Ryszard Sikora

Crack detection and recognition using an eddy current differential probe

This paper proposes a new eddy current differential sensor and a system for multi-frequency testing of conducting plates. Precise crack imaging was achieved by the use of spectrograms obtained from an eddy-current probe multi-frequency response and application of a neural network. Results of experiments with test specimens made of SUS304 showing very good sensitivity and spatial resolution are presented. The possibility of detection of an opposite side 20% crack was also confirmed.

Natural crack recognition using inverse neural model and multi-frequency eddy current method

In this paper a Multi-Frequency Excitation and Spectrogram Eddy Current System and an inverse neural model were used to detect and identify natural flaws in steam generator tubes. It is shown that the applied dynamic neural model of the ECT sensor offers very high speed of operation and guarantees reliability of the recognition results.

Neural network models of eddy current multi-frequency system for nondestructive testing

The purpose of this paper is to present new neural network models used for eddy current multi-frequency system simulation and flaws identification. Forward dynamic neural network models are proposed as the solution of this problem. The extended experimental verification of the developed technique is done and the results confirming usability of the models are presented.

Use of variational methods to the eddy currents calculation in thin conducting plates

In the paper eddy-currents are calculated in thin conducting plates of chosen shapes. It is assumed that the secondary magnetic field due to eddy-currents is negligible compared with the exciting flux. The stream function I is introduced to formulate field equations. The Ritz and Kantorovich varia - tional methods are applied for solving the field equation and calculating the power losses.

Analysis of electromagnetic field and power losses in three phase gas insulated cable

The following paper presents the electro-magnetic field distribution in a three phase gas insulated cable. Formulas for calculation of power losses in the cable sheath are also given. Applying the separation-of-variables method it was possible to obtain general fi - nal dependences. With the help of a computer, theoretical considerations were illustrated by numerical calculations.

Synthesis of magnetic fields

The paper deals with some problems of magnetic fields synthesis, depending on determination of the current density distribution, which generates the required magnetic field in the investigated region. Such problems can be reduced to the linear, or nonlinear Fredholm integral equations of the first kind, or to the set of these equations. Fredholm integral equation of the first kind belongs to the class of the ill-posed problems, and for its solving the method of regularisation has been used. In the paper there are given some useful results of synthesis of magnetic fields in few practical configurations.

Optimization of eddy-current sensor for multifrequency systems

In this paper, we propose an algorithm that could be utilized to design an optimal eddy-current sensor. The optimal sensor should provide high sensitivity, especially to deep located flaws and good spatial resolution. Such aims could be achieved only by simultaneous optimization of sensor construction and operating frequency.

Artificial neural network application for material evaluation by electromagnetic methods

The eddy current nondestructive testing of conductive materials is well known problem. For some eddy current transducers for flaw detection the mathematical models were constructed and the inverse problem (IP) were formulated In order to solve those problems the artificial neural network approach, relatively new, was adopted. The public domain software was used to teach and test the network. It was proved that, a standard feedforward multilayered neural network is sufficient to identify the parameters of different kind defects with a satisfying accuracy. Neural network approach could be extinguished to impedance tomography and to eddy current tomography. Several examples illustrated abilities of proposed approach will be presented in the paper. Two artificial neural network reconstruction methods for electrical impedance tomography have been presented in this paper. The problem under study concerns the reconstruction of the conductivity distribution inside the investigated area using the information collected from the boundary. The first approach consists in ANN learning using electrical potential vectors, which were obtained from numerical solution of the forward problems. The second method using a standard feedforward multilayered neural network applies the circuit representation for the finite element discretization. Using the quadrilateral finite element, the neural network structure for EIT problem has been proposed. The advantages and disadvantages of both methods with respect to the classical approach have been discussed in details.

Eddy Current Testing of Thick Aluminum Plates with Hidden Cracks

In this paper we present theoretical analysis which gives the possibility to determine optimum excitation frequencies in eddy current examination of thick aluminum plates. A computer controlled non‐destructive testing system and a probe with a magnetoresistive sensor were utilized in laboratory tests. Experiments with specimens containing hidden cracks were carried out for a wide spectrum of frequencies. The optimum operating frequencies achieved from the experiments are in a very good agreement with those obtained by using theoretical analysis. Application of the optimum frequencies makes it possible to detect shallow cracks located on the reverse side of the specimens. Detection of a 15 % crack in a 10 mm thick plate made of aluminum and a 20 % crack in a 20 mm thick plate has been confirmed.

Optimum design of iron-core electromagnets

General problems of optimization of iron-core electromagnets are considered. The use of analytical and numerical methods are compared. Various models of electromagnets are examined, taking into account the magnetization curve of iron, operating conditions, the construction of coils, etc. The possibility of tackling the automatic design of iron-core electromagnets with cylindrical symmetry is demonstrated. The optimization procedure can also be used in the design of magnetic devices of complicated structure. >