Complex transformations of chemical signals passing through a passive barrier

It has been recently observed that a passive barrier separating two excitable chemical media may transform the frequency of a train of incoming pulses. In this work we apply the FitzHugh-Nagumo-type model to study this phenomenon in a detailed way. Our numerical calculations demonstrate that at the barrier a periodic train of pulses may be transformed into a complex output signal. The ratio of frequencies of the output and the input signals, plotted as a function of the barrier's width or as a function of the input signal frequency, has a devil's-staircase-like shape.