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Pneumatically-Actuated Acoustic Metamaterials Based on Helmholtz Resonators

Novel Aerospace Materials group, Faculty of Aerospace Engineering, Delft University of Technology (TU Delft), Kluyverweg 1, 2629 HS Delft, The Netherlands
Author to whom correspondence should be addressed.
Materials 2020, 13(6), 1456;
Received: 24 February 2020 / Revised: 14 March 2020 / Accepted: 19 March 2020 / Published: 23 March 2020
(This article belongs to the Special Issue Designing and Manufacturing Hard and Soft Mechanical Metamaterials)
Metamaterials are periodic structures which offer physical properties not found in nature. Particularly, acoustic metamaterials can manipulate sound and elastic waves both spatially and spectrally in unpreceded ways. Acoustic metamaterials can generate arbitrary acoustic bandgaps by scattering sound waves, which is a superior property for insulation properties. In this study, one dimension of the resonators (depth of cavity) was altered by means of a pneumatic actuation system. To this end, metamaterial slabs were additively manufactured and connected to a proportional pressure control unit. The noise reduction performance of active acoustic metamaterials in closed- and open-space configurations was measured in different control conditions. The pneumatic actuation system was used to vary the pressure behind pistons inside each cell of the metamaterial, and as a result to vary the cavity depth of each unit cell. Two pressures were considered, P = 0.05 bar, which led to higher depth of the cavities, and P = 0.15 bar, which resulted in lower depth of cavities. The results showed that by changing the pressure from P = 0.05 (high cavity depth) to P = 0.15 (low cavity depth), the acoustic bandgap can be shifted from a frequency band of 150–350 Hz to a frequency band of 300–600 Hz. The pneumatically-actuated acoustical metamaterial gave a peak attenuation of 20 dB (at 500 Hz) in the closed system and 15 dB (at 500 Hz) in the open system. A step forward would be to tune different unit cells of the metamaterial with different pressure levels (and therefore different cavity depths) in order to target a broader range of frequencies. View Full-Text
Keywords: active noise control; acoustic metamaterial; broadband noise attenuation; pneumatic actuation; Helmholtz resonators active noise control; acoustic metamaterial; broadband noise attenuation; pneumatic actuation; Helmholtz resonators
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Hedayati, R.; Lakshmanan, S. Pneumatically-Actuated Acoustic Metamaterials Based on Helmholtz Resonators. Materials 2020, 13, 1456.

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