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  Realization of Point Acoustic Sink with Energy Conversion Functionality
 

 

 
 

Time: 2:00pm, July 17 (Thursday)

Title: Realization of Point Acoustic Sink with Energy Conversion Functionality*

Speaker: Prof. Ping Sheng
   (Department of Physics, Hong Kong University of Science and Technology)

Place: Science Building III 1F SC162

Abstract:
An impedance-matched surface has the property that an incident wave
generates no reflection. To diminish reflection from a hard reflecting surface,
it is traditionally the practice to add a gradient-index interfacial layer or
a quarter-wavelength layer, accompanied by dissipation1. For acoustic sound,
such additions can be bulky and cumbersome, owing to the large wavelength.
Here we demonstrate that by using simple construct, an acoustically reflecting
surface can acquire hybrid resonances and becomes impedance-matched to airborne sound
at tunable frequencies, so that no reflection is generated.
The hybrid resonance cell is deep-subwavelength in all its spatial dimensions,
breaking the quarter-wavelength constraint by two orders of magnitude.
It has two degrees of freedom that can be independently tuned;
one is the average membrane displacement, which can be tuned to impedance match
with the air-borne sound, and the other is the variance of the membrane displacement,
which is decoupled from the radiation mode and hence "deaf."
At the particular tunable hybrid resonant frequency of 152 Hz, for example,
the membrane's maximum displacement amplitude can reach 45 μm,
more than an order of magnitude larger than that of the incident sound with
an intensity of 120 dB, even though the surface-averaged displacement is much smaller
and matches that of the incident sound. As there can be no transmission,
the acoustic wave is hence either completely absorbed at one or multiple frequencies,
or converted into other form(s) of energy such as electrical current.
A high acoustic-electrical energy conversion efficiency of 23% is achieved.

* Guancong Ma, Min Yang, Songwen Xiao, Zhiyu Yang, and Ping Sheng, Nature Materials DOI: 10.1038/NMAT3994 (2014).

     
 
Update: 2014/7/11
Contacts: Li-Chun Chen

 
   
 
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