Y. Le Bihan

Adaptive Mesh Refinement and Probe Signal Calculation in Eddy Current NDT by Complementary Formulations

A local error estimation and adaptive meshing method for finite element analysis in eddy current nondestructive testing problems is proposed. Two dual formulations using Whitney elements have been applied to solve the magnetodynamic problem. By using this property of complementary, different error estimators were defined and were studied. These estimators are used for determining the mesh refinement zones. Numerical evaluations are given at the end of the paper, where the procedure of the adaptive meshing is presented and validated.

Overlapping Finite Elements Used to Connect Non-Conforming Meshes in 3-D With a Vector Potential Formulation

Overlapping elements can be used to connect non-conforming meshes in the finite-element method. This approach has been developed with the scalar potential formulation and used to solve magnetostatic problems but not in the case of the vector potential formulation. In this paper, we propose to introduce the overlapping element method in this second formulation.

Microwave characterization using ridge polynomial neural networks and least-square support vector machines

Motivated by the slow learning properties of multilayer perceptrons which utilize computationally intensive training algorithms and can get trapped in local minima, this work deals with ridge polynomial neural networks (RPNN) and least-square support vector machines (LSSVM) technique. RPNN and LSSVM are combined with the finite element method (FEM), to evaluate the dielectric materials properties. RPNN maintain fast learning properties and powerful mapping capabilities of single layer high order neural networks. LSSVM is a statistical learning method that has good generalization capability and learning performance. Experimental results show that LSSVM can achieve good accuracy and faster speed than those using conventional methods.

Thin Crack Modeling in ECT with Combined Potential Formulations

The finite element modeling of thin cracks in ECT using a-psi and t-Phi combined vector-scalar potential formulations is presented with edge and nodal Whitney element discretization. The crack is treated as a non-conductive surface on which appropriate conditions are applied. A team workshop benchmark problem has been solved

Use of Overlapping Finite Elements for Connecting Arbitrary Surfaces With Dual Formulations

In this paper, a method for the connection of non-conform arbitrary surfaces by overlapping finite element method is presented. Both scalar and vector degrees of freedom are considered. The use of reference elements allows to simplify the implementation of the method. Examples show the reliability of the method.

A hybrid finite-element method for the modeling of microcoils

This paper presents an original method for the modeling of microcoils at high frequency dedicated for different applications: radio frequency, nuclear magnetic resonance, nondestructive testing, etc. The aim of the modeling is to determine the elements of an electric equivalent circuit. A magneto-dynamic three-dimensional (3-D) finite-element formulation is used to calculate the resistance and the inductance of the microcoil at high frequency. Using the previous results, an electrostatic 3-D finite-element field analysis is then used to determine the capacitance. The method was tested by using an example of nuclear magnetic resonance microcoil. Numerical results obtained by the proposed method are compared with measurements and analytical results.

Novel Wideband Eddy Current Device for the Conductivity Measurement of Semiconductors

We report on the development and application of a brand-new contactless method based on eddy currents with a view to designing a generic apparatus for the characterization of some transport properties of a large range of semiconductors. The eddy current probe, constituted of a coil connected to a transmission line, interacts with the semiconductor wafer under inspection. The innovative approach of this letter consists in measuring the impedance of the coil by reflectometry using a broadband multicarrier test signal, i.e., containing multiple frequencies. An analytical electromagnetic model of the coil-wafer interaction is then used to estimate the conductivity of the wafer. This process results in a new contactless conductivity measurement system that exhibits a very wide conductivity measurement range and allows the characterization of a large variety of semiconductor materials. The device is also very fast potentially allowing the measurement of transport properties of semiconductors in fast transient conditions. As a practical example, the performance of our device is demonstrated by estimating the conductivity of a set of crystalline silicon wafers.

Modeling of thin conductive and magnetic layers in eddy current testing by overlapping finite elements

In this paper a new field of application of the overlapping finite element method is proposed for eddy current testing. This method, which has already been used to deal with the lift-off, is extended to the treatment of thin conducting and/or magnetic layers.

Direct and Inverse Modeling of a Microwave Sensor Determining the Proportion of Fluids in a Pipeline

A microwave sensor constituted of both low- and high-frequency probes is presented. The role of the sensor is to determine the proportion of mixed fluids in a pipeline used in petroleum engineering to extract oil from an oil layer. In this paper, the annular flow regime in the pipeline is considered. Since the analytical solution for this configuration is not available for high frequencies, a combination of numerical modeling and neural networks (NNs) is used. Two inversion configurations are compared. Good results are obtained with the better one.

Study for the Design of Eddy Current Microsensor Arrays for Non Destructive Testing Applications

In this paper, an experimental study was carried out for the design of microsensor arrays dedicated to eddy current non destructive applications. A 3-microcoil 1-D array sensor was realized thanks to microtechnology. Since each coil can be used as a transmitter or a receiver, five different transmission- reception strategies were considered for the inspection of a nickel based alloy target, featuring several calibrated surface notches. While the most basic strategy did not detect the smallest notch (0.1 x 0.1 x 0.1 mm3), the best strategy detected it with a 20 dB signal to noise ratio. The detection performances were then analyzed versus frequency and versus notch size.