Enhanced real-time optical detection of micron-sized particles in water using standing ultrasonic wave fields

The overall goal of the research was to develop a water quality monitoring system that simultaneously concentrates micron-size particles and bacterial cells in the nodal planes of a standing ultrasonic wave field and monitors the level of contamination using light transmission measurements. Ultrasonic concentration is an attractive method for in-line, continuous sensing since it has no moving parts and is not limited by a physical barrier, e.g., a filter, which may get plugged over time. The degree of concentration was evaluated over a range of initial particle concentration. Results showed that particle banding occurred within seconds of sonication - allowing for real-time analysis - and the degree of concentration increased with decreasing initial concentration of particles in the suspension. Concentration factors of 5 to 10 were achievable. Results from this study can be used in the design and fabrication of sensitive water quality monitoring systems that would permit real-time water quality analysis.