High power laser shocks with a 0.6 ns pulse duration have been used to study the debonding of coatings electrolytically deposited on the opposite face of the substrate than the one shocked. Experiments have been carried out on various substrate/coating systems such as stainless steel/copper or nickel and hastelloy X/platinum. Experimentally, a lower intensity debonding threshold has been determined for each of these systems. On the other hand, an upper threshold above which a systematic removal of the coating is obtained has been evidenced. By the numerical simulation of these experiments, a traction range for debonding at the interface has been determined for the three systems. A significant difference for the adhesion levels of these systems has been evidenced using this method. Thus, the possibility to use the laser shock technique as a non destructive adhesion test for coatings of some tens microns is clearly demonstrated.

This paper deals with the modeling of Printed Circuit Boards (PCB) for numerical resolution of a power circuits electromagnetic Compatibility (EMC). The well-adapted model for numerical resolution is the thin wire model. Thus, the PCB trace is replaced by N thin wires. Each wire radius is calculated as a function of the PCB dimensions. This model is applied to calculate the radiated electric field from a PCB circuit using the moment method which is well-suited for thin wire modeling. By observing the influence of the electromagnetic field radiated from the circuit, the number of equivalent wires required to have coherent results is established. The study of the current distribution in the wires shows that the thin wire model takes into account both the skin and the proximity effects.

L'article présente une méthode itérative de type point fixe, pour calculer le champ magnétique dans un dispositif présentant de l'hystérésis magnétique. La méthode est appliquée à un calcul de champ bidimensionnel, par la méthode des éléments finis, dans lequel l'hystérésis est modélisé par un modèle scalaire analytique simple. La convergence du calcul est vérifiée. Un problème test élémentaire, qui ne converge pas par les méthodes habituelles, est résolu en potentiel magnétique scalaire d'une part, et en potentiel magnétique vecteur d'autre part. Les résultats prouvent l'efficacité de l'algorithme, appliqué à la modélisation d'un dispositif d'enregistrement magnétique.

We report the local study of an operating double hetero-junction GaAs/GaAlAs laser diode by apertureless Scanning Near-field Optical Microscopy (SNOM). This study allows the characterization of the spatial properties of the light emitted by the laser source. The optical probe used is a tungsten tip vibrating (at frequency f) perpendicularly to the emitting surface. Suitable experimental parameters permitting us to accede to near-field information have been defined. This has leaded to an experimental configuration in which the probe vibration amplitude is "optimal". A far-field detection at grazing angle is used and a second harmonic (at frequency 2f) lock-in detection is performed. This configuration has permitted us to obtain SNOM images in stimulated emission as well as in spontaneous emission. Above the threshold current, information concerning the emitted laser mode are obtained, whereas in spontaneous emission the SNOM images are linked to the index contrast of the laser diode front facet.

The failure of electrolytic capacitors is the cause of most breakdowns of static converters. The function of these capacitors is to filter and to store electrical energy. Accelerated aging tests showed that the increase of the internal resistance ESR of the capacitors is a good indicator of their faulty state. The filter function is affected by the capacitors wearout on the one hand. At high frequency, the voltage ripple at the terminals of the capacitors increases according to ESR rise. On the other hand, the storage function is not much influenced by the capacitors aging. As static converters work most of the time at variable load, high transient values of the voltage ripple occur when output current changes that can induce false alarms. These transients are verified theoretically and experimentally. In order to avoid these transients effects, we suggest to monitor the fundamental component of the voltage ripple. This latter waveform is the best signature of the capacitors state. The ESR of the capacitors and the time before their failure are deduced from the processing of this waveform with other converter parameters such as input voltage, output current and ambient temperature.

Gratings can be considered as resonant structures in near-field. The enhancement of the intensity recorded by Scanning Near-Field Optical Microscopes (SNOM) is due to interferences in relation with the ratio of the wavelength to the product of the optical index by the period of the grating. We discuss the effect of this ratio (in the range 0.9, 1.1) on the intensity patterns. The influence of the polarization on near-field data is analyzed in both theoretical computations and experimental result.

Using the technique of frequency-domain interferometry, we demonstrate a new way of studying laser-induced breakdown at the surface of dielectric materials. A theoretical model based on electron production by multiphoton ionisation, inverse bremsstrahlung heating, and collisional ionisation is in quantitative agreement with both the detailed time variation of the dielectric constant and the pulse width variation of the fluence threshold. From the complex reflection coefficient measured with the two probe pulse polarisations in quadrature, we deduce the time variation of the dielectric constant of silica during breakdown.

