Research And Design Of Frequency Selective Surface Absorber

The problem of electromagnetic information leakage in WLAN has attracted more and more attention of scholars.When the electromagnetic leakage information contains confidential documents,it will seriously endanger the information security performance of wireless networks.Frequency selective surface absorber has shown great advantages in absorbing electromagnetic energy radiation.It can reduce the intensity of leakage electromagnetic signals,thus reducing the ability of acquisition and decoding of leakage signals.Because the signal reflectivity in the absorption band is at a low level,equipped with the absorber will not interfere with the normal internal use.In addition,the structure designs a passband between the two bands of WLAN.The passband is a newly developed 5G communication band,which enables users to communicate with the outside world normally.Frequency selective surface absorber is more versatile than other forms of absorber.It can design the required passband in the specified frequency band,but the polarization and angle stability of frequency selective surface absorber should be paid special attention to in passband design.Aiming at this problem,based on the analysis and summary of the principle and design method of frequency selective surface absorber,combined with the idea of miniaturization to improve angle stability,a 2.5D frequency selective surface absorber with better transmission characteristics is designed.In addition,a new dual-band frequency selective surface absorber structure is designed to meet the needs of band-pass expansion.The main work of this paper is as follows:Aiming at the problem of air layer thickness in the design process of frequency selective surface absorber,according to the transformation relation of transfer and scattering matrix,combined with the consistency of the two absorption band resistance values,the variation range of air layer thickness and resistance values under ideal conditions of 2.4 GHz and 5.2 GHz absorbing at the same time is given.It is concluded that the thickness is determined by two absorption bands and independent of the passband.Based on the bending technology,the cross-ring structure is bent.The bandpass resonant frequency is about 3.5 GHz,the thickness of the section is 0.170 ?,and the size of the structure is 0.304 ?.The simulation results show that the transmittance of the structure reaches 96.34% at 3.57 GHz and the absorbing rate at 2.4 GHz and 5.2 GHz are 88.6% and 86.7% respectively.The TE and TM waves can maintain more than 80% of the absorbency at 30 degrees of incident angle for polarization and angle stability.On the basis of this structure,a 2.5D metal throughhole structure topology is carried out.The actual unit structure is reduced from 25.6mm to 14.4mm,which is only 0.170 ?.The transmittance at 3.55 GHz is 98.12%,and the absorbing rate at 2.4 GHz and 5.2 GHz are 86.53% and 89.38%,respectively.The stability of incident angle is below 30 degrees,and the working performance of absorbing rate is above 80%.The transmission rate of this structure has been significantly improved in passband performance.Through the angle stability analysis,the reason of the change of the absorbing performance is found,which plays a guiding role in the follow-up design.A frequency selective surface absorber structure based on resonant ring is designed,which is 0.291 ?.At 3.5 GHz,the transmittance reaches a peak of 93%,the bandwidth is 350 MHz,and the absorption rates at 2.4 GHz and 5.2 GHz are 88.26% and 89.25% respectively.When the incident wave angle is below 40 degrees,the better absorbing performance is maintained.Finally,the capacitance and inductance of lumped elements are introduced to realize the dual bandpass frequency selective absorber structure.The bandpass resonant frequencies are 3.9 GHz and 6.4 GHz,respectively-0.0383 dB and-0.4816 dB.There are three absorption bands on both sides of the passband.The absorption bands are 2.17GHz~2.6GHz,4.89GHz~5.9GHz and 8.28GHz~9.1GHz.In the aspect of angle stability,it can maintain 70% performance below 40 degrees.Fast expansion of multi-pass band of frequency selective surface absorber is realized.