| Structure/function integration is the important development trend of aircraft structures and the key technology to improve the structural efficiency and functional features.Comformal load-bearing composite structures with antenna function can not only improve syructural efficiency and aerodynamic performance,but also reduce radar cross section and improve stealth performance of aircraft.Bistable composite laminates have two stable configurations and are able to realize large transformation between stable configurations while no energy is needed to maintain the stable configuration.The light-weight,load-bearing,low profile,conformal and large deformable characteristics make them have potential applications in morphing structures and energy harvesting.A novel multifunctional composite structure with antenna function and morphing characteristics can be achieved by integrating antennat devices into bistable composite structures.In addition,radiation patterns of the antenna can be reconfigured markedly using large deformation during configuration transformations.In this thesis,a new design concept of integrated composte structure with bistablity and antenna function is proposed.The stable configurations and electromagnetic properities of the bistable composite antenna structure have been studied.The stable configurations are predicted by theoretical analytical model and finite element methods and the electromagnetic properities are designed and simulated by electromagnetic field analysis software.Prototypes of integrated bitable composite antenna structure are prepared by co-cure process.The theory and simulation results are verified by mechanical and electromagnetic test.The details are as follows:A membrane microstrip quasi-Yagi antenna is desined and prepared based on antenna theory and screen printing technology.The reflection coefficient and radiation patterns of the membrane antenna are investigaed.The effective elastic modulus of the antenna radiation layer predicted by micro-mechanics and superposition methods.To reveal the interface failure process during 90° peel test,the interface property between radiation layer and membrane substrate is studied based on cohesive finite element model.The peel strength is predicted and verified by experiment,which has the error of 8.11%.Finally,the effects of thermal cycling,ultraviolet light and ozone of the near space on the resistance,tensile and peel properites are experimentally studied.The results indicated that thermal cycle has the great effect on the interface peel strength.The peel strength decreases by 18.24% after 60 times of thermal cycling.Ultraviolet and ozone radiation mainly affect the radiation layer resistance,and have little influence on mechanical properties of the antenna.A new concept of bistable microstrip Yagi antenna structure based on bistable composite laminate,which acted as support structure,integrated with membrane antenna is proposed.Based on nonlinear lamination theory and Rayleigh-Ritz method,the theoretical shape prediction analytical model of bistable Yagi antenna structure is predicted and verified by FEA and experiment.The snap-through critical loads of bistable antenna structure are predicted by FE methods,the errors between FE and experimental results are within 10%.The influences of galss fiber reinforced plastics(GFRP)lay-ups,Polyimide(PI)film thickness and laying types of membrane antenna on stable configurations and critical loads of the laminate are studied.The designed bistable Yagi antenna structure has bistable characteristics when the GFRP layer thickness ratio is 0.35-0.75 and the PI film thickness is less than 0.2mm.The load bearing capacity of the antenna structure can be improved by increasing PI film thickness.Finally,the snap-throughs of the bistable antenna structure are realized using shape memory springs.The transformation time of the laminate can be governed by controlling the power consumption of the actuating circuitry.When an input power is 9.82 W,the transformation between stable configurations takes about 20 s.And the transformation time is about 0.2s with an imput power of 62.5W.Based on configuration analysis,a electromagnetic simulation model of the bistable Yagi anenna structure is established and pattern reconfigurable performance of the antenna is analyzed.The main beam direction is 30° off in the pitch plane which realizes radiation pattern large angle reconfiguration when the snap-through occurs.The pattern reconfiguration mechanism is explored by analyzing current distribution on the surface of the antenna.The effects of GFRP lay-ups and membrane antenna laying types on the maximum radiation direction of the antenna are studied.The results indicated that the wide reconfigurable angle can be realized by changing GFRP thickness ratio.Finally,a bistable antenna two-element array is presented and studied.Different from single main beam of traditional antenna array,the proposed bistable antenna two-element array can realize four different beams by controlling shapes of each element.And furthermore,the different patterns can be obtained by changing element's relative location.The bistable antenna two-element array will provide more designs,which maybe achieve more radiation patterns.To achieve significant reconfiguration of the radiation pattern,a novel bistable patch array antenna structure using bistable composite laminates(which acted as the substrate of the antenna structure)based on pattern reconfiguration mechanism is proposed.The antenna array has a good omnidirectional radiation pattern in wound-up state and good directivity in extended state.The gain of the antenna increase by 11.29 d B,which means that the corresponding communication distance increase by 3.7 times when the antenna form omnidirectional to directional pattern.Finally,the effects of GFRP lay-ups and grounding plane thickness on the stable configurations and radiation pattern performance of the antenna array are studied.The proposed bistable antenna array structure has potential applications in morphing,deployable and wearable structures. |
PDF Full Text Request