DENTON – Professors with the University of North Texas’ College of Science have rocked the world of physics by disproving the Rayleigh Reciprocity Theorem.


“Imagine a room where a conversation is taking place between two people,” said Arup Neogi, a distinguished research professor in the Department of Physics. “I speak to you and you hear me. You speak to me and I hear you. This will work even if we switch places. That is a basic explanation of Rayleigh’s theory of sound and reciprocity.


“Now, what if I tell you I can stop the sound going in one direction but not the other. I speak to you and you hear me. You speak to me and I don’t hear you. It works just like current flowing through a diode but with sound instead of electricity.”


Through a $2 million grant from the National Science Foundation, Neogi, along with Arkadii Krokhin, a professor in the Department of Physics, disproved Rayleigh’s theory by taking into account viscosity of fluid and not just air. Based on the revised theory, they created a nonreciprocal acoustic device. In one direction sound moves though the device but it is almost completely absorbed in the other direction.


“We have another device containing a cavity inside it that will not only reflect sound waves of certain frequencies but hold them as well,” explained Krokhin. Specially designed sound-scatterers inside the device reflect the wave which bounces back and forth.


“The applications are endless,” added Neogi. “Acoustics, communications and stealth technology are all areas that will benefit from our findings.”


Neogi and Krokhin’s research paper, “Nonreciprocal linear transmission of sound in a viscous environment with broken P symmetry” was accepted for publication by the prestigious Physical Review Letters journal and is currently on their website. The collective of authors includes two UNT researchers, Ezekiel Walker and Hyeonu Heo, two Ph.D. students, Andrii Bozhko and Yurii Zubov, and colleagues from Mexico and China.