The Study Of Electromagnetic Polarization Transformer Based On Chiral Metamaterials

Polarization is an important parameter of electromagnetic field,different statuses of the polarization can be applied in many aspects,such as communication,anti-interference and radar.A variety of artificial structural materials have been designed to manipulate polarized waves,including grating,bichromatic crystal regulation and manipulation of birefringence,etc.However,the problem is that most of the sizes of these materials are much larger than the working wavelengths,or they have a very large energy loss.Since the twenty-first Century,electronic metamaterials have attract more and more attentions because of their extraordinary physical properties.Based on the intrinsic characteristics of the chiral structure,it has a peculiar electromagnetic property,the most prominent ones are the strong optical activity and circular dichroism,which could be used to control electromagnetic waves.This thesis presents a study of the application of chiral metamaterial polarization transformer Two structural models of 90? polarization rotator and circular polarization device are designed.The performance of the polarizer is discussed by theoretical analysis and numerical simulation,and the mechanism has also been analyzed.The main contents of this thesis are as follows:(1)A kind of chiral metamaterial 90? polarization rotator based on the V structure is designed.The structure is composed of three layers of metal-insulator-metal and it has the properties fourfold rotational symmetry.From the calculation results,we know that this chiral metamaterial can achieve the 89.57° and 90.04° polarization rotation at the frequency of14.61 GHz and 20.06 GHz,which is very close to 90?.The cross polarization transmission coefficients at these two frequency points are 96.94% and 94.56%,respectively.Finally,by changing the geometric parameters,a 90? polarization rotator is designed to achieve polarization conversion at three frequencies.(2)A dual band chiral metamaterial of circular polarization device based on open ring is also proposed.The structure also has the fourfold rotational symmetry,so the structure is not sensitive to the incident polarization wave.The linearly polarized wave can be respectively transformed into left-and right-handed circularly polarized waves at two resonant frequencies11.65 GHz and 13.02 GHz with the values of ellipticity are-44.17? and 44.53°,respectively.They are very close to 45?.At the same time,the polarization extinction ratio(PER)at these two frequency points are-36.78 dB and 41.80 dB,which indicates that the structure has good polarization conversion ability.The manipulation of polarization shows that chiral metamaterials can provide more convenient and efficient way to control polarization.At the same time,metamaterials,as a new type of electromagnetic materials,have great potential for research.