Development of metacage for noise control and natural ventilation in a window system

Abstract

Ventilation window is one of the critical elements in sustainable building development, although frequently, outdoor factors such as environmental noise can limit their use. It is necessary to develop windows with both natural ventilation and noise mitigation functions. Acoustic Metamaterials (AMMs) set a new trend in solving physical challenges related to sound wave control, which can find their applications in ventilation window. This study presents a design based on acoustic metacage concept to enhance the window's natural ventilation and acoustic performance. Finite Element Method (FEM) is used to study and optimise the acoustic performance of the metacage window. The ventilation is evaluated at the same time following predefined guidelines related to the window's opening ratio and airflow directivity. The metacage window structure finally, reduces the noise transmission with a mean value of 30 dB within a frequency range of 350-5000 Hz and has an opening ratio of the 33% compared to the whole system surface. The front panel gives a mean high frequencies TL contribution of 17 dB (2000-5000 Hz). Additional lateral constraint and cavities increase the TL performance up to 70% on a wider lower frequency range (350-5000 Hz). Thanks to the cavities, the resonant unit cells among the acoustic metasurface (AMS) significantly suppress sound from exiting the structure in broadband frequencies and allow bigger opening on the lateral side. This significantly contributes to the natural ventilation potential of the metacage window, which in the long term, becomes equally effective to the conventional open windows.

A Metawindow with Optimised Acoustic and Ventilation Performance

“…Inspired by the acoustic black hole effect, the theoretical wave propagation in this specific system generates an acoustic stopband related to the resonant tubular array [36]. More details about the simulation results and theoretical analyses can be found in our previous publication [35]. The adaptation to a more ergonomic and common design is required for real application as a building feature.…”

“…The adaptation to a more ergonomic and common design is required for real application as a building feature. Following the analytical analysis from the previous acoustic metacage model [35], a specific impedance (Z 1,2 ) and refractive index (n 1,2 ) related to the different geometrical areas (Region 1 = R 1 and Region 2 = R 2 ) of the AMW unit are considered (see Figure 1b). Due to the contrast in the two regions' refractive indices, the sound waves passing through the AMM unit cell experience an out-of-phase condition, and this phenomenon is proved regardless of the sound wave angle of incidence for any value of n. This physical principle is verified for the AMW unit, and the preliminary numerical analysis confirms it: the AMW unit design can be used as an omnidirectional sound barrier for all-angle incoming waves.…”

“…In this study, an acoustic metawindow (AMW) unit for broadband noise control (50 to 5000 Hz) and natural ventilation is presented, and its performance is examined numerically and experimentally. Firstly, since our previous study numerically tested the feasibility of a metacage [35], the ergonomic adaptation of the window is investigated in order to determine the most regular window shape [3] with the closest noise control properties to the previous model [35]. This is not of immediate determination since the previous paper highlighted that acoustic properties are strictly related to the 3D geometry [35].…”

“…Firstly, since our previous study numerically tested the feasibility of a metacage [35], the ergonomic adaptation of the window is investigated in order to determine the most regular window shape [3] with the closest noise control properties to the previous model [35]. This is not of immediate determination since the previous paper highlighted that acoustic properties are strictly related to the 3D geometry [35]. In this model, the AMM system is incorporated in the window frame space for noise reduction and ventilation, while the central area allows a visual connection between the outdoor and indoor environment.…”

Analysis of Impact of Natural Ventilation Strategies in Ventilation Rates and Indoor Environmental Acoustics Using Sensor Measurement Data in Educational Buildings

“…al. [ 38 , 39 ] proposed a new metacage window which allows natural ventilation and noise reduction based on the principle of Snell’s Law. The used of this novel prototype showed an overall mean sound reduction of 15 dB within a bandwidth of 380 to 5000 Hz.…”