Miniature optical sensor boosts microphone performance
An optical sensor less than 1mm in diameter is set to improve the sensitivity of microphones, according to Norwegian research organisation SINTEF. The researchers have exploited optical diffraction and interference to allow the sensor to measure membrane movements of less than the diameter of an atom.
"In principle, a microphone acts like a drum," said Matthieu Lacolle, a SINTEF researcher. "You have a membrane that vibrates when it is impacted by a sound. Then you have a reference surface and the distance between these two surfaces registers the sound. We do this by measuring light waves from a microscopically small laser, so we can say that the sensor in microphones 'sees' the sound."
SINTEF says that if the membrane can be made light enough and be allowed to oscillate freely in air, the microphone can become directionally sensitive.
"We have created very special grooved microstructures on the reference surface, which lies directly underneath the microphone membrane," said Lacolle. "When the laser illuminates these microstructures, we can read the direction in which the light is reflected by means of photodetectors."
