| Since the development of human society entered the information age,with the rapid growth of communication demand and the continuous innovation of communication technology,the role of high-power devices in modern communication systems has become more critical and important.Compared with solid-state devices,vacuum electronic devices can provide greater power,wider bandwidth,and better efficiency,so they have certain application prospects in future communication systems.Centralized attenuators are an important part of vacuum high-power devices and directly affect the performance of traveling wave tubes.However,traditional attenuators have shown certain limitations when facing urgent demands such as miniaturization,standardization,high customization,and large-scale production of traveling wave tubes.Metamaterial absorber(MMA),as a novel artificial electromagnetic material,has subwavelength structure,strong absorption,wide bandwidth,and other characteristics.The introduction of MMA to replace the traditional wedge attenuator can not only improve the performance of the traveling wave tube device,but also benefit the miniaturization design of the traveling wave tube.The operation of vacuum high-power devices is often accompanied by high temperature and high-power signal irradiation,but there are few reports on the wave absorption performance of MMA in the higher temperature range(300K to 700 K)and under high-power signal irradiation,which makes MMA still have some uncertainties before it is applied to vacuum high-power devices.Based on the preliminary research of OSCC team,this thesis focuses on the research of thermal stable MMA in view of the problems faced by the application of MMA structure to high temperature and high power.In this thesis,the influence of high temperature and high-power irradiation on the performance of MMA is analyzed,and according to the analysis results,a thermal compensation strategy is established to guide the structural design of thermal compensation MMA.To verify the feasibility of the thermal compensation strategy,this paper proposes a thermal compensation MMA design based on indium antimonide semiconductor materials and compares it with the simulation results of traditional "metal-dielectric-metal" MMA.The simulation results indicate that in the same frequency range,compared with traditional MMA,the absorption performance of thermal compensation MMA is basically stable in the temperature range of 300 K? 600 K,and it also has certain stability in the face of high-power signal irradiation.In this thesis,a design of a thermal compensation MMA based on indium antimonide with a double-layer structure is further proposed.The simulation results demonstrate that at high temperatures from 300 K to 750 K,its effective bandwidth ratio is only reduced by 0.2%,and it still covers 81.1% of the initial effective bandwidth.This reveals that it can maintain stability at higher temperatures of 600 K to 750 K.To achieve the combination of thermal stability and excellent absorption performance,this paper proposes and verifies a thermally stable ultra-wideband MMA based on indium tin oxide(ITO)conductive film.The simulation results show that at the initial temperature of 300 K,the effective bandwidth ratio is 83.35%,and the frequency range with absorption rate greater than 90% is 8.00 GHz? 19.43 GHz.In addition,the effective absorbing frequency band remains basically stable in the temperature range of 300 K? 700 K and covers more than 95% of the initial frequency band.In addition,the absorbing performance of the MMA remains stable at 50 W high-power irradiation as well as 500 K ambient temperature.The ultra-wideband thermally stable MMA proposed in this chapter has certain potential application prospects in devices that require thermal stability(such as traveling-wave tubes,return-wave tubes). |
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