The null field approach to electromagnetic scattering from composite objects

An improved null-field approach to scattering from composite objects is reported. Several alternative expressions for the transition matrix of a composite object are derived that partly or completely avoid the geometrical constraints inherent in previous null-field results for a composite scatterer. Some of the new versions make use of Q-matrices for the open surfaces which are defined by the interfaces between the different parts of the composite scatterer. The numerical performance of the various alternatives is investigated for a number of test cases. Comparisons between alternative versions for the same scattering problem are made to provide a measure of the absolute accuracy of the computed null-field results. Whenever possible, the results are compared with other computed or measured results