A sensor developed by scientists at SINTEF’s MiNaLab will help to make microphones hypersensitive. With technology of this sort, a microphone will be able to “see” where the sound comes from, pick up the voice of the person speaking, and filter out other sources of noise in the room.

The microphone is packed full of microelectronics. What makes it really special, however, is an optical position sensor that is no more than a millimeter in diameter. The reason for giving a position sensor such an important role is that a microphone is completely dependent on a membrane, which picks up the pressure waves produced by the sound.

The sensor can measure incredibly small movements, and thus also extremely quiet sounds. If the membrane light enough, and it oscillates freely in the air, the microphone also becomes directionally sensitive. The technology that makes the microphone so sensitive is based on a combination of two optical phenomena; interference and diffraction, both of which are due to the wave character of light.

The microphone consists of several elements: an ultrathin membrane, tiny grooved microstructures, a miniaturized laser, and a number of photodetectors. Everything is integrated into a tiny circuit that is mass-produced on a silicon wafer on which all the structures are etched, using special equipment within a cleanroom.

In simple terms, the new microphone operates as follows: First, sound pressure is transformed into movements of the membrane. These movements are read optically via the light-sensitive detector. The light intensity is measured by a sensor that transforms it into an electronic signal capable of reproducing the sound.