Impedance Surfaces For Electromagnetic Interference Suppression

With the fast development of fifth-generation conmmunication,artificial intelligence,high performance compution,the high speed and high density circuits are widely applied in electronic facilities.They benefit human beings' life,but also introduce noticeable electromagnetic(EMI)problems.The deterioration of the electromagnetic environment brings new challenges for device working,human safety and military operations.Traditional electromagnetic absorbing,filtering and shielding methods no longer available in new scenes and new EMI suppressing strategies are in urgent need.Meanwhile,impedance surfaces,which are typically represented by 2-D materials and artificial metasurfaces,are bringing multifaceted application revolution to electronic area due to their unique electromagnetic properties.This work focuses on the new challenges in EMI suppressing.We propose new absorbing,filtering and shielding structures based on graphene and metasurface to meet the requirements of practical engineering.Finally,our proposed shielding structure is applied in the "heat sink+chip package" product of related company.The main content and innovation in this work are:1.Optically transparent microwave graphene absorbers are designed.Several microwave absorbers are fabricated based on graphene film and patterned graphene film.The patterned graphene film overcomes the drawback of unpatterned graphene that it is mainly resistive and barely reactive.It also breaks the limitation of substrate thickness in Salisbury absorber.An optical transmittance of around 80%and a peak absorption coefficient of above 90%are achieved in the sample.We also developed methods to enhance its working bandwidth and absorption coefficients,where 3 GHz working bandwidth enhancement and 100%peak absorption coefficient are realized.Futher,patterned graphene film is utilized in designing working frequency tunable microwave absobrers.By tuning the resistance and stacking layers,0.8 GHz and 1.2 GHz tunable range are realized,respectively.These absorbers have wide application prospect in smart windows of both civil and military use.2.The application of metasurface in EMI problem of multi-layer printed circuit board(PCB)is studied.To be compatible with the serried and compact circuit interconnecting traces,we pay special attention to metasurface with a finite width,namely,surface wave transmission line(SW-TL)structure.The analytical formula of its dispersion relationship is derived based on our proposed equivalent circuit model,which reduces the root-mean-square error as high as 50%in the best case compred with previous work.Further,we applied SW-TL in stripline structure to constitute a hybrid structure.Two methods are proposed to suppress different transmission modes in this structure for signal filtering.A low-pass filter is designed,which has pass band ot DC-9.2 GHz and stop band range as large as 18 GHz(9.6-27.6 GHz).Besides,a band-pass filter is designed,which has pass band of 6.4-21.1 GHz(relative bandwidth as high as 107%)and stop band of DC-6.4 GHz and 21.6-28.7 GHz.Compared with previous works,our fabricated filters realized larger working frequency range and lower radiation loss in stop band,which is important for maintaining the signal integrity of high speed circuit and suppressing EMI of filtering devices.3.New absorption-type waveguides based on metasurface are designed.First,different from traditional reflection-type waveguide filter,an absorption-type filtering structure is designed.By properly placing a periodically etched thin film iin the rectangular waveguide,different modes that have very large difference in propagation loss could be generated,which results in absorption band and transmission band.Iin experiment,an absorption band(reflection and transmission coefficients is lower than-10 dB)and two transmission band(reflection coefficient is lower than-10 dB,transmission coefficient is around-3 dB)is realized in 12-18 GHz.This kind of waveguide filter could solve the problem of the high reflection in the traditional waveguide filters and reducing mutual coupling of different poits with little power reflection.Secondly,different from the application of traditional shielding material.metasurface-type shielding material is designed and applied in the "heat sink+chip package" scene.This design could largely increase the transmission loss of the noise in parallel plate waveguide.Theretical result demonstrates an increase of 130 rad/m of loss factor in 12-28 GHz.This design was experimentally validated.Compared with traditional shielding material,this design improves the shielding effectiveness(SE)by 5 dB in 12-28 GHz.