Ultrathin Planar Metasurface-based Acoustic Energy Harvester with Deep Subwavelength Thickness and Mechanical Rigidity

Despite the growing attentions dedicated to the harvesting of acoustic energy that is a clean and renewable yet usually wasted energy source, the long wavelength of airborne sound still poses fundamental limits on the miniaturization of harvester devices and hinders practical applications. Here we present an ultrathin and planar acoustic energy harvester with rigidity. We propose a distinctive metasurface-based mechanism that reduces the effective wavelength to produce extraordinarily strong local energy within deep-subwavelength dimension and enable high-efficiently harvesting energy of incident airborne sound with considerably long wavelength. Our design idea is implemented by a foldy-structured metasurface capable of confining low-frequency energy within narrow channel at resonance, with a piezoelectric plate judiciously placed to converse acoustic to electric energy. The resulting device is downscaled to as thin as λ/63 while keeping flat shape and mechanical rigidity. We analytically derive the effective acoustical parameter of the unit cell, and verify the theoretical predictions via numerical simulations which shows the generation of the maximum output power at the prescribed working frequency. Our design with compactness and rigidity makes an important step towards the miniaturization and integration of acoustic energy harvesters and may have far-reaching implication in diverse applications ranging from microelectronic device design to wireless and self-powered active sensing.