Pattern interaction and spiral waves in a two-layer system of excitable units

A system composed of two coupled lattices, hence a layered structure, is studied when the unit at each site is an active electronic circuit possessing two accessible stable steady states. In the absence of interlattice coupling, each lattice taken separately represents a discrete, reaction diffusion system. We show that, depending on the strength of the diffusion coefficient, each lattice may exhibit either a wide variety of stable steady patterns or a number of different wave patterns including rotating spirals. Moreover, for fixed reaction kinetics each lattice can exhibit spiral waves of both excitable and oscillatory type. For nonoscillating kinetics, the metastable periodiclike behavior of the unit is at the origin of the oscillatory spirals. From initially different global patterns or waves in each lattice, the interaction may lead to synchronization and hence a new (controlled) form and the replication of a given one. We also show how there is reentry of spiral waves between the two coupled layers associated with the ``competition'' of their oscillatory and excitable spiral wave properties.