Asymmetric absorber with multiband and broadband for low-frequency sound

Abstract

We present the mechanism for the asymmetric absorption of acoustic waves in a two-port transparent waveguide system by shunting detuned Helmholtz resonators (HRs) pairs in cascade. Theoretical analysis, numerical simulations, and experimental measurements verify that sound energy is almost totally absorbed (96.1%) at ∼373 Hz when sound waves are incident from one side while it is largely reflected back from the opposite side by judiciously designed HRs to provide manipulated surface impedance matching/mismatching to that of air at the opposite sides of the waveguide. Thus, asymmetric acoustic absorber is achieved at a low frequency. We have further demonstrated the flexibility of this methodology to get non-reciprocal absorption and reflectance in multiband and broadband. Our design advances the concept of asymmetric acoustic manipulation in passive two-port systems and may enable sound-absorbing devices for more versatile applications.

Reconfigurable sound anomalous absorptions in transparent waveguide with modularized multi-order Helmholtz resonator

“…Moreover, due to the near-zero reciprocal transmittances, the system also plays the role of a bidirectional sound insulator. We emphasize that the asymmetric absorber here is due to the hybridization of the bright mode (produced by the four parallel-mounted MHRs) and dark mode (induced by the single preposed MHR) 23 , which is physically different from the ones relying on the hybridizations of the two slightly detuned dark modes in previous works 19 , 20 . (see Section Discussion for detailed comparison).…”

Coupled Resonators for Sound Trapping and Absorption

“…It should be noted that although the first bandgap of one unit is much wider than the others, it overlaps with the first band gaps of its neighboring units and thus the coupling between them is unavoidable so the wave will not be trapped in the desired unit. Indeed, those first band gaps can be obtained by utilizing a single HR, which is not a good candidate to realize perfect sound trapping 4 , 31 . In this study, we provide an optimal solution via coupled HRs, producing stopbands with various widths, many of which have flat band edges and do not interact with band gaps of their neighboring units.…”

“…However, it is in general difficult to satisfy such condition for airborne sound. Broadband perfect sound absorption has been realized by slow sound phenomena in closed 6 , 14 – 26 and non-closed 3 – 5 , 27 – 31 sub-wavelength waveguides. If the leakage of the energy and the inherent loss of the device at the resonance frequency are balanced, critical coupling between the system and the environment is achieved 32 , 33 .…”

Fractal Acoustic Metamaterials with Subwavelength and Broadband Sound Insulation

“…ese metamaterials provide a way to control low-frequency sound waves with small-scale structures, but most of the above metamaterials only can achieve improved sound insulation within a single resonant frequency range, which thus provides only narrowband insulation. Researchers have adopted methods based on introduction of multiple coupled resonance units to broaden the insulation bandwidth [15][16][17][18][19][20][21][22][23]; however, most of these methods mainly broadened only their initial bandgaps. If a structure with multiple resonance modes can be developed to form multiple bandgaps, it will provide a promising basis for achievement of broadband sound insulation.…”