Mechanical characterization of microparticles by scattered ultrasound

A technique for determining the compressibility and density of individual microparticles in suspension is described. The particles have diameters on the order of 10 pro. Ultrasonic tone bursts of 2-ps duration and 30-MHz center frequency scatter from individual particles as they traverse the confocal zone of two transducers. The resulting scattered tone bursts are detected at 90 ø and 180 ø (backscattering). The received rf signals are demodulated, peak detected, digitized, and stored in computer memory. Using Rayleigh scattering theory, the compressibility and density of a particle can be computed given knowledge of the particle size and host fluid properties. Results of experiments with latex microspheres are presented and compared with calculations based on long-wavelength (Rayleigh) and elastic scattering theory