A virtual instrument for the adaptive analysis of low-frequency magnetic-field emissions

A virtual time-frequency analyzer designed using LabVIEW programming environment, which implements a quadratic joint time-frequency representation for the spectral analysis of the time-varying magnetic field is presented. The adaptive method of time-frequency analysis, based on a matching pursuit algorithm was applied. The matching pursuit is an iterative procedure using a redundant dictionary of functions in order to select the ones, which best match the signal components. The choice of the dictionary is of high importance, since its atoms should ideally be able to fit the features of the investigated signals. The Gaussian chirp atoms are very well adapted to the representation of non-stationary magnetic field induction occurring on board of the vessel. The level of the magnetic field emissions was estimated, in reference to the magnetic field exposure limits for occupational environment. The exemplary results of the performed analysis of the low-frequency magnetic field recorded onboard the vessel are presented.