Multidirectionally Patterned Interdigital Transducers for Enhancing Acoustofluidic Streaming with Flexible Printed Circuit Board

Abstract

Acoustic streaming generated by surface acoustic waves (SAWs) enables diverse acoustofluidic functions, such as fluid mixing, particle manipulation, and enhanced fluid transport, making SAWs valuable lab-on-a-chip systems. However, conventional SAW devices are often limited to a specific acoustofluidic function once fabricated. Each function typically requires different devices or designs to produce other wave modes, making exploration costly and time-consuming. A Multidirectional Interdigital Transducer (M-IDT) on a Flexible Printed Circuit Board (FPCB) is presented, allowing easy reconfigurability and multidirectional SAW propagation. This versatile device enables rapid, multifunctional experimentation on a single replaceable substrate, facilitating efficient exploration of acoustofluidic effects. This device, alongside finite element simulations, investigates substrate in-plane rotation angles (0°, 30°, 60°, and 90° relative to the X-axis) and wave modes. Favorable acoustic velocities are observed using Rayleigh SAW (R-SAW) at 0° and 30°, and using combined wave modes at 60°, and 90°. The pseudo shear-horizontal SAW (P-SH-SAW) at 90° exhibits higher velocities than R- SAW at 0°. P-SH-SAW also improved acoustic streaming at lower power, with high-viscosity fluids, substantial fluid volumes (1 mL), and within a 96-well plate. The M-IDTs reconfigurable nature allows rapid, cost-effective testing, making it ideal for prototyping a wide range of acoustofluidic applications.