Moving towards materials with humanoid functionality: Sensing their speech with piezoelectric nanowebs

Abstract

The new concept of “humanoid matter” is presented by exploring if the sound emitted by materials embeds phonetic signatures. This overarching topic is here narrowed down to the analysis of the acoustic sound emitted by the sudden hierarchical rupture of microfibers in a composite. While such a low-energy pain-like event for the material is hardly detected with the most advanced structural health monitoring systems, here it is accurately captured (i.e., “listened”) with a piezoelectric nanoweb that weighs less than 0.25% than the reference microphone. As humans react to pain with an unarticulated voice pattern, the composite delivers an unvoiced/voiced pattern when suddenly damaged. The phonetic analysis demonstrates the feasibility of using the energy released by a mechanical failure as sound source (i.e., vocal cords) that excites the acoustic resonances of the material (i.e., vocal tract). Differently from healthy humans, the progressive failures slightly modulate the vibration speed of the vocal cords (pitch) due to the stiffness changes of the vocal tract which thus modifies its sound shaping action. The sound signals from the material carry the phonetic fingerprints of the microdamage. This work represents a first step towards materials that possess humanoid functionalities which can potentially revolutionize human-object interaction.