Magnetic sensors and gradiometers for detection of objects

Disertační práce popisuje vývoj nových detekčních zařízení s anizotropními magnetorezistoryThis thesis describes development of innovative sensor systems based on anisotropi

An experimental comparison of complex excitation sequences for eddy current testing

Eddy Current Testing (ECT) is a Non Destructive technique widely used in many industrial application fields in which it is very important to detect the presence of thin defects (generally called cracks) in conductive materials. Features of this technique are the cost-effective implementation and the kind of retrieved measured data that make possible to estimate the geometrical characteristics of a crack as position, length, width and depth. The analysis of these characteristics allows the user to accept or discard realized components then improving the production chain. To accomplish for this task some aspects have to be taken into account during the measurement process. They mainly concern the realization of suitable measurement setup and post processing stages. As far as the measurement setup is concerned, crucial aspects are the choice of measurement and excitation devices. The choice of optimized excitation devices and strategies is of interest for research on Non Destructive ECT (ND-ECT): together with common aspects as the amplitude and the frequency of the exciting signal, the attention has been paid to issues as the type of signal to be adopted. In particular it has been found as the use of complex excitation signals, meant as signals different from the sinusoidal ones and with wide frequency content, might raise eddy current responses trying to support the measurement, detection and characterization stages when "difficult cases" are explored (i.e. very small and/or annealed cracks). In this paper the authors propose an experimental comparison of different excitation signals designed to improve the quality of experimental data when difficult cases are experienced and, consequently, to obtain a more reliable extraction of defects geometrical features

Non-Destructive Techniques Based on Eddy Current Testing

Non-destructive techniques are used widely in the metal industry in order to control the quality of materials. Eddy current testing is one of the most extensively used non-destructive techniques for inspecting electrically conductive materials at very high speeds that does not require any contact between the test piece and the sensor. This paper includes an overview of the fundamentals and main variables of eddy current testing. It also describes the state-of-the-art sensors and modern techniques such as multi-frequency and pulsed systems. Recent advances in complex models towards solving crack-sensor interaction, developments in instrumentation due to advances in electronic devices, and the evolution of data processing suggest that eddy current testing systems will be increasingly used in the future