Broadband sound absorption with subwavelength bubble metascreens: Realization of an anechoic water tank

Underwater acoustic experiments, particularly those investigating marine animal behavior or bioacoustic signals, are frequently conducted in laboratory water tanks to overcome logistical challenges of field measurements. However, these controlled environments introduce significant acoustic distortions due to reflections from tank walls, leading to modified frequency content and resonance effects. While solutions exist for ultrasonic acoustics, reducing these effects at audible frequencies remains difficult. This paper introduces a bubble-based metasurface, a thin flexible coating consisting of air cavities embedded in a rubber elastomer, that achieves acoustic absorption down to the kilohertz range. We demonstrate this by characterizing a standard commercial aquarium, identifying its resonances, and designing an optimized bubble screen configuration that effectively reduces reflections in the 3-6 kHz range, approaching the acoustic behavior of an infinite open-water environment. Time-domain analysis confirms that applying this coating significantly reduces tank reflections, offering a practical method for improving the accuracy of underwater acoustic research.