Advanced Instrumentation for Polyharmonic Metal Detectors

This paper describes the application of polyharmonic sinc signals in devices for metal object detection. A basic problem of conventional eddy current metal detectors (induction devices in general) lies in their limited possibilities of discrimination or identification of detected objects. To better characterize the detected object, the excitation signal and the following signal processing in the detector should be done. The application of polyharmonic excitation signal and its processing could bring an opportunity to improve the determination ability. This paper is focused on the polyharmonic sinc signal. Spheres of different diameters and from different ferrous and non-ferrous materials were used as specimens. Experimental measurements were processed in frequency-domain amplitude, and phase spectra were calculated and presented. As part of the work, classifications of ferrous and non-ferrous materials were done based on measured data as well as the classification of individual ferrous, including non-ferrous materials and estimation of the size of the classified object. Support vector classifier was primarily used for data classification.