Active acoustic metamaterials are one path to acoustic properties difficult to realize with passive structures, especially for broadband applications. Here, we experimentally demonstrate a 2D metamaterial composed of coupled sensor-driver unit cells with effective bulk modulus ([Formula: see text]) precisely tunable through adjustments of the amplitude and phase of the transfer function between pairs of sensors and drivers present in each cell. This work adopts the concepts of our previous theoretical study on polarized sources to realize acoustic metamaterials in which the active unit cells are strongly interacting with each other. To demonstrate the capability of our active metamaterial to produce on-demand negative, fractional, and large [Formula: see text], we matched the scattered field from an incident pulse measured in a 2D waveguide with the sound scattered by equivalent continuous materials obtained in numerical simulations. Our approach benefits from being highly scalable, as the unit cells are independently controlled and any number of them can be arranged to form arbitrary geometries without added computational complexity.
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Extreme material parameters accessible by active acoustic metamaterials with Willis coupling
Active acoustic metamaterials incorporate electric circuit elements that input energy into an otherwise passive medium to aptly modulate the effective material properties. Here, we propose an active acoustic metamaterial with Willis coupling to drastically extend the tunability of the effective density and bulk modulus with the accessible parameter range enlarged by at least two orders of magnitude compared to that of a non-Willis metamaterial. Traditional active metamaterial designs are based on local resonances without considering the Willis coupling that limit their accessible effective material parameter range. Our design adopts a unit cell structure with two sensor-transducer pairs coupling the acoustic response on both sides of the metamaterial by detecting incident waves and driving active signals asymmetrically superimposed onto the passive response of the material. The Willis coupling results from feedback control circuits with unequal gains. These asymmetric feedback control circuits use Willis coupling to expand the accessible range of the effective density and bulk modulus of the metamaterial. The extreme effective material parameters realizable by the metamaterials will remarkably broaden their applications in biomedical imaging, noise control, and transformation acoustics-based cloaking.
more » « less- Award ID(s):
- 2037565
- NSF-PAR ID:
- 10363954
- Publisher / Repository:
- Acoustical Society of America (ASA)
- Date Published:
- Journal Name:
- The Journal of the Acoustical Society of America
- Volume:
- 151
- Issue:
- 3
- ISSN:
- 0001-4966
- Page Range / eLocation ID:
- p. 1722-1729
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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