Exploring broadband sound-absorption technology is of great significance in acoustics, with wide applications in noise control and sound mitigation. In this work, a multiband sound-absorbing device was proposed with two air cavities. A double resonant structure was constructed by embedding a sound-absorbing material in the Helmholtz resonator’s neck and a microperforated board inside the Helmholtz resonator, respectively. In particular, we systematically discussed the sound absorption coefficient of each assembly unit and shed light on the mechanism and structure-activity relationship of the proposed double-cavity resonant device (DCRD). The results showed that the sound absorption performance of the prepared DCRD was about twice higher than that of the Helmholtz resonance structure under the same air cavity content. Thus, it could greatly improve the absorption ratio of low-frequency sound without sacrificing high-frequency performance with the microperforated plate assistance. Overall, we believe this work provides a new toolbox to enrich the family of resonant sound absorption materials, especially realizing noise reduction optimization of low-frequency sounds through a flexible design approach.

α-1,3-glucan is a linear homopolymer produced through the enzymatic polymerization of sucrose using recombinant glucosyl transferase J (GtfJ) enzyme. Two series of α-1,3-glucan short- and long-chain mixed esters, namely α-1,3-glucan acetate hexanoate and α-1,3-glucan propionate hexanoate, with different ratios of short to long sidechains were synthesized via heterogeneous chemical esterification. α-1,3-glucan propionate hexanoate, with a stable crystalline structure, had a significantly higher melting temperature than α-1,3-glucan acetate hexanoate. Melt-spun fibers of both series of esters were successfully prepared at lower temperatures than those required for conventional α-1,3-glucan homo esters, without decreases in molecular weights. The tensile strength of melt-spun fibers increased as the proportion of the short sidechain increased, reaching 367 MPa (ratio of acetate to hexanoate groups of 2.2:0.8), which was much higher than α-1,3-glucan tripropionate with a tensile strength of 115 MPa. X-ray diffraction analyses indicate that this high tensile strength is due to the high orientation of the molecular chains.

The broadband sound-absorption technology exploration is of great significance in acoustics, with wide applications in noise control and sound mitigation. In this work, natural materials were used for sound absorption. The straw and rice husk are abundant and easily accessible biological resources, considered excellent candidates as sound absorption materials for their natural porous structure. The sound absorption characteristics were evaluated by classifying the rice straw into thick, thin, and mixed groups, and the optimum thickness was clarified. The typical sound absorption materials were prepared from different kinds of rice straws (thickness) and rice husks. A systematic exploration was devoted to studying the rice straw type and cavity volume effects on the sound-absorbing performance. The results showed that rice straws with a diameter of ≥3 mm exhibited an optimized sound absorption capacity, and the performance continued to be enhanced after mixing with rice husks. In addition, the sound absorption performance on the low-frequency side of the multi-layer sound-absorbing structure, composed of porous medium density fiberboard, thick straw, and rice husk, was better than that of the multi-layer sound-absorbing structure using non-woven fabrics.