Alignment of particles in microfluidic systems using standing surface acoustic waves

We report on the use of standing surface acoustic waves, formed on a single-crystal piezoelectric substrate, to organize micron-scale latex particles into an array comprising a series of lines in an adjacent microfluidic system. The lines of particles are formed parallel to the substrate surface and perpendicular to the surface acoustic wave vector. They extend across the width of the acoustic beam aperture, with a periodicity of one-half the surface acoustic wavelength. The position and spacing of the particle arrays can be altered by adjusting the acoustic wave frequency within the device passband. We discuss the mechanism responsible for the formation of the lines, which could be widely applicable to the alignment of microscopic objects held in suspension. (c) 2008 American Institute of Physics.