A Circulator for Sound

The control of sound transmission is desirable in a number of circumstances from noise suppression to imaging technologies. We have presented the first-of-its-kind nonreciprocal circulator for acoustic waves, a subwavelength meta-atom made of a resonant ring cavity biased by an internally circulating fluid. The direction of rotational flow of the fluid (air) changes the resonant properties of the ring cavity, allowing the propagation of sound waves within the cavity to be controlled. With several ports connected to the cavity, sound can be directed to a certain port in one direction, while isolating transmission in the reserve direction.  In the figure (cover of Science) he arrows represent acoustic signals flowing through the device (diameter: ~20 centimeters), which circulates sound in a nonreciprocal fashion: Signals can flow from left to top, from top to right, and from right to left, but not in the opposite directions. This creates one-way communication channels for sound, allowing listeners to hear but not be heard in return.

To learn more:

C. Q. Choi, “A One-Way Street for Sound,” Scientific American, Vol. 310, No. 4, p. 31, April 1, 2014.
M. Largey, “Creating a One-Way Mirror for Sound,” Radio Interview on KUT News, February 28, 2014
C. Winter, “One-Way Sound Transmission,” Bloomberg Businessweek, February 20, 2014. Longhorn Extra: Campus Minute, February 6, 2014.
A. Wood, “World first acoustic circulator puts sound on a one-way street,” Gizmag, February 5, 2014.
A. Dangelis, “Device Lets You Hear Without Being Heard,” Discovery News, February 5, 2014M. Passarello, “La macchina per il suono «a senso unico»,” Il Sole 24 Ore, February 5, 2014.
V. Woollaston, “The Audio invisibility cloak: One-way sound device could let spies listen in on people without being heard,” Daily Mail, February 2, 2014.“Da Invisible a Inaudibile,” La Repubblica, January 31, 2014.
T. Commissariat, “Sound follows one direction,” Physics World, January 31, 2014.
R. Fleury, D. L. Sounas, C. F. Sieck, M. R. Haberman, and A. Alù, “Sound Isolation and Giant Linear Nonreciprocity in a Compact Acoustic Circulator,” Science, Vol. 343, No. 6170, pp. 516-519, January 31, 2014. (web)
T. Ghose, “Spies, Take Note: Scientists Create One-Way Sound Machine,” NBC News, Live Science, January 30, 2014.
S. Zaragoza, “Engineers Build First Nonreciprocal Acoustic Circulator: A One-Way Sound Device,”  UT Austin Press Release, Phys.org, Science Daily, January 30, 2014.
S. Cummer, “Selecting the Direction of Sound Transmission,” Science, Vol. 343, No. 6170, pp. 495-496, January 31, 2014.
B. Ferreria, “To Eliminate Feedback, Engineers Invented the Acoustic Equivalent of One-Way Glass,” Motherboard, January 31, 2014.