Andrew Corselli
A new breakthrough from the Zhang Lab at Boston University is making waves in the world of sound control. Led by Professor Xin Zhang, 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, its research on an Acoustic Metamaterial Silencer — or "sound shield" — aimed to "significantly block sound while maintaining airflow, based on Fano resonance effects," according to the Lab. 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 tradeoff 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," said 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."
Here is an exclusive Tech Briefs interview, edited for length and clarity, with Zhang.
Tech Briefs: What was the biggest technical challenge you faced while developing PGUOM?
Zhang: Our biggest challenge was evolving our 2019 breakthrough — an ultra-open silencer effective for narrowband noise — into a broadband design without sacrificing airflow. Narrowband Fano-resonance designs are like tuning a radio to block one station, but real-world noise spans many frequencies. With the PGUOM, we engineered each supercell using three subwavelength unit cells: a variable-length central cell that remains fully open to form an unobstructed air channel, flanked by two outer cells precisely tuned to shift the sound wave’s phase. This arrangement generates a complete 2π phase gradient, converting sound into spoof surface waves that are trapped and dissipated along the surface across a broad frequency range. The result: broadband silencing with high airflow — up to 70 percent openness — adaptable to unpredictable noise environments.
Tech Briefs: You are quoted in the article I read as saying, "We’re focusing on integrating our designs into specific products and applications, while optimizing the metamaterials for scalable manufacturing processes. We’re also working to further enhance noise-blocking performance — aiming for high attenuation across even broader frequency bands, while preserving low airflow resistance and minimizing overall thickness." Do you have any updates you can share about this?
Zhang: To push performance further, we are moving from manual tuning to data-driven optimization. The current prototype uses solid barriers in the first and third cells to impose precise phase shifts, with an added waveguide to correct impedance mismatch. We are now rethinking this layout to achieve even deeper, broader-band attenuation without sacrificing — and ideally improving — ventilation. Earlier designs were refined by hand, meaning some optimal configurations may have been missed. By combining machine-learning algorithms with high-throughput simulations, we can explore vast design spaces, pinpoint the true global optimum, and translate those insights into the next generation of ultra-open metamaterials with substantially higher silencing efficiency.
Tech Briefs: Do you have any set plans for further research/work/etc.? If not, what are your next steps?
Zhang: We are working to deploy PGUOM across a wide range of applications — starting with fans, propellers, and HVAC modules, and expanding to full ventilation systems in factories, offices, and public spaces. The design’s modular unit cells can be tailored to each installation’s dimensions, airflow requirements, and target frequency bands while accommodating aerodynamic, assembly, and cost considerations. In parallel, my team is using machine-learning–guided design sweeps to identify geometries that achieve even greater attenuation without increasing airflow resistance, ensuring scalability from niche use cases to mass-market solutions.
Tech Briefs: Is there anything else you’d like to add that I didn’t touch upon?
Zhang: Noise pollution is often dismissed as a nuisance rather than a serious health and environmental threat, but it affects cardiovascular health, cognitive performance, and even wildlife behavior. Our PGUOM offers a scalable way to address these challenges without compromising ventilation — critical for energy efficiency, indoor air quality, and comfort. What excites me most is that the same principle can be adapted across industries, from transportation to manufacturing to consumer products. Our goal is to make environments quieter, healthier, and more sustainable, while proving that high-performance engineering can also be practical and widely accessible.
Tech Briefs: Do you have any advice for researchers aiming to bring their ideas to fruition?
Zhang: Know the landscape, design with reality in mind, and prototype early. Our PGUOM concept actually began in a completely different field — electromagnetics — and failed there, but it sparked the insight that solved a long-standing problem in acoustics. Don’t let early results box you in; if you stay true to the process, it will guide you to the breakthroughs that matter. Embrace failure as part of learning — never the other way around. And remember, the spark still comes from you, so keep your curiosity burning.