Electrical-Modulated\nFlexible Acoustic Metamaterial:\nEnhancing Low-Frequency Absorption via an Ionic Electroactive Polymer

The growing concern over low-frequency noise pollution\nresulting\nfrom global industrialization has posed substantial challenges in\nnoise attenuation. However, conventional acoustic metamaterials, with\nfixed geometries, offer limited flexibility in the frequency range\nadjustment once constructed. This research unveiled the promising\npotential of ionic electroactive polymers, particularly ionic polymer–metal\ncomposites (IPMCs), as a superior candidate to design tunable acoustic\nmetamaterial due to its bidirectional energy conversion capabilities.\nThe previously perceived limitations of the IPMC, including slow reaction\nand high energy expenditure, owning to its inherent sluggish intermediary\nionic mass transport process, were astutely leveraged to expedite\nthe attenuation of low-frequency sound energy. Both our experimental\nand simulation results elucidated that the IPMC can generate voltage\npotentials in response to acoustic pressure at frequencies significantly\nhigher than those previously established. In addition, the peak absorption\nfrequency can be effectively shifted by up to 45.7% with the application\nof a 4 V voltage. By further integration with a microperforated panel\n(MPP) structure, the developed metamaterial absorbers can achieve\ncomplete sound absorption, which was continuously tunable under minimal\nvoltage stimulation across a wide frequency spectrum. In addition,\na microslit structure IPMC metamaterial absorber was designed to realize\nmodulation of the perforation rate, and the absorption peak can be\nshifted by up to 79.2%. These findings signify a pioneering application\nof ionic intelligent materials and may pave the way for further innovations\nof tunable low-frequency acoustic structures, ultimately advancing\nthe pragmatic deployment of both soft intelligent materials and acoustic\nmetamaterials.