Research On Microwave Absorber Based On EBG Structure

Absorbing material is a kind of functional material that absorbs most power of the incident wave and yield little reflection.Material with such properties is in great demand in industries exposed to electromagnetic pollution,such as the broadcasting and TV industry,the electrical power industry,the medical industry,the telecommunication industry,and so on.Absorbing material with thin thickness,light weight and wide-band absorbing ability is most expected and being widely studied.This thesis first deals with the mechanism of the interaction between microwave and absorber,then tries to work out a novel thin microwave absorber but with considerate absorbing bandwidth,based on the single-layer form of a classical absorber,named Salisbury screen.Electric Salisbury screen is easy to prepare but it has to be 1/4λ_g thick to realize absorption.Magnetic screen can be quite thin,but magnetic lossy material is hard to prepare and is unstable and weighty.It has been demonstrated that if we closely place a high-impedance ground plane(HIGP) surface above a perfectly conducting plate,then put a resistive sheet on top of this surface,we can achieve a thin structure that can be an efficient sheet absorber for incident electromagnetic energy.Metal/dielectric composite planar EBG (Electromagnetic Band-gap Structure) structure is a fair way of compositing HIGP.Based on the concept introduced above,this thesis devised two thin microwave absorbers and verified their behavior by simulation.In the first design,the HIGP surface is composed of a period of flat square metallic patches with a "plus" shape slot in each patch.Chip resistors of proper resistance value were loaded between the patches to dissipate incident energy and, function as impedance matching with free space to minimize reflectivity.Reflectivity reached its lowest point at reflection phase null.The second design was based on a resistance-loaded double-square loops structure.This thesis creatively applied Minkowski fractal style to this given absorbing strcture and effectively lowered its absorbing frequency without enlarging the dimensions of the absorbing structure.Moreover,this thesis successfully improved the angle-sensitivity of the conventional double-square loops absorbing structure.