Liste des communications
MAGNETIC, MICROWAVE AND ABSORBING PROPERTIESFe-Co OF ALLOY SYNTHESIZED BY MECHANICALALLOYING PROCESS
Nanocrystalline Fe(1-x) Cox mixtures have been prepared by mechanical alloying using aplanetary ball mill under several milling conditions. Their structures and magnetic propertieswere investigated. Mechanical alloying is a non-equilibrium process for materials synthesis. Thestructural effects of mechanical alloying of powders were investigated by scanning electronmicroscopy, X - Ray diffraction analysis and bench of microwaves. Consequently, the alloypowder with average grain size 10-13 nm was obtained. Maximum saturation magnetization Mswas obtained at the composition of 65 % Co. Microwave measurements were performed on themechanically milled Fe(1-x) Cox powder. It has been shown that fine nanocrystalline Fe-Co alloypowders prepared by mechanical milling are promising for microwave applications. Voir les détails
Mots clés : Fe-Co powder, Mechanical Alloying, Magnetic Properties, Microwave
DETERMINATION OF MECHANICAL AND PHYSICAL PROPERTIES OF MATERIALS BY ULTRASOUNDS
The ultrasonic waves, with the matter interaction study, is an increasingly effective tool for qualitative and/or quantitative characterization of industrial materials. In this article, we describe experimental studies, which were the work object at the Welding and Control Center (CSC), based on the measurement of some simple ultrasonic parameters such as propagation velocities and attenuation coefficients of the longitudinal and transverse waves through various samples. These measurements were taken on samples of suitable nature, shape and dimensions and eventually heat treated in order to obtain the required properties. Voir les détails
Mots clés : Ultrasounds, Attenuation, Velocity
MONTE-CARLO SIMULATION OF PRIMARY ELECTRONS IN THE MATTER FOR THE GENERATION OF X-RAYS
The x-rays imagining chains components from the source to the detector, rest on the first part of simulation to the energy production of x-rays emission (source), which suggest us to identified the losses energies result from interaction between the fast electrons and the particles of metal : the energies losses due to “collisional losses” (ionization, excitation) and “radiative losses”. For the medium and the primary electron energy which interests us, the electrons slowing down in the matter results primarily from the inelastic collisions; whose interest is to have to simulate the x-rays characteristic spectrum. We used a Monte-Carlo method to simulate the energy loss and the transport of primary electrons. This type of method requires only the knowledge of the cross sections attached to the description of all the elementary events. In this work, we adopted the differential cross section of Mott and the total cross section of inner-shell ionization according to the formulation of Gryzinski, to simulate the energy loss and the transport of primary electrons respectively. The simulation allows to follow the electrons until their energy reaches the atomic ionization potential of the irradiated matter. The differential cross section of Mott gives us a very good representation of the pace of the distribution of the energy losses. The transport of primary electron is approximately reproduced. Voir les détails
Mots clés : X-rays, Monte-Carlo method, inelastic collision, energy loss
Reconstruction of Pulsed Ultrasonic Fields by Deconvolution of the Spatio-temporal Effects of the Receiving Hydrophone: Theory and Simulation
In this study, it has been shown that it is possible to deconvolve the spatio-temporal transmission properties effect of the hydrophone. The resolution of this ill-posed inverse problem permitted the reconstruction of the pulsed ultrasonic pressure field from the signals furnished by the « measuring » system with higher resolution. The reconstruction results have shown the dependency of the reconstruction quality upon SNR, receiver aperture dimensions and axial distance to the source. The greater the SNR is, the better are results. The farther the scanned field region is, the greater the aperture dimensions can be before the limits of the reconstruction procedure are reached. The study concerned the pulsed field of a planar circular transducer and a PVDF membrane hydrophone as receiver. It can, however, be generalized to any other transmitter-receiver configurations. Voir les détails
Mots clés : Deconvolution, spatio-temporal transmission properties, SNR, PVDF membrane hydrophone
Spatio-temporal deconvolution of pulsed ultrasonic fields received by a transducer of linear aperture : a simulation study