In this paper, we propose a model for the LDMOS transistor used for power amplification in the frequencies band 1.8–2.2 GHz dedicated to the mobile telephony system Digital Cellular System (DCS). This model takes into account the behaviour of each internal region of the power structure. A new representation of the non-linear inter-electrode capacitances, drain-gate Cgd and drain-source Cds, is proposed. The obtained model is implemented in the circuit simulator PSPICE, which gives an overall evaluation of the transistor performances in the radio frequency power amplification mode. This model is Maynly intended to the system designer. A study of the power amplification in the SHF band at 2 GHz is performed. A good agreement between experimental and simulation results is found.

Notre recherche consiste à concevoir et réaliser une source de flux statique à aimants permanents générant un champ de 4 à 5 Tesla dans un volume de quelques mm3. Un des aspects novateurs de cette approche est que nous avons cherché à obtenir un champ magnétique intense (principe du dipôle ponctuel) et non pas un champ magnétique homogène (principe du dipôle infini utilisé dans les structures de Leupold/Halbach). Après optimisation du modèle analytique, nous avons discrétisé la structure de manière à obtenir un modèle réalisable à partir de pavé d'aimants réels. Une originalité du travail est la recherche d'une géométrie performante et une combinaison de divers matériaux magnétiques durs (nuances d'aimants Néodyme-Fer-Bore) et de matériau magnétique doux (Fer-Cobalt). Les configurations particulières d'aimants sont optimisées par simulation numérique grâce à des logiciels complémentaires, développés par le LEG : DIPOLE-3D (calcul analytique de champ), FLUX2D et FLUX3D (éléments finis). L'étude de faisabilité du projet a été réalisée en calculant les forces et les champs démagnétisants lors de la séquence de montage. Le modèle de source actuel fournit un champ atteignant 4,3 T dans un volume de diamètre de 6 mm pour une hauteur de 2,8 mm et ayant un diamètre extérieur de 100 mm.

This contribution presents an application of scanning near-field optical microscopy to the characterization of semi-conductors. It is based on the photocurrent mapping of a patterned Au/GaAs structure (Schottky barrier) under local illumination by the nanosource. The results obtained with different wavelengths, metallized or dielectric probes and different bias voltages exhibit photocurrent variations independent of the topography and induced by interface defects. Finally, from this study of a patterned planar structure, we propose a method to determine the mean free path of the charge carriers in the volume.

Previous modeling techniques of P–N junctions have been applied for studying the annealing of Gamma-ray damage in power MOSFETs. The degradation of the physical parameters of the body-drain junction for a dose rate of 103.8 rad/min is presented. Large decrease of the reverse recombination current, of the series resistance and of the ideality factor are shown to be related to the thermal anneal. These effects are discussed and explained by the evolution of the radiation-induced defects.

Results of investigation concerning a new application of ferrofluids (magnetic fluids) in the doMayn of non-reciprocal X-band devices are shown. Values of ferrofluid slab position x0, biasing field and ferrofluid saturation magnetization are determined for the optimum performance of an insulator. The advantages of using ferrofluids in non-reciprocal devices are also highlighted.

We have developed an apertureless Scanning Near field Optical Microscope (SNOM) in transmission, devoted to near field magneto-optics. Our apertureless SNOM combines an inverted optical microscope, which has been adapted to Faraday effect imaging, with a commercial stand-alone Scanning Probe Microscope, used in Atomic Force Microscope (AFM) mode. Two different probes are validated as apertureless SNOM tips: a home-made etched tungsten wire and a commercial AFM silicon probe. We present and analyze preliminary images of the doMayn structure in iron garnets. They indicate a SNOM resolution clearly in the sub-micrometric range. Besides, the near field magneto-optical image presents some unexpected features, not revealed in far field images.

In Near-Field Optical microscopy, the resolution is directly related to the experimental conditions of illumination and separation between tip and sample. In general, there is no well-defined linear transfer function of the measurement system. The local resolution can be described by the signal-to-noise ratio, by the separation of individual objects or in terms of data shape sharpness. In this paper we use wavelet analysis to determine local resolution. We deduce the resolution from the characteristics of the wavelet and with the help of the local energy in the decomposition.

The N2 dissociation yield has been measured in a flowing post-discharge containing H2 between 0 to 5%. The N atom density has been determined in the fast post-discharge (Δt = 5 × 10−2 s) electric field has been measured by electrostatic probes as a function of H2 relative concentration. It is demonstrated that the H2 produces a significant increase in the N-atom concentration measured in the post-discharge. For our experimental conditions it was determined an increase up to 3 times in comparison to pure nitrogen discharge. The maximum yield of N-atoms was obtained for a H2 relative concentration of about 2%. This result cannot only be explained by the decrease of N atoms surface losses. It is demonstrated that the N2 dissociation increase is also the result of an increase of the discharge reduced electric field.

