Cochlea-inspired tonotopic resonators

The cochlea has long been the subject of investigation in various research fields due to its intriguing spiral architecture and unique sensing characteristics. One of its most interesting features is tonotopy, the abil- ity to sense acoustic waves at different spatial locations based on their frequency content. In this work, we propose a novel design for a tonotopic resonator, based on a cochlea-inspired spiral, which can dis- criminate the frequency content of elastic waves without the use of sub-wavelength resonators. The structure is the result of an optimization process to obtain a uniform distribution of displacement max- ima along its centreline for frequencies spanning nearly two-decades, while maintaining a compact design. Numerical simulations are performed to demonstrate the concept and experimental measure- ments to validate it on a 3D printed structure. The resulting frequency-dependent distribution is also shown to be a viable means to discriminate signals with various frequency components. We also show that for appropriate parameter ranges, the tonotopic behaviour can be inverted, i.e., lower frequencies can be made to concentrate in narrower regions, as happens in the real cochlea. The harnessed tonotopic features can be used as a fundamental principle to design structures with applications in areas such as non-destructive testing and vibration attenuation.