Nonlinear Wave Propagation in a Transmission Line Loaded with Thin Permalloy Films

This paper considers the propagation of waves in a transmission line loaded with thin permalloy films. Since the films are driven to saturation, the transmission line equations which are derived to describe the wave propagation are nonlinear. The nonlinearity requires the use of shock wave analyses, and a derivation of the appropriate shock relations is included. The problems of a line loaded with a single film and a line loaded with a periodic array of films are both treated. The saturation front moving along a string of films is shown to be the shock front. The shock speed, which is determined in terms of the parameters of the circuit, is then the operational speed limit of a thin film memory.