Standing surface acoustic waves (SAWs) and standing bulk waves (BWs) are combined to pattern two populations of particles with differing sizes. Patterns with large differences in wavelength in each direction and simultaneous generation of different patterns for each population are demonstrated. Particles are trapped at nodal positions of orthogonal standing wave fields in patterns determined by device voltage amplitudes and frequencies. 10-μm beads are trapped at points at the intersection of the pressure nodes of the SAW and BW fields, and 1-μm beads are trapped in lines at the pressure nodes of the SAW field, producing a multi-scale pattern.
Zhang, J., Meng, L., Cai, F., Zheng, H., & Courtney, C. R. P. (2014). Multi-scale patterning of microparticles using a combination of surface acoustic waves and ultrasonic bulk waves. Applied Physics Letters, 104(22), . https://doi.org/10.1063/1.4881261