A parametric study of metamaterial-based, acoustically insulating and ventilated louvers

The significant environmental benefits resulting from the use of natural ventilation in buildings are often accompanied by undesired side effects related to an increase in background noise due to the minimal sound insulation provided by an open window. To this purpose, many solutions have been identified in the literature, from partially open windows to metamaterials. The latter are among the most promising solutions, collecting significant research efforts, even though at the moment it seems difficult to achieve the desired performance, particularly in terms of bandwidth for building applications. Taking as a reference a louver system, the incorporation of a space-coiling metamaterial capable of originating a Fano-like resonance (due to the interference of monopolar/dipolar modes developing in the coil and the sound propagating through the ventilated opening), allows to obtain a relatively wide band sound attenuation in a range of about 1000 Hz at mid-frequency. Numerical simulation and parametric analysis are used to quantify the sound insulating performance of the proposed device while keeping the unit dimensions within practical limits, exploring how the system should be modified to maximize the acoustical performance without affecting the ventilation rate and possibly extend the response toward the low-frequency range.