Acoustic waves can be guided through a narrow “tunnel” that lacks walls and thus presents no obstruction to sound traveling across its path.
Researchers have devised a “ghost tunnel”—a nearly perfect waveguide for sound that allows other sound waves to pass across its path undisturbed [1]. The tunnel is essentially invisible to external waves. The researchers expect the 2D acoustic structure to find use in situations such as complex sonar devices, where multiple signal channels must cross without interacting.
The hard walls of metal pipes and other ordinary waveguides keep sound trapped inside, but they also present obstructions that scatter external sound waves. This scattering can be a major problem in environments such as integrated acoustic circuits or sonar applications, where sound waves are propagating in multiple directions outside of waveguides. These nonguided waves can potentially suffer from signal-clarity degradation.