In ultrasonic field measurements, the signal delivered by the receiving transducer is affected by the receiver spatio temporal transmission properties. The pressure is spatially averaged over its finite-size aperture. Furthermore, frequency variations of its transfer function may distort the output signal. The efficiency of the deconvolution of these effects is shown by means of numerical simulations. The pulsed pressure field radiated by a wideband 10.3mm-radius planar transducer, with a central frequency fc = 2.25 MHz ( c: corresponding ultrasonic wavelength in water) is considered. The receiver is a linear aperture 25 μm- thick PVDF membrane hydrophone. The study shows that the quality of the reconstructed signal depends strongly upon the signal-to-noise ratio (SNR), the aperture dimensions and the distance from the source. For an aperture of length L = 2.6 mm ≈3.9c, placed on axis at z = 3 mm, correlation coefficients between the reconstructed pressure and the original one, rppˆ , of 0.999, 0.988 and 0.655 have been obtained, for SNRs of 60, 40 and 20 dB respectively. For a greater aperture (L = 4.6=mm ≈6.9c) and SNR = 40 dB, no satisfactory results could be obtained at this distance ( rppˆ = 0.912). At a greater axial distance (z = 20 mm), better deconvolution results could be achieved ( rppˆ = 0.928). Voir les détails
Mots clés : PVDF hydrophones, SNR, Wiener filtre, aperture, spatio -temporal
Comparative analysis of the performance of the information theoretic criteria for model order estimation of InSAR signals corrupted by multiplicative noise
In this paper, we study the behaviour of information theoretic criteria in order to select the order of the model of InSAR signals corrupted by multiplicative noise. We compare the performance of these criteria when using the number of degrees of freedom derived in D. Williams (November, 1994) with the performance of these criteria computed in F. Gini and F. Bordoni (2003) when using the number of degree of freedom derived in M. Wax and T. Kailath (April 1985). We show, through numerical simulations, that one of the efficient detection criteria evaluated with the number derived in D. Williams (November, 1994) has the best performance. Voir les détails
Mots clés : Model order estimation, information theoretic criteria, multiplicative noise, Multicomponent signals, SAR interferometry, Layover phenomenon
Model order estimation of InSAR signals corrupted by multiplicative noise using the Capon method
In this paper, we compare the performance of the Capon approach and the efficient detection criteria when applied to model order estimation of InSAR signals corrupted by multiplicative noise and additive white noise. This study is done in terms of the normalized baseline, the number of looks, the signal to noise ratio and the interferometric phase separation. Through the numerical simulations, we show, except the case of very closed sources, that the Capon method has the best performances. Voir les détails
Mots clés : Model order estimation, information theoretic criteria, multiplicative noise, Multicomponent signals, SAR interferometry, Capon method
Defect Detection by Split Spectrum Processing and Discrete Wavelet Transform in Coarse Grains Materials
In this work, we propose in one hand, to develop algorithms based on Split Spectrum Processing (SSP) with Q constant method associated to "Group delay moving entropy" (GDME), and on the second hand, to develop a method based on Discrete Wavelet Transform (DWT). These algorithms allow detecting and locating imperfections echoes drowned in the structural noise of materials. Voir les détails
Mots clés : Ultrasonic NDE, Defect Detection, split spectrum processing, DWT
Comparative study of defect detection in coarse grains materials
In this work, we propose to develop on the first hand, algorithms based on Split Spectrum Processing (SSP) with Q constant method associated to "Group delay moving entropy" (GDME), on the second hand, we develop a method based on Discrete Wavelet Transform (DWT). These algorithms allow detecting and locating imperfections echoes drowned in the structural noise of materials. The investigation is performed with known defects echoes with different characteristics (position, amplitude, center frequency and bandwidth). The defect echoes frequency is varied around the frequency of the input signal in order to evaluate, by SNR calculation, the robustness of the detection method. The grain noise signal is generated first, by a simple clutter model which consider the noise, in the time domain, as the superimposed of signal coming from backscatterers in the medium and second, experimentally by a material with a coarse grains. Voir les détails
Mots clés : Ultrasonic NDE, SSP, DWT, SNR
Characterization of the cementation layer by the ultrasonic pulse echo method
it is necessary to measure this layer with a sufficient precision.In this study, we use the ultrasonic pulse echo method as a non destructive testing in thecementation layer characterisation of 12 NC6 steels with a rang of 0.6 mm to 1.5 mm for thecementation thickness.The ultrasonic measurement are based on the reflection of signal at the interface of twomaterials having different impedance and on the determination of the longitudinal elastic wavesvelocity as well as the sound attenuation coefficients based on the Rayleigh model.The paper discuss also the microstructure influence on the ultrasonic measurement parametersand the precision obtained.We conclude our work by analysing the ability of the ultrasonic pulse echo for the cementationlayer measurement Voir les détails
Mots clés : Cementation process, ultrasonic attenuation, reflection coefficient, pulse –echo method