Transmission line protection with thin film chalcogenide glass devices

We present the theoretical analysis of a lossless transmission line excited by voltage pulses of the type associated with high altitude nuclear explosions or with lightning. The line is protected by a thin film chalcogenide glass ovonic threshold switch (OTS). The OTS is very simply modelled as a lumped parameter network, and its OFF-ON transition is represented by a time-varying resistance which is characterized by a time constant τ. The analytical solution for the voltage transients along the line considers the applied voltage pulse as a succession of narrow component pulses whose effect is computed according to the value of the time-varying reflection coefficient at the device location. The analytical solution includes the effect of multiple reflections, and it is evaluated numerically so as to determine the voltage profile along the line. We show that the OTS device is well suited for electromagnetic pulse line protection. The effects of the delay time and of the values of the OFF and ON resistances of the switch are discussed.