Electromagnetic Radiation Characteristics Based On Smith-Purcell Effect

When the moving charge passes over the surface of the periodic structure,there will induced current appearing on the surface of the periodic structure,producing outward scattering waves,which is called Smith-Purcell effect.In recent years,the amplitude,phase and polarization of the radiation wave can be controlled by design the unit cell reasonably for its subwavelength and relative negligible thickness.This paper mainly solves the scattering problem between the frequency and direction of the radiation wave when changing the velocity of electron beam.The direction of the radiation waves can be modulated by the velocity of electron beam(the voltage)without changing the geometric parameters or adding extra coupling structure at a fixed frequency.The concrete researches are displaying as follows:1.Based on the three slits metasurface,the influence of Fano resonance is analyzed when changing the geometric parameters of the unit cell.Based on the feature that the resonant frequency remains nearly unchanged when varying the period of the unit cell in a certain range,using the velocity of electron beam to control the direction of THz radiation waves at fixed frequency is confirmed theoretically.The correctness of the above theory is verified by the effective surface current and PIC simulation.The radiation power and the corresponding radiation efficiency are calculated to study the performance of the three slits structure.2.The concept of double electron beams stimulating mono-layer structure and single electron beam stimulating dual-layer structure is proposed to improve the corresponding radiation power and efficiency over 50 percent on the basis of controlling the direction of radiation waves.In addition,changing the study object from diffraction order-1 to-2 indicates that with the increasing of diffraction order,the performance of steering the direction of radiation wave by the velocity of electron beam can still be realized.Meanwhile,the velocity of electron beam will decrease.3.From the perspective of dispersion and microscopic multipoles scattering power,the phenomenon that the resonant frequency of three slits unit cell remains basically unchanged when varying the period length of the unit cell has been studied.The results illuminate that there is a leaky mode lying at the resonant frequency and the Fano resonance is generated for the destructive interference between toroidal mode and magnetic mode at the resonant frequency.The phenomenon of the interference does not change when varying of period length of the unit cell.4.The dispersion properties of an open metal grating with high duty-ratio are analyzed,and when the coupling between adjacent resonators can be almost ignored,the radiation mode of the metal grating shows a form of one-mode.The radiation performances of the above grating are performed in PIC simulation.The results show that the direction of radiation waves can be freely controlled by the velocity of electron beam at resonant frequency.