The purpose of this paper is to explore the relationship between the characteristics of particles and ultrasonic impedance spectra. Although the ultrasonic attenuation and velocity spectra methods are becoming the sophisticated technology for particle size characterization

they are not available in some actual projects

either because the particulate matters to be investigated are too dense or because there are some bubbles inside. However

ultrasonic impedance spectra technology emerges as a potential technique to provide a non-destructively detecting way in the aforementioned occasions. By modifying the ultrasonic attenuation spectral model

the theories related the ultrasonic impedance spectra to particle concentration and size are established to implement quite a few numerical simulations

showing that the acoustic impedances of particles is sensitive to the changes in particle concentration and size. After that

three kinds of polystyrene suspensions with different volume median diameters (7.69 mm

21.58 mm and 66.64 mm) are investigated experimentally using the transducers with center frequencies varied from 10 MHz to 100 MHz. The results are quantitatively validated by the theory whereby a conclusion can be yielded that it is possible to distinguish the particles with different sizes by using ultrasonic impedance spectra. The comparison of the inversion results and image analysis indicates that the impedance technique is available to particle size characterization.