High absorption asymmetry enabled by a deep-subwavelength ventilated sound absorber

Abstract

Ventilated sound isolation platforms enabling asymmetric absorption have demonstrated great scientific significance and promising applicability. However, common designs composed of variant resonant meta-atoms present complicated frameworks and poor flexibility in operating frequency modulations, let alone for a high degree of absorptive asymmetry. Here, we propose a paradigm to realize high absorption asymmetry in a deep-subwavelength ventilated absorber coupled by a lossy meta-atom with a non-resonant impedance boundary, which can be served by a folded Fabry–Pérot (FFP) resonator and a narrow slit channel, respectively. For illustration, an asymmetric absorber showing 97.4% (2.4%) absorptance at 100 Hz (wavelength λ being approximately 101 times of absorber thickness) for sound incident from the left (right) port is constructed, in which the degree of asymmetry up to 40.8 enables extraordinary unbalanced absorbed and reverberated fields in opposite sides of the system. Moreover, due to the non-resonance characteristics of the narrow slit channel, the designed operating frequency can be modulated only by FFP, which illustrates larger flexibility than previous ones relying on multiple resonators. Additionally, the reported recipe can be extended to construct broadband asymmetric absorbers. As a concept proof, we assemble an absorber showing > 85% (<3%) absorptance for left (right)-incident sound within 308–352 Hz (λ from 33.2 to 29.1 times of thickness). Our results open potential possibilities for developing ultrathin ventilated functional devices capable of absorbing sound asymmetrically.