Multi-frequency And Multi-functional Controls Based On Digital Coding Metamaterial

Metamaterials are artificial composite materials with subwavelength-scale elements.Metamaterials derive the electromagnetic(EM)properties from the elements and their arrangements and are endowed with numerous unparalleled physical properties such as negative refractive index,negative reflection and so on.Utilizing metamaterials to modulate EM waves is an enduring topic in the field of electromagnetism,the EM properties such as amplitude,phase,and polarization are the objects of modulation.The concept of digital metamaterials and programmable metamaterials further simplify the methods of metamaterial modulation,which can realize the regulation of reflected wave amplitude,beam deflection and polarization through digital regulation.From the perspective of coding metamaterials and multi-frequency and multi-function regulation,this article has carried out the following three parts of research step by step:Firstly,for amplitude control,metamaterial absorber is one of the major applications and the absorption property can also be realized by amplitude regulation of digital coding metamaterial.Based on this idea,a passive metamaterial absorber based on microstrip resonator is proposed in this paper.The structure of the absorber is simple,which can achieve95.2%,93% and 99.1% absorption rate at 5.2 GHz,5.61 GHz and 6.64 GHz,respectively.Secondly,in order to realize the programmable amplitude coding design,a multi-frequency tunable coding metamaterial absorber based on nested metal patches is further proposed in this paper,which is a three-layer and simple structure with good absorbing performance.The element is encoded as “11”,“10”,and “00” corresponding to the ON/OFF states of two diodes.By switching two states of the PIN diode,the simulation results show that the corresponding absorption rate is all larger than 98.7%.For the whole metasurface,the magnitude of the reflected beam can be modulated with some specific coding patterns.Further,we design and implement a wireless communication verification by using the multi-frequency tunable coding metamaterial absorber.In this experiment,a field programmable gate array(FPGA)is connected to the metamaterial and its output signal is viewed as a baseband signal.The signal generator generates the specific high-frequency carrier wave.Under the influence of the metasurface,the amplitude of the tuned signal carries the information to be transmitted,which can be observed by an oscilloscope.So three frequency channels can be used to transmit the information.Finally,this paper also proposes a multi-functional coding metasurface with amplitude,phase,and transmission modulation.The element is composed of seven layers,based on hexagonal antenna structure with integrated a radio frequency(RF)switch,an attenuator and so on.Under the control of FPGA,the state of the RF switch of the element can be switched.Code “00”,“11” correspond to phase modulation(180°phase difference),code “00”,“10”correspond to amplitude modulation(total-reflection and perfect absorption),and code “01”correspond to transmission state.For the whole metasurface,the modulation of amplitude,transmission and beam deflection can be realized by applying different coding sequences.