Experimental demonstration of a three-dimensional bioinspired tonotopic metasensor

Abstract Spiral structures are widely recurrent in nature to serve different purposes, including the spatial mapping of acoustic frequencies in the mammalian cochlea—a feature referred to as tonotopy. Motivated by this fundamental characteristic, we explore the elastodynamics of a three-dimensional seashell-like structure with frequency-selective capabilities and, in addition, a polarization-dependent response, a feature rarely found in nature. We experimentally demonstrate how these properties can be exploited to discriminate between out-of-plane and in-plane waves, while producing a discrete spectrum that displays tonotopic behaviour. The polarization capabilities are a consequence of the realization of a tonotopic response in the spiral plane and perpendicular to it. Results can be of interest for the design of low-power, low-latency smart sensors for structural health monitoring and non-destructive testing, where discrimination between frequency and polarization is usually accomplished through digital signal processing.