Transparent, Tunable Acoustic Metasurface for Noise Pollution Reduction
Noise pollution is an invisible danger that impacts millions of people around the world on a daily basis. World Health Organisation believes that environmental noise exposure is responsible for a range of negative health effects, from an increased risk of ischaemic heart disease to sleep disturbance, noise-induced hearing loss and stress-related mental health risks. This is exacerbated by a global trend towards urbanisation, with the United Nations projecting that 68% of the world’s population will live in urban areas by 2050, up from 55% in 2018.
Given that transportation is one of the largest contributors of noise pollution, the ability to buffer road and rail noise could be key to protecting the health and well-being of urban communities.
This invention is a new, transparent, and tunable micro-perforated metasurface that can absorb low-to-mid frequency sounds with varying dominant frequencies. The innovative metasurface is composed of three main components: a fixed micro-perforated membrane, a movable micro-perforated membrane, and a transparent electrode layer. The micro-perforated holes on the double-layer membrane have controllable diameters, which means that hole sizes can be easily adjusted from a fully-open to fully-closed state in real time. This ensures optimal sound absorption and allows for broadband noise attenuation and tenability (404Hz to 1882Hz for an air gap of 20mm). Its noise adaptive feature, thin absorber setup, and lightweight design makes it ideal as a smart transparent sound barrier along train tracks while its all-metal construction makes it simple to clean and gives it a long lifetime. The invention can also be used along bus stop linkways as well as on windows to improve indoor noise protection.
In a simpler version of this invention, the transparent electrode layer can be replaced with a guided wedge mechanism that uses a stepping motor to slide the movable panel. A low-angled wedge of less than 5° enables the use of low-power, low-precision, and low-cost stepping motors.