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For homes too close to highways, the sound of silence may be close at hand. A sonic barrier that relies on pre-crimped aluminium may be able to block a wider range of traffic sounds than ever before.
Manoj Thota and Kon-Well Wang at the University of Michigan in Ann Arbor have designed a noise barrier that can reduce acoustic energy by 90 per cent, so traffic noise previously audible at 1.6 kilometres away only travels half a kilometre.
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To date, most attempts at blocking traffic noise rely on erecting concrete walls, but sound can bend over their rigid, flat tops and then continue onward. Then there are barriers made of hollow, perforated cylinders that let air through, but they only block sounds at certain pitches. The distance between one cylinder and the next dictates the range of sounds they can dampen.
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Thota and Wang’s design gets around that problem using the Miura origami fold, which relies on preset creases. The barrier has three rows of vertical cylinders mounted on a sheet of creased aluminium. When the sheet is flat on the ground, the cylinders are far apart.
The cylinders are mounted where the folds meet, so that they rise and fall as sheet is folded, and create an undulating upper edge to the barrier. When the sheet lies flat, the cylinders are far apart.
The acoustic-shielding properties of the entire barrier can be changed with a simple shove of the aluminum sheet at its base. One end of the sheet is fixed and a push from the other end bends the sheet into its preset folds, forming a different arrangement of cylinders on top.
When the angle each fold makes reaches 55 degrees, the barrier blocks low-frequency noise that you might hear during rush hour, and at 70 degrees, higher-frequency sounds such as those from free-flowing traffic.
Thota says a real-world application of this design would work best if the barrier is programmed to be in certain configurations at certain times of the day, depending on anticipated traffic conditions.
If the barrier works as claimed, says Louis Hagler, a retired physician previously at the Alta Bates Summit Medical Center in Berkeley, California, then any or all adverse effects associated with noise might get less severe.
“People who lived near highways might find improvements in sleep; performance at work, home, and school; emotions and mood; and perhaps decreased cardiovascular morbidity,” he says.
Federica Morandi at the University of Bologna, Italy, says this design could be costly to maintain. She says it may be better suited to indoor use, such as in a factory with machines that emit sounds at different frequencies.
Journal reference: Journal of Applied Physics, DOI: 10.1063/1.4991026