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 microns Ultrasonic tone bursts of 2-microseconds 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 degrees and 180 degrees (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.