Controllable Transmission/Absorption Frequency Selective Surface

Frequency Selective Surface(FSS),as a class of generalized metamaterials,can be applied to the design of absorbers,which can break the thickness restrictions of traditional absorbers(such as Salisbury screens and Jaumann absorbers)to achieve the advantages of “light,thin,wide,strong”.Because it is difficult for the traditional absorbing materials to meet the requirements of both the transmission in the working frequency band and the absorption outside the working frequency band at the same time,according to the filtering characteristics of FSS,FSS can be combined with the absorber,and a new type of absorbing / transmitting frequency selective surface structure is proposed,and the function can be switched by loading the active device.This structure can adjust the absorption / permeability function and deal with the interference of complex electromagnetic environment.It has important theoretical significance and engineering application value in the fields of electronic countermeasures,electromagnetic shielding and stealth technologThe main work and several points of innovation are as following:1)Deeply study the basic theory of FSS and realize the design of broadband FSS absorberThe electromagnetic simulation software CST was used to design a broadband FSS absorber.The structure has two layers: one layer is a loss layer,which generates losses by loading resistance and frequency-selected self-resonance,and it can widen the bandwidth;The other layer is a metal base plate.And the simulation results are analyzed to obtain the general rules of the absorber design.The correctness is verified using the equivalent circuit method,and experience is accumulated for subsequent structural design.2)Complete the design of the absorbing / transmitting FSS structure to solve the problem of in-band transmissionA two-layer FSS is designed.The loss layer realizes electromagnetic losses by loading resistors.In order to realize the transmission characteristics,a parallel capacitor and inductor are used as LC resonators in this layer.The transmission layer is a square loop slot FSS and its transmission frequency is the same as that of the loss layer.The two-layer structure is worked together to form a wave transmission window as a whole.Finally,it achieved transmission at 5.5GHz and 90% absorption at 3.3GHz-14.3GHz.The transparent wave band of the structure is in the absorbing frequency band,which solves the challenge of in-band transmitting wave,and the absorbing frequency band is wider.To validate the simulation,a prototype is fabricated and measured,and a good agreement is achieved between the measured and simulated results,demonstrating stable performance with respect to both incident angles and polarizations.3)Complete the multi-functional absorbing/transmitting FSS design and realize the controllable absorbing / transmittingTwo kinds of multifunctional absorbing/transmitting FSS were designed by simulation: 1)The controllable absorbing / transmitting FSS structure realizes the switching of two states,one state is full absorption in the 5.3GHz-18.1GHz band;the other state is that the transmission frequency is at 8GHz and the absorption bands are 4.4 GHz-6GHz and 9GHz-18.9GHz.In addition,in the design process,a bias circuit is used reasonably,which reduces its influence on the wave-absorbing function.2)The absorbing / transmitting FSS structure with adjustable transmission band,which transmission band can be adjusted at 5.4GHz-6.8GHz,and the absorption band has a 90% absorption rate at 4.4GHz-14 GHz.The design of this structure widens the bandwidth of the transparent wave band.4)Using equivalent circuit model to optimize design and improve structural design speedEstablish corresponding equivalent circuit models for different absorbing / transmitting FSS structures,and analyze and obtain corresponding circuit component parameters.Scattering parameters are calculated from the equivalent circuit model.The electromagnetic simulation model is optimized by the equivalent circuit model,which effectively improves the speed of structural design.