Blood Concentration by Superposition of Higher Harmonics of Ultrasound

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Abstract
A method for concentrating cells in blood using an acoustic radiation force generated by superposition of the higher harmonics on fundamental ultrasound has been investigated. From the theoretical estimation, the efficiency of concentration of blood cells in a chamber based on a rectangular acoustic radiation force slope calculated by integration of the higher harmonics of ultrasound was 17% better than that based on a sine wave, while the peak pressure was reduced to 82% of that in the sine wave case. Concentration of blood cells was also performed experimentally using superposition of higher harmonics on a 500 kHz sine wave. At a 1.2 m l/min fluid flow rate, the blood cells were concentrated on the pressure node within 9 s, with a cell distribution half-width of 348 µ m (i.e., 76% of blood cells concentrated within 23% of the chamber width), which is 5% narrower than that of the sine wave. Though the experimental result was insufficient for the realization of the theoretical estimation because of the incomplete synthesis of the desired waveform, these results suggest the potential usefulness of this superposition method for improving the concentration efficiency with maintenance of the width of the potential slope and reduction of peak pressure.

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