The Upper Bound of the Speed of Propagation of Waves along a Transmission Line

According to theory, once certain conditions are fulfilled, current and voltage pulses propagate along ideal transmission lines with the speed of light. One can reach such a conclusion only when the conductors are assumed to be perfectly conducting, which cannot be realized in practice. A wave can only propagate along a transmission line with the speed of light if no energy has to be spent in establishing the current in the conductor. However, in establishing a current in a transmission line, energy has to be supplied to the electrons to set them in motion since they have a mass. The energy transfer to the electrons manifests itself in the form of an inductance which is called the kinetic inductance. The effect of the kinetic inductance has to be taken into account in signal propagation along high carrier mobility conductors including super conductors. In the case of transmission lines, the kinetic inductance leads to a change in the characteristic impedance and a reduction in the speed of propagation of waves along the transmission line. The goal of this paper is to show that the kinetic inductance will set an upper bound to the speed of propagation of waves along transmission lines, which is smaller than the speed of light.