experiments were undertaken. Several inorganic fibres such as man made and asbestos fibres as well as calcium silicate were wetted using different processes: spraying, dipping and capillary adsorption in order to measure the distribution of wetting agents on individual fibres. Insulation materials, usually composed of calcium silicate and asbestos fibres from asbestos removal sites, were collected and also analysed by Raman microspectroscopy. Finally, the effectiveness of suppressing dust was measured on wet industrial samples using a rotating drum tester and the data correlated with Raman measurements