Anechoic
Chamber
零回音室
表面結構單元由三層材料組成：裝飾膜諧振器（DMR）丶反
射背板、和之間密封的六氟化硫氣體層。DMR是一片彈性
膜，其中心有小板以增強隔音功能。超表面系統可在聽覺頻
率範圍內(如測試所用的152Hz)產生共振。當系統與空氣中
的聲波阻抗匹配時，就會達到近乎完美的吸音和零反射的
效果[1]。
這項發明的重要性有兩方面：1) 超表面是優良的聲能
吸收器；2) 系統吸收特定聲波時不會產生反射。進一步的改
良，是要在膜上加上更複雜的配件，以提供不同的共振頻
率，從而調節可被吸收的聲波範圍。
研究所得的混合共振聲學超表面，可以成為能量採集
器，尤其是在嘈雜的環境中。共振產生時，能量集中在膜
內。研究人員以銅線將釹磁鐵與膜連接起來，整個系統
就像一個逆揚聲器。當銅線按法拉第定律在釹磁鐵的磁
場內運作時，膜上的聲能便會
轉化為電力。
molecular collisions, which is why sound cannot
be transmitted in a vacuum in the absence of
particles. An anechoic chamber is insulated by
thick concrete and steel to prevent external sound,
but the real magic occurs internally, where sound
absorbing, fibrous and gradient-index materials
are lined in a cross-hatched fashion to eliminate
echo or reverberation. Foam wedges and sponges
are often used for this purpose, but they are space-
consuming and do not last very long.
In a paper publ ished in
Nature Mater ial s
last year, scientists at the HKUST constructed an
acoustic metasurface that can completely absorb
acoustic waves. A thin, three-layer metasurface
unit cell is composed of a decorated membrane
resonator (DMR), a reflective backing and a sealed
sulphur hexafluoride (SF
6
) gas layer sandwiched
in between. DMR is an elastic membrane, with a
platelet located at the centre to increase acoustic
absorption. The metasurface exhibits resonance
at audible frequencies (e.g., 152 Hz in the reported
exper iment). When the sys tem matches the
i m p e d a n c e o f
a i r bo r ne s ou nd
waves, it achieves
near perfect sound
ab s o r pt i on and
zero reflection [1].
There are two significances over this invention
– first, the metasurface is an excellent absorber of
acoustic energy, and second, the system does not
reflect waves when absorbing a particular sound
wave. A further improvement to the device would
be to tune the metasurface into absorbing a range
of sound waves by making more sophisticated
decorations on the membrane to provide profuse
resonances in variant frequencies.
The hybrid resonant acoustic metasur face
is a likely energy har vester, par ticularly if the
metasurface is installed in a noisy environment.
When resonance is present, energy is concentrated
on t he memb rane. Resea rche r s coup l ed
neodymium magnets to the membrane through
copper wires so that the whole system behaves like
an inverse speaker. While the copper wires move
in the magnetic fields of neodymium magnets,
according to Faraday’s law, the noise energy on
the membrane will be converted into electrical
current.
References
[1] Ma, G., Yang, M., Xiao, S., Yang, Z., Sheng, P. Acoustic
metasurface with hybrid resonances. (2014)
Nature
Materials
. DOI: 10.1038/NMAT3994. Retrieved from
http://
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