Noise pollution is a persistent environmental concern with severe implications for human health and resources. Acoustic metamaterials offer the potential for ultrathin devices with exceptional sound control capabilities. However, most lack practical openness and offer limited functional bandwidth. This paper introduces an approach utilizing a 3-unit cell phased array-based ultra-open metamaterial (3-PAUOM) to simultaneously achieve high-efficiency, broadband sound insulation combined with a high degree of ventilation. The central unit cell allows for ventilation and forms a phase gradient together with the side unit cells. The transformation of the incident plane waves into surface waves effectively blocks sound. Our design accommodates various boundary conditions and provides adjustable openness, ensuring sustained broadband sound insulation. Using length-varying straight barriers and waveguides, we theoretically, numerically, and experimentally validate our concept. This innovative approach represents a significant advancement in ventilated acoustic metamaterials, providing both ventilation and high-performance, broadband sound insulation simultaneously.
