RESUMO
Objective To measure the axial flowing velocity of a suspension carbon particles of tens of micrometer-scale with an autocorrelation method.Methods The photoacoustic Doppler frequency shift was calculated from a series of individual A scans using an autocorrelation method.A 532 nm pulsed laser with the repetition rate of 20 Hz was used as a pumping source to generate photoacoustic signals.The photoacoustic signals were detected using a focused PZT ultrasound transducer with central frequency of 5 MHz.The suspension of carbon particles was driven by a syringe pump.The complex photoacoustic signal was calculated by the Hilbert transformation from time-domain photoacoustic signal.The complex photoacoustic signal was then autocorrelated to calculate Doppler frequency shift. The photoacoustic Doppler frequency shift was calculated by averaging the autocorrelation results of individual A scans.Results The feasibility of the proposed autocorrelation method was preliminarily demonstrated by quantifying the motion of a carbon particles suspension flow from 5 to 60 mm/s. The experimental results showed that the autocorrelation result approximately agreed with the setting velocity linearly.Conclusion It's feasible to measure photoacoustic Doppler flowmetry of carbon particles,and an ultrasonic transducer with high central frequency may promote the linear correlation between the autocorrelation result and flow rate during frequency shift measure-ment.