Air-transparent selective sound silencer using ultra-open metamaterial
A bilayer metamaterial silencer allows substantial fluid through the apparatus, while mitigating the propagation of sound through the apparatus, and while providing a form factor that is significantly more compact than previously-known devices. Moreover, illustrative embodiments allow a designer to specify one or both of the frequency or frequencies at which the apparatus mitigates sound propagation, and/or the bandwidth around the frequency or frequencies at which the apparatus mitigates sound propagation.
1. An apparatus comprising:
a first channel having a first inlet and a first outlet, the first channel open to propagation of a first wave at a target frequency therethrough and having a first area in cross-section, and
one or more second channels each open to the propagation of a second wave at the target frequency therethrough, and each having a second inlet and a second outlet, the one or more second channels defining a second area in cross-section,
wherein each of the one or more second channels is disposed relative to the first channel such that the second wave at the target frequency exiting the one or more second outlets is capable of destructively interfering with the first wave at the target frequency exiting the first channel, and
wherein the first area in cross-section is larger than the second area in cross-section such that the apparatus has an openness ratio of at least 0.8.
2. An apparatus according to claim 1 , wherein the first channel is open to a flow of fluid therethrough.
3. The apparatus according to claim 1 , wherein the first area in cross-section is larger than the second area in cross-section such that the apparatus has an openness ratio of 0.99.
4. The apparatus according to claim 1 , wherein the first channel defines an axis of fluid flow therethrough, and each second outlet is an un-ducted outlet.
5. The apparatus according to claim 1 , wherein the first channel defines an axis of fluid flow therethrough, and each second outlet is an axially-oriented outlet.
6. The apparatus according to claim 5 , wherein each second outlet is an un-ducted outlet.
7. An apparatus according to claim 1 , wherein each of the first wave and the second wave is a sound wave, and the destructive interference dampens the first wave at the target frequency by at least 94%.
8. The apparatus according to claim 1 , wherein each of the first wave and the second wave is a sound wave, and wherein acoustic energy at the target frequency exiting each second outlet destructively interferes with acoustic energy exiting the first channel to dampen sound at the target frequency by at least 24 dB.
9. An apparatus comprising:
a first channel open to the propagation of a first wave at a target frequency therethrough, and having a first inlet and a first outlet, the first channel configured to remain in a continuum state during propagation of the first wave therethrough; and one or more second channels each having a second inlet and a second outlet, the one or more second channels extending along an axis defining an axial direction, and open to propagation of a second wave at the target frequency therethrough, each of the one or more second channels configured to resonate at the target frequency; wherein the one or more second outlets open in the axial direction, and wherein the one or more second channels is disposed, relative to the first channel, such that the second wave at the target frequency exiting the one or more second outlets is capable of destructively interfering with the first wave at the target frequency exiting the first channel.
10. The apparatus according to claim 9 , wherein each of the one or more second channels is configured to resonate at the target frequency, and the first channel is configured to not resonate at the target frequency.
11. The apparatus according to claim 9 , wherein each of the one or more second channels is disposed, relative to the first channel, such that propagation of the second wave exiting the second outlet is capable of destructively interfering at the target frequency with the first wave exiting the first channel to reduce transmission of the first wave by at least 94 percent.
12. The apparatus according to claim 9 , wherein each of the one or more second channels is disposed, relative to the first channel, such that propagation of the second wave exiting the second outlet is capable of destructively interfering at the target frequency with the first wave exiting the first channel to dampen the first wave by at least 24 dB.
13. The apparatus according to claim 9 , wherein:
the first channel has a first area (A1) in cross-section, and
the one or more second channels define a second area in cross-section (A2),
and the ratio of the first area (A1) to the sum of the first area (A1) and the second area (A2) [A1/(A1+A2)] is greater than 0.6.
14. An apparatus comprising:
a first channel open to the propagation of a first wave at a target frequency therethrough, and having a first inlet, and a first outlet opening into an un-ducted volume,
one or more second channels, each extending along an axis and open to the propagation of a second wave at the target frequency therethrough, each having a second inlet, and a second outlet opening into the un-ducted volume;
wherein the one or more second channels is disposed, relative to the first channel, such that the second wave at the target frequency exiting the one or more second outlets is capable of destructively interfering with the first wave at the target frequency exiting the first channel.
15. The apparatus according to claim 14 , wherein each of the one or more second channels is configured to resonate at the target frequency, and the first channel is configured to remain in a continuum state during propagation of the wave therethrough.
16. The apparatus according to claim 14 , wherein each of the one or more second channels is configured to resonate at the target frequency, and the first channel is configured to not resonate at the target frequency.
17. An apparatus according to claim 14 , wherein the first channel is open to a flow of fluid therethrough.
18. An apparatus according to claim 14 , wherein the first wave is a sound wave, and the destructive interference dampens the sound wave at the target frequency.
19. The apparatus according to claim 14 , wherein the first channel has a first area in cross-section, and the one or more second channels define a second area in cross-section, and first area in cross-section is larger than the second area in cross-section such that the apparatus has an openness ratio of at least 0.8.
20. The apparatus according to claim 14 , wherein the first channel has a first area in cross-section, and the one or more second channels define a second area in cross-section, and first area in cross-section is larger than the second area in cross-section such that the apparatus has an openness ratio of at least 0.99.
21. An apparatus comprising:
a first channel open to propagation of a first wave at a target frequency therethrough, and having a first inlet and a first outlet, wherein the first channel is configured to remain in a continuum state in the presence of a wave at the target frequency;
one or more second channels, each open to propagation of a second wave at the target frequency therethrough and configured to resonate at the target frequency, and each having a second inlet and a second outlet;
wherein each of the one or more second channels is disposed, relative to the first channel, such that the second wave at the target frequency exiting the one or more second outlets is capable of destructively interfering with the first wave at the target frequency exiting the first channel.
22. The apparatus according to claim 21 , wherein the first channel is open to the flow of a fluid therethrough.
23. The apparatus according to claim 21 , wherein the first channel is configured to not resonate at the target frequency.
24. The apparatus according to claim 21 , wherein the first wave is a sound wave, and the destructive interference dampens the sound wave at the target frequency, to reduce transmission of the sound wave exiting the first channel by at least 94 percent.
25. The apparatus according to claim 21 , wherein the first wave is a sound wave, and the destructive interference dampens the sound wave at the target frequency, to dampen the sound wave exiting the first channel by at least 24 dB.
26. The apparatus according to claim 21 , wherein:
the first channel has a first area (A1) in cross-section, and
each of the one or more second channels define a second area in cross-section (A2), and
the ratio of the first area (A1) to the sum of the first area (A1) and the second area (A2) [A1/(A1+A2)] is greater than 0.6.
27. The apparatus according to claim 21 , wherein:
the first channel has a first area (A1) in cross-section, and
each of the one or more second channels define a second area in cross-section (A2), and
the ratio of the first area (A1) to the sum of the first area (A1) and the second area (A2) [A1/(A1+A2)] is greater than 0.8.
28. The apparatus according to claim 21 , wherein:
the first channel has a first area (A1) in cross-section, and
each of the one or more second channels define a second area in cross-section (A2), and
the ratio of the first area (A1) to the sum of the first area (A1) and the second area (A2) [A1/(A1+A2)] is greater than 0.9.