Supplementary material from "Experimental Demonstration of a Three-Dimensional Bioinspired Tonotopic Metasensor"

Spiral structures are widely recurrent in Nature to meet the most diverse functionalities, 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 follows tonotopic behavior. The polarization capabilities are a consequence of the realization of 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.