Analysis Of Internal Surface Discharge And Skin Breakdown Of Frequency Selective Metamaterial

Frequency-selective metamaterials are a special electromagnetic modulated surface structure formed by periodically arranging metallic superstructures on a dielectric substrate.The metamaterials have the advantages of high in-band transmissivity,strong out-of-band rejection,and excellent frequency characteristics in a wide range of angles of incidence such as electromagnetic properties,these properties make it tremendous potential for application and development in the improvement of antenna performance.However,due to the presence of these metal superstructures,the cover has a certain metal properties,resulting in its lightning attachment characteristics are different from the conventional radome,the conventional lightning shielding failure,the lightning damage is more prominent.The paper analyzed the particularity of lightning protection of metamaterial radome.The research ideal of lightning protection of metamaterial radome was determined.A 100kV pulse voltage test system to simulate lightning pulse voltage was designed.The characteristics of surface discharge of metamaterials and the characteristics of the skin breakdown of metamaterials was studied.The electric field distribution around metamaterials was analyzed.The impact of the surface charge on the skin breakdown process of metamaterial was investigated.The work focuses mainly on the following content:(1)The influence of lightning on the aircraft was introduced.From the two perspectives of the failure of the conventional lightning protection method and the change of the discharge path,the differences between the metamaterial radome and the conventional radome were compared.The particularity of lightning protection of metamaterial radome was analyzed.The research ideal of lightning protection of metamaterial radome was determined.According to the requirements of surface discharge test and streamer breakdown test of metamaterials,a 100kV lightning impulse voltage test system was developed.(2)The surface discharge test of metamaterials was conducted.The discharge morphologies of the metamaterials along the surface were investigated.The discharge voltages were measured at different positions of the two electrodes on the metamaterials surface.Effect of two electrodes distance on surface discharge characteristics was studied.Effect of the angle between the periodic direction of superstructure units and the connecting line of two electrodes was investigated.The experimental results show that the development of discharge channels can be fitted with broken line,and consist of two types of discharge paths.The first type of path is parallel to the periodic direction of the superstructure units,the second type of path is along the direction at an angle of 45° between the path and the periodic direction of superstructure units.Further analysis shows that main discharge channels of the metamaterial surface occur along the path having the shortest total length of the insulation gap.As the shortest distance between the two electrodes increases,surface flashover voltage linearly increases.As the angle between the periodic direction of superstructure units and the connecting line of high-low electrodes increases,surface flashover voltage first increases and then decreases,when the deviation angle is 0° or 45°,surface flashover voltage is lower;when the deviation angle is 22.5°,the 50%surface flashover voltage is higher.(3)The skin streamer breakdown test was conducted for two frequency selective metamaterials.The discharge characteristics of the two metamaterials were studied from discharge morphology,breakdown voltage and charge deposition in three aspects.The electric field distribution of the two metamaterials was analyzed.The results show that,for ring resonator-type metamaterial,breakdown voltages is the highest.Besides,discharge filaments are darker and lesser.More discharge filaments are occurred near the ground.For Jerusalem-type metamaterial,breakdown voltage is the lowest.Besides,discharge filaments are brighter and more.Further analysis shows that charged particles accumulate on the skin surface to form surface charges by discharge filaments.Surface charge density is hundreds of?C/m2,generating electric fields of several kV/cm inside the skin in the same direction as the applied electric field.The electric field strength inside the skin is significantly increased,resulting in the skin to break down under double effect of applied voltage and surface charge.