A possible solution for noise attenuation material for urban buses: The downtown São Paulo case study

Urban buses, particularly in large cities, are exposed to significant noise pollution. This paper presents a new family of materials at the micro/nano level designed for urban noise attenuation, specifically for application in urban buses. Melamine foam is combined in series with nanomembranes, creating a composite material that functions as a Helmholtz resonator. As sound waves pass over the nanomembranes, they are disturbed, and the sound resonates within the melamine foam. This interaction reduces the energy of the sound waves and enhances the noise absorption coefficient. In ten cases studied, the average sound absorption coefficient was approximately 89%, with peak frequencies ranging from 2400 Hz to 4300 Hz. The average thickness of the nanomembranes was around 5.0 µm, while the melamine foam had a thickness of 13 mm. The mean noise reduction achieved was about 11 dB, which depends on factors such as the morphology, thickness, and pore size of the nanomembranes. A case study conducted in downtown São Paulo demonstrated that applying these materials to urban buses can significantly reduce interior noise levels. Finally, the proposed system is fully scalable and adaptable for various applications where acoustic insulation is required.