Dual‐Tube Helmholtz Resonator‐Based Triboelectric Nanogenerator for Highly Efficient Harvesting of Acoustic Energy

With the rapid consumption of global energy, the utilization of new energy is of crucial importance for the development of society and the protection of the ecological environment.[1,2] Triboelectric nanogenerators can effectively collect low-frequency vibration energy and convert it into electrical energy.[3–9] These nanogenerators are a milestone in the development of new energy research.[9,10] Their discovery has provided new ideas for the collection of many forms of environmental energy, such as vibrational energy, wind energy, hydropower, and bioenergy.[11,12] A sound wave is a special form of mechanical vibration.[13] As a clean, abundant, and sustainable form of energy, sound waves are ubiquitously present in our surroundings, including various sounds from human activities, airport construction sites, and transportation. Unfortunately, most sound wave energy has been wasted because of its very low energy density and the lack of effective technologies for harvesting acoustic energy.[14,15] Energy harvesters operating on the basis of electromagnetic induction or the piezoelectric effect have been proposed to collect various types of vibrational energy, such as vehicle vibration and human movement.[16–19] However, their application has encountered severe difficulties in regard to acoustic wave energy. The mechanism of power generation using electromagnetic induction is that the conductor in the magnetic field cuts the magnetic induction line to generate induced currents.[20] However, due to the small acoustic energy density and the rapid change in sound pressure, effective cutting of the magnetic line under the action of an acoustic wave force is very difficult for conductors.[21,22] Therefore, using electromagnetic induction to collect acoustic wave energy remains a great challenge. In contrast, piezoelectric materials have good sensitivity to slight disturbances, and most of the previous studies regarding acoustic energy harvesting have concentrated on piezoelectric nanogenerators.[23] However, thus far, such nanogenerators have been limited by low electrical output performance and high structural complexity.[24] Therefore, an advanced acoustic energy harvester with high output performance and good practicability must be proposed soon. An acoustic wave is a type of energy that is clean and abundant but almost totally unused because of its very low density. This study investigates a novel dual-tube Helmholtz resonator-based triboelectric nanogenerator (HR-TENG) for highly efficient harvesting of acoustic energy. This HRTENG is composed of a Helmholtz resonant cavity, a metal film with evenly distributed acoustic holes, and a dielectric soft film with one side ink-printed for electrode. Effects of resonant cavity structure, acoustic conditions, and film tension on the HR-TENG performance are investigated systematically. By coupling the mechanisms of triboelectric nanogenerator and acoustic propagation, a theoretical guideline is provided for improving energy output and broadening the frequency band. Specifically, the present HR-TENG generates the maximum acoustic sensitivity per unit area of 1.23 VPa−1 cm−2 and the maximum power density per unit sound pressure of 1.82 WPa−1 m−2, which are higher than the best results from the literature by 60 and 20%, respectively. In addition, the HR-TENG may also serve as a self-powered acoustic sensor.