Achievement Of Non-diffraction Beam Based On Electromagnetic Ewave-front Control

The non-diffraction beam is a kind of ideal beam which is based on a set of special solutions for the Maxwell free space wave equation and whose energy can be transferred to an infinite distance without any loss in free space.It solves the problem of energy loss caused by diffraction everywhere in real life,and can break through the limitations of Rayleigh distance to realize long-distance and high-efficiency energy transmission,thus becoming one of the research hotspots of radio energy transmission and telecommunication at present.Bessel beam is the most typical representative of all kinds of non-diffraction beams.Compared with other beams,Bessel beam has better lateral resolution and better orientation.Besides,there are many mature methods to produce practical and usable pseudo-Bessel beam,so it has strong practical application value,so it has a strong practical application value in the fields of radio energy transmission,telecommunication,accurate detection and imaging.However,at present,the energy efficiency of Bessel beam still needs to be improved,so combining new materials,using new methods or using new methods combined with mature technology to further generate more efficient non-diffraction Bessel beam is the main goal of this paper.This paper focuses on the theory and technology of the realization of non-diffraction beam based on electromagnetic wave-front control.The main research contents are as follows:1)In view of the feasibility of using the metasurface method to generate non-diffraction Bessel beam,two types of common substrate non-diffraction metasurface at 5.8GHz are designed in this part,namely,common substrate transmission metasurface and common substrate reflection metasurface.The common points of the two are as follows:first,the materials used are all common materials for metasurface design,which are suitable for basic verification design;second,the method they adopted to generate Bessel beam is the metasurface method in non-diffraction theory,which is more simple and efficient than other methods;third,the biases of the beams are both controlled by the generalized Snell’s law,which can verify the arbitrary direction of energy transmission.The difference is that the former is a transmission metasurface,who specifically uses the generalized law of refraction to control beam deflection and put forward the concept of focusing efficiency to verify the correctness of the non-diffraction Bessel beam,and the latter is a reflection metasurface,who specifically uses the generalized law of reflection to control beam deflection and put forward the concept of modulation efficiency to verify the correctness of the non-diffraction Bessel beam.The feasibility and universality of using the metasurface to generate non-diffraction Bessel beam from transmission and reflection angles are verified respectively,and the latter improves the performance of the unit on the basis of the former,providing relevant basis and reference standards for the subsequent in-depth design.2)Aiming at the broad application prospects of non-diffraction beam and the excellent characteristics of graphene in the terahertz band,a 1.52 THz graphene-based non-diffraction metasurface is designed according to the study in the first tip.Firstly,the conductivity model of graphene in terahertz band is studied and analyzed,and the impedance of graphene in 1.52 THz is obtained.Then,the corresponding unit cell of graphene metasurface is designed,and the excellent performance of the unit is guaranteed by the use of double-parameter adjustment,that is,the unit could completely cover the phase of 3 60° and have a very high amplitude at the same time.Then,the graphene metasurface models are established,and great wave-forming phenomena of non-dirraction beam and focusing characteristics are observed.The focusing distance is 3358.85 um,which is basically consistent with the theoretical design.Finally,the focusing efficiency of first increasing and then decreasing and the modulation efficiency of about 70%are obtained by calculation,which proves the reliability of the whole design.This design provides an important research content for the development of 6G terahertz communication,and with the development of metamaterials,it will also lay a foundation for related non-diffraction researches on graphene,vanadium dioxide and other metamaterials in the future.3)Aiming at the practical application of non-diffraction theory in the present stage,a 5.8 GHz non-diffraction microstrip array antenna is designed in this part.Considering that the placement of the feed used in the metas surface is easily affected by the actual operation,which is not conducive to the machining test and practical application,a micro strip array antenna directly fed by SMA is used instead.According to the metasurface method based on the above researches,the core idea of this design is to use the change of microstrip line length in the feed-network to replace the change of metasurface unit size to provide the phase required for generating Bessel beam.The whole design is divided into three parts:first,according to the experience formula of the microstrip line patch,the patch unit with great performances is designed.And then the 8×8 patch array is set directly,every patch of which can be fed by the lumped port directly and separately according to the phase distribution.Excellent non-diffraction focusing properties are observed,proving that using microstrip array antenna to replace metasurface to realize the non-diffraction beam is reliable;Second,the feed-network is designed independently to provide different phases by adjusting the length of the feed-line,and the return loss(|S11|<-10 dB)of the entire feed-network is the evaluation standard to ensure that as much energy as possible is sent into the antenna from the source.Finally,by combining the patch array and the fee-network,the complete non-diffraction Bessel microstrip array antenna is realized,with the lump-port is replaced by the actual SMA port.The final antenna array is processed and it has good non-diffraction focusing characteristics.The frequency band of the whole microstrip array antenna is[5.54 GHz,6.34 GHz],the return loss |S11| is-17.01 dB at the center frequency of 5.8GHz,and the antenna gain is 17.02 dB.This design proves the feasibility and puts forward the reliable design method of non-diffraction application by replacing metasurface with microstrip array antenna.Moreover,with the help of mature microstrip line processing technology,non-diffraction microstrip array antenna will have high practical value at the present stage.