Feedforward control of sound transmission using an active acoustic metamaterial

Abstract

Metamaterials have received significant interest in recent years due to their potential ability to exhibit behaviour not found in naturally occurring materials. This includes the generation of band gaps, which are frequency regions with high levels of wave attenuation. In the context of acoustics, these band gaps can be tuned to occur at low frequencies where the acoustic wavelength is large compared to the material, and where the performance of traditional passive noise control treatments is limited. Therefore, such acoustic metamaterials have been shown to offer a significant performance advantage compared to traditional passive control treatments, however, due to their resonant behaviour, the band gaps tend to occur over a relatively narrow frequency range. A similar long wavelength performance advantage can be achieved using active noise control, but the systems in this case do not rely on resonant behaviour. This paper demonstrates how the performance of an acoustic metamaterial, consisting of an array of Helmholtz resonators, can be significantly enhanced by the integration of an active control mechanism that is facilitated by embedding loudspeakers into the resonators. Crucially, it is then also shown how the active acoustic metamaterial significantly outperforms an equivalent traditional active noise control system. In both cases a broadband feedforward control strategy is employed to minimise the transmitted pressure in a one-dimensional acoustic control problem and a new method of weighting the control effort over a targeted frequency range is described.

Active feedforward control of flexural waves in an Acoustic Black Hole terminated beam

“…It is interesting to observe that a similar advantage was observed when combining active control elements with a Helmholtz resonator based metamaterial in [52] and the results presented here thus begin to demonstrate the advantage of the AABH termination compared to a constant thickness active beam termination.…”

Broadband low-frequency sound isolation by lightweight adaptive metamaterials

“…23 By placing a loudspeaker inside the resonators, the sound insulation performance could be actively tailored through a feedforward control strategy. 24 Piezoelectric materials attracted lots of interests due to their small size, light weight, and easy tunability. They have been implemented in several plate structures, making the STL peak frequencies tunable by the means of the shunted inductance circuit.…”

Pneumatically-Actuated Acoustic Metamaterials Based on Helmholtz Resonators

“…Particularly, acoustic metamaterials can manipulate sound and elastic waves both spatially and spectrally in unpreceded ways [2]. Such properties include super-focusing [3], super-lensing [4], active membrane structures [5,6], cloaking [7,8], phononic plates [9], fluid cavities separated by piezoelectric boundaries [10], and tunable noise attenuation based on Helmholtz resonators [11][12][13][14][15]. The capability of metamaterials to tune their physical behavior just based on their geometrical characteristics offers a great benefit over conventional materials for application in various high-demand industries such as aerospace, automobile, and construction.…”

“…When the air pressure inside the cavity decreases, it sucks air around the neck area back again, and this phenomenon repeats itself several times making the air inside the cavity work similar to a spring. In recent years, there has been extensive research in development of acoustic metamaterials constructed from Helmholtz resonator unit cells [13][14][15] to generate tunable band gaps.…”