No abstract

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.

The two-dimensional concentration and manipulation of micron-scale particles by orthogonal, surface acoustic, standing waves is demonstrated. The particles are organized by liquid pressure waves in a microfluidic system over a piezoelectric substrate and form a uniform two-dimensional array with a spacing governed by the mechanical nodes of the two orthogonal, surface acoustic, standing waves. The nodal spacing can be controlled in each orthogonal direction independently by adjustment of the radio frequency applied to the separate acoustic wave transducers. This technique could be used to enhance the particle concentrations at sensing locations in DNA or protein array detectors.

We investigate the effect of substrate thickness on the transmission bandwidth of on-chip terahertzfrequency-range planar Goubau lines both experimentally and theoretically. The bandwidth and frequency resolution are improved through substrate thinning and geometry modifications (reducing reflections arising from the THz photoconductive generators and detectors). We demonstrate that the 10 enhanced bandwidth (2 THz) and resolution (3.75 GHz) allows this type of on-chip waveguide to be used for spectroscopic measurements of polycrystalline materials from cryogenic (4 K) to room temperature (292 K) by recording vibrational absorption spectra from overlaid samples of lactose monohydrate.