Analyzing the far field in railgun using finite difference method

A current loop in the railgun has been closed by solid projectile. In this paper, the railgun has been modeled as a loop antenna which it has been simulated with three-dimensional finite difference time domain method. Normally, one assumes that the railgun is operated in the far-field region, and radiation patterns are computed in the far-field region. The railgun included copper rails and an aluminum armature. The caliber of railgun is 15 mm ×19 mm and rail thickness is 10mm and 1000mm long. Directivity has been computed for versus frequency (100Hz - 1MHz) in the far field region and it is shown in the some figures. The H-field is calculated for versus frequency and the energy is computed as a function of time and these results are shown in the some figures. Finally, two case studies with different dimensions are simulated and the H-field is compared together which it shown in figure.