IMPROVING THE EDDY CURRENT IDENTIFIER OF METALS BASED ON THE CORRELATION APPROACH

Context. The article considers the problem of improving the eddy current device for metal identification on the basis of the correlation approach. This approach is convenient for the accumulation of a database of known leading materials, as well as for the comparison of the signal from an unknown metal object with the available standards in the database. The proposed approach allows to determine the type of metal from which the sample is made, without damaging its surface. 
Objective. The aim of the work is the identification of metals by type on the feedback signals from the eddy current converter, due to the identification of new informative features and the creation of a database of images of metals. 
Method. The paper presents the results of an experimental study of the proposed approach to increase the reliability of identification of metal objects that are detected using an eddy current device. These studies are conducted on the basis of a radio system that operates on the eddy current principle and has low-frequency magnetic loop antennas. The eddy current method allows the identification of metals by type remotely and without damaging their surface, in contrast to X-ray fluorescence, optical emission or chemical methods. A correlation approach for processing the response signal spectrum from a hidden metal object is proposed. The correlation approach allows to increase the reliability of the identification of metals by type when processing the signal in the spectral region based on the Fourier transform. Studies have been conducted on the example of metals that have similar spectral characteristics (silver, gold, lead). The updated approach allowed to increase the percentage difference between the information parameters of signals – responses from 1.87% to 5.02% for silver and gold, from 2.24% to 4.34% for silver and lead and from 0.36% to 0.7% for gold and lead. 
Results. The developed radio system is a laboratory model, which consists of an analog part and a digital one. The analog part is an antenna unit, a signal amplifier and a bandpass filter, a digital part – a microcontroller with an ADC for digitizing and transmitting data to a laptop, which software implements the proposed approaches to signal processing. The paper experimentally confirmed the possibility of using a radio engineering system to solve the problem of metal identification within a subset of nonmagnetic and magnetic materials. 
Conclusions. The development of modern eddy current devices is aimed at increasing the reliability of the identification the hidden metal objects, which is relevant in geophysical exploration, archeology, and law enforcement agencies in the search for hidden non-ferrous metals. The development and improvement of such systems includes both the development the hardware and the discovery new information parameters in the feedback signals from metals. One such direction may be the correlation approach to signal processing in the spectral region.