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Scientists Have Discovered a Shape That Blocks All Sound (fastcompany.com)
Scientists have developed an "acoustic meta-material" that can catch certain frequencies passing through the air and reflect them back toward their source. When a loudspeaker was placed into one end of a PVC pipe with a 3D-printed ring of the metamaterial, the ring "cut 94% of the sound blasting from the speaker, enough to make it inaudible to the human ear," reports Fast Company. From the report: Typical acoustic paneling works differently, absorbing sound and turning the vibrations into heat. But what's particularly trippy is that this muffler is completely open. Air and light can travel through it -- just sound cannot. The implications for architecture and interior design are remarkable, because these metamaterials could be applied to the built environment in many different ways. For instance, they could be stacked to build soundproof yet transparent walls. Cubicles will never be the same.
The researchers also believe that HVAC systems could be fitted with these silencers, and drones could have their turbines muted with such rings. Even in MRI machines, which can be harrowingly loud for patients trapped in a small space, could be quieted. There's really no limit to the possibilities, but it does sound like these silencers will need to be tailored to circumstance. "The idea is that we can now mathematically design an object that can blocks the sounds of anything," says Boston University professor Xin Zhang, in a press release. You can see a demo of the noise cancellation device here.
The researchers also believe that HVAC systems could be fitted with these silencers, and drones could have their turbines muted with such rings. Even in MRI machines, which can be harrowingly loud for patients trapped in a small space, could be quieted. There's really no limit to the possibilities, but it does sound like these silencers will need to be tailored to circumstance. "The idea is that we can now mathematically design an object that can blocks the sounds of anything," says Boston University professor Xin Zhang, in a press release. You can see a demo of the noise cancellation device here.
If it lets through normal air flow, can it be used for engine exhausts?
Like the diesel electric trains, the Chevy Volt (IIRC), is only powered by electric motor. The gas engine only provides electricity to the motor/batteries, thus allowing it to operate at the most efficient engine speed when the battery is low. Since it only operates in a very narrow range, the exhaust can be finely tuned for that frequency. From what I have heard though, there is still room for improvement in this area... I'd really like to see a Sterling engine version though