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Researchers at the University of Michigan in Ann Arbor have demonstrated an origami lattice prototype that can potentially reduce acoustic noise on roadways.

As more drivers take to the road, there has been growing concern about the impact noise has on blood pressure, hearing loss and attentiveness at work and school. Managing traffic noise pollution has vexed researchers in large part because of the broad range of frequencies we encounter on the road. Currently, only heavy, wall-like barriers can effectively dampen all of these various sounds.

Now, a new technique allows researchers to selectively dampen noise at various frequencies by adjusting the distance between noise-diffusing elements. In a prototype, researchers Kon-Well Wang and Manoj Thota claim their barrier reduced acoustic pressure by 10 decibels or 90 per cent.

"Our main contribution we're developing is an adaptive structure that can change its periodicity between different Bravais lattices with distinct symmetry properties," said Wang. "If you reconfigure the lattice structure in such a manner, you will change the wave propagation characteristics significantly."

In the origami sonic barriers, noise-diffusing cylinders called inclusions are placed on an aluminium 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.

"The lattice contains only one degree of freedom, making it particularly easy to collapse and expand," said Thota. "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."

Manipulating a lattice of inclusions might allow traffic experts to adjust noise-dampening devices to particular frequency ranges. Heavier vehicles produce noise at lower frequencies than lighter vehicles. Cars traveling quickly during off-peak times skew toward higher frequencies than cars stuck in traffic jams.

Concrete walls that line the roadway are effective across a broad spectrum of noise frequencies, but the wind they block can add unwanted force on their foundations. Since they feature flat surfaces, the reflected wave is not diffusive enough to reduce the sound on the road. 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' work draws on periodic sound barriers, in which a series of inclusions dampen sound at certain frequencies while allowing wind to pass through. The drawback, Thota said, is that these systems are fixed designs. If a system is designed to alleviate noise from traffic jams, it is not as useful when cars are moving fast.

Benefits of origami structures might extend out of traffic noise reduction to wave guiding and acoustic diodes, Wang claimed. "Overall, origami structures give us an effective platform to adapt to environmental change," he said.

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Title Annotation:DESIGN IDEAS
Publication:Environmental Engineering
Date:Dec 1, 2017
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