Abstract
A nonlinear system possessing a natural forbidden band gap cantransmit energy of a signal with a frequency in the gap, as recently shown forthe nonlinear chain of coupled pendula [Phys Rev Lett 89 (2002) 134102]. Thisprocess of nonlinear supratransmission, occurring at a threshold exactlypredictable in many cases, is shown to have a simple experimental realizationwith a mechanical chain of pendula coupled by a coil spring. It is thenanalyzed in more detail by first going to different (non-integrable) systemswhich do sustain nonlinear supratransmission. Then a Josephson transmissionline (one dimensional array of short Josephson junctions coupled throughsuper-conducting wires), is shown to sustain also nonlinear supratransmission,though being related to a different class of boundary conditions, and despitethe presence of damping, finiteness and discreteness. Finally the mechanism atthe origin of nonlinear supratransmission is a nonlinear instability, and it isbriefly discussed here.