A small flexural wall rigidity brings unique features to cross-sectional shapes and blood flow within veins, which are characterised by a non-uniform hemodynamical environment acting upon endothelial cells. Velocity fields and related wall shear stress were numerically determined for a large number of conditions, assuming a fully developed, steady, incompressible laminar flow through an uniform smooth pipe with a constant cross-section. It was shown that the flatness greatly influences the resulting distribution of the wall shear stresses along the lumen perimeter. For instance, under a steady longitudinal pressure gradient at about 500 Pascal per meter inside a constant oval-shaped tube, with a lumen perimeter of the order of 5 × 10−2 meter, the maximum wall shear stress is found at about 2 Pascal where the local curvature is minimal. On the other hand, the minimal wall shear stress of the order of 1 Pascal is found where the local curvature is maximal. Clear indications have been reported showing that the hemodynamical wall shear stress does alter endothelial cell morphology and orientation. These results are being used for developing an experimental set-up in order to locally map out the characteristic shear stresses looking for endothelial shape modifications whenever a viscous fluid flow is applied.

Results obtained using a new technique for studying cell metabolism are presented. The technique, consisting in CO2 production monitoring, has been applied to Saccharomyces cerevisiae yeast cells. Also the cells were irradiated using the soft X-ray laser-plasma source at Rutherford Appleton Laboratory with the aim of producing a damage of metabolic processes at the wall level, responsible for fermentation, without great interference with respiration, taking place in mitochondria, and DNA activity. The source was calibrated with PIN diodes and X-ray spectrometers and used Teflon stripes as target, emitting X-rays at about 0.9 keV, with a very low penetration in biological material. X-ray doses delivered to the different cell compartments were calculated following a Lambert-Bouguet-Beer law. Immediately after irradiation, the damage to metabolic activity was measured again by monitoring CO2 production. Results showed a general reduction in gas production by irradiated samples, together with non-linear and non-monotone response to dose. There was also evidence of oscillations in cell metabolic activity and of X-ray induced changes in oscillation frequency.

Structural rheological modelling of complex fluids developed in Part I of this series and applied to shear thickening systems (Parts II & III), is now used to improve such a modelling in the case of unsteady behaviour, that is, in the presence of thixotropy. The model is based on an explicit viscosity-structure relationship, η(S), between the viscosity and a structural variable S. Under unsteady conditions, characterized by a reduced shear, Γ(t), shear-induced structural change obeys a kinetic equation (through shear-dependent relaxation times). The general solution of this equation is a time-dependent function, S(t) ≡ S[t, Γ(t)]. Thixotropy is automatically modelled by introducing S[t, Γ(t)] into η(S) which leads directly to η(t) ≡ η[t, Γ(t)], without the need for any additional assumptions in the model. Moreover, whilst observation of linear elasticity requires small enough deformation i.e. no change in the structure, larger deformations cause structural buildup/breakdown, i.e. the presence of thixotropy, and hence leads to a special case of non-linear viscoelasticity that can be called “thixoelasticity”. Predictions of a modified Maxwell equation, obtained by using the above-defined η(S) and assuming G = G0S (where G0 is the shear modulus in the resting state defined by S = 1) are discussed in the case of start-up and relaxation tests. Similarly modified Maxwell-Jeffreys and Burger equations are used to predict creep tests and hysteresis loops. Discussion of model predictions Maynly concerns (i) effects of varying model variables or/and applied shear rate conditions and (ii) comparison with some experimental data.

The plasma plume created during photoablation of various targets by an excimer KrF laser beam is studied in typical conditions of pulsed laser film deposition. For the examination of transport phenomena of ejected species, the space and time resolved evolution of the luminous plume is investigated by fast imaging as a function of laser fluence (from 7 to $200~\mathrm{J/cm}^{2}$) and nitrogen background pressure (from 5 × 10−3 to 500 Pa) for five different target materials (boron nitride, graphite, alumina, molybdenum, a superconducting oxide YBCO). Under "vacuum" (5 × 10−3 Pa and for nitrogen background pressures up to 10−1−1 Pa, the plume expands freely. For higher background pressures $(\geq 10~\mathrm{Pa})$, three successive regions above the target can be distinguished: at first the expansion is free, then the plume expands according to a shock wave-like behaviour, and lastly a drag force model correctly describes the plume shape evolution. Velocities of the luminous plasma front and of the "mass center" of the plume are determined versus laser fluence and background nitrogen gas pressure.

Detailed derivations and further analysis are presented of a recent concept for a plasma-based accelerator scheme incorporating a strong circularly polarised magnetic wiggler field producing relativistic-strength diamagnetic transverse plasma currents. The increase in the plasma Lorentz factor leads to a substantial increase in the longitudinal component of the wave electric field and therefore of the acceleration rate. It is also found that ultra-high acceleration gradients are possible with relatively low plasma densities and long wave lengths. It also appears possible that the transverse wiggling motion of the electrons of the beam is able to delay the dephasing with the accelerating wave leading to much higher values of the energy gained by the beam at saturation and even electron bunches that have been injected with the "wrong" phase seem to be able to reverse their motion and accelerate to very high energies in short distances.