Development of tunable acoustic materials with inline cavity structure for enhanced sound absorption and transmission loss

Abstract

This article presents an innovative approach to design and characterize an acoustic material with tunable sound absorption and transmission properties. The material incorporates an inline cavity structure, created by extracting a sphere and a cylinder from a cubic unit cell, resulting in unique inlet and outlet ports. Four samples of varying thicknesses (in multiples of 5 mm) were prepared using 3D printing technology from UV-cured standard resin. Sound Absorption Coefficient (SAC) and Sound Transmission Loss (STL) were determined in the frequency range of 0.5–6.3 kHz using an Impedance Tube Apparatus. Peak SAC values gradually declined from 0.99 to 0.85 with sample thickness increasing from 5 to 20 mm. Likewise, the corresponding peak absorption frequencies of the test samples decreased from 4.95 to 1.95 kHz. The STL values varied between 4 dB to as high as 50 dB within the frequency range of 0.5–2 kHz. In addition, the STL values clearly showed a periodic pattern over the entire range of measurement, irrespective of the changes in thickness. Beyond 2 kHz, the periodic variation remained within a range of 18–38 dB for all the samples. Hence multiplying the unit cells along the transmission path had no remarkable effect on STL. Also, the impact of air gap thickness (10 mm, 20 mm, and 30 mm) on the acoustic properties of the samples was investigated. With the insertion of an air gap thickness of only 10 mm, the peak absorption frequency drastically shifted from 4.95 kHz to 1.275 kHz in the case of a 5 mm thick sample. Similar changes in the material's resonant behaviour with changing air gaps were visible for all other samples. The experimental results, summarily illustrate the role of thickness, internal structure, and air gap thickness in tailoring sound absorption and transmission capabilities. Hence the acoustic properties of the developed material are tunable which offers promising applications in soundproofing and noise reduction across both indoor and outdoor installations. In conclusion, this research demonstrates a novel approach to acoustic material design and its characterization, paving the way for optimized acoustic performance in engineering applications.