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Design, Characteristics And Application Of The Fiber Reinforced Polymer Composite Frequency Selective Surface

Posted on:2015-12-18Degree:DoctorType:Dissertation
Country:ChinaCandidate:C L LiFull Text:PDF
GTID:1221330479979600Subject:Materials Science and Engineering
Abstract/Summary:PDF Full Text Request
High loading capacity and low electromagnetic transmission loss are demanded by high frequency radomes. In this thesis, composite frequency selective surfaces(FSSs) were used to design high frequency radomes. Mechanical and electromagnetic transmission characteristics of the composite FSS and laminated structures with the composite FSS were studied. Emphases were given on the electromagnetic transmission mechanism, effects of fabrication process and design parameters on the electromagnetic transmission characteristics of the composite FSS. Effects of the composite FSS on the electromagnetic transmission characteristics and mechanical properties of both laminates and sandwich structures were also studied. The main work includes:Electromagnetic transmission mechanism and impact factors on electromagnetic transmission characteristics of the composite FSS were studied by finite integral technique. Results show that the electromagnetic transmission characteristics of the composite FSS are effected by aperture-to-cell ratio, thickness, electrical conductivity and dielectric constant. The minimum transmission loss of the composite FSS can be reduced by increasing the electrical conductivity of composite materials, especially the one which is vertical to the direction of the electric field, and the resonant frequency of the composite FSS changes little. Carbon composite FSS was fabricated by 3D engraving technique and its electromagnetic transmission characteristics in the range of 10.00-20.00 GHz were measured by free space method. Calculated results have a good agreement with experimental ones and the minimum transmission loss of the carbon composite FSS is much higher than metallic FSSs.In order to increase the electrical conductivity of the composite material, conductive silver paste was coated onto the quartz and carbon fabrics by screen printing technique. The mechanical properties of the composite material were not effected. The equivalent electrical conductivity of the composite material was measured and the results show that it increases significantly after the fabrics printed by the conductive silver paste. Carbon composite FSS with silver paste and quartz glass one were fabricated and their electromagnetic transmission characteristics were measured. Results show that the carbon composite FSS with silver paste has lower minimum transmission loss and the same resonant frequency as the FSS without silver paste. The minimum transmission loss of the quartz galss composite FSS is close to zero. Double-layered model was adopted to calculate the electromagnetic transmission characteristics of the composite FSS with silver paste. The calculated results are in agreement with the experimental data. To the carbon composite FSS with silver paste, its minimum transmission loss is lower than the single layer FSS made of silver paste and higher than the carbon composite FSS. The factors impacting the transmission characteristics of the single layer FSS have the same effects on the double-layered FSS.Effects of the structure and property parameters on the electromagnetic transmission characteristics of laminated structures with the composite FSS were studied by Design of Experiment Technique. Key parameters were distinguished and interactive effects between the key structure parameters and key property ones were analyzed. Results show that the minimum transmission loss of the carbon composite FSS with silver paste was determined by one of the two outside layers which has higher minimum transmission loss, so excellent composite FSS must have two outside silver paste layers. For the three-layered composite FSS with two outside silver paste layers, increasing the thickness of the middle layer increases the minimum transmission loss of the composites FSS, but the change is little when the electrical conductivity along the thickness is high. Resonant frequency and transmission bandwidth of the composite FSS with two sided coating are greatly effected by structure parameters of the FSS element. Dielectric material can shift the resonant frequency of the composite FSS downward, increase the minimum transmission loss and reduce the transmission bandwidth.Mechanical properties of composite laminates and sandwich structures with the composite FSS were studied. Results show that because of the interface properties improving, the flexural strength, flexural stiffness, specific flexural strength, specific flexural stiffness, short-beam strength and specific short-beam strength of the laminates with the composite FSS increase by 2.45%, 2.57%, 16.33%, 16.40%, 4.76% and 19.44% than the one with the copper FSS, respectively. The flexural strength, specific flexural strength and specific flexural stiffness of the sandwich structure with the composite FSS increase by 16.79%, 84.85% and 7.80%, respectively. Effects of four-legged slot on the mechanical properties of the laminates and sandwich structures with FSSs were investigated. Under three point bending load, because of the higher stress concentration introduced by the copper FSS aperture, strength ratios of the laminates and sandwich structures with the composite FSS are higher than the ones with the copper FSS. For the sandwich structures with the composite FSS, epoxy resin in the four-legged slot damages before PMI core.The composite FSS was used in the laminates and sandwich structures to solve the conflict between the high stiffness and low transmission loss. After optimizing the mechanical properties and electromagnetic transmission characteristics, the electromagnetic transmission curves of the laminates and sandwich structures with the composite FSS have obviously ―flat top‖ character and lower transmission loss at certain frequency than the structures without FSSs. For the laminates with the composite FSS, when the thickness deviation changes from-0.50 mm to 0.50 mm, their transmission loss at certain frequency is lower and its transmission bandwidth is bigger than the laminates without FSSs. For the sandwich structures, the rule is also right when their thickness deviation is in the range of-0.30 to 0.30 mm. For both the laminates and the sandwich structures with the composite FSS, their transmission loss at certain frequency is lower than the counterpart without FSS when the incident angle is smaller than 5 degree and their transmission bandwidth is bigger when the incident angle is smaller than 10 degree. So, when the radomes which have low transmission loss and big transmission bandwidth are designed, the angle between the directions of external normal line and the incident microwaves should be smaller than 5 degree.
Keywords/Search Tags:Frequency selective surface(FSS), Fiber reinforced polymer matrix composite, Conductive properties, Laminated structure, Numerical analysis, Optimization, Electromagnetic transmission, Mechanical properties
PDF Full Text Request
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