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Développement d’algorithme temps réel pour capteur optique de vélocimétrie. Application à la mesure de vitesse de micro-canaux fluidiques

Bendy Tanios 1
1 LAAS-OSE - Équipe Optoélectronique pour les Systèmes Embarqués
LAAS - Laboratoire d'analyse et d'architecture des systèmes
Abstract : Velocity measurements contactless mobile targets such as mechanical structures are often used in various industrial applications for non-destructive testing and quality control. In addition, the process of measuring speed can be critical if it is one of the parameters that govern the safety and performance of a system as in transportation. Accurate measurement and non-contact speed fluid flowing in microchannels is a major challenge for the chemical industry producing pharmaceuticals. In medicine, the knowledge of the velocity of blood flow in the vessels can help to anticipate cardiovascular disease.Such non-contact measurement can be performed by ultrasonic or microwave but these methods have a relatively low spatial resolution. On the other hand , the conventional optical sensors are often costly. For example , the conventional laser Doppler velocimetry ( LDV or for Laser Doppler Velocimetry) is a technique for high-precision measurements of the speed , but the use of a large number of optical components involves a high price. The rétroinjection optical interferometry is an attractive solution that allows us to design low-cost laser with high precision sensors . With optical non-contact sensors using just a diode laser subject to optical rétroinjection come to measure speeds , the objective of this thesis is to develop devices suitable for this type of measurement and operating in real time. In optical interferometry rétroinjection ( OFI or Interferometry for Optical Feedback ) , commonly called self -mixing , interference occurs in the active laser cavity between the existing field in the cavity and the one backscattered by a target located outside in front of the diode laser inducing changes in optical power output due mainly to the Doppler effect.By measuring the Doppler frequency of the optical power , the speed of the target can be determined. In this thesis , we study the main technical signal processing to provide real-time measurements of Doppler frequency of acceptable accuracy. The first technique is based on a conventional spectral analysis and requires the calculation of a fast Fourier transform (FFT ) . This technique is robust but requires a complex and expensive resource for signal processing in real time electronics. The second is based on a 2 -order autoregressive ( AR2) of the self -mixing signal by a linear prediction filter . The Doppler frequency corresponding to the resonance frequency of this filter.This technique is more accurate , faster and less resource intensive than the FFT . By cons , it presents a risk of divergence and requires calibration at startup. The third is an original technique for processing real - time signal has improved sensor performance in terms of range of measurable velocities. This technique is not as resource-intensive FFT and does not require calibration as AR2 . This technique has been implemented and validated experimentally in real configurations. It has provided good accuracy of measurements , similar to that of the FFT . We then apply the methods of signal processing on signals from the self -mixing passage of particles carried by a fluid in the beam of the laser diode used . In fact, in this case, the self -mixing signal no longer exhibits a Doppler peak but a distribution of Doppler frequencies for the particles passing through the beam are of different speeds from zero canal jusqu'une maximum value at the center . Another phenomenon that can contribute to the spectral broadening is multicast particles . The AR2 and technology have developed to obtain reliable measurements of the fluid flow rate in a channel on a microscopic scale .On the other hand , we study the optical configurations of the measuring device . We show that the device using a single laser diode is sensitive to changes in angle of incidence with the target. This angle must be known to calculate the speed . We then propose a system using two laser diodes and show its robustness to variations of angles of incidence and its ability to calculate the speed of the target without knowing the angles of incidence. We analyze this system to determine the optimum configuration to ensure the best performance. Simulations and experimental results validate the performance of this device in terms of accuracy and robustness. Finally, we apply the laser device and the double-headed processing technique developed in this thesis for measuring the flow rate of a gas injected into a macroscopic channel by a peristaltic pump in non -flow liquid . This thesis has helped develop a robust low cost to measure the speed in real - time using optical rétroinjection optical sensor.
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Bendy Tanios. Développement d’algorithme temps réel pour capteur optique de vélocimétrie. Application à la mesure de vitesse de micro-canaux fluidiques. Micro et nanotechnologies/Microélectronique. Université Toulouse 3 Paul Sabatier, 2014. Français. ⟨tel-01080083⟩

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