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Developed in the Zhang Lab at Boston University in Massachusetts, the sound shield is a metamaterial – an artificially engineered material that has properties not found in nature, thanks to its structure.
Led by Professor Xin Zhang, the new shield is the latest prototype from the long-running Acoustic Metamaterial Silencer project. In 2019, the researchers set out to “significantly block sound while maintaining airflow” using Fano resonances. Potential applications included reducing narrowband noise (a small range of frequencies) from fans, propellers and HVAC systems.
Since then, the Zhang lab has extended its work to explore a broader range of acoustic silencing strategies, including multi-band, broadband and tuneable approaches. That could make the technology viable in new environments such as factories, offices and public spaces, an announcement said, where diverse and unpredictable sound frequencies are common and airflow is essential.
The latest prototype is centred around broadband silencing. “While this broader control came with a modest trade-off in peak silencing performance – a common challenge when shifting from narrowband to broadband suppression – it unlocked powerful new possibilities,” the announcement said.
The breakthrough was made possible through the use of phase-gradient metamaterials, the researchers continued, which can control the phase of a wave as it passes through them.
“Earlier designs based on Fano resonance – developed by our team – were like tuning a radio to block a single station,” said Zhang. The new metamaterial “takes a smarter approach – more like noise-cancelling headphones – effectively silencing a broadband of unwanted sounds. It remains highly effective even as the noise shifts in pitch or volume, making it far more practical in dynamic settings like open offices, ventilation systems or transportation hubs, where sound sources are unpredictable and span a wide range of frequencies.”
The metamaterial is composed of single or repeating ‘supercells’, each consisting of three sub-wavelength unit cells. Solid barriers are incorporated into the first and third unit cells to induce controlled phase shifts in the incoming sound waves, while the central unit cell remains open to allow unobstructed airflow.
“Our design isn’t one-size-fits-all,” Zhang said. “It’s customisable in both frequency range and airflow level, depending on the application.”
Chronic exposure to excessive noise can seriously affect human health, contributing to hearing loss, sleep disruption, heightened stress and even cardiovascular disease. The team aims to deploy its metamaterials, ultimately hoping to apply them across industries “to make the world a quieter, healthier place”.
The work was reported in Scientific Reports.
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