The more people that live on our planet, the harder it becomes to avoid noise—especially during July 4th celebrations. Small surprise that noise reduction is a booming business. Your Airpods might have active noise canceling, but do they have a plasmacoustic metalayer? Maybe they soon will.
At the moment, you can either use materials that absorb or scatter noise, such as earplugs or foam mattresses. Or you can have active noise cancellation that works by creating a signal that destructively interferes with the one you want to get rid of. The problem with both of those approaches is that they don’t work for all frequencies or only work for steady signals, like the constant or continuous hum of an engine or air-conditioning unit.
The ions stop the air motion and thereby the noise.
A group of Swiss researchers has now created a prototype for an active noise canceling device that uses plasma. In a recent paper in Nature Communications, they explain how they used nothing but ionized air and wires to deaden sound. Their device works very much like noise canceling headphones, but it doesn’t have a membrane, or a flexible material that vibrates in response to electrical signals—instead it moves the air directly. This works much faster and over a larger range of frequencies.
It works like this. The prototype device has two metallic electrodes that conduct electricity separated by a tiny air gap. That’s the metalayer. The researchers use a microphone to pick up sound and calculate the required voltage to cancel it. The voltage will differ depending on the kind of sound the device needs to eliminate. When one electrode receives power, it ionizes the air nearby with the appropriate voltage, converting the molecules from neutral to charged, which pushes them around. The ions stop the air motion and thereby the noise.
In their experiment, the researchers used a device just about three centimeters thick to absorb sound waves from 20 to 2,000 Hertz almost perfectly.
That’s really impressive. But we must remember to think about the potential impact of this new technology on our social lives. If it wasn’t for the noise, maybe we’d never get to speak to our neighbors. 
This post is adapted from Sabine Hossenfelder's "Science Without the Gobbledygook," on Patreon.
Lead image: Aleutie / Shutterstock
