Analysis of an Eddy-Current Transducer with Impulsive Excitation in the Nondestructive Testing of Cylindrical Objects
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ANALYSIS OF AN EDDY-CURRENT TRANSDUCER WITH IMPULSIVE EXCITATION IN THE NONDESTRUCTIVE TESTING OF CYLINDRICAL OBJECTS Yu. V. Kuts,1 Yu. Yu. Lysenko,1, 2 A. L. Dugin,1 and А. F. Zakrevskii1 We study the possibility of application the eddy-current method with impulsive excitation for the monitoring of the diameter and electric conductivity of cylindrical objects. For the processing of informative signals of a transducer, it is proposed to use the Hilbert transformation and a condition for the narrowand wide-band “eddy-current transducer–tested object” systems, which would enable us to specify the spectral composition of the signals in the stage of design of the eddy-current devices. Keywords: pulsed eddy-current testing, Hilbert transformation, frequency and decay of signals, monitoring of the diameter and conductivity.
Statement of the Problem Nondestructive eddy-current testing is now extensively used in the industry due to its simplicity and reliability. As one of the most actual directions of its development, we can mention the elevation of the informativity of output signals of the eddy-current transducers (ECT) [1] realized by improving the methods used for the excitation of fields and signal processing. Special attention is given to the design of ECT, which determines the degree of complexity of its tuning [2]. In the case of nondestructive eddy-current testing of products made of conducting materials, it is customary to use the procedures of continuous harmonic excitation of eddy currents in the investigated specimens [3, 4]. In this case, the electrophysical and geometric parameters of the materials are determined according to the amplitude and phase of informative signals. Thus, the process of growing of cylindrical semiconductor specimens can be monitored by a through-type transformer ECT in a continuous mode [5]. The impulsive mode is used in eddy-current testing, as a rule, for the purposes of nondestructive testing of multilayer materials with complex surfaces. As a result of the excitation of ECT by periodic impulsive currents, the informative signal contains various frequency components with the help of which it is possible to increase the informativity and speed of testing and detect defects in multilayer materials at larger depths. The signals of ECT are usually analyzed in the frequency domain with the use of the Fourier or Laplace transformations [6] or in the time domain by using the convolution of two functions [7] one of which corresponds to the initial signal of excitation voltage and the second corresponds to the transition function of the system. The solution of the problem is reduced to the determination of the transition function of the system as a function of the monitored parameters according to the known action and the response of the system to this action. There are numerous procedures aimed at the practical application of the impulsive operating mode of ECT [3, 4]. Special attention of the researchers is given to the evaluation of the characteristics of the transient process according
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