Spatiotemporal parametric instabilities in a soft strip.

Period doubling is a robust feature of systems subjected to time-dependent parameter modulation, which manifests among a variety of fields including physics, chemistry, and biology. When the parameter is modulated in space, an analogous behavior can occur, characterized by the emergence of patterns with a wavelength twice that of the underlying modulation. Here, we consider the case of a system depending both on time and space. Using a simple mechanical model, here a vibrating strip, we show that such a modulation yields a dynamics richer than in the classical (i.e., purely temporal or spatial) case. In particular, instead of standard period doubling, we report a dual subharmonic response exhibiting occurrences of tristability. These features are captured within a unified framework, which further reveals that the frequency content of the response can be tuned via the ratio of the system size to the modulation length scale, a control parameter that can be adjusted through the strip's material properties, length, or tension.