This paper proposes a method to generate Bessel-like collimated beams with suppressed side lobes using the flexural vibration modes of a fixed boundary circular plate,which is excited by a longitudinally vibrating tra...This paper proposes a method to generate Bessel-like collimated beams with suppressed side lobes using the flexural vibration modes of a fixed boundary circular plate,which is excited by a longitudinally vibrating transducer in a ring excitation manner.The factors affecting the generation of Bessel-like collimated beams are investigated by theoretical analysis,numerical simulation and experimental methods.The results indicate that Bessel-like wave can be generated by a thin circular plate with fixed boundaries.The third-order mode of the circular plate can be modified to generate a collimated beam with suppressing side lobes when it is excited in a ring excitation manner and the excitation position lies between the first two nodal circles of the plate.As the excitation radius increases,the main lobe width of the resulting Bessel-like collimated beam decreases,the extent of the focusing region increases,and the amplitude of the side lobes initially increases and then decreases.Based on the simulation results,a prototype Bessel-like collimated beam generation system is made and measured experimentally.The experimental results are in good agreement with the numerical results.The Bessel-like collimated beam can be generated by the proposed system,which has potential application in the fields of long-range detection,imaging of highly attenuated materials,and airflow acceleration.展开更多
Multipactor and low-pressure gas discharges have a negative impact on the performance and security of microwave components in space.In this manuscript,a 2-dimensional parallel flat plate structural model was designed ...Multipactor and low-pressure gas discharges have a negative impact on the performance and security of microwave components in space.In this manuscript,a 2-dimensional parallel flat plate structural model was designed to simulate the breakdown of multipactor to low-pressure gas discharges.The breakdown levels in the pressure range of 0.1 to 100 torr were verified under the conditions of the Ag material,4-mm gap,2.6-GHz frequency,and air as the background gas.Random secondary electron emission and gas molecule collision processes are incorporated,and the effect of their transition section is studied using trajectory tracking and Monte Carlo methods.A comparison of the model to the available experimental data demonstrates the model’s accuracy.On this basis,the variation of gas adsorption in relation to the surface secondary electron yields was considered,and the effect of the gas adsorption issues on breakdown level was calculated by means of numerical simulations based on some assumptions.The calculation reveals that in a finite volume of space,smaller desorption volumes cause negligible pressure changes,but the secondary electron emission capacity of the material decreases,which,in turn,leads to a flat or rising breakdown level.On the contrary,the larger the desorption volume,the more the gas is collisionally ionized and the breakdown level decreases.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.12474440).
文摘This paper proposes a method to generate Bessel-like collimated beams with suppressed side lobes using the flexural vibration modes of a fixed boundary circular plate,which is excited by a longitudinally vibrating transducer in a ring excitation manner.The factors affecting the generation of Bessel-like collimated beams are investigated by theoretical analysis,numerical simulation and experimental methods.The results indicate that Bessel-like wave can be generated by a thin circular plate with fixed boundaries.The third-order mode of the circular plate can be modified to generate a collimated beam with suppressing side lobes when it is excited in a ring excitation manner and the excitation position lies between the first two nodal circles of the plate.As the excitation radius increases,the main lobe width of the resulting Bessel-like collimated beam decreases,the extent of the focusing region increases,and the amplitude of the side lobes initially increases and then decreases.Based on the simulation results,a prototype Bessel-like collimated beam generation system is made and measured experimentally.The experimental results are in good agreement with the numerical results.The Bessel-like collimated beam can be generated by the proposed system,which has potential application in the fields of long-range detection,imaging of highly attenuated materials,and airflow acceleration.
基金substantially supported by the National Natural Science Foundation of China(grant nos.61901361 and 51827809).
文摘Multipactor and low-pressure gas discharges have a negative impact on the performance and security of microwave components in space.In this manuscript,a 2-dimensional parallel flat plate structural model was designed to simulate the breakdown of multipactor to low-pressure gas discharges.The breakdown levels in the pressure range of 0.1 to 100 torr were verified under the conditions of the Ag material,4-mm gap,2.6-GHz frequency,and air as the background gas.Random secondary electron emission and gas molecule collision processes are incorporated,and the effect of their transition section is studied using trajectory tracking and Monte Carlo methods.A comparison of the model to the available experimental data demonstrates the model’s accuracy.On this basis,the variation of gas adsorption in relation to the surface secondary electron yields was considered,and the effect of the gas adsorption issues on breakdown level was calculated by means of numerical simulations based on some assumptions.The calculation reveals that in a finite volume of space,smaller desorption volumes cause negligible pressure changes,but the secondary electron emission capacity of the material decreases,which,in turn,leads to a flat or rising breakdown level.On the contrary,the larger the desorption volume,the more the gas is collisionally ionized and the breakdown level decreases.
