Daniel C. Ross

Electromagnetic scattering from simple jet engine models

The mode-matching (MM) technique is employed for the evaluation of the radar cross section (RCS) of structures that simulate a jet engine inlet. The geometry consists of a perfectly conducting cylindrical inlet terminated by an array of blades mounted on a cylindrical hub. Comparisons of numerical results with actual measurements are presented for the first time.

The mode matching technique for electromagnetic scattering by cylindrical waveguides with canonical terminations

The Mode Matching Technique is employed for the evaluation of the Radar Cross-Section (RCS) of cylindrical inlets terminated by a perfectly conducting cylindrical hub or a cylindrical array of grooves that may be straight or curved. In the case of curved grooves, the geometry is analyzed via the generalized transmission line theory and a closed form solution is given for the first time. The method is formally exact, and yields accurate RCS patterns for geometries that have not been previously investigated. Analytical expressions are derived for the coupling factors between the various modes and RCS results are presented which may be used as a reference in validating other, more general numerical techniques.

Three-dimensional edge-based finite-element analysis for discrete bodies of revolution

An extension to three-dimensional (3-D) edge-based finite-element analysis for modeling electrically large fan-like bodies as discrete bodies of revolution is given. By exploiting the overlapping symmetries between a fan-like body and a modal expansion of the electromagnetic fields, only one lobe of the problem need be solved by the finite-element method without introducing approximations. This computational scaling makes possible the solution of electrically large structures much more efficiently. However, a periodic phase-boundary condition (PBC) must be applied to the faces of the mesh describing a single slice of the body and this condition must be enforced on both the electric and magnetic fields for a robust solution. Details on the implementation of the PBCs are given along with results which validate the overall technique.

Overlapping modal and geometric symmetries for computing jet-engine inlet scattering

By examining the scattering from a cylindrical inlet terminated by a fan-like structure possessing discrete angular symmetry, it is found that only very limited intermodal coupling is possible. This fact is exploited in a hybrid finite element/modal scheme to develop a very efficient solution where only one slice of the geometry need be modeled. It is shown that a phase boundary condition at the interior walls of the mesh is sufficient for the complete solution of the problem. The implementation of the phase boundary condition is detailed for the full three-dimensional case, including special considerations for enforcing the boundary conditions along the axis. A simple example is shown for the sliced, hybrid finite element/modal scheme to validate the method. >

Adaptive integral method applied to multilayer penetrable scatterers with junctions

We present a generalization of the adaptive integral method (AIM) for multilayer scatterers. We also provide a new methodology for treating junctions between differing material types. This is a generalization of the case recently proposed by Shin et al., (2000).

Efficient computation of radar scattering modulation from jet engines

By making use of the overlapping symmetries between the modal inlet fields and the engine face, it is found that the radar modulation due to a set of rotating blades can be computed using only one solution for any blade position. Frequency domain solutions for the stationary engine face can immediately produce modulation data with a simple postprocessing step. The validity of the modulation scheme is demonstrated with the aid of a simplified engine model possessing a semianalytical mode-matching solution.

An AIM based analysis of electromagnetic scattering from jet engine blades

In this paper we investigated the application of the adaptive integral method (AIM) to scattering from structures occurring in jet engine terminations. The method was applied to a curved perfectly electrically conducting blade, and the results were shown to be in excellent agreement with the method of moments. Given the methods low memory and CPU requirements, AIM is considered very promising for the accurate analysis of realistic, very large scale jet engine problems.

Acceleration of moment method solutions for discrete bodies of revolution in free space

Previous related works have dealt with discrete bodies of revolution enclosed within a circular waveguide structure. We generalize these methods to discrete periodic structures in free space for any given field excitation. This paper summarizes the mathematical approach introduced in the literature and discusses two issues relating to the free space problem-namely, how to handle an arbitrary incident field and how to enforce the periodic boundary condition. Finally, we provide examples for numerical validation.

New time-frequency techniques for identification and extraction of scattering mechanisms

Many scatterers such as cavities, jet engines, antennas, appendages on large vehicles and small perturbations in an otherwise homogenous medium are best characterized by distinct higher order scattering phenomena. Their scattering contributions can have significant influence on the overall scattering of the structure and may also contain unique attributes/features that can be exploited for various post-processing functions. Available radar imaging methods based on SAR and traditional time-frequency methods do not possess the necessary resolution needed to extract features in some cases. The authors introduce the adaptive optimal kernel spectrogram approach and discuss higher order mechanisms.

Overlapping geometric and modal symmetries in jet engine scattering and modulation

Discusses a radical solution to the reduction in complexity of radar scattering models for jet engines. Overlapping modal and geometric symmetries are considered as are phase boundary conditions for 3D FEM, modulation and validation.