PERTURBATION FORMULA FOR THE NATURAL FREQUENCIES OF AN OBJECT IN THE PRESENCE OF A LAYERED MEDIUM

It is well known that the natural frequencies of an object are importa nt distinguishing features which can be used in target detection and d iscrimination schemes. These natural frequencies are governed by the s ize, shape, and material composition of the object, as well as the env ironment in which the object resides. Since a given object of interest may reside in many different environments, it is of interest to relat e the natural frequencies of an object when in free-space to the natur al frequencies of the same object when immersed in a non-homogeneous e nvironment. In this paper a perturbation formula is developed which re lates the free-space natural frequencies of an object to those of the same object in the presence of a planarly layered medium. The perturba tion formula is valid for intermediate spacing between the object and the nearest planar interface. Numerical results are shown for the natu ral frequencies of a wire in the presence of a layered medium.