This smarter sound shield blocks more noise—without blocking air

A new breakthrough from the Zhang Lab at Boston University is making waves in the world of sound control. Led by Professor Xin Zhang (ME, ECE, BME, MSE), the team has published a new paper in Scientific Reports titled “Phase gradient ultra open metamaterials for broadband acoustic silencing.” The article marks a major advance in their long-running Acoustic Metamaterial Silencer project.

The Zhang lab is renowned in the fields of metamaterials and microsystems for its continual advancement of real-world applications. Back in 2019, their research on an Acoustic Metamaterial Silencer—or “sound shield”—aimed to “significantly block sound while maintaining airflow, based on Fano resonance effects,” in the lab’s words. At the time, applications focused on fans, propellers, and HVAC systems, targeting the reduction of narrowband noise while preserving air passage. 

The Zhang lab has since extended its work to explore a broader range of acoustic silencing strategies—including multi-band, broadband, and tunable approaches—making the technology viable in new environments such as factories, offices, and public spaces, where diverse and unpredictable sound frequencies are common and airflow remains essential.

Their latest advance centers on 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 breakthrough was made possible through the use of phase-gradient metamaterials, giving rise to the Phase Gradient Ultra-Open Metamaterial (PGUOM).

“PGUOM takes a smarter approach—more like noise-canceling headphones—effectively silencing a broadband of unwanted sounds,” says Zhang. “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.”