An In-Line, High-Flowrate, and Maintenance Free Ultrasonic Sensor With a High Dynamic Range for Particle Monitoring in Fluids

A new highly sensitive ultrasonic sensor for the detection of particles in fluids is presented. The design differentiates from other methods by working on any fluid as the signal to detect is pressure waves, which allows for detection in optically opaque materials, such as oil, blood, and so on. The sensor is essentially maintenance free, and the low power consumption enables battery powered designs. The sensor provides true online measurements with a total measurement time well below 1 s. The detection limit as a function of particle size was investigated both theoretically and experimentally for polystyrene and silicon dioxide particles, and an excellent agreement was observed. An experimental detection limit that approaches 1 particle per mL for particle diameters above 20 μm is observed. In comparison, the output of the ultrasonic sensor scales with optical turbidity for particles with a specific size. However, this scaling relation is different for different particle sizes, and for this reason, there is no universal relationship between the output of the ultrasonic sensor and optical turbidity.