  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.
