Technology

Acoustic ultrasonic sensors with piezoelectric crystals rely on mechanical vibrations induced by sound waves to deform the crystal. The patented technology of the Optical Microphone takes a completely different approach: instead of mechanical vibrations, it utilizes the effect of sound on the speed of light.

In a rigid Fabry-Pérot laser interferometer, consisting of two miniaturized mirrors, the sound pressure changes the refractive index of the air. This alters the optical wavelength and the light transmission which consequently leads to the respective electrical signal. In contrast to conventional microphones, the Optical Microphone is the world's first microphone without any moving parts. No mechanically movable or physically deformable parts are involved. By consequence, the sensors exhibit a compelling frequency bandwidth, free from mechanical resonances. The sensor principle is highly sensitive. In fact, refractive index changes below 10^-14 can be detected with this technology. This corresponds to pressure changes as small as 1 µPa.