_{1}

The paper presents an inverse derivation method for the excitation signal of NEMP simulator and the field distribution near the simulator, and only one field measurement system is needed. Transformation functions from feeding point to arbitrary point have been calculated by the simulator’s external shape and the geometrical relationship between simulator and the ground, then with the waveform measured in one point, the excitation signal of NEMP simulator can be obtained, and the field distribution near the simulator can be depicted.

NEMP simulator is a device which forms NEMP field. Several NEMP simulators had built in last century, to examining the electromagnetic vulnerability of military electronic equipment [

In principle, the field near the simulator can be determined by the excitation signal in the feed point of cone and the electromagnetic boundary condition. The electromagnetic boundary condition can be determined by the simulator’s external shape and the geometrical relationship between simulator and the ground, the information of which can be obtained by the design drawing of simulator and the simulator’s height in a specific experiment. It is hard to measure the excitation voltage signal in the feed point of cone directly, because the voltage signal is about MV level. According to the simulator’s boundary condition, the paper calculates the transformation function from the feed point to the point measured, with the data of the measured field signal, the feeding signal on the cone can be calculated. The transformation function from the feed point to other space point can also be calculated by the same way, associate with the feeding signal calculated ahead, the field of other space point can be obtained. Therefore, only one field measure system is required to get field distribution, one can also verify another system’s measured data by two field measure system.

In order to calculate the transformation function from the feed point to the point measured, the simulator can be modeled shown as in _{r} = 9.

The simulator’s geometric size along the Z axis is about hundred meters, in order to improve the calculation efficiency, symmetry planes can be set as H_{t} = 0 on plane x = 0 and Et = 0 on plane z = 0. PML boundary causes the space truncation of the simulator, so Gauss pulse has been employed as the excitation signal for its excellent time local performance, which could depress the deviation of transformation function in low frequency range. Moreover, Gauss pulse with proper parameter can cover the spectrum of NEMP pulse, shown as in

In order to weaken ground scatter, the point chosen for field measurement should be near the feed point and far from the ground, point (5,0,0) has been chosen in this paper, the length unit is meter. Another point (3,0,0) has been chosen for method verification. The field amplitude in the two chosen point are both in the dynamic range of the field measure system.

Transformation function from the feed point to the arbitrary point could be expressed by

H r − f e e d ( ω ) = F T [ E r ( t ) ] / F T [ i g ( t ) ] (1)

where FT[•] is Fourier transformation, i_{g}(t) is the Gauss excitation signal, r presents the position. The field signal of every point can be acquired by FIT simulation, according to the equation [

The transformation function H(3,0,0)-feed(ω) and H(5,0,0)-feed(ω) could be resolved by equation [

A numerical simulation has been carried out instead of practical experiment for the technique validation. An NEMP waveform is employed to excite the same simulator model, the field waveform of point (5,0,0) can be obtained like practical measurement, so the excitation waveform of feed point can be deduced by the following equation with the transformation function gained ahead.

i I F T ( t ) = I F T [ F T [ E ( 5 , 0 , 0 ) ( t ) ] / H ( 5 , 0 , 0 ) − f e e d ( ω ) ] (2)

where IFT[•] is inverse Fourier transformation. The excitation signal i1 set in the simulation can be regard as the actual excitation signal. The calculated excitation signal i_IFT is identical with i1, shown in

Furthermore, the waveform of point (5,0,0) can be calculated by

E ( 3 , 0 , 0 ) ( t ) = I F T [ H ( 3 , 0 , 0 ) − f e e d ( ω ) ⋅ F T [ E ( 5 , 0 , 0 ) ( t ) ] / H ( 5 , 0 , 0 ) − f e e d ( ω ) ] (3)

Similarly, the field of point (3,0,0) simulated by FIT arithmetic can be regard as the real field. The deduced waveform of point (3,0,0) reverts the real field waveform precisely including the reflection from the ground scatter, shown in

The paper presents an inverse derivation method for the excitation signal of simulator and the field distribution near the simulator, and only one field measurement system is needed. The simulator’s external shape and the geometrical relationship between simulator and the ground determine the electromagnetic boundary condition and the transformation function; these transformation functions contain complete information of the transmission in the boundary determined system.

Thanks to Jiang Ting-Yong for giving the opportunity and supports to do the work.

The author declares no conflicts of interest regarding the publication of this paper.

Zhou, H. (2018) An Inversion Transformation of Feeding Waveform and Field Distribution on NEMP Simulator. Journal of Computer and Communications, 6, 210-214. https://doi.org/10.4236/jcc.2018.612020