Researchers have removed a long-standing “railroad track” limitation in topological acoustic devices by showing how to reposition Dirac points—momentum-space features that dictate wave transport and radiation. Instead of locking sound propagation to a fixed direction, the new platform allows emission and tunneling behavior to be actively steered across the Brillouin zone.
In conventional designs, the Dirac points remain pinned by geometry, so the resulting transmission direction is constrained. Here, the team built a two-dimensional acoustic topological insulator where horizontal and vertical coupling strengths between resonator cavities can be tuned independently, giving designers a direct handle on the underlying band structure.
The key control knob is the width of connecting tubes linking cavities. By varying tube widths, the researchers shift the positions of paired Dirac cones to arbitrary locations inside the Brillouin zone. This effectively rewrites how topological edge states respond to sound waves.
Leveraging this ability, the group demonstrated two fully passive devices with angle-tunable behavior. The first operates as a full-space scanning topological antenna: acoustic signals guided by a topological interface are radiated into free space at an angle set by the Dirac point position.
As the tube widths are adjusted, the Dirac point moves, and the emitted beam sweeps continuously from negative to positive angles. Because the device is passive, the steering does not require active amplification or electronic control—only geometric tuning.
The second device realizes fully angle-tunable Klein tunneling. In this acoustic analogue, an incoming wave can pass through a barrier with nearly perfect transmission, but only within a narrow incidence window.
By relocating the Dirac points through geometrical parameter changes, the researchers control that transmission window, making the tunneling angle tunable rather than fixed. In other words, the directionality of “nearly perfect” barrier crossing becomes a design parameter.
By eliminating the angular constraints that have limited previous topological sound platforms, the work offers a flexible blueprint for next-generation acoustic wave steering, sensing, and robust sound routing—turning topological physics into a practical routing tool for sound.
The study was published in National Science Review (DOI: 10.1093/nsr/nwag346).
Keywords
topological acoustics, Dirac points, Brillouin zone, Klein tunneling, topological antenna, acoustic insulator, edge states, wave steering
