System for the Measurement of Velocity of Microscopic Particles in Liquids

A system for the measurement of velocity of particles suspended in liquids was developed, based on the on-line computation of the time to maximum cross correlation between the optical signatures made by particles, as their image traverses two adjacent photo-detectors aligned in the direction of flow. Cross correlation computation is performed with a commercially available computer, and the time to maximum cross correlation is detected by digital pulse circuitry. The system is particularly suited for measurements of blood flow in vivo and in vitro. Frequency response is linear to 1 Hz where the phase lag is 30°.