Scientists build acoustic rainbow, splitting sound by frequency

The Story in Brief

Researchers have made sound behave like a rainbow by separating frequencies of white noise into different directions. A team used computational morphogenesis to shape a single hard material into an acoustic rainbow emitter (ARE). When a monopolar source emits sound from 7,600 to 12,800 Hz, the structure directs each frequency to a different angle, producing a continuous shift from -50° to 50°. The 3D-printed device showed close agreement between experiment and simulation, with efficiency exceeding that of the source radiating into free space. A second device, a lambda splitter, sends sound above 9.4 kHz to -35° and lower frequencies to +35°, achieving over 82% efficiency.

Separately, two teams working with elastic waves in solids have demonstrated rainbow trapping. They used patterned aluminium plates and silicon chips with topological edge states to trap different wave frequencies at different positions in the material without real magnetic fields. Laser scanning visualised elastic waves near 1.1 MHz stopping at different spots depending on frequency. The structures showed no obvious backscattering under tested conditions, though energy loss and fabrication imperfections remain challenges.