Holographic surface-acoustic-wave tweezers for functional manipulation of solid or liquid objects

Noninvasive surface-acoustic-wave (SAW) tweezers provide a powerful tool for on-chip object manipulation. However, the piezoelectric materials for generating SAWs are anisotropic with misaligned directions of wave momenta and energy flow, making the conventional interdigital transducer (IDT) inappropriate for perfect SAW control. Here we propose a holographic IDT for phase-velocity engineering, which improves the focusing quality of SAWs with smaller focal size, larger enhancement of intensity, and precise control of focal position. For the holographic IDT, the focal size is approximately 78.2 μm at 40 MHz, which is 36% smaller than the one produced by a circular IDT. About twofold enhancement of focal intensity and focal length of 10λ are further demonstrated for our design. Nonetheless, we show that the holographic SAW tweezers can implement accurate sorting for solid objects of different sizes as well as large active deformation for liquid droplets even at relatively low input power, which have important biomedical applications. © 2023 American Physical Society.