Preparation and Characterization of Gradient Compressed Porous Metal for High-Efficiency and Thin-Thickness Acoustic Absorber

Abstract

Increasing absorption efficiency and decreasing total thickness of the acoustic absorber is favorable to promote its practical application. Four compressed porous metals with compression ratios of 0%, 30%, 60%, and 90% were prepared to assemble the four-layer gradient compressed porous metals, which aimed to develop the acoustic absorber with high-efficiency and thin thickness. Through deriving structural parameters of thickness, porosity, and static flow resistivity for the compressed porous metals, theoretical models of sound absorption coefficients of the gradient compressed porous metals were constructed through transfer matrix method according to the Johnson–Champoux–Allard model. Sound absorption coefficients of four-layer gradient compressed porous metals with the different permutations were theoretically analyzed and experimentally measured, and the optimal average sound absorption coefficient of 60.33% in 100–6000 Hz was obtained with the total thickness of 11 mm. Sound absorption coefficients of the optimal gradient compressed porous metal were further compared with those of the simple superposed compressed porous metal, which proved that the former could obtain higher absorption efficiency with thinner thickness and fewer materials. These phenomena were explored by morphology characterizations. The developed high-efficiency and thin-thickness acoustic absorber of gradient compressed porous metal can be applied in acoustic environmental detection and industrial noise reduction.

Improving and Optimizing Sound Absorption Performance of Polyurethane Foam by Prepositive Microperforated Polymethyl Methacrylate Panel

“…It could be easy to confirm that reasonable range of the porosity φ was (0,1) according to its definition, as shown in Equation (18). Meanwhile, it was reported by the present literatures [1][2][3][4][8][9][10][11][12][13][14] that normal possible boundary of the static flow resistivity σ was [10000, 50000], so the investigated range in this research was set to [1000,200000], as shown in Equation (19). Moreover, the optimization target was to achieve minimized differences between the sound absorption coefficient of the experimental data α a f , d p f and that of the theoretical data α t f , d p f , as shown in Equation (20).…”

“…The transfer matrix T mpma of the prepositive microperforated polymethyl methacrylate panel was derived according to Maa's theory [18][19][20], as shown in the Equation (8). Here, Z s was acoustic impedance, as shown in Equation (9), and its real part and imaginary part were symbolled as R and X respectively; j is the still symbol of the imaginary number, j = √ −1.…”

“…Similar with the polyurethane foam, porous metal was another common porous material used in the field of sound absorption [8,17,22,27,29,33,35]. Besides common standard porous metal, some novel sound absorbers had been proposed, such as uniform compressed porous metal [35], gradient compressed porous metal [8,22,27], microperforated compressed porous metal panel [29], and so on. The horizontal comparisons of the actual average sound absorption coefficient of the optimal composite sound absorbing structure with that of other porous materials were conducted when total thickness was 20 mm, as shown in Table 5.…”

“…The nitrile butadiene rubber-polyurethane foam composites (NBRPFCs) with stratified structure were designed and optimized by Jiang et al [4], and the sandwich structure with thickness ratio 1:8:1 could achieve the optimal average sound absorption coefficient of 0.56 in the 500-1600 Hz range. These sound absorbers with fine sound absorption performance [1][2][3][4] prove that the polyurethane foam has huge potential in the noise reduction, which makes it a new research hotspot in acoustics and material science.In order to promote practical application of the polyurethane foam in the sound absorption and noise reduction, it is essential to identify its acoustic characteristic parameters, especially the porosity and static flow resistivity, because they are the most important factors to determine the sound absorption performance [5][6][7][8][9]. Zhang et al[5] studied sound absorption performance of the polyurethane foam with porosity in the range from of 16.0% to 88.6%, which achieved the optimal sound absorption coefficient of 0.66 in the low frequency range of 250-600 Hz.…”

“…In order to promote practical application of the polyurethane foam in the sound absorption and noise reduction, it is essential to identify its acoustic characteristic parameters, especially the porosity and static flow resistivity, because they are the most important factors to determine the sound absorption performance [5][6][7][8][9]. Zhang et al…”