Finite Difference Time Domain Method In The Analysis Of The Fast Emp Simulator Field Spread And Distribution Applications

The basic theory and Absorbing Boundary Conditions of Finite Difference-Time Domain method are discussed in this paper.We combined FDTD method with cantour path method and simulated numerically EMP transmission in the simulator with fast rise-time.The influence of transmission line structure on electric-field distribution and transmission are studied.The relations of the transitional section angle(by changing the length of transitional section of transmission line)and risetime is sought.We analyze electric-field radiation and the effection of the wall to the EMP simulator's work zone,which offer theoretical basis for design of transmission line.Three different forms EMP simulator with fast rise-time is discussed in this paper:subnanosecond risetime EMP guided wave simulator,large-scale EMP guided wave simulator with fast rise-time and GTEM cell.In the development of the subnanosecond EMP simulator,Transmission line structure adapted to subnanosecond pulse is analyzed.The relationship of Transmission line structure and rise time is theoretically analyze.The FDTD method is used to calculate transmission characteristic of three kinds of exponential.We measured the real electric-field distribution. The actual electric-field transmission and spatial distribution agree with the numerically results.Conclusions are drawn.The rise time of the subnanosecond EMP simulator reach 0.8ns and have good stability.Maximum field intensity reach 50kV/m in the work zone,and field distribution is uniform about the axle.This simulator meet mainly the needs of test on EMP effect and electronic-magnetic compatibility for electronic equipments.This simulator have advantages of fast rise time(2.5～5ns) and big test zone (6m×6m×4m).When we used FDTD method to calculate,we need consider except numerical stability and numerical dispersiveness for memory space of computer and calculating time.The influence of transmission line length and angle change on rise time is studied in order to solve the question of transmission line design.Transmission line with symmetrical structure is more in favor of fast rise time than unsymmetrical structure with the same length of transmission line.Calculating results agree with the theory analyse.Field distribution is symmetrical about the center line.The center field is high and fall gradually apart from the center line.We bring forward a method that apply medium lens on the design of large-scale EMP simulator transmission line structure.In order to find out the frequency characteristics of GTEM cell.we select gauss pulse source,which has perfect requency characteristic and has 1.5GHz and 5GHz bandwidth of incident wave are used as actuater to analyze.Transmission characteristic of different conditions and distribution of±1dB and±2dB are drawn.