The correlation between the sound absorption performance of a ceramic fiber needle punched blanket and its fiber diameter is essentially a reflection of the influence of the material's microstructure on the sound wave dissipation mechanism. The uniformity of fiber diameter distribution, fiber fineness, fiber packing density, fiber morphology, and the coupling effect between the fibers and air collectively determine the material's ability to absorb sound waves at different frequency bands.
The uniformity of fiber diameter directly affects the pore structure of the fiber assembly. When the fiber diameter distribution is uniform, the pore size formed by the interlacing of fibers is more consistent, resulting in a more stable collision frequency and energy dissipation path for sound waves propagating within the material. This uniformity reduces the randomness of sound wave reflection, allowing more sound energy to be converted into heat energy through the viscous friction between the fibers and air. If the fiber diameter varies significantly, the pore size becomes uneven, making it easier for sound waves to resonate or diffract in larger pores, reducing sound absorption efficiency.
Fiber fineness is a key factor determining sound absorption performance. At the same bulk density, a ceramic fiber needle punched blanket made of finer fibers contains more fibers per unit volume, significantly increasing the total area of the fiber interface. After sound waves enter the material, the friction with the fiber surface becomes more frequent, enhancing viscous dissipation. Fine fibers also form more micropores, which scatter high-frequency sound waves more effectively, absorbing high-frequency noise in the 2500-6000Hz range. Experiments show that reducing the fiber diameter by half can increase the sound absorption coefficient by more than 30% in the high-frequency range.
Fiber packing density indirectly regulates sound absorption performance by affecting pore morphology. When the fiber diameter is fine, the packing density can be controlled by adjusting the needle-punching process. A suitable packing density allows the material to maintain high porosity (typically >70%) while ensuring pore connectivity. When sound waves are incident, the viscous resistance generated by air flowing through the pores, combined with the elastic deformation of the fiber, converts sound energy into heat energy. If the fiber diameter is too large, the number of fibers needs to be reduced to achieve the same packing density, leading to increased pore size, making it easier for low-frequency sound waves to penetrate the material, and reducing the sound absorption effect.
The influence of fiber morphology on sound absorption performance is reflected in the fiber's bending stiffness and surface roughness. Fine fibers have low bending stiffness, making them more prone to forming a three-dimensional interwoven structure during needle punching, increasing the complexity of the sound wave propagation path. Simultaneously, the higher surface roughness of the fine fibers increases the coefficient of friction with air, further enhancing sound energy dissipation. This structure is particularly effective for absorbing mid-to-high frequency sound waves, enabling the material to achieve a sound absorption coefficient of over 0.9 in the 1000-4000Hz frequency range.
The coupling effect between the fiber and air is the core of the sound absorption mechanism. As a porous material, the sound absorption process of ceramic fiber needle punched blankets relies on the vibration and friction between sound waves and air within the pores. The tiny pores formed by the fine fibers (typically <150μm in diameter) restrict airflow and enhance viscous resistance. When the sound wave frequency matches the pore size, the air vibration amplitude increases, and frictional energy dissipation increases significantly. This coupling effect gives the material selective absorption characteristics for specific frequency bands of sound waves; the sound absorption effect for the target frequency band can be optimized by adjusting the fiber diameter.
In practical applications, the sound absorption performance of ceramic fiber needle punched blankets needs to meet both high-frequency and low-frequency requirements. For high-frequency noise (such as equipment operating noise), using ultrafine fibers (diameter <5μm) can significantly improve absorption efficiency; for low-frequency noise (such as mechanical vibration noise), it is necessary to increase the material thickness or add an air layer to enhance low-frequency absorption capacity. This adjustable performance makes ceramic fiber needle punched blankets promising for wide application in building sound insulation, industrial noise reduction, and other fields.
