Noise Control in Air Mechanical Ventilation Systems with Three-Dimensional Metamaterials

Abstract

The diffusion of mechanical ventilation systems increased rapidly due to the climate changes in all parts of the world. The mechanical ventilation systems are mainly used in the summer for many difficulties to face very hot temperatures. One of the biggest problems considered if every residential unit is equipped with a mechanical ventilation system is the generation of noise by the rotating blades of the fan for refrigeration. This paper discusses the applications of metamaterials to create attenuation filters to be installed inside the encases of the mechanical ventilation systems in order to obtain sound attenuation. A three-dimensional reticular structure made with spheres has been studied in different configurations related to the numbers of layers employed. The sound attenuations were measured at some specific octaves, depending on the particular configurations. In general, the sound attenuation peaks have been measured between 4 kHz and 8 kHz; this is expected to mitigate the tonal noise component typical of fans based on different variables that compose the whole system (e.g., fan diameter, number of blades, fan speed). However, the outcomes shall be considered in terms of laboratory conditions since material properties of the enclosure and potential polarization effects due to reflection of sound waves at the boundaries may occur.

Research Progress on Thin-Walled Sound Insulation Metamaterial Structures

“…Peng et al proposed a novel acoustic met amaterial of air-permeable multiple-parallel-connection folding chambers and achieved a balance between sound insulation and ventilation [105]. Trematerra et al studied three dimensional metamaterials that can both realize ventilation and sound insulation for air mechanical ventilation systems [106] based on the authors' previous research on acoustic barriers [107,108]. Other research also includes the response of acoustic metamaterials un der fluid excitation [109,110] and nonlinear band gaps [111,112].…”

An Affordable Acoustic Measurement Campaign for Early Prototyping Applied to Electric Ducted Fan Units

“…Therefore, propulsion noise should be considered early, indicating a motivation for this investigation at the conceptual design stage [15]. For instance, the ducted fan offers the potential to combine a variety of rotor blade and stator vane designs to minimize noise, offer noise shielding options, and the placement of acoustic liners [43,44] with the use of acoustic metamaterials (e.g., [45,46]). Figure 3 shows possible locations to apply noise mitigation measures.…”

Study on Sound-Insulation Performance of an Acoustic Metamaterial of Air-Permeable Multiple-Parallel-Connection Folding Chambers by Acoustic Finite Element Simulation

“…This was pioneering of Ghaffarivardavagh et al, and provided effective guidance for the development of more practical sound insulators. Using this method, some novel acoustic metamaterials have been developed, such as a ventilated acoustic meta-barrier based on layered Helmholtz resonators [ 31 ], a three-dimensional reticular structure made with spheres [ 32 ], a ventilation barrier with space-coiling channels [ 33 ], a subwavelength acoustic metamaterial based on labyrinthine structures [ 34 ], an arch-like labyrinthine acoustic metasurface [ 35 ], a ventilated soundproof acoustic metamaterial consisting of resonant cavities arranged around a central air passage [ 36 ], nonlocal ventilating metasurfaces [ 37 ], etc. However, the shapes of these air-permeable acoustic metamaterials were complex, which meant that corresponding fabrications were difficult to realize and that their actual applications were limited.…”