For studying the nanoparticle size distribution

under the condition of “long wave-length”

the technical approaches of increasing frequency

increasing frequency band width

and improving ultrasonic stability were used to obtain the exact ultrasonic attenuation spectrum (UAS).A 50MHz broad-band high-frequency ultrasonic transducer was used for measuring the testing sample suspensions of nanoAg with volume fraction of 0.5% by the method of variable acoustic-path and the comparison of the first reverberation which was reflected by the interface between buffer block and suspensions. The broad-band UAS of 25—62 MHz was obtained in the experiment. The particle size distribution of nanoAg was inversed by combining the McClements & BLBL theoretical model and the optimum regularization technique (ORT).The average particle size d32 was 13.69 nm

the size distribution was from 3.414 nm to 24.34 nm

and the lower theoretical measurement limit was 5 nm at the frequency of 50 MHz. The UAS method showed good agreement with TEM (transmission electron microscope) pictures and centrifugal sedimentation particle size analyzer’s measurement

which indicated that measuring nanometer particle size distribution by UAS was feasible and reliable.