Electromagnetic Wave Polarization Converter Based On Field Transformation

Metamaterials,defined as artificial engineered materials with particular characteristics cannot be found among natural materials,is generally composed of orderly or random arrangement of sub-wavelength-sized unit-cells.In recent years,metamaterials have become the hotspot of research in electromagnetics and even optics because of their extraordinary physical properties.In particular,the Transformation Optics developed from the theory of metamaterial have been widely used in polarization modulation,beam transform and other aspects of electromagnetic wave control,and has a broad application prospect.With the deepening of research,the limitations of transform optics have become more and more obvious.As a result,field transformation that regarded as a complementary to transformation optics has been proposed and attracted the attention of researchers.In this paper,we mainly use a field transformation approach to design the electromagnetic wave control device that works in the microwave regime,and realize the functions of polarization conversion and vector beam conversion in free-space.The principle is to design the non-diagonal elements of the permittivity matrix by field transformation,so as to change the coupling coefficient between the electric field component and the magnetic field component of the electromagnetic wave,leading to change the polarization direction of the electromagnetic wave.The feasibility of the principle is verified by simulation analysis and experimental tests,and the test sample is made by 3D printers.The main contents of this paper are as follows:1.A polarizing half-waveplate operating in millimeter wave regime is proposed based on a field transformation approach and the theory of effective medium.Since the half-waveplate is fully made of dielectrics and operates in the zero-order mode,it has a wide bandwidth.Simulation results show that-3 dB polarization conversion can be achieved from 22GHz to 36GHz.The intrinsic parameters of the wave plate do not have limitations in the incident angle.In the simulation results,the conversion efficiency of-3dB can still be achieved within 21.8GHz to 32GHz when the incident angle is 60°.We have used the point-focusing lens antenna to carry out the experimental measurement.The experimental results are in good agreement with the simulation results,which verify the feasibility of using the field transformation to control electromagnetic waves.2.Based on field transformation,a vector beam converter working in X-band is designed to convert linearly polarized waves of different polarization directions into the corresponding vector beams in the free space.The vector beam converter consists of 8 regions.By designing 8 regions,the polarization direction of the incident electromagnetic field is converted into different directions in each region.Therefore,the linearly polarized wave is converted into a vector beam in the frequency band of 10 GHz-12 GHz.