While rubber and metal mesh can reduce noise from roads and train tracks, other researchers are also working on reducing interior noise. In a laboratory at the EPFL Technical University in Switzerland, for example, researcher Stanislav Sergeev and his colleagues have developed a new type of plasma-based noise reduction technology.
New walls create silence
Matter can have the well-known states of solid, liquid and gas, but there is also a fourth state: plasma. Plasma is an ionized gas, which means that positively charged ions and negatively charged electrons from gas molecules are torn apart and flow freely.
In the same way that you can create sound by moving air with a loudspeaker's diaphragm, you can also create sound by pushing plasma over air.
Sergeyev and his colleagues have exploited this principle in a series of threads made of nickel and chromium. As the current passes through the strings, heat is generated that ionizes the surrounding air and causes the ions to move in waves from one pole of the circuit, the strings, toward the other pole, a metal mesh facing space.
When a sound wave comes at a wall, it is neutralized by the counter-wave, so that the sound is absorbed and scattered instead of being reflected in the room and continuing to emit sound.
This method is in many respects an improvement of the well-known technology of headphones with active noise reduction. Here, the microphone measures the incoming audio signal, then the computer calculates the signal being sent in opposite phase across the speaker's diaphragm and compensates for the noise.
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