Abstract
Helmholtz resonators offer an ideal platform for advanced sound absorbers, but their utility has been impeded by inherent frequency range limitations and the lack of function reconfiguration. Here, we introduce a multi-order Helmholtz resonator (MHR) that allows multiple monopolar resonant modes theoretically and experimentally. The combination of these modularized MHRs further creates reconfigurable multi-band anomalous absorbers in a two-port transparent waveguide while maintaining undisturbed air ventilation. In asymmetric absorption state through coupling of artificial sound soft boundary with preposed MHR, sound energy is almost totally absorbed in multiple frequency ranges when sound waves are incident from one side while it is largely reflected back from the opposite side. Interestingly, the original asymmetric absorber would turn into symmetric bidirectional absorber if one post MHR concatenates after the soft boundary. Using combination of identical MHRs, we demonstrate function selective asymmetric/symmetric absorber in multi-bands, highlighting the potential to use MHRs in the design of diverse devices for more versatile applications.
Highlights
Owning to the excellent characteristics of manipulating low-frequency sound waves with subwavelength dimension, the acoustic metamaterials based on traditional Helmholtz resonator (THR) have emerged as an attractive option in various fields such as sound proofing[1,2], asymmetric sound transmission[3], sound metadiffusers[4], and acoustic superlens[5,6] et al many challenges have impeded the in-depth implementation of THR-based devices, including the frequency range limitations of strongly resonant devices, as well as adding reconfiguration to the devices
We mitigate the above limitations posed by the operational frequency range and reconfiguration effectively through the proposed multi-order Helmholtz resonator (MHR)
The MHR demonstrates multiple monopolar resonant modes which exhibit effective negative bulk modulus. Based on these identical modularized MHRs shunted in a double-port open waveguide, reconfigurable anomalous sound absorbers are constructed which can function as asymmetric and symmetric absorber, respectively
Summary
Owning to the excellent characteristics of manipulating low-frequency sound waves with subwavelength dimension, the acoustic metamaterials based on traditional Helmholtz resonator (THR) have emerged as an attractive option in various fields such as sound proofing[1,2], asymmetric sound transmission[3], sound metadiffusers[4], and acoustic superlens[5,6] et al many challenges have impeded the in-depth implementation of THR-based devices, including the frequency range limitations of strongly resonant devices, as well as adding reconfiguration to the devices. The absorber based on identical THRs demonstrates only one absorptive peak[7,8,9,10,11,12,13], let alone the function reconfiguration. The MHR demonstrates multiple monopolar resonant modes which exhibit effective negative bulk modulus. Based on these identical modularized MHRs shunted in a double-port open waveguide, reconfigurable anomalous sound absorbers are constructed which can function as asymmetric and symmetric absorber, respectively. Dn (mm) ln (mm) Dc (mm) lc (mm) N characteristics of the multi-band resonances of MHR This asymmetric absorber can be conveniently reconfigured into a symmetric bidirectional absorber which can absorb the sound waves impinged from the both sides effectively
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