THE NULL-FIELD APPROACH TO ELECTROMAGNETIC RESONANCE OF COMPOSITE OBJECTS

In the present article, the null-field approach to electromagnetic resonance properties of three-dimensional composite objects is reviewed. In this approach the resonance problem is solved by searching zeroes of the determinant of the total Q-matrix for the composite object. The derivation of the Q-matrix for three main classes of composite objects is given. It is noted that for each class, several alternative null-field approaches are usually available. The numerical implementation of the Q-matrix for homogeneous and composite objects is discussed, with special emphasis on consistency checks for the results. It is found that numerical convergence is obtained in a frequency interval that often contains ten or more resonance modes. The resonance frequencies and quality factors for some axially symmetric composite objects are compared with published numerical and experimental data whenever possible. In general, good agreement is found in these comparisons.