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Issue 5, 2010
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Measuring the local pressure amplitude in microchannel acoustophoresis

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A new method is reported on how to measure the local pressure amplitude and the Q factor of ultrasound resonances in microfluidic chips designed for acoustophoresis of particle suspensions. The method relies on tracking individual polystyrene tracer microbeads in straight water-filled silicon/glass microchannels. The system is actuated by a PZT piezo transducer attached beneath the chip and driven by an applied ac voltage near its eigenfrequency of 2 MHz. For a given frequency a number of particle tracks are recorded by a CCD camera and fitted to a theoretical expression for the acoustophoretic motion of the microbeads. From the curve fits we obtain the acoustic energy density, and hence the pressure amplitude as well as the acoustophoretic force. By plotting the obtained energy densities as a function of applied frequency, we obtain Lorentzian line shapes, from which the resonance frequency and the Q factor for each resonance peak are derived. Typical measurements yield acoustic energy densities of the order of 10 J/m3, pressure amplitudes of 0.2 MPa, and Q factors around 500. The observed half wavelength of the transverse acoustic pressure wave is equal within 2% to the measured width w = 377 μm of the channel.

Graphical abstract: Measuring the local pressure amplitude in microchannel acoustophoresis

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Publication details

The article was received on 01 Oct 2009, accepted on 07 Dec 2009 and first published on 27 Jan 2010

Article type: Paper
DOI: 10.1039/B920376A
Citation: Lab Chip, 2010,10, 563-570
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    Measuring the local pressure amplitude in microchannel acoustophoresis

    R. Barnkob, P. Augustsson, T. Laurell and H. Bruus, Lab Chip, 2010, 10, 563
    DOI: 10.1039/B920376A

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