Subwavelength acoustic metamaterial with tunable acoustic absorption
Described is an acoustic absorbing structure and system provided from a composite material having one or more channels provided therein with each of the one or more channels having an aperture opening onto a surface of the composite material. The channels are provided having a cross-sectional shape and dimensions selected to exhibit a low frequency resonance in response to a low frequency sound wave provided thereto such that acoustic absorbing structure has a predetermined response characteristic in response to an acoustic signal provided thereto. Techniques for operating an acoustic absorbing system are also described.
1. An acoustic absorbing system comprising:
a pumping system having a pump with an output;
a piping system having one or more pump ports coupled to the pump output of said pumping system and having one or more absorber ports; and
a subwavelength acoustic metamaterial having one or more channels provided therein with at least one of the one or more channels coupled to at least one of the one or more absorber ports of said piping system.
2. The acoustic absorbing system of claim 1 wherein said subwavelength acoustic metamaterial comprises a composite material having one or more channels provided therein wherein the channels are provided having dimensions such that in response to a low frequency sound wave intercepted by said composite material, the channels exhibit a low frequency resonance such that a wall of each channel oscillates in a plane which is substantially perpendicular to a central longitudinal axis of the channel.
3. The acoustic absorbing system of claim 1 wherein said subwavelength acoustic metamaterial comprises a composite material having one or more hollow cylinders provided therein wherein the hollow cylinders are provided having dimensions selected to exhibit a low frequency resonance in response to a low frequency sound wave provided thereto, and wherein walls which define the hollow cylinders oscillate isotropically in a plane which is substantially perpendicular to a central longitudinal axis of the hollow cylinder in response to the low frequency sound wave.
4. The acoustic absorbing system of claim 1 wherein in response to said pumping system providing one of a fluid or a gas to at least one of the one or more channels in said subwavelength acoustic metamaterial, an acoustic absorption characteristic of said acoustic absorbing system changes.
5. The acoustic absorbing system of claim 1 wherein said subwavelength acoustic metamaterial is provided as a multilayer acoustic absorber comprising a plurality of multilayer composite materials, each of said plurality of multilayer composite materials having one or more channels provided therein with at least some of the one or more channels having an exposed aperture coupled to at least one of the one or more absorber ports of said piping system.
6. The acoustic absorbing system of claim 5 wherein at least some of the channels having a single exposed aperture coupled to at least one of the one or more absorber ports of said piping system.
7. The acoustic absorbing system of claim 5 wherein at least some of the channels having first and second apertures exposed on first and second surfaces of a composite material and each of the apertures are coupled to an absorber port of said piping system.
8. The acoustic absorbing system of claim 1 wherein the channels have at least one closed end.
9. The acoustic absorbing system of claim 1 wherein the one or more channels have a diameter between about 50 microns and 200 microns.
10. The acoustic absorbing system of claim 1 wherein the one or more channels are filled with a fluid or gas that has a density greater than the density of air.
11. The acoustic absorbing system of claim 1 wherein the metamaterial includes an elastic matrix and the one or more channels are filled with a fluid having a density that is about the same as a density of the elastic matrix.