An alternative to the wall-like barriers currently lining roadways to reduce traffic noise is being offered by University Illustrations of different folding configurations of origami sonic barrier and their corresponding cross section views. The pink polygons in cross section views identify different lattice patterns and show that the lattice transforms from a hexagon to a square and to a hexagon when the origami sheet folding angle is shifted from 0 to 55 and to 70 degrees. Source: M. Thota, University of Michigan, Ann Arborof Michigan Ann Arbor engineers. They designed an origami lattice prototype as an adaptive structure that selectively muffles noise.

Inclusions in the form of noise-diffusing cylinders are incorporated into an aluminum sheet bent into a Miura fold, a common origami folding method. As the resulting lattice folds, the inclusions are drawn closer together or farther apart, diffusing noise in different frequency ranges.

Unlike periodic sound barriers with inclusions of fixed design, the new lattice system can be manipulated and might enable adjustments to target specific frequency ranges. Heavier vehicles produce noise at lower frequencies than lighter vehicles, and cars traveling quickly during off-peak times skew toward higher frequencies than cars stuck in traffic jams.

Concrete noise barriers are effective across a spectrum of noise frequencies, but the wind they block can add unwanted force on their foundations. The reflected wave is not diffusive enough to reduce sound on the road, due to the flat surfaces of these structures. With a straight top edge, the incidence of oblique waves onto these barriers leads to higher diffraction and increases the propagation across the barrier.

The researchers demonstrated a prototype barrier to reduce acoustic pressure by 10 decibels, or 90 percent. “The traffic noise that could otherwise be heard as far as a mile away would now only be perceived from a distance of 0.3 miles with these barriers,” said researcher Manoj Thota.