Acoustic Metacages for Shielding Acoustic Waves
Value Proposition Traditional noise shielding materials and structures, such as high areal density panels and micro-perforated panels with backing cavities, rely on sound absorption and reflection to prevent the transmission of sound. These materials or structures prevent both acoustic wave transmission and steady fluid flow. This characteristic severely limits their applications under circumstances in which the exchange of air is necessary or advantageous. This includes noise reduction in environments where ventilation requires that air should be able to flow freely, and circumstances where free circulation of air is imperative to allow heat transfer and dissipation.
Technology A novel Duke technology presents a solution to this problem. It is an acoustic metacage designed based on acoustic gradient-index metasurfaces (GIM). The strong parallel momentum on the metacage surface rejects sound at an arbitrary angle of incidence, which leads to low sound transmission through the metacage. A 3D printed prototype of the metacage has been fabricated. It is capable of shielding acoustic wave transmission from all angles and the transmission loss is around 10 dB with a bandwidth of approximately 300 Hz, regardless whether the source is inside or outside the metacage, while permitting constant air circulation.
Applications Noise or sound shielding while permitting airflow for:
- Networking equipment, eg servers
- Air-conditioning systems, etc.
- Low cost
- Arbitrary in shape
- Sound shielding in all or arbitrary direction
- Air circulation
- Shen, C., et al., Asymmetric acoustic transmission through near-zero-index and gradient-index metasurfaces, Appl. Phys. Lett., v. 108 (2016)
- Xie, Y., et al., Wavefront modulation and subwavelength diffractive acoustics with an acoustic metasurface, Nature Communications, v. 5 (2014)
Inventor Steven Cummer Professor of Electrical and Computer Engineering Duke University
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