Dual surface acoustic wave-based active mixing in a microfluidic channel

• We demonstrate active mixing in a microfluidic channel with surface acoustic waves.
• Two interdigitated transducer (IDT) configurations (dual excitation and single excitation) are investigated.
• Dual IDT design increased the mixing efficiency significantly as compared to traditional single IDT design.
• Mixing efficiency is increased by increasing the power and decreasing the flow rate.
• Increasing the aperture increased the mixing efficiency slightly.

Many applications need fast and efficient mixing of the sample and reagent with high throughput in a microfluidic channel. Due to low Reynolds number, mixing based on molecular diffusion plays an important role in a microfluidic channel. However, the diffusion based mixing process is very slow and the efficiency is low. The development of a highly efficient mixing technique is essential for lab-on-a-chip and micro-total-analysis systems. In this paper, we introduce a highly efficient active mixing technique using dual acoustic streaming field induced by surface acoustic waves in a microfluidic channel. The rapid and high efficiency active mixing of a fluorescent dye solution and deionized water in a microfluidic channel was demonstrated with single acoustic excitation by one interdigitated transducer (IDT) as well as dual excitation by two IDTs. The mixing efficiencies were investigated as a function of applied voltage and flow rates. Our results indicate that with the same operation parameters, the mixing efficiency with dual-IDT design increased to 96.7% from 69.8% achievable with the traditional single-IDT design. The effect of aperture length of the IDT on mixing efficiency was also investigated.