Dual-mode Shear Horizontal / Rayleigh-like surface-acoustic-wave configuration on lithium niobate 64° Y-cut

Technologies based on surface acoustic waves (SAWs) find widespread use in wireless communications, signal processing, and sensing applications. In this study, we present an innovative dual-mode SAW configuration using a 64° Y-cut lithium niobate (LN) substrate. The conventional setup, employing interdigital transducers (IDTs) oriented along the crystal X-axis, is known for generating the shear horizontal mode (SH-SAW) with in-plane polarization. Conversely, by utilizing IDTs oriented perpendicular to the X-axis, we introduce effective excitation of a Rayleigh-like SAW (R-SAW), a novel achievement in our research. Through finite element simulations and electro-mechanical analyses, we comprehensively characterize these modes in terms of frequencies, polarizations, propagation losses, and temperature coefficients. Furthermore, we investigate their interaction with liquids by analyzing damping characteristics and acoustic streaming effects using particle image velocimetry (PIV). SH-SAWs exhibit a leaky displacement during propagation with minimal damping in liquids, resulting in weak acoustic streaming—ideal for real-time sensing applications in wet environments. In contrast, non-leaky R-SAWs, characterized by a strong displacement component normal to the surface, exhibit enhanced acoustic streaming, facilitating microfluidic operations. Additionally, R-SAWs demonstrate high sensitivity to mass loading, making them optimal for real-time sensing in dry environments. The ability to generate both SAW modes on the same substrate offers the potential to develop fully electrical-driven, multifunctional integrated sensing platforms with SAW-driven microfluidic capabilities. This unique capability promises novel solutions in bio-sensing, leveraging the complementary strengths of the two acoustic modes in detection and sample handling.