A simple and robust optical scheme for self-mixing low-coherence flowmeters

The developed measuring system is based on a low-coherence source and a self-mixing (or inter- nal) detection. The proposed optical layout exploits the reflection from the internal wall of the duct as reference arm, thus reducing system complexity, cost, size and increasing its robustness to movements of the measurand. Moreover, the usage of a low-coherence source allows reducing the problems related to the poor definition of the volume under test (sensing region or measurement volume) typical of “coherent” self-mixing systems. Although preliminary analysis have been performed by simply investigating the frequencies rel- ative to the maximum in the Doppler spectrum, the obtained results demonstrates that by in- creasing scatterers concentration of +300%, the system sensitivity increases of about only +20%.