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This article deals with the study of a process based on the principle of eddy current sensors for the nondestructive evaluation of graphite composite plates. This research has been carried out in the Laboratoire d'Electricitd Signaux et Robotique by the team working on datacollecting sensors for robotics in collaboration with Aerospatiale. Eddy current sensors are characterized by their impedance, which varies when a conducting material is approached in their sensitive area. For a given sensor, the output signal depends directly on the electrical and geometrical properties of the object. In the case discussed here, the interesting data are the distance between the sensor and the object, and its local conductivity. In order to invert the relationships between the sensor signal and the properties of the material, an external parametrical model has been developed. A scanning of the surface with a sensor designed for good spatial resolution measurements gives two accurate maps of the useful data.

This paper presents a general view of the Non Destructive Testing (NDT) systems based on the use of inductive sensors where the potential users are likely to be more and more numerous. We describe the different phases of their conception. Firstly, we analyse the physical interaction between the sensor and the specimen material by the use of an enlarged concept of electrical images. The instrumentation problem is next reviewed by analysing the signals which are supplied by these sensors, and by the way leading to the definition of the differing range of applications of such sensors. Finally, we enumerate the various signal processing techniques usually applied in NDT and based on the general inversion techniques.

Cet article décrit une nouvelle structure de capteur à courants de Foucault qui permet d'améliorer la sensibilité du capteur tout en conservant sa résolution latérale. Nous avons développé un modèle analytique de ce capteur qui peut être inversé pour estimer la conductivité électrique, la perméabilité magnétique d'une cible homogène et/ou la distance capteur-cible. La procédure d'inversion a été décrite et montre une possibilité d'estimer ces trois paramètres avec précision. L'expérience a été effectuée sur des métaux magnétiques et amagnétiques.

This paper discusses the reasons why we need to change our habit of developing quick software to validate our theoretical results. It is explained here how to create computer programs, to use high level functions and to have a team's common strategy. To achieve this goal, an innovative concept of software development is presented, called AIS (Application Interface Software). This concept is illustrated by developing DPSM (Distributed Point Source Method) programs which is used for 3D ultrasonic field modeling.

This paper considers the images provided by a photothermal camera (flying-spot camera) dedicated to open-crack detection. In this type of active thermography, both thermal and optical effects contribute to the elaboration of photothermal images. Here the thermal effect is relative to the presence of open-cracks and the optical effects are due to surface conditions. In the case of open-cracks detection, the optical effects induce high magnitude perturbation signals, possibly masking the presence of open-cracks. In this contribution a signal processing method is proposed in order to identify both thermal and optical effects separately. The method lies uses multiple principal component analysis combined with a continuous wavelet transform. It is used to enhance the open-crack detection for the inspection of an industrial mock-up showing open-cracks and various surface conditions. The enhancement of the detection performance is characterized thanks to Receiver Operating Characteristic curves. The proposed method shows high detection performances and could be extended to a classification scheme.

Abstract: A new MEM varactor design is presented. It relies on the displacement of an isolated conductor in the air gap of a V-shaped capacitor. To estimate capacitance and tuning ratio of this structure the distributed point source method (DPSM) has been used for electrostatic simulations. The realisation and characterisation of glass motionless prototypes show the feasibility and the interest of this new concept for RF applications. To obtain actuated mobile devices, a novel silicon process has also been developed.