This thesis presents fundamental research in the field of laser vibrometry for the application to vibration measurements. A key concern for laser vibrometry is the effect of laser speckle which appears when a coherent laser beam scatters from an optically rough surface. The laser vibrometer is sensitive to changes in laser speckle which result from surface motions not in the direction of the incident beam. This adds speckle noise to the vibrometer output which can be indistinguishable from the genuine surface vibrations. This has been termed ‘pseudo-vibration' and requires careful data interpretation by the vibration engineer. This research has discovered that measurements from smooth surfaces, even when no identifiable speckle pattern is generated, can produce noise and therefore reference to speckle noise, in such circumstances, is inappropriate. This thesis has, therefore, adopted the more general term of pseudo-vibration to include noise generated from any surface roughness or treatment, i.e. including but not limited to speckle noise. This thesis develops and implements novel experimental methods to quantify pseudovibration sensitivities (transverse, tilt and rotation sensitivity) with attention focussed on commercially available laser vibrometers and consideration is given to a range of surface roughnesses and treatments. It investigates, experimentally, the fundamental behaviour of speckles and attempts to formulate, for the first time, a relationship between changes in intensity to pseudo-vibration sensitivity levels. The thesis also develops and implements models for computational simulation of pseudo-vibrations using the fundamental behaviour of speckles. The combination of experimentation and simulation improves current understanding of the pseudo-vibration mechanisms and provides the vibration engineer with a valuable resource to improve data interpretation. Two experimental methods of quantifying pseudo-vibration sensitivity are developed and successfully applied in the evaluation of transverse, tilt and rotation sensitivity for two models of commercial laser vibrometer. These evaluations cover both single beam (translational vibration measurement) and parallel beam (for angular vibration measurement) modes. The first method presented requires correction of the vibrometer measurement with an independent measurement of genuine velocity to produce an iii apparent velocity dominated by the required noise components. The second method requires a differential measurement using two vibrometers to cancel common components such as genuine velocity, leaving only uncorrelated noise from each measurement in the resulting apparent velocity. In each case, a third measurement is required of the surface motion component causing pseudo-vibration and this is used to normalise the apparent velocity. Pseudo-vibration sensitivity is then presented as a map showing the spectral shape of the noise, as a mean and standard deviation of harmonic peaks in the map and as a total rms level across a defined bandwidth. The simulations employ a novel and effective approach to modelling speckle evolution. Transverse and tilt sensitivity are predicted for the first time and are verified by the experimental study. They provide the vibration engineer with the potential to estimate pseudo-vibrations using a simple piece of software. The laser beam spot diameter has a large influence on the pseudo-vibration sensitivity. Transverse sensitivity has been quantified as around 0.03% and 0.01% (per order) of the transverse velocity of the surface for beam spot diameters of 100 μm and 600 μm respectively. Larger beam spots have been shown to significantly reduce transverse sensitivity and measurements from smoother surfaces have also shown a reduced level of transverse sensitivity. Tilt sensitivity has been quantified at about 0.1 μms-1/degs-1 and 0.3 μms-1/degs-1 (per order) of angular velocity of the surface for beam spot diameters of 100 μm and 600 μm respectively. Smaller beam spot diameters significantly reduce tilt sensitivity. The surface roughness or treatment has been shown to have little effect on the level of tilt sensitivity. Rotation sensitivity has been quantified at approximately 0.6 μms- 1/rads-1 and 1.9μms-1/rads-1 (per order) of rotation velocity of the rotor for 90 μm and 520 μm. Smaller beam spot diameters have shown a significant reduction in rotation sensitivity and measurements on smoother surfaces have shown a reduced rotation sensitivity. Focussing the laser beam approximately on the rotation axis has also shown a significant reduction in rotation sensitivity. Parallel beam rotation sensitivity has been quantified at 0.016 degs-1/rads-1 and it is demonstrated that this can adequately be estimated using the single beam rotation sensitivity.

Les dispositifs d’isolation galvanique intégrés au sein des systèmes de commande d’interrupteurs de puissance doivent répondre à une demande accrue en performance, facilité d’intégration et efficacité énergétique. Les transducteurs ultrasonores capacitifs micro-usinés (cMUT : capacitive Micromachined Ultrasonic Transducer), capables d’émettre et de recevoir des ondes ultrasonores, semblent une alternative tout à fait nouvelle à la fonction d’isolation galvanique. Ces travaux de thèse ont pour objectif de démontrer la faisabilité d’un dispositif basé sur la technologie cMUT. Le principe de fonctionnement consiste à transmettre une information grâce à une communication par onde acoustique de volume entre deux réseaux de cMUT placés de part et d’autre d’un substrat. Nous focalisons, en premier lieu, ces travaux sur le processus de fabrication par micro-usinage de surface des cMUT ainsi que les techniques de réalisation des dispositifs en structure double face sur substrat de silicium. L’étude permet d’identifier le collage de substrat comme une solution de fabrication industrialisable. Suite à la réalisation des dispositifs, la caractérisation électro-mécanique des cMUT est une étapeessentielle à la validation de leur fonctionnalité en tant que dispositifs émetteurs. L’étude débute par uneévaluation des propriétés mécaniques du matériau constituant la membrane et qui impactent directementle comportement global des cMUT. Puis, la caractérisation du comportement statique et dynamique descMUT permet d’extraire les paramètres tels que la fréquence de résonance, la tension de collapse etl’efficacité électro-mécanique qui définissent le mode de pilotage d’un tel système.Finalement, la validation du concept de transmission et de détection d’ondes ultrasonores est réaliséegrâce à des mesures de vibrométrie laser Doppler. Les résultats apportent des éléments de réponse quantau mode de propagation des ondes et permettent d’identifier les topologies de meilleure efficacité entransmission acoustique. Enfin, l’intégration du prototype dans l’application de commanded’interrupteur de puissance démontre la faisabilité du concept de transformateur acoustique basé sur latechnologie cMUT. / Galvanic isolation devices integrated into switch command systems must be able to answer all of the increasing demand for performance, energetic efficiency and integration easiness. The capacitive micro machined ultrasonic transducers (cMUT), able to emit and receive ultrasounds, could be an entirely new alternative to the function of galvanic isolation. This work aims to demonstrate the feasibility of a cMUT-based device. The operating principle consists in transmitting information thanks to a bulk acoustic wave between two cMUT arrays located on both sides of a substrate. We first focus on cMUT surface micromachining fabrication process and techniques of double-side device manufacturing. Our study allows us to identify wafer bonding as a realistic industrial solution. After device fabrication, electro-mechanical of cMUT is an essential step to validate their functionality as ultrasonic emitters. The study starts with the mechanical properties evaluation of the membrane material. These properties directly impact the global behavior of cMUT. Then, the characterization of cMUT static and dynamic behavior allows extracting parameters as resonance frequency, collapsing voltage and electro-mechanical efficiency which define the actuation mode of such a system. Finally, the validation of transmission and reception of ultrasonic waves is evaluated by vibrometer laser Doppler measurements. Results bring elements concerning the waves propagation modes and allow identifying the best acoustical efficiency in regard to the topology. In conclusion, the prototype integration in the application of power switch command demonstrates the feasibility of acoustic transformer concept based on cMUT technology.