Flat Fresnel-spiral acoustic metamaterials composed of several arms ventilated metamaterials for simultaneous broadband sound absorption and air circulation

With a steep rise in the urban population requiring an increased number of buildings, public and private transport systems, urban noise is posing a serious environmental problem affecting health. To attenuate the effect on the well-being of human health, a variety of conventional sound-absorbing materials suitable at mid and higher-frequency noise absorption are commonly being used but low and mid-frequency noise remains a challenge. These applications are further limited by the acoustic performance and ventilation efficiency in conventional noise barrier limits of their fields. Acoustic metamaterial presents a unique solution as an artificially designed material showing low-frequency noise mitigation. A novel subwavelength device having thickness of 15mm (<2 cm) ,with potential application in noise mitigation and air ventilation solution is presented herein. In this study, the design and fabrication of a small prototype based on a Fresnel-spiral shape composed of several arms are performed. Numerical and experimental investigations were carried out to determine the acoustical properties of the proposed ventilated metamaterial in terms of sound absorption and sound transmission loss. The experimental investigation shows significant sound absorption with a high bandwidth (more than one octave in the range of > 900 Hz ), acoustic properties leading to potential applications in urban noise control for low and mid-frequency ranges.