Finite Element Near Space Hypersonic Vehicle Electromagnetic Characteristics - Boundary Element Method

Analysis of the electromagnetic properties of the hypersonic target is a hotspot of computational electromagnetic simulation. Aircraft moving at a speed of more than seven times velocity of sound goes into the state of hypersonic flight. The aircraft surface’s friction with the air makes air temperature rising sharply and ionizes the air, which forms the highly inhomogeneous plasma sheath. This plasma sheath in some condition will greatly influence the aircraft’s electromagnetic scattering characteristics and deteriorate the flight’s communication with the ground station, leading to the "communication blackout" phenomenon.Finite element-boundary integral method (FE-BI) plays an important role in the computational electromagnetic numerical simulation. It inherits the finite element (FEM) method’s analysis ability of the target of any complex structure. At the same time, boundary integral equations are applied as the truncated boundary condition instead of the perfectly matched layer (PML) to reduce the computing resources greatly. The use of the multilevel fast multipole method in the boundary integral part of the matrix vector multiplication improves the efficiency of the algorithm. The finite element-boundary integral method is accurate and efficient. It skillfully combines the advantages of finite element method, method of moments and multilevel fast multipole algorithm and has strong analysis abilities. Due to the finite element-boundary integral method’s outstanding abilities in analysis of the complex medium, this method is very suitable for the analysis of plasma problems. But for the region of the flow field unknown, finite element-boundary integral method usually needs a large enough analysis area to ensure the accuracy of the analysis question. Since the air unknowns in the solving area will not affect the flight’s electromagnetic characteristic, a great amount of calculation is introduced and the air unknowns greatly influence the finite element-boundary integral method’s efficiency in solving this kind of problem.In this paper, the principle of the finite element-boundary integral method and some related knowledge of plasma are introduced firstly. Then, aiming at the problem of how to abandon air unknowns, the author selects a dielectric constant threshold to throw away the needless air, and reconstructs the surface of the integral method, which greatly improves the efficiency of the analysis of finite element-boundary integral method in reasonable precision. In addition, the author proposes the finite element-boundary integral method in solving general antenna’s radiation characteristics problems, and the plasma-covered antenna’s radiation problems are analyzed. Finally, a design scheme of "magnetic-window antenna", and verified the method’s feasibility of solving the "communication blackout" are proposed.