Pulse sharpening phenomena on a transmission system due to fast switching transients

A large, open transmission line, 10.5 m long with a flat earthplane made of tin-plate, was constructed for studies of fast B-dot/D-dot loop probes using sub-nanosecond rise-time pulses of several tens of kilovolt amplitude. During these experiments, it was noticed that the maximum rate of rise of the pulse, measured by the differential sensors, increased continuously as the pulse propagated from the start to the end of the line. The maximum increase was approximately 10%. Pulse sharpening is a well known phenomena in transmission lines containing saturating magnetic and nonlinear dielectrics, but is usually an order of magnitude rise-time increase associated with lines containing a considerable quantity of nonlinear material across their cross-section. However, the line described does not have any intentional nonlinear element. It is conjectured that the only possible nonlinear element present is an iron compound in the tin-plate skin of the earthplane